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The 500 mb (millibar) weather map has traditionally been the bread and butter of weather forecasters. Today, with so many new, high tech tools at their fingertips, is this map still relevant? You bet! The 500 mb level of the atmosphere is simply the height at which the air pressure is 500 mb (or 50 Kilopascals (KPa) if you want to be a metric purist). Since this height varies from place to place, the 500 mb level is really an undulating surface, perhaps resembling the swells on the sea, if you could see it. Map it out and you have a contour map, very similar to a topo map you might take hiking. Here’s the forecast 500 mb map for Alaska and surrounding oceans valid 4 am Sunday:

At the surface of the earth the pressure is around 1000 mb (or one bar, or atmosphere), so the 500 mb level is about 1/2 way up the atmosphere in terms of pressure or mass. in other words, half the air is below 500 mb and half is above. The actual height is another story. Air pressure does not decrease steadily as you go up in the atmosphere, it decreases logarithmically…the decrease in pressure happen quickly at first then gradually slows. The 500 mb level is  roughly 5,500 meters up (18,000 ft). The contour lines are labeled as to their individual heights.

What does this map tell us?

In general a 500 mb chart, or any upper level chart, shows the pressure pattern, and the wind flow for the valid time, whether that be the time of the actual measurements for a diagnostic chart, or the time of the forecast for a prognostic chart (prog for short). More interesting is what this upper level flow means for the weather down here on terra firma. But first a little more info way up high. The map above does not explicitly show the winds, but they can be deduced from the contours. Upper level winds flow pretty much parallel to the contours, counter-clockwise (northern hemisphere) around lows–an area of low heights on upper level charts being the same thing as an area of low pressure, for all practical purposes. The wind speed is proportional to how close together the contour lines are. In this map there are two lows, one big one in the upper left in the far western Bering Sea, and a smaller one half off the bottom of the frame. If you connected these two with a line, you’d be describing the axis of a larger, more general feature, a trough. To the east, or downstream in the wind flow, the contours bend up (north) then curve back south to describe a ridge. The strongest winds are around the west and south sides of the larger low, over the Kamchatka Peninsula and south of the Aleutian Islands, whereas the Alaska Peninsula is in a slower wind area, for instance.

What does it tell us about our weather?

Unless you are up in an airplane, where you will rely on upper air charts directly, what these maps mean for surface weather is of primary interest. The 500 mb chart is good for showing where surface lows and highs will develop and where and how fast they will move. Pretty useful, I’d say. Here’s the super condensed version of how this works: The area from a trough axis downstream to the following ridge is an area favoring development of low pressure centers and fronts at the surface. The area under and downstream from a ridge is an area favoring high pressure at the surface. Remember, entire books are devoted to this interconnection of the upper and lower layers of swirling air, the dynamics of the atmosphere, so what I’ve just let on could be the mother of all simplifications. Many 500 mb charts, this one included, show an additional parameter in an effort to reveal the dynamical processes at work. It the the vorticity field, and for now lets just say the higher vorticity values (shown in the color scheme as tending toward red), are where the dynamics are more favorable for low pressure development at the surface. This is also a big oversimplification, but I wanted to mention it since it is on the chart. Take a look at the 500 mb chart above and see if you can envision the areas where surface lows and highs might want to be, then look at the computer’s vision on the surface prog for the same time, from the same model:

The serious action at the surface is in the eastern Bering sea under and a little downstream (east) of the 500 mb tough and low. The smaller low at 500 mb (the one near the bottom of the map) also has a surface low counterpart a little downstream. But now look at the 500 mb ridge which has its axis a ways offshore of Southeast Alaska and continuing northwest through roughly Prince William Sound and the northwest arctic coast. On the surface there is high pressure a ways downstream from it, centered over Yakutat at the neck of the panhandle. There’s dynamics at work.

What does it all have to do with the Northern Lights?

Actually, the atmospheric patterns aloft or at the surface have nothing to do with the aurora (or northern lights). But they have everything to do with whether you will be able to see the potentially strong aurora likely to be happening over the next couple of days at the very upper edge of the atmosphere, roughly 30 times higher than the 500 mb level. The 500 mb ridge is nicely situated to give Southeast Alaska the best look at any auroral activity. The southcentral region may get some breaks, but it is not as well situated as the panhandle, were the offshore flow should make for talk-of-the-town good weather. The eastern interior, which has had its share of nice weather recently and is drier by nature won’t even do as well as the panhandle, as the high will probably not be strong enough to clear things up completely. For the panhandle, Sunday should be the best day, for the other areas, not so much difference between Saturday and Sunday. The western half of the state. on the other hand, things will be gong downhill fast as the dynamics of an upper trough come into play. Lots of moisture and even more wind are headed for the west coast and the Aleutian chain. The NWS has high surf advisories out already for many west coast areas.

You can check for yourself, not only the 500 mb chart, but all the levels, plus the latest info on solar activity that might spark a good aurora. Here are some links:

Upper air:
http://pafc.arh.noaa.gov/gfemodel/index.php
http://weather.uwyo.edu/upperair/uamap.html

Aurora:
http://www.swpc.noaa.gov/forecast.html
http://www.spaceweather.com/
http://www.gi.alaska.edu/AuroraForecast

Please let me know if you see the aurora, a coastal storm, or something in between. Use the comments link below for your report or any questions or comments you might have.

Fairbankskans and others in the Alaskan Interior have been enjoying plenty of sun and warm afternoons for the past week. The NWS office there even put out a statement about it, as if to rub it in to the rest of us who have been layering on the sweaters, if not rain coats, lately.

PUBLIC INFORMATION STATEMENT…CORRECTED
NATIONAL WEATHER SERVICE FAIRBANKS AK
316 AM AKDT TUE AUG 30 2011

CORRECTED THE HIGH TEMPERATURE AT FAIRBANKS

…THE UNSEASONABLY WARM WEATHER CONTINUES IN THE INTERIOR…

A RIDGE OF HIGH PRESSURE ALOFT HAS BEEN RESPONSIBLE FOR THE
WARM WEATHER DURING THE LAST SEVERAL DAYS ACROSS MUCH OF THE
INTERIOR. MONDAY WAS THE WARMEST DAY OF THE BUNCH IN MANY AREAS.
HERE ARE SOME HIGH TEMPERATURES THAT WERE OBSERVED MONDAY AFTERNOON:

DENALI NP HEADQUARTERS….74
FAIRBANKS INTERNATIONAL…72
NORTHWAY………………71
FORT WAINWRIGHT………..70
NENANA………………..70
TANANA………………..69
EIELSON AFB……………69
EAGLE…………………69
DELTA JUNCTION…………68
FORT YUKON…………….68

Only the southern end of the SE Panhandle could get near the interior’s highs today. Nothing record breaking, but very nice nonetheless. What is not mentioned in the statement is the low temperatures, which are getting downright chilly. This is no surprise, as the same weather pattern which allows the solar heating to warm the afternoons also allows the radiational cooling to cool the nights and early mornings. I covered this topic more thoroughly in this post. So it is also no surprise that the state’s high for today and low for last night are only a stone’s throw apart (Alaskan speaking) at Northway (68 F/20 C) and Eagle (31 F/-1 C). Eagle was 70 F/21 C yesterday.

Now take a look at the Fairbanks Airport temperature trace for August (shy a few hours):
(click for larger version)

The small magenta spikes near the bottom of the chart show precipitation (rain) which is a good indicator of the kind of heavy cloud cover which moderates the temperatures, keeping the diurnal range low. Most of the middle of the month was in this mode, with a few days of relief interspersed. The first five days and the last week were dry and more clear, allowing the large swings in temperature. This is nothing new to many, and as I mentioned, nothing new to this blog (here’s the other article).

What you might not have thought about, however, is how the daily average temperature records can mask the differences between these two regimes. I’m talking about the human experience…how nice it is or was for outdoor activities. To get this story from the weather records, the  daily average temperature downplays what you and I experience as the day’s weather. The recent interior warmth is a good example. During the past week it was so nice that the NWS folks made official acknowledgement. Sunny, warm, pleasant weather with the highs about 6-9 degrees F warmer than the climatological average. However, since the lows dropped lower with the clear weather (they were fairly close to the climatological average or “normal” in NWS lingo), the daily average [(high+low)/2)] was only 3-6 degrees warmer than usual. So when considering how the weather affects daily life, looking at high temperatures makes more sense to me than the day’s average temperature so commonly given in climatological reports. However, in the midst of the winter, I think low temperatures are the more important factor for the human experience. I’ll save that explanation for another post. What do you think…of which measure to use and whether those Fairbankskans deserve this good weather?

No, the rain gauges are not malfunctioning, (although that has happened before at some weather stations). It has been very dry in the north end of the Inside Passage. There is a natural dry pocket in this rainforest to the point of really stretching the term rainforest. This year the first part of summer has been drier than usual over the region meaning the driest areas are getting pretty dusty. There have been drier years, but not many.

Here’s the precipitation data for the past three months in map form, then more completely in table form–arranged top-bottom in case you need some help in identifying what towns the numbers on the map belong to. Look at the large variation in a bit over a hundred mile radius, with the dry bulls eye over Skagway:

The “years” column is the number of years of data that went into the average and extremes.

What’s behind the dry spell/dry spot?

Check out this recent surface map, a very recurring pattern this summer. The large high over the North Pacific is a semi-permanent summer feature and is in fact officially called the North Pacific High. Strong highs like this are effective at keeping frontal systems from impacting Southeast with any strength or regularity. That front slicing down through the interior and Cook Inlet brought about a quarter of an inch of rain to Anchorage and other areas, but fell apart (as most have) while trying to rake across the top of the high, and the panhandle got almost no rain.

However, for coastal stations, highs do not mean all is dry and sunny, for they push the ample oceanic low clouds (commonly called the marine layer) onshore, bringing not only clouds, but a mix of fog and drizzle and a smattering of light rain as the moisture gets wrung out of the marine air by our abrupt coastal mountains. But rainfall will stay below average with this kind of pattern. Bet why are the northern inner channels so much drier? They are protected from the both the low marine layer and the orographic (mountain induced) precipitation by the first several ridges of the coastal mountains. In a sense Skagway and Haines are not very coastal, but a little more like the interior. Everything is in shades in the weather business.

What’s next?

Will the dry weather continue? Climatology indicates that things must start getting wetter fairly soon. Even in super-dry 2009 the rains came in August and September, playing a strong catch-up game in the area. Such is the flip-floppy nature of the weather in much of Alaska.

The computer models are not showing a major shift for the next week anyway. There is some weakening of the pattern and there will probably be a little more moisture than we’ve seen, but probably very little in the protected areas discussed above. Our gardens could use a lot more than I think we’re likely to get over the next week. The real weather is the continuing strong lows moving into the Bering Sea, an example of which is pictured in the surface chart above. The west coast is getting way more storms than they probably want. The longer range maps from the Climate Prediction Center are not wanting to deviate from climatology (in other words they’re not sticking their neck out for above or below normal precipitation), except for continued wetter than normal for the next two weeks for the southwest part of the state.

The big issue for Haines is the upcoming Southeast Alaska State Fair coming up in two weeks. Despite Murphy’s laws on rain, its too early to say whether the fair will be warm and sunny, cool and rainy or somewhere in between.

I’d love to hear any comments or questions on this article, or any weather topic. Click on “comments” below, and let me know whether your hoping for rain or sun where you live.

Alaska is a great place to celebrate Independence day, and historically, the weather is decent, more often then not.

This histogram shows the percentage of time each station received the listed amount of precipitation on July 4th over their period of weather records, 68 years minimum. Of these 4 metro (“Alaskan metro”) centers it is surprisingly Anchorage that comes out driest. Another surprise is that Juneau and Fairbanks are right about the same! I’d guess that Fairbanks’ rain is more showery and therefore more brief, allowing more sunshine than Juneau’s marine cloud layers. Barrow has more dry days than Fairbanks as well, but fewer days with more than a tenth of an inch…the kind of rain that can really soak a picnic.

What about this year?

The following computer forecast is for 10 am on the 4th and shows wind barbs at the 700 mb level (~3,000 m/~10,000 ft) and relative humidity through all levels.

There are three lows threatening to rain on our parades. One near Kaktovik in the northeast corner of the state, one over the Seward Peninsula between Kotzebue and Nome, and one offshore of Southeast Alaska. Each is feeding moisture via some strong onshore winds. The Seward Peninsula low will hit a little later, hopefully after the celebrations.  If its not raining it will certainly be cloudy in for the Panhandle, especially the southern parts. Similar for the north slope although leaning more towards low clouds, drizzle and fog. It does not look quite so bad for the the interior and Southcentral…clouds and perhaps some light rain or showers. Click here for a more detailed, up to date NWS forecast. Then let me know how your 4th was, weatherwise and otherwise.

Today is the summer solstice, the longest day of the year, and the start of summer in the Northern Hemisphere, at least from the astronomer’s point of view. From the climatologist’s perspective, the start of summer is a little more subjective, but the months of June, July and August are generally accepted as defining summer. Does this hold in Alaska? Yes and no (you knew it could not be so simple). In most of Alaska, the nicest summer-like weather tends to come more in the early part of the summer and even before "official" summer starts. Savvy Alaskans take advantage of this, as do most school districts here, letting kids out of class earlier in the spring. Down south (the Lower 48 states) certainly has more of a "spring," but summer comes on quicker and in some cases earlier in Alaska. Let’s compare some Alaskan towns with Seattle (we compare lots of things to Seattle).

Number of Days with the Max Temperature 70F (21C) or warmer:

You can see how May brought more 70+ days at each the Alaskan stations shown than at Seattle, even at Bettles, north of the arctic circle. Now 3 weeks into June, Seattle is warming up while none of the Alaskan stations have yet to exceeded the May 70F tally.

West and north coasts in another world

So far I am referring to the interior and the south and southeast coasts. The Aleutian and Bering Sea Islands, and the west and North coastal areas warm up much slower due to the cold ocean waters. The Aleutians are about a month behind the rest of the state in the pace of spring warming, even though the entire chain lies farther south than the southernmost part of the southeast Panhandle. It is really quite dramatic. The north slope—Wainwright, Barrow, Prudhoe Bay, Kaktovik, etc—are so cold overall that despite the large increase in temperatures since mid winter, nothing remotely resembling summer can really happen until about now, mid June, and by mid August it’s all over.

Let’s look at some graphs, arranged north to south, showing both the averages and what’s happened so far: (note: each graph is a little different, but they show the same thing. The first two look similar, but the temperature scale for Fairbanks covers a wider range.) See how both the records (top line) and this year’s traces have quickly rising spikes of high temperature in May and early June that flatten as they approach the warmest average period of the year.

Long Range forecast

What about the rest of the summer? As mentioned above, most of Alaska experiences the best weather early in the spring-summer. Climatologically speaking, average temperatures keep rising till mid July at most places, although high temperatures and records don’t go up much. However, cloudiness and precipitation increase after June, slowly at first then more rapidly into the fall. This fits what we’ve seen above with the nice warm sunny weather favoring early summer. The cloudier weather limits high temperatures, but also keeps nighttime lows from dropping as much. So daily average temperatures (average of the daily high and low) show a more optimistic picture for mid-late summer  than just looking at highs.

But what about this year? Below are the Climate Prediction Center’s July-September forecast maps. They’re saying there’s a fairly strong probability of above average temperatures for the northern interior and north slope, but beyond that, they’re not saying. Nothing statistically significant coming out of their models to indicate above or below normal for temperature or precipitation. This is not surprising since in summer, variations from average are smaller than in winter and don’t seem to correlate very well with climate forcing such as El Niño/La Niña and the PDO. However, with the PDO in the cool phase and a La Niña winter just ending I would tend to lean toward a normal to cooler than normal summer for most of the state. This is consistent with the previous few summers and what we’ve had so far this summer.

How do you define summer? What kind of July and August do you think we’ll have? I’d love to hear your thoughts on these or other questions. Please leave a comment via the comment link below.

Some days have boring clouds, or worse yet*, no clouds. Others I call good cloud days, because of the interesting, and often fast-changing, cloudscapes. Here are some of photos of a few of good cloud days I’ve experienced recently. I hope you appreciate the clouds you see, not just for their beauty but for the interesting stories they tell about the past, present and future weather. If you enjoy these or have some of your own to share let me know via the comment link at the bottom of the post.

Click on any photo for a larger version.

April 13, 2011, Haines. An angry sky of low, turbulent nimbostratus.

April 14, 2011, Haines. An unusually shaped pair of lenticular or lee wave clouds produced by strong winds and moisture flowing over the Fairweather Range.

April 25, 2011, Haines. Interesting slanted, narrow cumulus tower. With spring comes warmer land surfaces and therefore a change to more convective clouds, like this cumulus, vs. stratiform (stable, layered) clouds like in the previous two photos. On our mountainous saltwater coast we seem to get a lot of the narrow- and odd-shaped small cumulus.

May 7, 2011, Inside Passage just north of Juneau. There are plenty of stratiform clouds in this photo, but over land areas there is enough thermal energy to create some of the small cumulus I mentioned in the previous photo—look at them hugging the island. Its amazing any formed since there is not much solar heating. Note that they are over the mostly snow free slopes of Douglas Island (left of center), but not the snowy slopes of Admiralty Island (right of center).

May 7, 2011, Inside Passage north of Juneau, about 20 miles farther north than the photo above. The stratus (left) and the cumulus coexisting—stratus over the water (some on land too) and the cumulus exclusively over the land. The land is warmer and can promote the updrafts needed for the cumulus, while the water is quite cool, but for that reason causes condensation by contact. In early to mid winter the reverse situation is sometimes true: the water is warmer than the air above it causing convection over the water.

May, 11, 2011, Haines. Another example of convective and stratiform clouds coexisting. In this case the small active cumulus are rising due to shallow thermals off the warm ground, while the much higher lenticular clouds (seen above and a little left of the trees in the right part of the photo — they really are higher even though they are at a lower angle…they are farther away) are in a stable, windier part of the atmosphere above. Higher still are some cirrus clouds.

Stay tuned

Coming in the next post, a wrap up of the 2010-2011 winter in Alaska. What areas were warmer, colder, snowier etc than normal? Did my winter forecast hold water? check back soon.

*OK, I do like a little sunshine now and then, so I suppose no clouds actually might beat boring clouds. If you can relate to this you might want to join the Cloud Appreciation Society.

About this time of year, most Alaskans are thinking about Spring with every other brain cycle. Old timers will often say “If you put that snow shovel away now you’re just asking for a big dump of snow.” Are these late season dumps a likely reality, or do the few that have happen just stick in the memory so well?

Here’s a graph that shows the climatological occurrences of a calendar day snowfall of 6 inches (15 cm) or more for a selections of Alaskan stations. (click on image for larger version).

The reality is that for most of Alaska, winter is over, at least for significant snowfalls. The “chances” in April are under 10% for the vast majority of Alaska. Part of the reason is the warming of spring, but another reason, probably a larger reason for the colder parts of the state, is that storms and precipitation slack off quite a bit from late March through June in most areas of the state. Click here to see a table with this data plus five more stations.

Lets take a closer look at the exceptions on the graph: Denali Park and Valdez.

Snow standouts

Denali Park is up in the mountains, elevation a little over 2,000 ft (610 m). Its elevation plus its almost 64 degree north latitude mean snow is possible any month, and significant amounts have occurred in all months except July and August. This data is for McKinley Park coop station near the Denali NP entrance. Higher elevations in the park are obviously going to have more snow and longer winter (the mountain glistens with snow all year).

Valdez is not only at sea level but on the sea, so its snow record is nothing short of amazing. The difference with Valdez is that although it is a port city, the salt water is but a narrow arm of the Pacific, connected to the interior by the valleys which lead through Thompson Pass. The town is well situated to allow the right mix of moist, relatively warm marine air necessary for heavy precipitation, and the cold air of the interior which keep the precipitation as snow. There are a few other weather stations with this situation (see Haines Customs on the spreadsheet), and many more such valleys without habitation or measurement.

Barrow is also worth a mention. North of 71 degrees, Barrow’s arctic climate means precipitation of any type is scarce and follows the temperature curve through the year: The warmest months are the wettest, the coldest the driest. Snow is not rare in any month, and the heavier snows are actually less likely in the coldest months. Note on the graph how the months with a 6+ inch snowfall on record seem almost random. July has one but not December or February. April-June have none, primarily for the reason stated above. Keep in mind, however, that in any season snowfall more than 6 inches is very rare, so even with almost a century of records, patterns are a bit speculative.

So, go ahead, put that snow shovel away…I dare you.

The simple answer: It’s the elevation above which any precipitation is expected to be snow, and below which, rain.

It is interesting that the term is not found in the NWS online glossary http://www.weather.gov/glossary/ nor in the AMS’s online glossary http://amsglossary.allenpress.com/glossary/ nor in their printed version, Glossary of Weather and Climate. It is, nonetheless, a term frequently used in official NWS forecasts in Alaska and mountainous areas of the lower 48:

MOTORING FORECAST FOR SOUTH KLONDIKE AND HAINES HIGHWAYS
ISSUED JOINTLY BY NATIONAL WEATHER SERVICE JUNEAU AK
AND ENVIRONMENT CANADA VANCOUVER BRITISH COLUMBIA
1000 AM AKST FRI FEB 11 2011

SOUTH KLONDIKE HIGHWAY - SKAGWAY TO WHITE PASS
.TODAY...RAIN. BREEZY. SNOW LEVEL 600 FEET. HIGHS AROUND 39.
SOUTH WIND 15 TO 25 MPH.
.TONIGHT...RAIN LIKELY THROUGH THE NIGHT. SNOW LIKELY LATE.
LITTLE OR NO SNOW ACCUMULATION. SNOW LEVEL 700 FEET DECREASING TO
300 FEET LATE. LOWS AROUND 32...RANGING TO AROUND 21 NEAR WHITE
PASS. LIGHT WINDS.

But maybe what you really wanted to know is…

How can I determine the snow level?

First let’s talk about a more precise term, the freezing level. It is the elevation where the temperature of the air is zero Celsius (32 Fahrenheit…but Celsius is so much easier when dealing with freezing level and such). It’s not quite as simple as it sounds, though…here are several situations to consider:

1. Zero freezing level: If the surface temperature is at or below 0 C, and the air above remains 0 C or colder all the way up, the freezing level is zero, or “surface.” This is the usual situation for the colder parts of Alaska during the winter (and spring and fall for the Arctic). The temperature might be way below freezing at the surface and aloft, but we still say the freezing level is zero or surface—even though it really is a non-issue.
2. Single freezing level: If the surface temperature is above 0 C, and the air cools to below 0 C above the surface and remains below freezing above that, then we have the simplest case of a single above-surface freezing level.
3. Multiple freezing levels: If there are inversions (layers where the temperatures increase with height) in the atmosphere that straddle the freezing point, then there are multiple freezing levels. This can happen with surface temperatures above or below freezing (the latter being the more common case in Alaska). These situations can be quite complex and can lead to freezing rain or drizzle or sleet. More about this will have to wait for a future post.

In a single above-surface freezing level situation, the snow level will be a certain distance below the freezing level. This distance varies but the rule of thumb is 1,000ft (~300 meters) below the freezing level. This is because as the snow falls into above-freezing air, it does not melt immediately. This is obvious from those times that it is snowing at ground level while the temperature is a bit above freezing, in rare cases by 5 or 6 Celsius degrees (~10 Fahrenheit degrees). Two things come into play. One is that it simply takes some time for the flakes to melt. Another is that melting snow absorbs a lot of heat and cools the air, slowing the melting process. [see my comment update below]

How can I find the current snow level?

Unless you want to carry a thermometer aloft on foot or in an aircraft, you can take advantage of the global 3D weather observing system perfected over the past 70 years or so, and now available to anyone with Internet access. Weather balloons are still the backbone of the system, and you could find the exact freezing level(s) where and when the balloon soundings are taken. This data is ingested into the massive computer models, which not only provide a interpolation of the current freezing level for any location, but then project all weather parameters, including freezing level, into the future. Here’s a map from the Alaska Aviation Weather Unit giving the current day’s freezing levels:

click for larger version

You will notice most of the state—almost everything north of the red line—is in situation #1 above, SFC (surface) freezing level. In the Aleutians, the freezing level ranges up to around 5,000 ft (020 means 2,000 ft in aviation speak). In Southeast Alaska it ranges from 2,000 to almost 4,000 ft, but notice how the surface line crosses the green line and runs down eastern part of the panhandle. This is indicating multiple freezing levels…in some places (within the area between the SFC line and the 020 line) the surface is below freezing but there is above-freezing air aloft .

You can find the current version at http://aawu.arh.noaa.gov/index.php?tab=1

How can I know what the snow level will be in the future?

This map from the Alaska Weather TV show gives the next day’s freezing level (but be sure to check the time since the maps are only produced once per day in the afternoon.

click for larger version

You can find the current version at http://pafc.arh.noaa.gov/tvwx.php. Look under the aviation maps drop down.

If you want to move beyond this simple chart, you can find more detail and longer reach forecasts by looking at the model graphics. Most show lower atmosphere temperature trends, which can be used to surmise changes in the freezing and snow levels, but some include actual freezing level maps. There are also precipitation type maps which show whether rain or snow, or freezing precipitation is forecast. Visit this UAF site and scroll down near the bottom for freezing level maps. Look for “precipitation category” for rain vs snow, and if you know how to read a sounding plot, you can also see forecast soundings for four stations under “Skew-T/Log-P.”

hhttp://knik.iarc.uaf.edu/AtmGroup/ForcastGraphics.htm

Can I estimate the freezing level or snow level from the surface temperature?

Yes, but with plenty of caveats. What is needed is to know how fast the temperature decreases with height (a weather element called the lapse rate). The bad news is that the lapse rate is a) not always constant, and b) not always even lapsing (in the case of an inversion–warming with height). The good news is that we can usually spot those situations where there are probably inversions or otherwise tricky temperature profiles. In most situations where you are dealing with a large scale weather system bringing wind and rain or snow, the atmosphere becomes more homogeneous, rather than layered. It is said to be well mixed. This is more often true on the coast and less often true where mountains block the low level flow from the storms, such as most of inland Alaska. If clear high pressure weather is in place, this method is likely to fail. Caveats done for now, the lapse rate in the mixed situations tends to be about 3.5 degrees F per 1,000 ft, or 6.5 degrees C per 1,000 m. Simply figure how many feet or meters needed to reduce the surface temperature to the freezing point. The snow level will be about 1,000 ft or 300 meters below that. Any error is most likely to be on the low side, since the lapse rate is not usually greater than the figures given, but often less. However if there are lots of cumulus buildups then you have an unstable situation and the lapse rate is probably greater, meaning the freezing level may be lower than calculated. In this case the snow level may be lower yet, since showery type precipitation tends to be more vigorous, with a downdraft to push snow flakes and cool air to a lower level.

Is the snow level ever so high that there is, for practical purposes, no snow level?

Not in Alaska. Virtually all precipitation that falls outside the tropics starts out as snow. Rain is simply snow that melted before reaching the ground. So the freezing level really would be better called the melting level. The one significant exception is drizzle, which can form and fall from shallow, above-freezing stratus clouds.

I hope I answered more questions than I raised, but just in case, the comments feature (link below) is a good place to ask for clarification, or add your own ideas or experiences with snow levels, freezing levels or anything weather.