Warming By Season

A few weeks ago I alluded to the fact that the temperature increase of recent decades has been smaller in summer than at other times of year in northern Alaska; but when we consider that temperature variability is lowest during summer, the warming is still very significant at that season.  It's worth illustrating this in a bit more detail.

First, the chart below shows the simple temperature difference between the 1971-2000 and 2001-2017 periods for 12 overlapping 3-month seasons throughout the year, for Utqiaġvik (Barrow) as well as Kotzebue, Nome, and Fairbanks.  The temperature difference peaks in late autumn (October-December) for all 4 sites, and the amount of warming that has occurred in summer is ostensibly quite small in comparison.

However, when we normalize the temperature difference by the interannual standard deviation of the seasonal temperatures (during 1971-2000), the picture changes - see below.  Autumn is still the time of peak warming, but the summer warming no longer appears insignificant.  Interestingly, the summer temperature change at Kotzebue has been larger in standardized terms than the winter and spring warming; but at Utqiaġvik the summer trend remains less pronounced than at other times of year.

None of this is a big surprise, but I think it provides a bit of useful perspective on the significance of relatively "small" summer warming trends in the Arctic.

Are Fairbanks Summers Getting Wetter?

Hi,  Rick T. here with a post about Fairbanks summer rainfall.

I was at a meeting a few weeks ago and one of the folks there, who works in community planning, was wondering if Fairbanks summers are becoming wetter. After all, the past five years (especially 2014 and 2016) have featured two of the wettest summers of record. If summers are getting wetter, that is something that planners need to take into account when considering things like downtown storm drainage capacity, rural road culvert sizing or generally higher river levels. Happily, here in Fairbanks we have enough historical data to take a stab at answering that question.

Since summer precipitation often comes in the form of showers and thunderstorms (especially the first half of summer) and these are much less frequent (climatologically speaking) over the flats as compared to areas closer to higher terrain, it's not a good idea to use the usual Fairbanks "threaded" climate record, since we know that the Fairbanks Airport, being out on the flats, receives significantly less rain than areas not far to the north and east. Luckily, we have precipitation observations taken in almost the exact same place, from the UAF Ag Farm, since July 1911. While there are some data quality problems with the Ag Farm observations over the decades, summer precipitation looks reasonable. Amazingly, there appears to be only one month that is actually missing, August 1969. For this one month I used the College Observatory data (taken on West Ridge near what is now called Jack Townshend Point, about 3/4 of a mile northeast of the Ag Farm). Here is scatter plot of the accumulated June through August precipitation at the Ag Farm for the past 106 years (1912 through 2017):

Just glancing at the graphic there is nothing obvious to my eye. The ten wettest and driest years are not all bunched-up on one or the other side of the plot. Naturally, there is some clustering: the 1920s saw a number of very dry summers and the 1940s several wet summers. Of course, we need not rely on our eyeballs; statistical analysis is our friend.

The simplest analysis is just linear regression. In the chart above I've plotted the observations along with ordinary linear regression (green line), which in effect is modeling the average (mean), and a technique called linear quantile regression, which here I use to model the median. A reason to check both is that ordinary linear regression is sensitive to individual values that are far from other values (i.e. "outliers"), while quantile regression of the median is not sensitive to extremes. In this case, we see that both flavors of linear regression show an increase of about an inch precipitation over the past century. For the ordinary linear regression this is significant at the 90% confidence level but not at the 95% level. The trend of the median summer precipitation is not significant at even the 90% level.

Of course, it's entirely possible (even likely) that changes in summer precipitation are not best described by a simple linear fit. Often in Alaska, a piecewise linear regression (i.e. "hockey stick") provides a better estimate of trend – but not in this case. There is no evidence of any significant changes in the linear trend.

Another change we can check for are any abrupt "step" increases. When we do this, the results are also mixed:

Here, the results are mostly dependent on the required length of any segment. Since we are looking a long term changes that might be important for community planning, I restricted the analysis to changes that persist at least couple of decades. Requiring a minimum length of 20 years shows one step increase, at 1998 (note: the analysis was not restricted to a single step change. With 106 years of data, as many as five step changes are possible). Interestingly, increasing the minimum length to 25 years results in no step changes of statistical significance.

The last analysis I'll look at here is a simple smoothing of the observed precipitation:

Here the brown line is a cubic spline fit to the data. Cubic splines are very commonly used to detect patterns (not just linear) in noisy data. In this case, looking only at the brown line, we see, much like the linear regression analysis, a general upward trend, especially since the 1990s, with a total increase of nearly two inches between 1912 and 2017.  However, this is only part of the analysis. Since we don't know what the hypothetical "true" fit is, in this case primarily due to the spread in the summer to summer rainfall, we can construct confidence intervals that give us a better idea of where the actual (but unknown) fit lies. I've done that here, shown as the gray shading. Notice that the confidence interval at least partially overlaps itself for the full 106 years of records, e.g. look along the total precipitation 6" grid line. This suggests that we don't (quite) have high confidence that there really is a significant change in the spline fit.

So where does this leave us as to the original question? Are summers becoming wetter? It looks to me like the answer is an unequivocal "maybe".

On the yes side, the ordinary linear regression trend is significant at the 90% level, as is the 20-year minimum length step change.

On the no side, the trend of the median summer precipitation is not significant, and there is no significant step change when requiring a 25-year (or longer) length.

In the maybe camp, the cubic spline analysis is certainly suggestive of a significant change, just barely falling into the no trend camp (using a 95% confidence interval).

While this analysis is perhaps not satisfying from a community planning perspective, since "maybe"  seems like it's not an "actionable" answer, from a climate perspective it is interesting that we are close to being able to detect an increase, which for precipitation in Alaska is not (yet) usually the case. However, increasing precipitation during the 21st century is exactly what the the climate model consensus have for nearly all of Alaska, and we may be starting to see that reflected in Fairbanks. The next several years will help to clarify the trend for the early 21st century.

Update on Lightning and Fire

Prompted by some comments on my post about Alaska fire acreage a couple of weeks ago, I acquired the most recent data from the Alaska Lightning Detection Network and pulled up a comparison to recent years - see below.  Earlier this month the cumulative number of lightning strikes recorded by the network was the highest for the time of year in the modern data set, but ever since last week's cold blast there has been almost no activity (at least until today).  (Note that the lightning sensors were changed in 2012, so it's not possible to do a direct comparison with earlier years.)

Fire acreage statewide currently stands at about 210,000 acres, which is also above most recent years, although 2013 and 2015 really took off in the latter part of June.  Today's cumulative acreage is about 10 days ahead of the long-term median in terms of the rate of burning statewide.

The year-to-year variability in fire acreage is obviously much higher than that of lightning, as there are other critical factors that control fire growth.  For example, both lightning and acreage were very high in 2015, but in 2013 acreage was high while lightning was relatively sparse; of course 2013 was very hot and dry, so fuel conditions were very conducive to the spread of fire.

Unsurprisingly, the ratio of acreage to lightning strikes is wildly variable - see below (calculated here whenever the cumulative number of strikes exceeds 1000).  In 2015, over 30 acres burned for every lightning strike detected, on average.  It would be interesting to compare this number to fire behavior in the lower 48.

While fiddling with the lightning data, I also determined the days on which the most lightning strikes were detected within 100 miles of a few different sites.  This allows us to look at the typical weather patterns associated with particularly intense lightning activity in different parts of the state.  For example, here's the average 500mb height pattern (the departure from normal) for strong lightning activity near Fairbanks: unusually high pressure aloft is centered to the northeast, and Fairbanks lies just to the south of the anomalous ridge axis.

When lightning activity is intense within 100 miles of McGrath, the ridge axis tends to be located much farther west, and a trough is evident over the Gulf of Alaska.

Below are the maps for strong lightning activity within 100 miles of Ambler and Eagle, respectively.

Chilling in Summer

Northern and interior Alaska has seen some very chilly weather for the time of year in the past few days, as a strong upper-level trough and an unseasonably cold air mass plunged south out of the Arctic at the beginning of the week.  Despite the fact that the summer solstice is now less than 10 days away, and daylight is continuous, sub-freezing temperatures have occurred in many of the usual cold spots in the interior.

In the Fairbanks area, three consecutive days have seen temperatures falling into the 30s, with upper 20s at the colder spots like North Pole and the Goldstream valley.  The Smith Lake site on UAF's North Campus recorded 26°F yesterday morning; but the chart below (note the Celsius scale) shows that only a few days since late May have NOT dipped below freezing at this spot - even when daily high temperatures were well into the 70s.

The airport has seen 37°F, 36°F, and 37°F in the early mornings of the past three days, which is a remarkably cold series of daily minimum temperatures for this time of year.  In fact, this is the closest to the solstice that Fairbanks has ever observed 3 straight days with low temperatures of 37°F or lower at the official climate site (1930-present).

It's also interesting to note that with a high temperature of only 53°F, Monday's daily mean temperature was a mere 45°F.  It's been almost 70 years (1949) since Fairbanks saw such a chilly day this late in June (or in July).

The mid-level atmospheric pattern that created the midsummer chill is evident in the sequence of maps below.  The charts show the 500mb analysis at 24-hour intervals from 4am on Saturday through 4am today, and for ease of reference the red dot shows Fairbanks' location.  Notice the very tight pressure gradient and associated strong northerly flow that rushed down from the high Arctic into Alaska at the beginning of the week - this was a remarkable cold blast for the time of year.

Saturday:

Sunday:

Monday:

Tuesday:

Wednesday:

Finally, here's a nice view from Monday of the fresh snow that fell at Toolik Lake (2400' elevation) on the north side of the Brooks Range.  The lake is still mostly frozen despite the fact that the air temperature reached 60°F earlier this month.

Fire Season Begins

Lightning has been widespread over Alaska in the past several days, and wildfires have sprung up as an inevitable consequence.  According to the latest information on akfireinfo.com, fires have burned about 25,000 acres statewide so far this season, which is about normal for the time of year.  Fire activity typically ramps up quickly in June, with burn acreage often exceeding 200,000 acres by the end of the month.

Year-to-year variability of fire acreage in Alaska is a very interesting topic and a fascinating and challenging prediction problem.  I'd like to do an in-depth study of it one day, but today I'll just make a couple of points.  First, consider the map below, showing a 23-year correlation between sea surface temperatures in May and the subsequent fire acreage rank.  I've used the rank of the fire acreage (with higher rank for higher acreage) rather than actual acreage numbers because the distribution is strongly non-Gaussian.

The color scheme on the map rather exaggerates the statistical significance of the correlations, as the highest values are only 0.4-0.5, but nevertheless it's interesting to see that fire activity is favored by warmer ocean conditions in both the northern North Pacific and the central tropical Pacific.  The horseshoe-shaped pattern looks quite reminiscent of the PDO pattern, but actually it's a bit different; the typical PDO horseshoe hugs the coast of North America more closely and has a strong inverse correlation with SSTs extending east of Japan to south of Alaska.  Alaska fire acreage is actually nearly uncorrelated with the PDO index in May.

There is a better correlation (+0.44) between Alaska fire acreage and the North Pacific Mode (NPM) index.  The NPM pattern is focused between 40 and 50°N across the North Pacific, and according to the first map above, this is an area that shows some connection with Alaska fire activity.

So what do current conditions look like?  The map below shows the May analysis; the NPM was slightly positive, as it has been for the last 4 months, but it's not a dramatic anomaly (excepting the Bering Sea warmth).  This suggests that ocean temperature patterns are only slightly favorable for enhanced fire activity this year.  As an aside, there seems to be no sign of the strongly positive NPM phase that the long-range models were predicting earlier in the year (and are still predicting).

We can also search for fire-acreage-related precursor patterns in the atmosphere.  According to the map below, there is a statistically significant - but not highly robust - correlation between 500mb heights over Alaska in May and subsequent fire acreage.  This makes sense; if the weather pattern sets up with a ridge over Alaska during May, then dry and sunny conditions will reduce fuel moisture, and the next month or two are also more likely than not to be warm and dry.

How about May 2018?  Rather than having a ridge over the state, there was a trough over the southwest, and most of the interior was wetter than normal.  So this points to reduced fire activity, albeit with low confidence.

And now perhaps the most interesting result that I've stumbled upon in this brief analysis.  The map below shows the average SST anomaly in winters following the 6 most active fire seasons since 1995.  Most readers will recognize the pattern immediately: the warm band along the equator in the central and eastern Pacific is a classic El Niño pattern.  This suggests that very active fire seasons in Alaska have a strong tendency to be followed by significant El Niño episodes.

The chart below confirms the rather remarkable statistical connection; the 4 strongest El Niño's since 1995 were preceded by Alaska fire acreage in the top quartile (6 of 23) since 1995.  Naively this suggests we can use Alaska fire acreage as a predictor for El Niño - but why would this be?  My take is that the atmospheric and oceanic patterns that evolve into major El Niño events are already unfolding in the summer months prior to the classical winter peak of El Niño, and those patterns happen to be very favorable for Alaska wildfire.

The last point to make is that the latest data from the long-range computer models have recently shifted quite decisively in favor of El Niño for the coming winter (2018-19); so it will be most interesting indeed to see how the rest of the fire season evolves in Alaska.

North Slope Warmth Subsides

After a winter of record-breaking warmth in Alaska's northernmost city, temperatures have returned to near-normal levels recently, and even a bit below in the past week or so, as easterly flow has kept a chilly Arctic air mass in place.

The slight preference for cool conditions lately has prevented Utqiaġvik (Barrow) from seeing a sustained thaw so far this season; there has not yet been a day with mean temperature above freezing this year.  It has been a few years since the first such day occurred as late as June, but we would have to go another 10 days or so for the absence of warmth to become really unusual.  The chart below shows the long-term trend towards earlier first thaw day, and earlier first 50°F; both dates have advanced by more than a day per decade over the long-term history at Utqiaġvik.

The relative magnitude and persistence of the recent warming trend at different times of year is illustrated by the chart below.  For each month in the past 15 years, I've plotted up the monthly mean temperature as a departure from the 1971-2000 normal, and the red markers highlight the anomalies since 2013.  As we all know, warming has been most amplified in autumn as a direct result of sea ice loss.  The absolute magnitude of change has been smaller in summer, as Arctic summer temperatures are rather strongly constrained by the presence of at least some sea ice; but the summer warming is nevertheless very significant as the variance is much smaller in the warm season.

The year labels at the top of the columns indicate months in which the monthly-mean temperature records were broken in the past winter.  Remarkably, from November-March, 4 of 5 months saw monthly mean temperatures higher than any observed before.

Just to drive home the magnitude of what happened in the winter that recently ended, the chart below shows the November-March mean temperature for each winter since 1930-31; and the high-quality CRN data are fully consistent with the airport temperatures over the past 16 years.  A linear trend obviously doesn't capture what is happening here.

Sunshine at CRN Sites

After reviewing the status of Alaska's CRN data last week, curiosity led me to take a look at the solar radiation measurements from these sites.  For example, it's interesting to find out what these instruments have to say about how solar radiation varies across the state - at least for the last few years.

The chart below shows a summary of April-October total solar energy for the 11 sites that have been in operation since at least 2013 and have essentially complete data for these months.  The horizontal black lines show the 5-year mean for each site, and the blue bars indicate the minimum and maximum values within this brief 5-year period.

The sites near Fairbanks and Tok are the only interior sites represented here, and as we would expect they are at the top for solar energy.  Interestingly Metlakatla, on Annette Island in Alaska's far southeast, is in 3rd place and close behind Fairbanks.  It's not surprising to find that rainy Sitka is easily in last place; but note that the difference in solar energy between the cloudiest site and the sunniest site is less than 50%.

The range between minimum and maximum seasonal totals is remarkably high at the Red Dog site, but this is mostly because of a very low total from 2013; this looks suspicious and might be incorrect.  (If we exclude 2013, Red Dog actually comes in above Fairbanks for mean solar energy, and the Red Dog instrument also reported the highest seasonal total of any site in any year.)  More robust, perhaps, is the very low variance of solar radiation at the sites near Barrow (Utqiaġvik) and Tok; it's quite extraordinary, actually, how consistent the solar energy has been at these locations in the past 5 years.  But in the case of Barrow, data from earlier years showed higher values - see below.

The decrease of solar energy at the Barrow CRN site, evident in the chart below, is highly statistically significant even over such a short period.  Presumably this is related to the increase in open water area in the Arctic Ocean and therefore higher evaporation and increased cloudiness in recent years.

Improvement in CRN Data

I've mentioned the US Climate Reference Network program on previous occasions - it's a national effort to install high-quality climate monitoring instruments throughout the nation in locations that are unlikely to be affected significantly by urbanization in the coming decades.  So far 21 such sites have been installed in Alaska, with the most recent being near Toolik Lake and Cordova last summer.  Several more are planned:

Read more about the program here:

https://www.ncdc.noaa.gov/crn/

https://www.ncdc.noaa.gov/news/new-climate-observing-stations-alaska

In previous years it has been very disappointing to see that several of the sites had serious and persistent problems with missing temperature data in the winter months.   This is apparently caused by the fuel systems being unable to produce sufficient electrical power to operate the instruments and other electronics during cold weather.  It's a little surprising that the system engineering wasn't up to the challenge of Alaska's climate, but one must concede that it's no small task to run a complex array of instruments without external power throughout the deep cold and dark of the high-latitude winter.

But happily there is now some good news: some modifications were made in last summer's maintenance visits, and the past winter saw a significant reduction in the amount of missing data from a number of sites.  The chart below shows (in green) the statewide percentage of all November-March days for which daily high and low temperature data are available in GHCN, and the black columns show the number of sites.  The network was in a rather sorry state in winter 2015-2016, with more than 20% of days missing from the 18 sites around the state, but in the past winter only 7% of days were missing statewide.  If the improving trend continues, we'll soon be in good shape.

Here's the percent complete over the lifetime of each site.  Notice that the really bad locations are some of the coldest and most remote locations, whereas the instruments in southeast Alaska are performing just fine.

The sites that improved dramatically this winter were Deadhorse, Nowitna (Ruby 44 ESE), and the sites near Selawik and King Salmon: whatever tweaks were made at these locations worked nicely.  On the other hand, there are still significant problems at Ivotuk and Denali 27 N.  Let's hope that one more year does the trick to get the network running as intended.

Chena Basin Snowpack

Continuing with the theme of snowpack, here's an update on the conclusion of the snow season in the Chena Basin above Fairbanks.  Back in March I noted that the amount of snow on the ground was at near-record levels based on data from 5 SNOTEL sites in the hills, and it turns out that the snowpack did indeed reach an unprecedented level by late in April.  Historical data goes back to 1981.

As of a week ago, 3 of the 5 sites were reporting a greater snowpack (in terms of water equivalent) than in any other year on the same date.  Of course the major warm-up in the past few days has melted most of the snow at the lower elevation sites - Teuchet Creek (1640') melted out yesterday - but Mt Ryan (2800') still has 8" of water equivalent on the ground.  Even more remarkably, Munson Ridge (3100') is reporting 15.2" still on the ground (a record for the date) and a 47" snow depth.  The beginning of hiking season will be somewhat delayed in the White Mountains this year.

Here's a chart of snow water equivalent at Munson Ridge for this year and some other notable years.  The greatest snowpack of record occurred in 1991, but no other year retained so much snow at this late date.  It will be interesting to see how long it lasts; in 1982 there was still snow on the ground on June 13.

And here's an update to the multi-station chart that I showed before; the late winter snowpack has been much greater than in any recent year.  (The rapid rise in percent of normal at the end of April reflects the rapidly diminishing median value, as the median snowpack drops to zero in early May for 3 of the 5 sites.)

Snowpack Season

The winter snow cover melted out on Friday in Fairbanks, according to measurements by the National Weather Service at the airport.  This is somewhat later than normal, which is not surprising in view of the healthy snowpack at the end of winter and the rather cool temperatures of late.

The chart below shows the 88-year history of dates when the continuous winter snowpack began and ended in Fairbanks.  The variance of dates is greater for snowpack onset, but that's nearly all because of two major outliers in 1934 (the great December chinook) and 1992 (early arrival of winter).

The dashed lines show long-term linear trend lines for the two series of dates, but instead of least squares regression I've used quantile regression, with each trend line showing the best estimate of how the median has changed over time.  The reason to go with quantile regression is to avoid an undue influence from outliers, which seem likely to be a problem here, especially for the snowpack onset dates.

It's interesting to see that the regression estimates indicate that snowpack onset has become earlier by nearly a week, and meltout has become slightly (about 3 days) later, over the 88 years.  But it's important to note the degree of uncertainty: the 90% confidence interval includes a zero trend for both series, so neither trend is statistically significant; we can't confidently rule out the possibility that the trends are just a reflection of random chance.

One thing we can say with confidence, however, is that snowpack meltout has not become significantly earlier over time, and this is intriguing.  We know that April - when most of the melting occurs - has become significantly warmer, so how is the snow not disappearing more quickly?  There might be a variety of explanations involving changes to sunshine or precipitation during melt season, but the simplest explanation may be the best: it seems there is just more snow on the ground these days.  The chart below shows the snow depth in Fairbanks on April 1st each year, and there's an upward trend that is significant at p~0.05.

More investigation will be required to determine whether and how this trend is related to precipitation changes during winter; my impression from previous work is that Fairbanks winter precipitation has NOT increased over the long haul, so it seems this is a rather interesting question.

Nenana Breakup

Tuesday was the big day for tripod watchers in Nenana, as the ice moved enough to stop the Ice Classic clock early in the afternoon.  May 1st is just about normal compared to recent decades, but it's interesting to note that the ice went out very "easily" when we consider how little warmth was available for thawing.  The normal (1981-present) accumulation of thawing degree days (excess of mean daily temperatures above freezing) by May 1 is about 170°F, but this year the total was barely half of that (88°F through May 1).

Here's an update of the figure I produced last week, with the observed (green) line extended to the right to show the forecast verification.  The last week or so before breakup turned out to be cooler than the previous week's forecast indicated for Fairbanks, and indeed the second half of April was significantly colder than normal in Fairbanks, but that didn't keep the ice in place for long.

The chart above shows that breakup occurred this year with cumulative TDDs not even reaching the 5th percentile of the historical range, and the scatter plot below confirms this point: only a small handful of other years since 1930 had so little thawing by the time breakup arrived.

As an aside, the relationship of TDDs and breakup date also reveals an interesting tendency for the latest breakups to occur after a relatively small quantity of thawing; in other words, the later the ice holds on, the less cumulative warmth is needed to produce breakup.  This undoubtedly reflects the increasing influence of solar insolation as the calendar advances; by mid-May, the strong direct influence of the sun on the ice accelerates breakup compared to when it would be expected from temperatures alone.

Another interesting aspect of how "easily" breakup occurred this year is that May 1 was one of the coldest days on record for the conclusion of the Nenana Ice Classic.  It's unusual for the daily high temperature in Fairbanks to be less than 50°F on breakup day, and breakup is usually late when this does happen; but this year the high temperature was only 43°F.  The chart below shows how unusual this is, especially compared to recent decades.

How can we explain the relative ease with which the ice moved out this year?  I think at least two factors were at play: first, the ice was very thin - barely over 24" thick at the end of March - owing to the combination of a thick snowpack and a warm winter.  Second, the ample snowpack across the region has produced higher than normal runoff, leading to increased pressure on the ice.  It's also possible that the rain and snow on Monday and Tuesday was the straw that broke the camel's back; Fairbanks reported nearly a quarter-inch of rain and snow (that soon melted).

Here's a webcam view of the scene at Nenana on Wednesday morning, with a dusting of fresh snow from overnight snow showers; the wreckage of the tripod sits in the broken ice on the left.

Finally, and for the record, it's fun to note that there was a trace or more of fresh snow on the ground at UAF's West Ridge for 3 consecutive mornings this week (Monday, Tuesday, and Wednesday) - see below.  Such are the travails of spring in interior Alaska.

Snow in the Hills

Spring suffered another setback in the interior today, as a round of steady precipitation brought the snow line down to valley-level in the Fairbanks area for a few hours.  Mixed rain and snow was reported from the airport during the morning hours and there was a brief threat of a fresh snow cover at UAF:

Snowfall of 2-4" was reported from the hills, according to the NWS, and temperatures have been below freezing all day above about 2000'.  The webcam views from Cleary Summit showed the Steese Highway becoming snow-covered between 5 and 6 am this morning:

However, the road surface cleared off by mid-morning (10:30 in the image below) under the influence of solar heating despite thick cloud cover and ongoing snowfall.

As Rick noted the other day, this spring is turning into something of a cool one relative to recent norms, although it's been more notable for the lack of warmth than the occurrence of unusual cold: there have been only 2 days above 50°F so far this year, compared to 12-22 such days by the end of April in the past 4 years.  This April's mean temperature has been below freezing in Fairbanks for the first time since the record cold April of 2013, but for most of the 20th century it was more common than not to have a sub-freezing monthly mean in April.

More chilly and damp weather, with snow in the hills and probably in town too, looks rather likely in the next couple of days.  It's unusual to see lengthy spells of rain and snow at this time of year - the chart below shows that the long-term frequency of rain or snow reaches its seasonal minimum in early May, based on hourly reports from Fairbanks airport since 1950.

This morning's 500mb chart shows a very typical set-up for wet weather in Fairbanks-land: vigorous flow out of the west-southwest in the middle levels of the atmosphere.