Persistence

Here is a an updated plot of standardized daily temperature departures for Fairbanks thus far this year. Recall that standardized departures are simply a way of scaling the absolute departure from normal to reflect the typical variability for a given time of year Technically, it's the departure from normal divided by the standard deviation. In this case, the daily normal and the standard deviation are taken from the 1981-2010 NCDC normals. This month, the outstanding feature is the nearly unbroken persistence of the warm anomalies rather than any major daily extremes.

Tanana River at Nenana goes out

The ice broke on the Tanana River at Nenana Monday evening, tipping the tripod on the Nenana Ice Classic at 839pm ADT. This is the fourth earliest break-up of the ice on the Tanana since the Nenana Ice Classic started in 1917. Here is a plot of break-up dates since 1917. The black lines represent simple linear regression. From 1917 through 1976 there is no trend at all. Since 1977 (corresponding to the shift of the phase of the PDO from negative to positive), the trend is not (yet) statistically significant, due to the comparative small sample size since then. However, for the entire 96 years of record, the trend toward earlier break-up dates, by more than a week is significant.

Seasonal Snowfall Comparison

The snow season is not necessarily done with yet, but with mild weather here and the snow melted out in town, here is a comparison of total seasonal snowfall between the Fairbanks Airport and here on Keystone Ridge. The percentage of snowfall on the ridge compared to the airport is plotted by the orange line. As Keystone Ridge is more than 1000 feet higher elevation than the airport, it's no surprise that every year there is more snow on the ridge than the airport, and the 16 season average is 39 percent more on the ridge than the Airport. It is somewhat surprising that in some seasons the difference is not very great: in three of sixteen winters the difference is less than 20 percent. This reflects the fact that the transition season from rain to snow in the autumn is often abrupt, and that spring is usually quite dry, so contributes little to the seasonal total. The winters with the biggest percentage difference, this past winter and 2009-10, both resulted from Keystone Ridge receiving much more snow in one or more events when winds aloft were west to southwest, a favored direction for copious precipitation.

Snowpack Meltout

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
257 AM AKDT FRI APR 20 2012

...FAIRBANKS WINTER SNOW PACK MELTS OUT...
...RIGHT ON SCHEDULE...

PERSISTENTLY MILD WEATHER AND PLENTY OF SUNSHINE THE PAST TWO
WEEKS HAVE NOW MELTED AWAY THE WINTER SNOW PACK IN FAIRBANKS. THE
LAST DAY WITH MEASURABLE SNOW ON THE GROUND AT THE FAIRBANKS
AIRPORT WAS APRIL 19TH. THIS IS VERY CLOSE TO THE LONG TERM AVERAGE
DATE FOR LOSS OF THE WINTER SNOW PACK...WHICH IS APRIL 22ND.

FAIRBANKS HAS HAD AN INCH OR MORE OF SNOW ON THE GROUND SINCE OCT
18TH...RESULTING IN 184 CONSECUTIVE DAYS WITH SNOW ON THE GROUND.
THIS IS AGAIN VERY CLOSE TO THE LONG TERM AVERAGE OF 186 DAYS.

SNOW COVER REMAINS AT HIGHER ELEVATIONS AND IN SHADED AND WOODED AREAS
EVEN AT VALLEY LEVEL. SNOW DEPTHS THURSDAY EVENING INCLUDED
19 INCHES AT KEYSTONE RIDGE...SOUTH OF MURPHY DOME AT 1600 FEET
ELEVATION...AND 29 INCHES AT MUNSON RIDGE...SOUTH OF CHENA HOT
SPRINGS AT 3200 FEET ELEVATION.

$$
RT APR 12

Chena Slush Out

Here's a somewhat fuzzy webcam photo looking south across the Chena River just before 8pm ADT Thursday from Front Street (image courtesy of Pro Music). There are some open areas but most of the water visible is water on top of ice.

AO and Alaska Temperatures

A reader asked if the yo-yo temperatures since last autumn are related to the Arctic Oscillation. Short answer, no.

Long answer:

For starters, the Arctic Oscillation Index is a way to describe (near) surface pressure patterns in the Northern Hemisphere at mid and high latitudes. However, as the plot below illustrates, the long term (1949-2012) correlation with surface temperatures in the cold season (Oct-Mar) are not very high over western North America and most of Alaska (the correlation is marginally significant over a small area over south-central Alaska).



For this past cold season, below is a plot of the daily AO index and the standardized daily mean temperature anomaly for Fairbanks (through April 13). As you can see, there was no patterning of the AO Index with how much above or below normal the temperature was in Fairbanks. Notice that the very cold weather in mid-November occurred with a somewhat positive AO, while the cold weather at the end of January occurred when the AO was at largest negative value of the whole winter. Similarly, the very mild weather in early December occurred with a strongly positive AO, while at the end of December the AO was again strongly positive but Fairbanks was considerably colder than normal. For the whole period (Oct 1-Apr 13), the correlation was functionally zero (0.02).

New Webcam

Yahoo! The FAA's webcam high atop Ester Dome, northwest of UAF, is finally online. Here's the southeast view from 418pm ADT Wednesday. There are also views looking north, southwest and west. You can plainly see Chena Ridge and the Tanana River.

Snowpack Meltout

With record heat in progress, and the snow depth down to 7 inches and going fast, here's a look at the winter snowpack meltout date since 1930. For this exercise, meltout date is the latest date with 1 inch or more snow on the ground which was preceded by a week of days with an inch or more of snow on the ground. This last bit is there to exclude the few years like, say, 2001, when the winter snowpack was gone by April 22nd, but there were two consecutive days with accumlating snow in early May that resulted in an inch on the ground on the morning of May 5th. For most of the period of record, this is the depth of snow on the ground early in the morning. The plot on the right shows this date for each year through 2011; the black line is the 5-year running mean. As you can see, since 1972 the winter snowpack has lasted into May only four times, though since the early 1970s there is no trend at all in meltout dates.

Meltout date this year will be April 17-19, so just a touch earlier than the long term average.

Hot April Heads-Up

The average temp the first half of April in Fairbanks was 30.1F, which is 3.0F above normal. Left is the updated plot of standardized daily mean temp departures for 2012, with the current warmth falling right in with yo-yo pattern we had all winter.

The 90% percentile April mean temps for Fairbanks (1905-2011 data) is 36.9F. In order for this month to make the top 10% warmest Aprils, the second half of the month would have to have a mean temp of 43.7F, which is 5.7F above normal for April 16-30th.

That's a tall order, but with the valley snowpack now going fast and the CFS and CPC weeks 1 and 2 guidance showing no end to the warmth, it looks to be within reach. Of course, six of the ten warmest Aprils of record have occurred since 1990.

Temperature Differences

Measuring the temperature of the air seems like a simple thing, but in fact getting an accurate measure is actually not so trivial. For meteorological/cimatological purposes we of course want to keep the sensor out of the sun (because we're interested in the temperature of the air, not the temperature of the thermometer). This is done by enclosing the thermometer (or temperature sensor) in some kind of enclosure. But you want to keep the air moving through the enclosure, otherwise the mere fact that there is an enclosure will impact the temperature of the air inside.

So, there are basically two approaches used. First, have a fan move air from outside the enclosure across the thermometer and then out, or design you enclosure so that air can move freely through. The fan approach is termed aspirated, the second is termed passive. Usually there is not not much difference, but conditions this week, with brilliant sunshine, a still solid snow cover and not much wind are producing small but consistent differences. The graphic above shows the high temperatures on Wednesday. As you would expect, aspirated sensors run a little bit cooler.

First 50F of the Year

Updated: The high temperature at the airport was 51F.

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
426 PM AKDT TUE APR 10 2012

...HIGH TEMPERATURE HITS 50 DEGREES IN FAIRBANKS....
...FIRST 50 DEGREE DAY OF THE YEAR...

THE TEMPERATURE AT THE FAIRBANKS INTERNATIONAL AIRPORT ROSE TO 50
DEGREES AT 330PM TUESDAY AFTERNOON. THIS IS THE WARMEST IT HAS BEEN
THIS YEAR AND IS FIRST TIME THE TEMPERATURE HAS BEEN AS HIGH AS 50
DEGREES SINCE OCTOBER 14TH.

OVER THE PAST 80 YEARS...THE AVERAGE DATE OF THE FIRST 50 DEGREE
OR HIGHER TEMPERATURE IN THE SPRING IN FAIRBANKS IS APRIL 10TH.

$$
RT APR 12

Spring time Inversion

Clear skies overnight and a still solid snowpack helped a reasonably strong inversion to form overnight. Valley min temperatures were in the lower teens while higher elevations barely got below freezing. Some specific low temperatures include:

Goldstream Creek: 10F
Chena Hot Springs: 11F
Woodsmoke PWS: 13F (near North Pole)
Fairbanks Airport: 14F

Keystone Ridge: 29F
Nenana Hills RWIS: 31F
Cleary Summit RWIS: 32F

Sunny Sunday

View from the Keystone Ridge weather station on Sunday, looking east. Snow depth is at 28 inches. We've not completely lost the snow cover in April any time snow depth has been two feet or more on April 8th.

Anchorage Sets Snowfall Record

After much adieu…


PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
740 PM AKDT SAT APR 7 2012

UPDATED WITH LATEST SNOW TOTAL

...ANCHORAGE SETS NEW SEASONAL SNOWFALL RECORD...

SNOW HAS TAPERED OFF TO FLURRIES AT THE NATIONAL WEATHER SERVICE
FORECAST OFFICE AND NO ADDITIONAL ACCUMULATION IS EXPECTED FROM
THIS STORM. AN ADDITIONAL 0.9 INCHES OF SNOW FELL BETWEEN 4 PM
AND 7 PM WHICH BRINGS THE TOTAL FOR THE DAY TO 4.3 INCHES.

THIS MAKES THE 2011-2012 WINTER SEASON THE SNOWIEST EVER WITH
A TOTAL OF 134.5 INCHES. THE PREVIOUS SEASONAL SNOWFALL RECORD
WAS 132.6 INCHES SET IN 1954-1955.

$$

SEB/CC

it's a Hot One

Yesterday was the warmest day since early October in Fairbanks-land. Some high temperatures included:

Woodsmoke: 50F (near North Pole)
Fairbanks Airport: 49F
Fort Wainwright: 49F
Goldstream Creek: 49F
Eielson AFB: 48F
Keystone Ridge: 45F

Fairbanks March Summary

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
244 PM AKDT SUN APR 1 2012

...MARCH WEATHER SUMMARY FOR FAIRBANKS...
...COLD AND SNOWY...

FOLLOWING A VERY MILD FEBRUARY...THE WEATHER PATTERN OVER NEARLY
ALL OF ALASKA FLIPPED...AND MOST AREAS HAD WELL BELOW NORMAL
TEMPERATURES FOR MOST OF MARCH. FAIRBANKS WAS NO EXCEPTION.

THE AVERAGE TEMPERATURE OF 4.5 ABOVE WAS NEARLY SEVEN DEGREES
COLDER THAN NORMAL AND RESULTED IN MARCH...QUITE UNUSUALLY...BEING
COLDER THAN FEBRUARY. AS WAS THE CASE IN JANUARY...DAILY
TEMPERATURES WERE NOT EXCESSIVELY LOW...AS THERE WERE NO
TEMPERATURES EVEN CLOSE TO RECORD LEVELS. RATHER...THE PERSISTENCE
OF CHILLY TEMPERATURES WAS MOST NOTABLE. EVERY DAY BUT ONE FROM
THE 10TH THROUGH THE 23RD WAS TEN OR MORE DEGREES COLDER THAN
NORMAL.

FOR THE MONTH...THE AVERAGE HIGH TEMPERATURE AT THE AIRPORT WAS
18 ABOVE AND THE AVERAGE LOW WAS 9 BELOW. THE TEMPERATURE ROSE
ABOVE FREEZING FOR THE FIRST TIME SINCE BEFORE CHRISTMAS ON THE
27TH...AND THE HIGH FOR THE MONTH WAS 44 DEGREES ON THE 28TH. THE
LOW TEMPERATURE IN MARCH WAS 30 BELOW ON THE 5TH...WHICH IS VERY CLOSE
TO THE LONG TERM AVERAGE LOWEST TEMPERATURE IN MARCH. THERE WERE
EIGHT DAYS WITH LOWS OF 20 BELOW OR LOWER...A BIT MORE THAN IN AN
AVERAGE MARCH.

MARCH IS TYPICALLY A DRY MONTH IN FAIRBANKS...BUT NOT THIS YEAR.
TOTAL SNOW OF 14.7 INCHES AT THE AIRPORT MADE THIS THE THIRD
SNOWIEST MARCH IN THE PAST 45 YEARS. MOST OF THE SNOW CAME ON THE
5TH THROUGH 7TH...WHEN SOME PLACES NORTH AND EAST OF TOWN RECEIVED
MORE THAN 18 INCHES OF SNOW. THE SNOW WAS QUITE POWDERY...WHICH IS
USUAL FOR THIS TIME OF YEAR. THIS BROUGHT THE SEASONAL TOTAL
SNOWFALL UP TO 57.4 INCHES...ABOUT 4 INCHES BELOW NORMAL. THE SNOW
DEPTH REACHED 29 INCHES ON THE 8TH...THEN COMPACTED TO 22 INCHES
BY THE 31ST.

SOME PRECIPITATION FELL ON MORE THAN HALF THE DAYS IN MARCH. THE
SNOW MELTED DOWN TO 0.74 INCHES OF WATER...NEARLY THREE TIMES
NORMAL.

LOOKING AHEAD TO APRIL...NORMAL TEMPERATURES CONTINUE TO INCREASE
RAPIDLY. AVERAGE HIGH TEMPERATURES RISE FROM 35 DEGREES ON THE FIRST
TO 54 DEGREES IN THE 30TH. APRIL IS OFTEN QUITE DRY. IN THE PAST
20 YEARS...HALF THE APRILS HAD LESS THAN ONE TENTH OF INCH OF
PRECIPITATION. MOST OF WHAT DOES FALLS TYPICALLY FALLS AS
SNOW...THOUGH RAIN SHOWERS SOMETIMES OCCUR...ESPECIALLY THE SECOND
HALF OF THE MONTH. ON RARE OCCASIONS SIGNIFICANT SNOWFALL OCCURS
IN APRIL...THOUGH ONLY FIVE APRILS IN THE PAST 60 YEARS HAVE
RECEIVED MORE THAN 10 INCHES OF SNOW. THE WINTER SNOWPACK USUALLY
MELTS OUT IN TOWN DURING APRIL. THE AVERAGE DATE FOR LAST DAY WITH
AN INCH OR MORE OF SNOW ON THE GROUND IS APRIL 22ND.

APRIL IS OFTEN A SUNNY MONTH...AS POSSIBLE SUNSHINE INCREASES FROM
13 HOURS AND 41 MINUTES ON THE FIRST TO 17 HOURS ON 30TH. DURING
THE LAST WEEK OF APRIL...SOME TWILIGHT REMAINS VISIBLE IN NORTHERN
SKY ALL NIGHT LONG.

$$
RT APR 12

Springtime in Alaska

A lovely April 1st at Denali National Park. Headquarters has a snow depth of 25 inches...which is pretty close to normal. Webcam photo from the FAA.