Friday, May 3, 2019

Snow After Green-Up

According to the National Weather Service office in Fairbanks, green-up occurred on West Chena Ridge on Wednesday evening after the temperature reached a summer-like 70°F earlier in the day.  This means that the hillside turned distinctly green for the first time as birch and aspen leaves emerged en masse.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
1101 PM AKDT WED MAY 1 2019

AKZ222-021400-
MIDDLE TANANA VALLEY-
INCLUDING FAIRBANKS, FORT WAINWRIGHT, EIELSON AFB, ESTER, 
NORTH POLE, MOOSE CREEK, TWO RIVERS, FOX, CHATANIKA, 
CHENA HOT SPRINGS, AND SOURDOUGH CAMP
1101 PM AKDT WED MAY 1 2019

...GREEN UP OCCURRED IN FAIRBANKS THIS EVENING...

GREEN UP OCCURRED IN FAIRBANKS THIS EVENING, MAY 1, 2019. CHENA 
RIDGE WAS BEGINNING TO SHOW A FAINT SHADE OF GREEN THIS 
AFTERNOON, BUT THE RIDGE TURNED MORE DISTINCTLY GREEN BY THIS 
EVENING. 

THE MEAN DATE OF GREEN UP IN FAIRBANKS IS MAY 9. THE EARLIEST 
GREEN UP DATE RECORDED IN FAIRBANKS WAS APRIL 26, 2016.
 

The 70°F on May 1st was one of the earliest occurrences on record for such warmth, but a wild swing back to colder weather has occurred in the short time since.  This morning rain turned to mixed rain and snow at valley level, and then finally to plain snow before tapering off.  Some accumulations were observed in the hills, but apparently not in Fairbanks itself.

Looking back at the history of Fairbanks hourly weather data since 1950, I can't find any other instance of plain snow in the hourly observations after the date of the first 70°F.  There have been a number of instances of light mixed rain and snow, but most were very light with visibility of 10 miles or more, and plain snow (as occurred for a couple of hours this morning) appears to be unprecedented after the first 70°F day.  However, it should be noted that May 27, 1978 brought enough wet rain/snow to accumulate 0.1" , and that was 2 weeks after the first 70°F of the year.

More substantial snow occurred today at locations farther up the Tanana River valley, such as Tok and Northway.  And the history shows this isn't unprecedented; in mid-May 1995, 5 inches of snow fell in Northway less than a week after the temperature reached a remarkable 82°F.  The temperature only reached that level on 3 more days that year in Northway (elevation 1715').


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