Blizzard in Alaska, April 5, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
205 PM AKDT THU APR 5 2012

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVEL PATTERN HAD A LARGE
BROAD TROUGH OVERT HE NORTHERN PART OF THE BERING SEA WITH A HIGH
AMPLITUDE RIDGE OVER THE EASTERN GULF AND ALONG THE ALCAN BORDER.
THE JET STREAM IS JUST TO THE SOUTH OF THE ALEUTIAN ISLANDS HEADING
DUE WEST TO EAST UNTIL IT IS STEERED SOUTHEAST AND AWAY FROM THE AREA
BY AN UPPER LEVEL CUT OFF LOW THAT IS DEVELOPING SOUTH OF THE WESTERN
GULF.

.MODEL DISCUSSION...MODELS ARE VERY CONSISTENT WITH EACH OTHER AND
HAVE ONLY MINOR DIFFERENCES WITH THE COMPLEX PATTERN IN THE BEING
SEA. ONE DIFFERENCE THAT IS SMALLER BUT IMPORTANT LIES BETWEEN THE
NAM AND THE GFS IN REGARDS TO THE LOW LEVEL TEMPERATURES IN THE COOK
INLET AND SUSITNA VALLEY AREAS TONIGHT THROUGH FRIDAY. THE NAM IS
BRINGING IN COLDER AIR QUICKER TONIGHT AND THE GFS IS DELAYING IT
INTO FRIDAY. THIS WILL HAVE AN IMPACT ON THE FORECASTS IN THESE
AREA...AND IT IS LIKELY THAT THE GFS IS A BETTER REPRESENTATION WITH
THE WARM AIR REMAINING IN THE AREA AT LITTLE BIT LONGER.

.SHORT TERM FORECAST...THE MOST CHALLENGING AREA TO CALL THE WEATHER
ON FROM TONIGHT THROUGH TOMORROW WILL BE IN SOUTH CENTRAL ALASKA.
THERE HAVE BEEN CHINOOK WINDS AND GAP WINDS ALONG THE KENAI AND
CHUGACH MOUNTAINS WHICH WILL SLOWLY DIMINISH THROUGH THE NIGHT. THESE
WINDS ARE STILL ADVECTING IN WARM AIR AND AS LONG AS THEY ARE AROUND
ANY PRECIPITATION THAT IS NOT IN THE MOUNTAINS WILL FALL AS RAIN.
THERE IS ALSO COLDER AIR TO THE WEST THAT WILL BE FILTERING INTO THE
AREA OVERNIGHT. THE ISSUE IS WHETHER THE COLD AIR WILL MOVE IN FAST
ENOUGH TO CHANGE PRECIPITATION TO SNOW BEFORE THE PRECIPITATION
STOPS. AT THIS TIME IT LOOKS LIKE THE WARM AIR WILL BE AROUND LONG
ENOUGH THAT AS THE DOWNSLOPE WINDS DIMINISH ANY PRECIPITATION THAT
FALLS IN THE ANCHORAGE AREA WILL BE LIGHT RAIN THROUGH MOST OF THE
NIGHT. TOWARD MORNING IT MAY TURN TO SNOW A GIVE SMALL ACCUMULATIONS
BUT NOTHING MORE IS EXPECTED THROUGH FRIDAY MORNING. FRIDAY NIGHT MAY
BE A DIFFERENT STORY AS THE COLD AIR WILL BE ENTRENCHED IN THE AREA
AND THE DOWNSLOPE WILL HAVE ENDED WITH A WEAK SURFACE REMAINING OVER
THE AREA. THERE IS ALSO A SHARP UPPER LEVEL WAVE APPROACHING FROM THE
SOUTHWEST WHICH SHOULD PRODUCE SOME SNOW FRIDAY NIGHT INTO SATURDAY
FOR THE ENTIRE ANCHORAGE AREA.

SOUTHWEST ALASKA WILL SEE SOME PARTIAL CLEARING THIS EVENING WHICH
WILL ENHANCE THE CHANCES FOR FOG IN THE AREA LATER TONIGHT THROUGH
TOMORROW MORNING.
FROM THE CENTRAL ALEUTIANS THROUGH ALASKA PENINSULA THERE WILL BE
SOME PERIODS OF SNOW AND SOME BLOWING SNOW AS THE FRONT MOVES THROUGH
THE AREA. BLIZZARD CONDITIONS ARE NOT EXPECTED AS BOTH WINDS AND
PRECIPITATION INTENSITY WILL NOT BE ENOUGH TO SEVERELY RESTRICT
VISIBILITY.

.LONG TERM FORECAST...THE STRONG STORM IN THE BERING SEA THIS WEEKEND
WILL WEAKEN AS IT MOVES NORTHWEST EARLY NEXT WEEK AND A NEW LOW
SKIRTS JUST SOUTH OF THE ALEUTIANS. THIS SECOND LOW WILL GET
DEFLECTED SOUTH OF THE GULF OF ALASKA MID WEEK AS A RIDGE OF HIGH
PRESSURE BUILDS ALONG THE WESTERN COAST OF THE STATE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 175.
FIRE WEATHER...NONE.

APR 12

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
155 PM AKDT THU APR 5 2012

AKZ101-060800-

...ACCUMULATING SNOW EXPECTED AGAIN IN ANCHORAGE...

AFTER NEARLY A MONTH OF NO ACCUMULATING SNOW IN THE ANCHORAGE AREA
THERE IS SNOW EXPECTED LATE TONIGHT INTO FRIDAY MORNING AND THEN
AGAIN FRIDAY NIGHT INTO SATURDAY MORNING.

THE FRONT THAT HAS BEEN CAUSING THE GUSTY SOUTHEAST WINDS IN THE
ANCHORAGE AREA WILL WEAKEN TONIGHT AND MOVE EASTWARD WITH COLDER AIR
MOVING INTO THE AREA FROM THE SOUTHWEST. PRECIPITATION IS EXPECTED TO
START LATE THIS EVENING AS LIGHT RAIN AND REMAIN LIGHT RAIN MOST OF
THE NIGHT BEFORE CHANGING TO SNOW TOWARD MORNING. SNOW SHOULD FALL
INTO THE MORNING HOURS BUT THE ACCUMULATIONS ARE EXPECTED TO TOTAL IN
THE ONE TO ONE AND A HALF INCH RANGE.

THE SECOND WAVE WHICH MOVES INTO THE AREA FRIDAY NIGHT WILL BE COLD
ENOUGH FOR PRECIPITATION TO REMAIN SNOW THE ENTIRE TIME. AT THIS TIME
WE EXPECT 1 TO 2 INCHES OF SNOW IS LIKELY WHICH RESULTS IN TOTAL SNOW
ACCUMULATIONS IN THE 2 TO 3.5 INCH RANGE. THE CURRENT SEASONAL TOTAL
IS 3.2 INCHES SHORT OF THE ALL TIME RECORD. THIS WOULD LIKELY KEEP US
SHY OF THE RECORD AS THE LOCATION OF RECORD IS LIKELY TO BE ON THE
LOWER END OF THE RANGE.

HOWEVER...THERE IS THE POSSIBILITY THE FRONT WILL STALL OVER THE
ANCHORAGE AREA FRIDAY. IF THIS HAPPENS...SNOW WILL PERSIST OVER THE
AREA FOR THE MAJORITY OF TOMORROW AND THE RECORD WOULD LIKELY BE
BROKEN.