000
FXAK68 PAFC 140005
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKDT MON MAY 13 2013

.ANALYSIS AND UPPER LEVELS...
THE MORNING WEATHER MAP REVEALS A PATTERN THAT IS BECOMING QUITE
FAMILIAR...WITH AN UPPER LEVEL LOW NEAR THE BROOKS RANGE AND AN
ASSOCIATED COLD UPPER LEVEL TROUGH ENCOMPASSING MOST OF THE MAINLAND.
A WEAK LOW OVER THE NORTHERN GULF IS PUSHING MOISTURE INLAND ACROSS
THE COASTAL MOUNTAIN RANGES...PRODUCING STEADY PRECIP FROM PRINCE
WILLIAM SOUND TO THE COPPER RIVER BASIN. MOST OF THIS IS CURRENTLY
FALLING IN THE FORM OF RAIN...BUT COLD AIR IS ALREADY BEGINNING TO
MOVE INTO THE REGION FROM THE NORTHWEST. OUT WEST...GENERALLY BENIGN
CONDITIONS CONTINUE WITH OVERALL HIGH PRESSURE IN CONTROL OF THE
BERING SEA AND ALEUTIAN REGION. A FAIRLY WEAK LOW COMPLEX SOUTH OF
SHEMYA IS GENERATING SOME GUSTY EASTERLY WINDS OVER THE WESTERN
ALEUTIANS. OVERALL...MARINE FOG/STRATUS ARE ENTRENCHED ACROSS THE
AREA AS INDICATED BY CURRENT OBS AND SATELLITE IMAGERY.

.MODEL DISCUSSION...MODELS ARE DOING WELL THROUGH WEDNESDAY NIGHT
WILL LITTLE VARIANCE BETWEEN THEM. ON THURSDAY THERE IS A SHIFT
OCCURRING WITH THE MODELS BEGINNING TO MOVE THE LOW SOUTH OF THE
ALEUTIANS INTO THE GULF INSTEAD OF OVER THE ALASKA PENINSULA.
THE MORE INTERESTING DIFFERENCE IN MODELS IN LATE IN THE WEEK WHEN
THE GFS AND ECMWF AGREE ON THE OVERALL PATTERN WITH VERY COLD AIR
ONCE AGAIN MOVING INTO SOUTHERN ALASKA. THE MODEL TO WATCH IS THE
ECMWF AS IT IS NOW SHOWING A PATTERN SIMILAR TO THE GFS WHICH
POSITIONS THE UPPER LEVEL LOW IN A MORE FAVORABLE POSITION FOR
PRECIPITATION INLAND OVER SOUTH CENTRAL ALASKA.

.SHORT TERM FORECAST...THE SOUTHERN EXTENT OF THE COLD FRONT THAT
SWEPT THROUGH THE INTERIOR OF THE STATE THIS MORNING IS NOW PUSHED UP
ALONG THE TALKEETNA MOUNTAINS AND CHUGACH RANGE. THE LOW IN THE GULF
IS PUSHING MOISTURE INTO THE COPPER RIVER BASIN WHERE THE FRONT WILL
STALL OUT OVERNIGHT. THIS IS SETTING UP A FAVORABLE SITUATION FOR
SIGNIFICANT SNOWFALL ACCUMULATIONS OVER THE COPPER RIVER BASIN.
LOW AND MID-LEVEL CLOUDS ARE PERSISTING OVER PARTS OF THE SUSITNA
VALLEY AND COOK INLET REGION BEHIND THE FRONT. SOUTH CENTRAL ALASKA
WILL CLEAR OUT BY TOMORROW AS DRIER AIR MOVES INTO THE AREA.
FARTHER WEST CONDITIONS HAVE DRIED OUT ENOUGH TO KEEP THE WIDESPREAD
CLEAR SKIES OVER THE AREA.

.LONG TERM FORECAST...
EXTENDED MODELS ARE IN GENERAL AGREEMENT THAT AN UNSEASONABLY COLD
ARCTIC AIRMASS WILL DIVE DOWN INTO THE SOUTHERN MAINLAND ON FRI/SAT.
MODELS ARE ALSO IN AGREEMENT THAT A WEAK SURFACE LOW IN THE NORTHERN
GULF WILL BRING WIDESPREAD PRECIP TO SOUTHCENTRAL DURING THIS PERIOD.
THERE ARE STILL KEY DETAILS THAT ARE UNCERTAIN WITH THIS
EVOLUTION...BUT THE MAIN FORECAST CHALLENGE WILL BE DETERMINING
PRECIPITATION TYPE AND THE POSSIBILITY FOR AN EARLY WEEKEND SNOWFALL
MAINLY FROM ANCHORAGE NORTHWARD.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...SNOW ADVISORY 141.
MARINE...NONE
FIRE WEATHER...NONE

MAY 13