Small Craft Advisory 945, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
600 AM AKST WED NOV 27 2013

.MODEL DISCUSSION...MODELS REMAIN IN GOOD AGREEMENT ON SYNOPTIC
FEATURES. BUT THERE ARE STILL SOME SUBTLE DIFFERENCES IN TIMING AND
STRENGTH THAT WILL PLAY A ROLE IN THE SENSIBLE WEATHER...ESPECIALLY
ACROSS SOUTH CENTRAL ALASKA. WHAT IS LEFT OF A DECAYING SYSTEM NEAR
THE KENAI PENINSULA CONTINUES PUSH MOISTURE INTO ALL AREAS FROM THE
ALASKA RANGE TOWARDS THE ALCAN BORDER. THE NAM AND GEM HAVE THE BEST
HANDLE ON THIS FEATURE THIS MORNING. IT IS TAKING MUCH LONGER THAN
ORIGINALLY THOUGHT TO MOVE EAST...AND THIS WILL PLAY A ROLE IN HOW IT
INTERACTS WITH A STRONGER TROUGH DROPPING IN FROM THE CHUKCHI SEA.
BECAUSE THE FORMER PIECE OF ENERGY HAS BEEN SLOWER TO EXIT...THIS HAS
ALLOWED MORE COLD AIR TO BUILD UP WITH THE LATTER TROUGH. THE NET
EFFECT IS THAT IT WILL BE STRONGER AND SLIGHTLY FURTHER SOUTH AS IT
MOVES ACROSS SOUTH CENTRAL LATE TONIGHT. THE NAM WAS FAVORED FOR THIS
FORECAST PACKAGE.

THE PATTERN OVER THE BERING AND ALEUTIANS IS MUCH MORE STAGNANT. AN
UPPER LEVEL RIDGE IS BUILDING THIS MORNING NORTH OF A MASSIVE CUT OFF
LOW CENTERED IN THE NORTH PACIFIC. THIS ULTIMATELY RESULTS IN A
BLOCKING PATTERN CALLED A REX BLOCK. ALL MODELS TELL A VERY
SIMILAR...BUT THE GFS WAS PREFERRED SLIGHTLY.

.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL TROUGH EXTENDS THROUGH MAINLAND ALASKA FROM NORTH TO
SOUTH AND OUT OVER THE GULF. UNDERNEATH...INSTABILITY IS BRINGING
PRECIPITATION TO AREAS THROUGHOUT THE SOUTHCENTRAL AND AREAS ALONG
THE GULF COAST. FURTHER WEST HIGH PRESSURE DOMINATES THE BERING SEA
AND ALEUTIAN ISLANDS. THIS HIGH PRESSURE IS KEEPING A LOW SOUTH OF
THE ALEUTIANS FROM MOVING IN OVER THE AREA.

.SHORT TERM FORECAST...
SOUTHCENTRAL...LIGHT BUT STEADY SNOW WILL CONTINUE THROUGH MUCH OF
THE DAY. THE MORNING SOUNDING AT ANCHORAGE SHOWS DECENT MID-LEVEL
INSTABILITY AND A MOSTLY SATURATED COLUMN RIGHT AROUND THE SWEET-SPOT
FOR DENDRITIC GROWTH (-12C TO -18C). THIS MEANS WE SHOULD CONTINUE TO
ACCUMULATE A FEW INCHES OF SNOW THROUGH MUCH OF THE DAY. THEN AS THE
TROUGH APPROACHES FROM THE ARCTIC THIS AFTERNOON...IT SHOULD PROVIDE
ADDED LIFT AND SOME COLD AIR ADVECTION. THIS WILL HELP TO "WRING-OUT"
ANY LINGERING MOISTURE IN THE COLUMN AND PROVIDE A BURST OF HEAVIER
SNOWFALL. NORTH WINDS WILL START TO USHER IN MUCH DRIER AIR STARTING
LATE TONIGHT AND BRING AN END TO THE SNOW. HOWEVER...MOISTURE WILL
HANG ON INTO THE COPPER RIVER BASIN AND THUS...A FEW MORE INCHES OF
SNOW ARE EXPECTED THERE THROUGH THANKSGIVING DAY.

THE OTHER STORY WITH THE TROUGH FROM THE ARCTIC IS THE COLD AIR IT
WILL BRING. THE GEFS 850MB TEMPERATURES ARE SHOWING STANDARDIZED
ANOMALY VALUES OF -3. THIS MEANS AN UNUSUALLY COLD AIRMASS...EVEN FOR
THIS TIME OF YEAR. THE COLD AIR AND ACCOMPANYING HIGH PRESSURE WILL
LEAD TO OUTFLOW WINDS THROUGH THE TYPICAL AREAS NEAR THE COAST. WINDS
WILL START TO INCREASE TODAY AND CONTINUE TO BLOW AT LEAST THROUGH
FRIDAY.

SOUTHWEST ALASKA AND BERING SEA...HIGH PRESSURE HAS BEEN BUILDING IN
OVER THE BERING SEA FROM THE WEST AND WILL CONTINUE TO DO SO INTO THE
WEEKEND. THIS IS ALREADY KEEPING MOST AREAS IN THIS REGION VOID OF
PRECIPITATION AND THESE DRIER CONDITIONS WILL PERSIST WHILE THE HIGH
REMAINS DOMINANT. THROUGHOUT THIS TIME THE CENTER OF THE HIGH
PRESSURE WILL SLOWLY TRACK EAST MAKING IT TO THE EASTERN BERING BY
SATURDAY. THE EXCEPTION TO THE EFFECTS OF THE HIGH WILL BE THE
CENTRAL ALEUTIANS. THEY ARE FAR ENOUGH SOUTH TO STILL SEE IMPACTS
FROM THE LOW THAT IS SITTING ALMOST STATIONARY TO THEIR SOUTH.
PRECIPITATION WILL BE LIGHT BUT WILL LAST THROUGH MUCH OF THURSDAY.

.LONG TERM FORECAST...THE MODELS ACTUALLY REMAIN IN RELATIVELY GOOD
AGREEMENT THROUGH THE MIDDLE OF NEXT WEEK. THE REX BLOCK OVER THE
BERING BREAKS DOWN OVER THE WEEKEND AND HIGH PRESSURE MOVES OUT OVER
THE STATE. THE HIGH REMAINS THERE THROUGH AT LEAST THE EARLY PORTION
OF NEXT WEEK AS A FEW LARGER SYSTEMS GET ORGANIZED OVER THE BERING.
AS THE HIGH SLOWLY SHIFTS EASTWARD TOWARDS WEDNESDAY...MODELS AGREE
THAT OUR PATTERN WILL SHIFT FROM COLD AND DRY TO RELATIVELY WARM AND
WET FOR EARLY DECEMBER.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORMS...130 131
         GALES...170 172 173 174 175 176 177 132 138
FIRE WEATHER...NONE

MSO/DK NOV 13