Small Craft Advisory 137, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKST THU FEB 13 2014

.ANALYSIS AND UPPER LEVELS...
THE OVERALL WEATHER PATTERN IS STABLE AND FEATURES A NEARLY
STATIONARY UPPER LOW NEAR KODIAK ISLAND WITH A RIDGE OVER THE WESTERN
BERING SEA. A 140 KT NORTHERLY JET IS LOCATED BETWEEN THESE
FEATURES...AND CROSSES THE CENTRAL ALEUTIANS EN-ROUTE TO THE PACIFIC.
A SIGNIFICANT MOVEMENT OF ARCTIC AIR HAS OVERTAKEN THE
MAINLAND...WITH COLDEST TEMPERATURES LOCATED OVER SOUTHWEST ALASKA
WHERE GUSTY WINDS HAVE LED TO WIND CHILL ADVISORIES ACROSS THE AREA.
IN THE GULF...A SERIES OF WEAK SURFACE LOWS ARE SPINNING AROUND UNDER
THE UPPER LOW. THE HEAVIEST SNOW IS FALLING AROUND AND EAST OF PRINCE
WILLIAM SOUND...WHILE OTHER AREAS INCLUDING INLAND AREAS AROUND COOK
INLET ARE SEEING MUCH LIGHTER SNOWFALL.

.MODEL DISCUSSION...
MODELS REMAIN IN STELLAR OVERALL AGREEMENT THROUGHOUT THE SHORT TERM
(3.5 DAY) FORECAST PERIOD. ALL MODELS SHOW THE RIDGE IN THE BERING
GRADUALLY BREAKING DOWN TO MORE ZONAL FLOW...ALLOWING THE UPPER LOW
PARKED NEAR KODIAK ISLAND TO ELONGATE AND RETROGRADE TO THE WEST. AS
THIS HAPPENS...ALL MODELS SHOW A SIGNIFICANT SHORTWAVE MOVING UP INTO
THE GULF WITH DEEP MOISTURE AND STEADY SNOW BEING PULLED WESTWARD
BACK TOWARD PRINCE WILLIAM SOUND. THERE IS SOME DISAGREEMENT ABOUT
THE TIMING OF THIS FEATURE...WHICH WILL MAKE A DIFFERENCE FOR HOW FAR
WEST THE SNOW WILL MAKE IT (POSSIBLY AS FAR AS ANCHORAGE). THE NAM IS
CURRENTLY AN OUTLIER WITH A SLOWER SHORTWAVE MOVEMENT...WHILE THE GFS
AND ECWMF ARE IN MUCH BETTER AGREEMENT. THUS WILL START OUT THE
FORECAST USING THE NAM BUT SHIFT TO THE CONSENSUS GFS/ECWMF SOLUTION
BEGINNING FRIDAY NIGHT.

.SHORT TERM FORECAST...
SOUTHCENTRAL...PINPOINTING THE TIMING AND PLACEMENT OF INDIVIDUAL
SURFACE LOWS IN THE GULF IS AND WILL REMAIN PROBLEMATIC FOR THE NEXT
SEVERAL DAYS. THE OVERALL POSITION OF THE CIRCULATION IS SHIFTING TO
TOWARD THE SOUTHERN KENAI PENINSULA...WHICH HAS ENHANCED
SOUTHEASTERLY DOWNSLOPING WINDS AND ENDED THE LIGHT SNOW AROUND
ANCHORAGE AND THE MAT-SU. MEANWHILE...A MORE SIGNIFICANT BAND OF SNOW
PUSHED INTO CORDOVA AND VALDEZ THIS MORNING...EVEN SPLASHING SOME
LIGHT ACCUMULATING SNOW INTO THE SOUTHERN COPPER RIVER BASIN. THE
MODELS ARE TRYING TO HINT AT ANOTHER WEAK LOW DRIFTING UP TOWARD
PRINCE WILLIAM SOUND ON FRIDAY...WHICH COULD LEAD TO ANOTHER BRIEF
PERIOD OF LIGHT SNOW IN THE USUAL DOWNSLOPE AREAS. OVERALL...MOST
SNOWFALL WILL REMAIN ALONG THE COAST FOR THE NEXT FEW DAYS...WITH
LESSER CHANCES FOR AN ADDITIONAL DUSTING OF SNOW INLAND.

SOUTHWEST MAINLAND...COLD AIR AND GUSTY WINDS WILL KEEP ALL AREAS
NEAR OR EXCEEDING WIND CHILL CRITERIA THROUGH MIDDAY FRIDAY WHEN
TEMPERATURES BEGIN TO SLOWLY WARM AND WINDS BEGIN TO DECREASE. WHILE
IMPROVEMENT WILL OCCUR...CONDITIONS WILL STILL REMAIN DRY AND VERY
COLD THROUGH THE WEEKEND.

BERING SEA AND ALEUTIANS...THE ARCTIC AIRMASS OVER THE MAINLAND IS
NOW SPILLING INTO THE WESTERN BERING...WHERE INTENSE SNOW SHOWERS AND
VERY STRONG WINDS HAVE BROUGHT BLIZZARD OR NEAR-BLIZZARD CONDITIONS
FROM THE ALASKA PENINSULA TO THE EASTERN ALEUTIANS AND PRIBILOF
ISLANDS. THIS WILL CONTINUE THROUGH TOMORROW MORNING BEFORE
SIGNIFICANT IMPROVEMENT OCCURS. HIGH WINDS ARE BEING AMPLIFIED BY AN
UPPER LEVEL POTENTIAL VORTICITY ANOMALY THAT IS ESSENTIALLY SQUEEZING
THE LOWER ATMOSPHERE FROM THE TOP AS WELL AS THE AFOREMENTIONED 140
KT JET OVER THE CENTRAL ALEUTIANS. MEANWHILE...A GALE-FORCE FRONT
WILL MOVE INTO THE WESTERN ALEUTIANS TONIGHT AND WEAKEN RAPIDLY AS IT
MOVES INTO THE CENTRAL ALEUTIANS ON FRIDAY IN RESPONSE TO THE
WEAKENING UPPER LEVEL PATTERN.

.LONG TERM FORECAST FROM PREVIOUS DISCUSSION...
FORECAST CONFIDENCE REMAINS HIGHER THAN NORMAL GOING INTO THE
EXTENDED TERM AS THE DEEP UPPER LOW CURRENTLY OVER THE SOUTHWEST
MAINLAND WILL REMAIN ANCHORED OVER THE NORTHWESTERN GULF OF ALASKA
WELL INTO NEXT WEEK. THIS WILL GENERALLY CONTINUE TO YIELD COLD
TEMPERATURES AND GUSTY OUTFLOW WINDS OVER THE SOUTHERN HALF OF THE
MAINLAND...WITH THE BEST CHANCE FOR PRECIPITATION REMAINING ALONG THE
NORTHERN GULF COAST. PRECIPITATION CHANCES FURTHER INLAND WILL
CONTINUE TO DEPEND ON THE EXACT POSITION/STRENGTH OF THE PARENT LOW
AND THE VARIOUS WAVES ROTATING AROUND IT. MEANWHILE...A MORE ACTIVE
PATTERN WILL BE IN STORE FOR THE BERING AS UPPER LEVEL RIDGING OVER
THE WESTERN BERING BREAKS DOWN AND SEVERAL DISTURBANCES MOVE THROUGH
AND PROVIDE OCCASIONAL CHANCES FOR PRECIPITATION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 181 185
         BLOWING SNOW ADVISORY 195
         WIND CHILL ADVISORY 152 155 161
MARINE...GALE 127 130 131 150 155 160 165 170 171 172 175176 177 179
         180
         HVY FRZG SPRY...121 126 127 129 130 131 132 136 137 138 139
         140 141 150 155 160 165 170 179 180 185
FIRE WEATHER...NONE

AMD/CC/CB FEB 14