Small Craft Advisory 878, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
504 PM AKST WED NOV 4 2015

.ANALYSIS AND UPPER LEVELS...
THE MAIN STORM OVER THE AREA TODAY IS A LARGE STRONG MATURE LOW
NOW OVER THE CENTRAL ALEUTIANS. THE STORM NOW MOVING ALONG THE
ALEUTIAN ISLANDS IS PRODUCING STRONG PRE-FRONTAL WIND AND STRONG
GUSTY WIND AROUND THE NORTH TO WEST SIDE OF THE STORM. THE
ASSOCIATED FRONT IS PUSHING EAST SPREADING RAIN IN ADVANCE OF IT
ACROSS THE ALEUTIANS AND ALASKA PENINSULA. THIS INTENSE LOW IS
SUPPORTED BY A STRONG UPPER LOW AND A 140 KT JET IS ROUNDING THE
BASE OF THIS UPPER LOW AND TROUGH. COLD AIR ALOFT IS FEEDING IN
AROUND THE WEST SIDE OF NORTHWEST SIDE OF THE LOW. THIS WILL
ENHANCE THE INSTABILITY RESULTING IN STRONG GUSTY NORTHWEST WIND
AROUND THE WEST TO SOUTHWEST QUADRANT OF THE LOW.

THE REMNANTS OF THE LOW THAT MOVED ACROSS THE SEWARD PENINSULA AND
THE ASSOCIATED FRONT MOVED INLAND OVER THE KUSKOKWIM DELTA. THIS
HAS RESULTED IN RAIN THROUGHOUT THE DAY TODAY IN THE DELTA.

&&

.MODEL DISCUSSION...
MODEL GUIDANCE IS IN VERY GOOD AGREEMENT WITH RESPECT TO THE
INTENSE LOW MOVING EAST ALONG THE ALEUTIANS AS IT MATURES THEN
SLOWLY BEGINS TO FILL AS IT CONTINUES TO MOVE EAST. THE FRONT WILL
MOVE INTO THE GULF OF ALASKA TONIGHT TO ALONG THE NORTH GULF COAST
THURSDAY.

THE MODELS DO DIVERGE ON THE SOLUTION OF THE THE DETAILS OVER
SOUTH CENTRAL ALASKA THURSDAY NIGHT AND FRIDAY. THESE IMPORTANT
DETAILS ARE CRITICAL TO THE FORECAST SOLUTION. THE GFS AND ECMWF
AGREE ON THE RAIN SNOW LINE AND COLD ADVECTION OVER SOUTH CENTRAL
ALASKA FRIDAY AS THE NAM IS THE OUTLIER. THE DIFFERENCE WHILE
MINOR MAKES A BIG DIFFERENCE IN WHAT MAY HAPPEN IN THE ANCHORAGE
AREA FRIDAY MORNING. ALL THE MODELS BRING A WEAK LOW TO THE NORTH
GULF COAST. THE NAM HOWEVER DOES BRING A LOBE OF THIS LOW INTO
PRINCE WILLIAM SOUND. THIS SOLUTION IS THE CLASSIC COLD ADVECTION
SNOW FOR THE NORTHERN COOK INLET ANCHORAGE AREA. THE GFS AND ECMWF
PREFER TO KEEP THE LOW FURTHER SOUTH AND ARE NOT AS AGGRESSIVE
ABOUT BRING COLD AIR SOUTH AND EAST. AT THIS TIME WE ARE
CONTINUING WITH THE RAIN SNOW MIX FORECAST AND WILL BE MONITORING
THIS CLOSELY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
PRECIPITATION AND WINDS WILL BE ON THE INCREASE OVER THE NEXT 24
TO 36 HOURS AS THE WELL DEVELOPED LOW NEAR ADAK THIS AFTERNOON AND
ITS ASSOCIATED FRONT PUSH EASTWARD INTO THE GULF OF ALASKA.
PRECIPITATION WILL BEGIN OVER KODIAK ISLAND TONIGHT AND CONTINUE
TO PUSH EASTWARD INTO THE KENAI PENINSULA AND THE NORTHERN GULF
COAST BY TOMORROW MORNING. PRECIPITATION MAY BE HEAVY AT TIMES
ALONG COASTAL REGIONS AND ALONG THE EASTERN SLOPES OF THE ALASKA
RANGE EAST OF THE PARKS HIGHWAY WHERE SNOWFALL TOTALS ON THURSDAY
OF 6 TO 10 INCHES ARE EXPECTED. INTERIOR AREAS OF THE KENAI
PENINSULA WILL LIKELY SEE A QUICK 1-3 INCHES OF SNOW TONIGHT WITH
AN ADDITIONAL 2 TO 5 INCHES IN HIGHER ELEVATIONS TOMORROW.
PRECIPITATION TYPE ALONG COOK INLET AND INTO THE MATANUSKA VALLEY
IS GENERALLY EXPECTED TO BE MOSTLY RAIN AT LOWER ELEVATIONS
EVOLVING INTO A RAIN-SNOW MIX BY FRIDAY MORNING. WITH THE
ORIENTATION OF THE FRONT...THE ANCHORAGE BOWL INTO THE MATANUSKA
VALLEY WILL GENERALLY REMAIN DOWNSLOPED UNTIL FRIDAY MORNING WHEN
THE LOW MOVES INTO THE NORTH CENTRAL GULF.

OVER THE MARINE AREAS...WIDESPREAD UPPER GALE FORCE WINDS ARE
EXPECTED WITH THIS FRONT OVER MOST OF THE GULF OF ALASKA AND
SOUTHCENTRAL COASTAL WATERS. STORM FORCE WINDS ARE EXPECTED ALONG
THE NORTHEASTERN GULF COAST WITH THE DEVELOPMENT OF A BARRIER JET
ON THURSDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
RAIN AND SNOW WILL PICK BACK UP OVER THE SOUTHWEST MAINLAND
TONIGHT AS THE DECAYING FRONT CURRENTLY OVER THE AREA TRACKS
FURTHER NORTH THIS EVENING...AND IS QUICKLY REPLACED WITH
STEADIER RAINFALL FROM A FRONT ASSOCIATED WITH THE DEEP BERING SEA
LOW. WARMER AIR FROM THE NORTH PACIFIC WILL FILTER IN OVER THE
MAJORITY OF THE SOUTHWEST MAINLAND AHEAD OF THIS SYSTEM...KEEPING
RAIN AS THE DOMINANT PRECIPITATION TYPE THROUGH THURSDAY EVENING.
BY FRIDAY THE LOW WILL MOVE EAST OF THE AKPEN...AND RESIDUAL RAIN
SHOWERS WILL BEGIN TO CHANGING OVER TO SNOW SHOWERS AS COLDER
NORTHWEST FLOW FILTERS INTO THE SOUTHWEST MAINLAND BEHIND THIS
SYSTEM. THE GUSTY WINDS ASSOCIATED WITH THIS SYSTEM WILL START OUT
AS GUSTY SOUTHEASTERLY FLOW...WITH THE STRONGEST AREAS BEING
LOCALIZED TO ALONG THE COAST AND ALEUTIAN RANGE. THE WINDS WILL
THEN SHIFT TO A MORE NORTHWESTERLY FLOW FRIDAY MORNING AS THE LOW
TRACKS EASTWARD INTO THE GULF...WITH THE STRONGEST WINDS MAINLY
ALONG THE COAST AND OVER THE ALASKA PENINSULA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
AS THE ALEUTIAN LOW MIGRATES EAST IT WILL SPREAD STORM AND
HURRICANE FORCE WINDS OVER THE CENTRAL ALEUTIANS TONIGHT...THEN
BEGIN TO GRADUALLY WEAKEN AS IT TRACKS INTO THE EASTERN ALEUTIANS
THURSDAY. STRONG GUSTS ARE EXPECTED TO MIGRATE OVER TO THE EASTERN
PORTION OF THE ALEUTIAN CHAIN THURSDAY...THEN INTO THE ALASKA
PENINSULA BY FRIDAY. A HIGH WIND WARNING REMAINS IN EFFECT FOR THE
CENTRAL ALEUTIANS FOR TONIGHT. WHILE WINDS SLOWLY TAPER OFF FROM
THE CENTRAL ALEUTIANS TO THE EASTERN ALEUTIANS OVER THE NEXT FEW
DAYS...AN ABUNDANT AMOUNT OF RAIN IS EXPECTED TO FALL OVER THE
BERING AND ALEUTIAN CHAIN INTO FRIDAY AS THE LOW PROGRESSES
EASTWARD AND INTO THE GULF.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
EVEN THOUGH THE MODELS HAVE THE SAME GENERAL IDEA WITH THE MAIN
PRESSURE CENTERS FOR THE EXTENDED FORECAST THERE IS STILL QUITE A
BIT OF UNCERTAINTY IN TERMS OF IMPACTS. THE LOW THAT WILL BE IN
THE GULF BY FRIDAY HAS THE MOST AGREEMENT WITH IT MOVING OFF TO
THE EAST AS IT WEAKENS THROUGH THE WEEKEND DIMINISHING
PRECIPITATION FOR THE SOUTHCENTRAL. THE LOW CONFIDENCE PORTION OF
THE FORECAST FOR THIS LOW IS THAT SOME OF THE GUIDANCE IS HINTING
AT A LOW ALSO FORMING IN PRINCE WILLIAM SOUND WHICH COULD LEAD TO
INCREASED SNOWFALL FOR ANCHORAGE. AT THIS TIME THERE IS LOW
PROBABILITY OF THIS HAPPENING. THE OTHER PROBLEM IS THE LOW MOVING
INTO THE NORTHERN BERING OVER THE WEEKEND. THERE IS A LOT OF
DIFFERENCE WITH THE TIMING OF THE FRONT ASSOCIATED WITH THIS LOW.
SOME OF THE MODELS BRING IT INTO THE SOUTHWEST EARLY ON SUNDAY
WHILE SOME OF THE ENSEMBLES ARE MUCH SLOWER RESULTING IN AN ALMOST
24 HOUR TIME DIFFERENCE. THERE IS ALSO DISAGREEMENT AS TO WHETHER
THE PRECIPITATION WILL FALL AS RAIN OR SNOW DEPENDING ON THE
STRENGTH OF THE SYSTEM AND HOW MUCH WARM AIR IT BRINGS UP FROM THE
SOUTH. THIS RESULTS IN A LOW CONFIDENCE FORECAST BY LATE WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC......HIGH WIND WARNING 187.
MARINE...HURRICANE FORCE WIND WARNING 176.
         STORM WARNING 119 155 170 172 173 174 175 177.
         GALE WARNING 120 125 130 131 132 137 139 141 150 160 165
                      171 178 179 180.

&&

SYNOPSIS AND MODEL DISCUSSION...SA
SOUTHCENTRAL ALASKA...RF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...DK