Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 231324
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
424 AM AKST SUN NOV 23 2014

.ANALYSIS AND UPPER LEVELS...

A LARGE STACKED UPPER LEVEL LOW CONTINUES TO SPIN IN VICINITY OF
THE SHUMAGIN ISLANDS THIS MORNING JUST TO THE SOUTH OF THE ALASKA
PENINSULA. WATER VAPOR AND INFRARED IMAGERY INDICATE A FAIRLY
UNSTABLE REGIME TO THE NORTHEAST THROUGH SOUTH OF THE LOW PRESSURE
CIRCULATION FROM SOUTHCENTRAL THROUGH THE GULF OF ALASKA
GENERATING SCATTERED TO NUMEROUS SNOW SHOWERS.

OUT WEST...A PAIR OF SHORTWAVE RIDGES MAKE UP THE GENERAL
RIDGINESS OVER THE NORTHERN AND WESTERN BERING SEA. A STRONG LOW
PRESSURE SYSTEM NEAR KAMCHATKA IS BEGINNING TO STRENGTHEN AS IT
BEGINS TO SLOWLY MOVE EAST TOWARD THE WESTERN BERING SEA.

&&

.MODEL DISCUSSION...

MODELS ARE IN GENERALLY GOOD AGREEMENT SYNOPTICALLY. THEY ALL TAKE
THE SHUMAGIN ISLANDS OCCLUDED LOW AND DRIFT IT EAST INTO THE
CENTRAL GULF BY LATE MONDAY INTO TUESDAY...MAKING IT BROAD AND
DIFFUSE IN THE PROCESS. MODELS DIFFER SOMEWHAT IN ITS DEPICTION IN
THE GULF BUT WITH NO SIGNIFICANT IMPACT ON THE FORECAST.

OUT IN THE FAR WEST...THE KAMCHATKA LOW CONTINUES TO STRENGTHEN
AND MATURE INTO A STRONG CYCLONE CENTERED NORTH AND WEST OF ATTU
THROUGH MON NIGHT. A LOW PRESSURE SYSTEM WILL STRENGTHEN ALONG ITS
ASSOCIATED FRONT AS IT MOVES INTO THE WESTERN ALEUTIANS LATE
SUNDAY INTO MONDAY...THEN CIRCLE BACK TOWARD BACK TOWARD THE
PARENT LOW AND MERGE WITH IT LATE MONDAY INTO TUESDAY NORTH AND
WEST OF ATTU.

THE IMPACT OF THE STRONG LOW PRESSURE SYSTEM BECOMING STATIONARY
OVER THE FAR WESTERN BERING LATE MONDAY INTO MID-WEEK WILL RESULT
IN HIGH PRESSURE RIDGING STRENGTHENING ALOFT OVER THE MAINLAND
TUESDAY INTO WEDNESDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A SERIES OF UPPER LEVEL DISTURBANCES MOVING NORTHWARD ACROSS THE
GULF OF ALASKA TO SOUTHCENTRAL CONTINUE TO PROVIDE QUITE THE
CHALLENGE FOR THE PRECIPITATION FORECAST. FOR THE MOST PART SHOWERS
ASSOCIATED WITH THESE DISTURBANCES HAVE BEEN CONFINED TO THE GULF
COASTAL REGION WITH VERY FEW SHOWERS MAKING IT OVER THE COASTAL
MOUNTAINS. THIS IS DUE TO WEAK DOWNSLOPE FLOW AND LOW LEVEL DRY
AIR SUPPORTED BY OFFSHORE FLOW AT THE SURFACE. HOWEVER...THERE
HAVE BEEN A FEW STRONGER UPPER WAVES (ONE OF WHICH IS MOVING
THROUGH THIS MORNING) WHICH TEMPORARILY MODIFY THE LOW LEVEL FLOW
(TO WEAKEN DOWNSLOPING). PINPOINTING THE LOCATION AND AMOUNT OF
PRECIP IS VERY DIFFICULT...ESPECIALLY SINCE NONE OF THE MODELS
HAVE A GREAT HANDLE ON THE PLACEMENT AND TIMING OF INDIVIDUAL
FEATURES. SATELLITE AND RADAR TRENDS ARE THE MOST USEFUL TOOL IN
THIS SITUATION. BECAUSE OF THIS...FORECAST CONFIDENCE IN THE
PRECIP FORECAST BEYOND THE FIRST SIX HOURS IS LOW.

THE AIR MASS ACROSS THE REGION HAS CONTINUED A STEADY COOLING
TREND. THE IMMEDIATE COAST REMAINS ALL RAIN...BUT INTERIOR
PORTIONS OF WESTERN PRINCE WILLIAM SOUND HAVE SEEN SOME PERIODS OF
SNOW OR RAIN AND SNOW MIXED WITH VERY MINOR SNOW ACCUMULATIONS.
AS PER THE ANCHORAGE SOUNDING ANYTHING ON THE LEE SIDE OF THE
COASTAL RANGE WILL FALL AS SNOW.

UPPER LEVEL FLOW WILL SHIFT SUNDAY NIGHT INTO MONDAY AS THE LOW
ALONG THE ALASKA PENINSULA EXITS EASTWARD ACROSS THE GULF AND
UPPER FLOW OVER SOUTHCENTRAL BECOMES WESTERLY. PRECIP WILL THEN
BECOME FAVORED ALONG THE WEST SLOPES OF MOUNTAINS WHILE PRECIP IN
WESTERN PRINCE WILLIAM SOUND WILL DIMINISH.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)...
ISOLATED TO SCATTERED SNOW SHOWERS WILL CONTINUE TO DEVELOP TODAY ALONG
A WEAK STATIONARY BOUNDARY ACROSS BRISTOL BAY. WITH TEMPERATURES
NEAR FREEZING ALONG THE EASTERN ALASKA PENINSULA AND ALEUTIAN
RANGE AND BELOW FREEZING TEMPERATURES TO THE NORTH...ISOLATED
POCKETS OF FREEZING RAIN ARE POSSIBLE MAINLY SOUTH AND EAST OF
DILLINGHAM. SCATTERED SNOW SHOWERS WILL MAKE IT INTO THE ALASKA
RANGE TODAY AS THE BROAD AREA OF LOW PRESSURE PUSHES A SHORTWAVE
WESTWARD. ISOLATED TO SCATTERED PRECIPITATION DIMINISHES MONDAY
NIGHT AS THE MAIN LOW CENTER SHIFTS EAST. THE NEXT FRONT PUSHES
INTO THE EASTERN BERING ON TUESDAY BRINGING INCREASED RAIN CHANCES
FOR RAIN AND GUSTY WINDS ALONG THE ALASKA PENINSULA AND WESTERN
COAST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
NORTHERLY FLOW WITH ISOLATED TO SCATTERED SHOWERS CONTINUE ACROSS
THE BERING TODAY. LOW PRESSURE EAST OF THE KAMCHATKA PENINSULA
WILL PUSH A WARM FRONT INTO THE WESTERN ALEUTIANS THIS AFTERNOON
BRINGING STRONG WINDS AND RAIN THROUGH TONIGHT. THE BOUNDARY MOVES
INTO CENTRAL BERING/EASTERN ALEUTIANS BY TUESDAY MORNING AND THEN
REMAINS STATIONARY AS THE LOW FILLS. ANOTHER LOW WILL MOVE UP FROM
THE NORTH PACIFIC WITH ANOTHER ROUND OF PRECIPITATION MID WEEK.


&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE EXTENDED FORECAST LOOKS MUCH THE SAME TODAY AND WILL STILL BE
DEPENDENT ON A COMPLEX LOW SETTING UP SHOP IN THE WESTERN/CENTRAL
BERING SEA. A CURRENTLY DEVELOPING KAMCHATKA LOW WILL ANCHOR THE
LONGWAVE PATTERN WHILE SEVERAL COMPACT SHORTWAVE TROUGHS WILL
DEVELOP AND JOIN THE LARGE SCALE CIRCULATION. THE FIRST WILL
STRENGTHEN ALONG THE FRONTAL BOUNDARY PROGRESSING EASTWARD ACROSS
THE CHAIN IN THE VICINITY OF THE CENTRAL/EASTERN ALEUTIANS
BRINGING RAIN AND GALE FORCE WINDS. ANOTHER WAVE QUICKLY FOLLOWS
BY WEDNESDAY REINFORCING THE CIRCULATION AND BRINGING MORE RAIN
AND WIND TO THE CENTRAL ALEUTIANS WHILE SENDING THE FRONT FURTHER
EAST IN THE BERING SEA. GLOBAL GUIDANCE HAS BEEN SIGNALING THAT
THIS ACTIVITY OUT WEST WILL PUMP UP A RIDGE OF HIGH PRESSURE IN
THE GULF WHICH WILL ACT TO SLOW THE PROGRESSION OF THE PATTERN AND
KEEP THE SOUTHCENTRAL DRY FOR THE FORESEEABLE FUTURE. EXPECT
SLIGHTLY ABOVE NORMAL TEMPERATURES AND LIGHT WINDS FOR THE WEEK.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY 181.
         GALE 175 176 177 178 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...MTL


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