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FXAK68 PAFC 030226 CCA
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
313 PM AKST MON MAR 2 2015
.ANALYSIS AND UPPER LEVELS...
THE CURRENT PATTERN HAS A FAIRLY HIGH AMPLITUDE. THERE IS A TROUGH
CENTERED ALONG ABOUT 170 DEGREES WEST LONGITUDE WITH SEVERAL
EMBEDDED LOWS. THE STRONGEST OF THESE IS LOCATED JUST SOUTHWEST OF
KODIAK AND HAS A FRONT THAT STRETCHES EASTWARD ACROSS THE GULF AND
ANOTHER NORTHWARD OVER SOUTHWEST ALASKA. THERE IS A NEGATIVELY
TILTED RIDGE OF HIGH PRESSURE OVER ALASKA THAT STRETCHES SOUTH-
SOUTHEAST ALONG THE PANHANDLE AND WESTERN CANADIAN COAST. THERE IS
ANOTHER RIDGE OVER THE WESTERN ALEUTIANS AND WESTERN BERING SEA
WITH A DEEP LOW TO THE WEST NEAR KAMCHATKA.

&&
.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN GOOD AGREEMENT THROUGH THE SHORT TERM
AND ARE NOT PROVIDING ANY FORECAST PROBLEMS. THIS IS OFFSET BY THE
DIFFICULTY OF FORECASTING VARIOUS PRECIPITATION TYPES (RAIN SNOW
AND FREEZING RAIN). THEREFORE THE FORECAST CONFIDENCE IS NEAR
NORMAL TODAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

THE UPPER LOW SOUTH OF KODIAK BEGINS TO LIFT NORTH THIS EVENING
AND MOVES THE FRONT INTO THE NORTHERN GULF. THE DRIER AIR MASS
CURRENTLY ACROSS SOUTHCENTRAL SLOWLY SATURATES AS THE FRONTAL
BOUNDARY MAKES NORTHWARD PROGRESS. THE EASTERN KENAI AND NORTHERN
GULF LOCATIONS WILL SEE THE HIGHEST PRECIPITATION AMOUNTS TONIGHT
AS SOUTHEASTERLY FLOW OVER THE MOUNTAINS CAUSE DOWNSLOPING ALONG
WEST FACING SLOPES. HOWEVER...THE UPPER LEVEL WAVE PICKS UP
MOMENTUM AROUND MIDNIGHT MOVING ACROSS THE KENAI PENINSULA AND
THEN THROUGH MUCH OF SOUTHCENTRAL BY MID TUESDAY MORNING. THE
CHALLENGE WITH THIS SYSTEM IS THE PRECIPITATION TYPE ALONG THE
FRONT OVER THE ANCHORAGE BOWL AND NORTH THROUGH THE MATANUSKA AND
SUSITNA VALLEYS. FOR THESE AREAS...PRECIPITATION ALONG THE FRONT
STARTS OFF AS SNOW AND THEN CHANGES OVER TO RAIN WITH A WARMER AIR
MASS ADVECTING INTO SOUTHCENTRAL FROM THE GULF. THE CHANGE OVER IS
EXPECTED TO OCCUR RATHER QUICKLY AS THE SYSTEM SPEEDS UP
OVERNIGHT...HOWEVER THERE ARE AREAS THAT WILL LAG IN WARMING UP AT
THE SURFACE DUE TO TERRAIN AFFECTS AND MAY BRIEFLY EXPERIENCE
FREEZING RAIN. ONCE THE FRONT PUSHES NORTH INTO THE SUSITNA VALLEY
THE FRONT DIMINISHES RAPIDLY. RAIN WILL CONTINUE ACROSS THE GULF
AND PRINCE WILLIAM SOUND AS ANOTHER SYSTEM MOVES INTO THE SOUTHERN
GULF OF ALASKA QUICKLY BEHIND THE FIRST LATE TUESDAY AFTERNOON.
SLIGHT CHANCE FOR PRECIPITATION REMAINS IN THE FORECAST ELSEWHERE
AS A WEAK UPPER LEVEL WAVE MOVES FROM WEST TO EAST ON WEDNESDAY.
 

&&
.SHORT TERM FORECAST SOUTHWEST ALASKA...
AN UPPER LEVEL TROUGH WILL PUSH THROUGH THE REGION BY TUESDAY MORNING
BRINGING MORE MOISTURE AND A WINTRY MIX OF PRECIPITATION TO THE
REGION. THE BRISTOL BAY TEMPERATURES ARE WELL ABOVE FREEZING AND
THEIR PRECIPITATION WILL FALL AS ALL RAIN. THE LOWER KUSKOKWIM
VALLEY TEMPERATURES REMAIN BELOW FREEZING. THIS WILL RESULT IN
LIGHT FREEZING RAIN THIS EVENING THROUGH TUESDAY MORNING AND
COINCIDES WITH THE FREEZING RAIN ADVISORY FOR THIS AREA. THE
KUSKOKWIM DELTA REGION WILL HAVE A RAIN/SNOW MIXTURE OF
PRECIPITATION WITH PERIODS OF SNOW HEADING INTO TUESDAY MORNING. A
SECOND DISTURBANCE WILL MOVE THROUGH THE KUSKOKWIM FROM THE WEST
BY TUESDAY AFTERNOON. THIS WILL BRING WARMER TEMPERATURES WITH THE
SOUTHWESTERLY FLOW BEFORE THE WINDS SHIFTING TO THE NORTHWEST WITH
THE TROUGH PASSAGE BY THE EVENING. THE PRECIPITATION WILL START
OUT AS RAIN/SNOW AND TRANSITION TO SNOW SHOWERS IN THE EVENING.
THIS WILL BRING MORE RAIN/SNOW TO THE BRISTOL BAY AND LOWER
KUSKOKWIM VALLEY THROUGH TUESDAY BEFORE TRANSITIONING TO SCATTERED
SHOWERS BY TUESDAY EVENING. BY WEDNESDAY AFTERNOON A LOW PRESSURE
SYSTEM WILL TRACK NEAR SAINT MATTHEW ISLAND WITH AN ASSOCIATED
WEATHER FRONT PUSHING INTO THE KUSKOKWIM DELTA AREA. THIS WILL
BRING WARMER TEMPERATURES WITH SOUTHERLY WINDS BEFORE SHIFTING TO
WESTERLY WINDS BY THURSDAY MORNING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
THE EASTERN BERING SEA WILL HAVE A WEAK LOW PRESSURE SYSTEM MOVE
ACROSS THE EASTERN ALEUTIANS NEAR PORT MOLLER INTO THE BRISTOL BAY
AREA THIS EVENING. THIS SYSTEM WILL MOVE INLAND NEAR THE KUSKOKWIM
DELTA BY TUESDAY MORNING. THIS WILL BRING WARMER TEMPERATURE
THROUGH THE EASTERN BERING SEA THROUGH TUESDAY MORNING BEFORE THE
NORTHWESTERLY WINDS UPSTREAM BRING COOLER TEMPERATURES. BY TUESDAY
AFTERNOON THE CENTRAL/EASTERN BERING SEA WILL BE UNDER THE INFLUENCE 
OF THE NORTHWESTERLY WINDS. THIS WILL RESULT IN SCATTERED SHOWERY 
PRECIPITATION EXTENDING INTO THE EASTERN ALEUTIANS. THE NEXT SYSTEM 
WILL BE A STORM FORCE LOW TRACKING ALONG THE KAMCHATKA PENINSULA 
WITH AN ASSOCIATED WEATHER FRONT EXTENDING THROUGH THE WESTERN 
ALEUTIANS NEAR SHEMYA BY LATE TUESDAY MORNING. THIS WILL BRING A 
LARGE SWATH OF MOISTURE WITH GALE FORCE SOUTHERLY WINDS TO THE 
WESTERN BERING SEA/ALEUTIANS. THIS FRONTAL BOUNDARY WILL PUSH TO THE 
PRIBILOF ISLANDS BY WEDNESDAY WITH STRONG GUSTY WESTERLY WINDS ON 
THE BACKSIDE OF THIS SYNOPTIC FEATURE EXTENDING THROUGH THE WESTERN 
BERING SEA/ALEUTIANS. BY THURSDAY THE SAME WEATHER SCENARIO WILL 
OCCUR FOR THE WESTERN BERING SEA/ALEUTIANS WITH ANOTHER NORTH 
PACIFIC LOW TRACKING ALONG THE KAMCHATKA PENINSULA AND AN ASSOCIATED 
WEATHER FRONT MOVING INTO THE WESTERN ALEUTIANS.


&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
SHOWER ACTIVITY WILL LINGER OVER THE SOUTHERN MAINLAND THROUGH
THURSDAY AS WEAK LOW PRESSURE REMAINS OVER THE GULF. AN ACTIVE
PATTERN WILL THEN CONTINUE THROUGH THE WEEKEND AS A SERIES OF
WAVES TRACK QUICKLY EASTWARD ACROSS THE REGION IN ZONAL FLOW
BENEATH A STRONG POLAR JET CENTERED BETWEEN 50N AND 60N LATITUDE.
THE FIRST OF THESE FEATURES WILL BE A SHARP SHORT WAVE TROUGH
WHICH WILL TRAVERSE THE SOUTHERN MAINLAND THURSDAY NIGHT INTO
FRIDAY. THAT SYSTEM WILL THEN BE FOLLOWED CLOSELY BY A SPRAWLING
LOW THAT WILL MOVE INTO THE NORTON SOUND REGION EARLY SATURDAY AND
SPREAD PRECIPITATION OVER MUCH OF THE MAINLAND FOR THE WEEKEND.
PRECIPITATION TYPE WILL REMAIN A CHALLENGE AS TEMPERATURES HOVER
NEAR FREEZING...WITH MIXED PRECIPITATION LIKELY FOR MANY
LOCATIONS. AFTER THAT...MODELS ARE IN REASONABLE AGREEMENT THAT A
MORE AMPLIFIED PATTERN WILL BEGIN TO TAKE SHAPE BY EARLY NEXT WEEK
AS AS A DEEP UPPER TROUGH DIGS OVER THE MAINLAND AND HIGH PRESSURE
BUILDS OVER THE WESTERN BERING. THIS SCENARIO WOULD RESULT IN A
RETURN TO MUCH COLDER TEMPERATURES ACROSS A WIDE SWATH OF THE
MAINLAND.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FREEZING RAIN ADVISORY 152.
MARINE...GALE WARNING 119 120 130 131 138 139 177 178. 
         HEAVY FREEZING SPRAY 180 185. 
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...CB


Alaska Region Headquarters
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Page Modified: 03 Feb 2008 18:00 UTC
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