Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 171239
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
439 AM AKDT WED SEP 17 2014

.ANALYSIS AND UPPER LEVELS...
A SPRAWLING LOW PRESSURE SYSTEM ALOFT CURRENTLY CONTROLS THE
PATTERN OVER THE GREAT LAND THIS MORNING. THIS SYSTEM IS THE
REMNANTS OF THE HUGE BERING SEA SYSTEM FROM THE WEEKEND. A NUMBER
OF SMALLER SCALE DISTURBANCES ARE ROTATING AROUND THE PERIPHERY OF
THAT LONG-WAVE...STRETCHING FROM THE NORTHERN COAST OF ALASKA
THROUGH THE WESTERN BERING SEA AND INTO THE NORTHERN PACIFIC WHERE
THE JET STREAM IS AMPLIFYING THESE SHORT-WAVE TROUGHS. ANOTHER
UPPER LEVEL LOW PRESSURE OVER NORTHERN JAPAN HAS PUMPED UP UPPER
LEVEL HEIGHTS OVER KAMCHATKA FORMING A WEAK OMEGA BLOCK. THE HIGH
LATITUDE BLOCK USUALLY SIGNIFIES THE PATTERN SHOULD REMAIN
STATIONARY OR VERY WEAKLY PROGRESSIVE...BUT WITH GOOD JET SUPPORT
OVER THE NORTHERN PACIFIC THE PATTERN SHOULD REMAIN SOMEWHAT
PROGRESSIVE.

THE MAIN LOW CENTER IS STACKED BETWEEN THE SURFACE AND ALOFT IN
THE BRISTOL BAY AREA WITH A GALE FORCE FRONT STRETCHING EASTWARD
ACROSS THE ALASKA PENINSULA INTO THE WESTERN GULF OF ALASKA. OUT
AHEAD OF THE FRONT IN THE NORTHERN GULF...THE RADAR LOOKS AWFULLY
CONVECTIVE WITH LAND BASED LIGHTING DETECTION SHOWING SEVERAL
STRIKES IN THE AREA. OVER THE MAINLAND...RADAR INDICATES A NICE
DRY DOWNSLOPE HOLE OVER THE KENAI PENINSULA WHILE BOTH INFRARED
SATELLITE AND WATER VAPOR CORROBORATE WITH A MOUNTAIN WAVE
SIGNATURE.

&&

.MODEL DISCUSSION...
SYNOPTICALLY GUIDANCE IS IN GOOD GENERAL AGREEMENT WITH THE
EVOLUTION OF THE UPPER LOW FOR THE NEXT COUPLE DAYS. THE GENERAL
CONSENSUS IS THE LOW WILL REMAIN ANCHORED OVER THE SOUTHWEST
MAINLAND WHILE TWO STRONG SHORTWAVE TROUGHS DEVELOP AROUND
IT...ONE ON THE DOWNSTREAM SIDE...ONE ON THE UPSTREAM SIDE. THERE
ARE SOME SLIGHT POSITION DIFFERENCES WITH THE SHORTWAVE
PROPAGATING INTO THE GULF BUT ALL GUIDANCE DEVELOPS A POTENT
SURFACE LOW PRESSURE IN THE 970 MB RANGE...WHICH BECOMES THE NEW
CENTER OF CIRCULATION AT THE SURFACE.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...CLOUDY CONDITIONS WILL CONTINUE TODAY WITH
LIGHT WINDS AS ANOTHER FRONT APPROACHES FROM THE SOUTH. DEEP LAYER
SOUTHEAST FLOW WILL MITIGATE PRECIPITATION EARLY THIS
MORNING...BUT AS LIFT INCREASES AHEAD OF THE UPPER TROUGH THROUGH
THE MORNING SOME LIGHT RAIN SHOULD BE ABLE TO OVERCOME THE
DOWNSLOPE DRYING. THE UPPER TROUGH WILL CONTINUE NORTHWARD TOWARD
THE ALASKA RANGE PUTTING THE WESTERN KENAI PENINSULA INTO THE DRY
SLOT WITH ANCHORAGE RIGHT ON THE EDGE. THE FRONTAL BOUNDARY WILL
STALL IN THE NORTHERN GULF KEEPING THE NORTH GULF COAST ENCASED IN
RAIN. ANOTHER SHORTWAVE IN THE FLOW MOVING INTO THE SOUTHERN GULF
TONIGHT WILL CONTINUE GEOPOTENTIAL HEIGHT FALLS OVER THE AREA AS
THE FRONT PIVOTS TO MORE OF AN EAST-WEST ORIENTATION...WHICH
SHOULD TEMPER DOWNSLOPE FLOW AND ALLOW FOR MORE LIGHT RAIN TO
SPREAD OVER THE CHUGACH. THE RESULTING COMPLEX LOW IN THE GULF
WILL KEEP RAIN ALONG THE COAST WITH A LESSER CHANCE FOR
PRECIPITATION INLAND ON THURSDAY. THE UPPER LOW PRESSURE WEAKENS
BUT REMAINS OVERHEAD THROUGH THE WEEKEND KEEPING CLOUDS AND SHOWERS
IN THE FORECAST.

SOUTHWEST ALASKA...A FRONTAL BOUNDARY AND UPPER LEVEL LOW PRESSURE
WILL KEEP RAIN OVER INTERIOR BRISTOL BAY AND THE LOWER KUSKOKWIM
VALLEY TODAY AND TONIGHT. THE SYSTEM WEAKENS THROUGH THE DAY BUT
WILL AT LEAST LINGER SOME SHOWERS OVER THE AREA. THROUGH THE REST
OF THE WEEK AND THE WEEKEND THE COLD POOL ALOFT SHOULD KEEP
THE CHANCE FOR SHOWERS IN MOST AREAS.

BERING SEA/ALEUTIANS...ON THE BACKSIDE OF THE DEPARTING LOW
PRESSURE SYSTEM...GENERALLY MODEST NORTHWEST FLOW IN THE CENTRAL
AND EASTERN BERING SEA WITH SCATTERED SHOWERS. HIGH PRESSURE AND
DRIER CONDITIONS SET UP OVER THE WESTERN BERING SEA AS A FRONT
APPROACHES TOWARD THE WEEKEND.


&&

.LONG TERM FORECAST...
A GENERALLY WET PATTERN LOOKS TO CONTINUE INTO THE WEEKEND AS THE
LONGWAVE TROUGH CENTERED OVER THE EASTERN BERING AND WESTERN
MAINLAND SHIFTS TO THE WESTERN GULF LATE THIS WEEK AND THEN
GRADUALLY WEAKENS THROUGH EARLY NEXT WEEK. THIS WILL RESULT IN
MORE RAIN FOR LOCATIONS ALONG THE NORTHERN GULF COAST AND SHOWERY
WEATHER FARTHER INLAND AS A SERIES OF DISTURBANCES ROTATE
NORTHWARD TOWARDS SOUTHCENTRAL AK. MEANWHILE...HIGH PRESSURE
BUILDING OVER THE CENTRAL BERING LATER THIS WEEK WILL BE SHORT
LIVED AS ANOTHER LOW PRESSURE SYSTEM APPROACHES THE WESTERN
ALEUTIANS THIS WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 125 130 131.
FIRE WEATHER...NONE.
&&

$$
MTL
SEP 14


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