Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 181239
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
439 AM AKDT THU SEP 18 2014

.ANALYSIS AND UPPER LEVELS...
A LONG-WAVE TROUGH/UPPER LOW PRESSURE REMAINS ANCHORED OVER THE
SOUTHWEST MAINLAND WITH CENTER OVER KING SALMON WILL BE THE
SYNOPTIC DRIVER OF ACTIVE WEATHER. WHILE THE DYNAMICS OF THE
SYSTEM ARE WEAKENING OVER THIS AREA...A ZONALLY ORIENTED 130 KT
JET STREAK/SHORT WAVE TROUGH ARE ROTATING AROUND THE BASE OF THE
LONGWAVE INTO THE GULF. A STALLED FRONTAL BOUNDARY ASSOCIATED WITH
THE BRISTOL BAY SYSTEM IS DRAPED OVER THE NORTHERN GULF. STRONGER
SOUTHEASTERLY WINDS TO THE NORTH OF THE FRONT HAVE BEEN KEEPING
THE EASTERN COOK INLET REGION DOWNSLOPED AND DRIER DESPITE
DISTURBANCES ALOFT TRYING TO FORCE PRECIPITATION. THE REMNANTS OF
A AGEOSTROPHICALLY DRIVEN BARRIER JET EXIST ACROSS THE NORTHERN
GULF AHEAD OF THE FRONT...BUT ARE BECOMING MORE GEOSTROPHIC WITH
TIME AS LOW LEVEL WINDS BACK IN RESPONSE TO THE DEVELOPING SURFACE
LOW PRESSURE IN THE GULF. SO WHAT DOES THIS MEAN FOR THE
SOUTHCENTRAL? THE LOW LEVEL FLOW REORIENTING WILL HAVE
IMPLICATIONS ON DOWNSLOPE DRYING AS MORE EASTERLY/NORTHEASTERLY
WINDS WILL LIMIT THE RESPONSE/INTERACTION TO THE CHUGACH ALLOW FOR
THE COLUMN TO MOISTEN ON THE LEE-SIDE.

&&

.MODEL DISCUSSION...
GUIDANCE REMAINS IN GOOD AGREEMENT WITH THE LARGE SCALE FEATURES
OF THE UPPER LEVEL FLOW. PREVIOUS RUNS WERE STRUGGLING WITH THE
EXACT TRACK OF THE SHORTWAVE TROUGH ALOFT AND HOW THE PRESSURE
FIELD AT THE SURFACE WOULD RESPOND. NOW MODELS ARE FIRMLY ONBOARD
WITH A COMPLEX LOW DEVELOPING IN THE NORTHERN GULF BECOMING THE
MAIN SURFACE CIRCULATION WHILE THE UPPER LEVEL TROUGH STAYS
ANCHORED TO THE WEST.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...WIDESPREAD RAINFALL WILL AFFECT AREAS TODAY
FROM THE SUSITNA VALLEY THROUGH THE WESTERN KENAI PENINSULA. THE
WESTERN SUSTINA VALLEY AND KENAI PENINSULA WILL SEE STEADIER RAIN
WHILE THE ANCHORAGE BOWL AND MATANUSKA VALLEY WILL SEE PERIODS OF
RAIN. WINDS WILL REMAIN LIGHT NORTHERLY IN MOST AREAS. RAIN WILL
LINGER LONGEST ALONG THE KENAI PENINSULA BUT SOME SHOWERS ARE NOT
OUT OF THE QUESTION FOR MOST AREAS. TOWARD THE WEEKEND...THE
REMNANTS OF THE DEVELOPING GULF SYSTEM WILL MOVE TOWARD THE AREA
BRINGING MORE LIGHT RAIN PLUS THE OPPORTUNITY FOR GUSTY
SOUTHEASTERLY WINDS ACROSS THE ANCHORAGE BOWL.

SOUTHWEST ALASKA/ALASKA PENINSULA...THE AREA OF LOW PRESSURE THAT
HAS OCCUPIED THE BRISTOL BAY REGION THE PAST FEW DAYS HAS FINALLY
DRIFTED INLAND JUST NORTH OF KING SALMON AND IS STARTING TO
WEAKEN. IT CONTINUES TO "PINWHEEL" AREAS OF ENERGY FROM SOUTHEAST
TO NORTHWEST CREATING WIDESPREAD RAIN SHOWERS. THE LOW WILL
CONTINUE TO FILL TODAY AND DRIFT SLIGHTLY TO THE NORTH.
HOWEVER...IT DOES APPEAR TO HAVE ENOUGH FORCING LEFT TO TAP INTO
THE ABUNDANT AVAILABLE MOISTURE AND MAKE FOR A SLIGHT CHANCE OF
THUNDERSTORMS TODAY OVER THE BETHEL AREA.

A SHARP RIDGE IS MOVING ACROSS THE BERING AND WILL SERVE TO
TIGHTEN THE GRADIENT FROM THE BERING STRAIT SOUTHWARD ALONG THE
WEST COAST LATER TODAY INTO FRIDAY. THIS WILL LEAD TO GUSTY NORTH
TO NORTHWEST WINDS DEVELOPING FIRST ALONG THE COAST AND THEN
SPREADING TOWARDS THE AK PEN DURING THE DAY FRIDAY. THESE
NORTHWEST WINDS WILL ALSO BRING PLENTIFUL SHOWERS TO THE FAVORED
AREAS ON THE BERING SIDE OF THE AK PEN THROUGH SATURDAY MORNING.

ON SATURDAY THE BERING RIDGE WILL START TO PUSH IN AND FINALLY
BRING SOME DRYING TO THE REGION. HOWEVER...WITH SO MUCH RAIN OVER
THE PAST FEW DAYS...THERE WILL BE HIGH POTENTIAL FOR FOG
DEVELOPMENT ONCE THE MORE STABLE ATMOSPHERE MOVES IN.

BERING SEA/ALEUTIANS...GUSTY NORTHWESTERLY FLOW WILL CONTINUE
TODAY WITH EMBEDDED RAIN SHOWERS. HIGH PRESSURE WILL CONTINUE OVER
THE WESTERN/CENTRAL ALEUTAINS UNTIL FRIDAY MORNING WHEN A FRONT
WILL SWING OVER THE WESTERN ALEUTAINS AND SLOWLY WEAKEN AS IT
MOVES EASTWARD THROUGH THE WEEKEND.


&&

.LONG TERM FORECAST...
BEGINNING THE EXTENDED PERIOD ON SUNDAY...THE UPPER AIR PATTERN
WILL CONSIST OF A BLOCKING HIGH OVER THE BERING AND A SPLIT TROUGH
OVER ALASKA AND THE GULF OF ALASKA. A SHARP NORTH AMERICAN RIDGE
WILL TRACK A SUBTROPICAL FRONT NORTHWARD INTO THE GULF LATE SUNDAY
INTO MONDAY. THE EXACT TRACK REMAINS UNCERTAIN...WITH MORE BULLISH
SCENARIOS FROM THE ECMWF AND CANADIAN GDPS FAVORING DEEP AND
STRONG LOW LIFTING INTO THE NORTHERN GULF COAST...WHILE THE GFS
FAVORS AN EASTWARD TRACK ALONG THE ALASKA/CANADA BORDER. THE
CURRENT FORECAST FAVORS A LESS AGGRESSIVE GFS/WPC APPROACH GIVEN
LARGE TRACK AND STRENGTH VARIABILITY AMONG THE DETERMINISTIC AND
ENSEMBLE GUIDANCE. WITH THAT SAID...PRECIPITATION CHANCES WILL
REMAIN THROUGH WEDNESDAY AS ALASKA REMAINS IN BETWEEN TWO LARGE
HIGH PRESSURE CENTERS ACROSS THE BERING AND WESTERN NORTH AMERICA.
NO SIGNIFICANT WET OR COLD PATTERNS ARE EXPECTED THROUGH THE
EXTENDED PERIOD.


&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 125 178.
FIRE WEATHER...NONE.
&&

$$

MTL SEP 14


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