Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 102233
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
233 PM AKDT THU JUL 10 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS A BROAD LONGWAVE TROUGH OVER THE NORTH PACIFIC WITH A
SPRAWLING AND COMPLEX UPPER LOW CENTERED OVER THE EASTERN BERING.
THIS SETS MAINLAND UP IN DEEP SOUTHERLY FLOW WITH COPIOUS AMOUNTS
OF MOISTURE EVIDENT ON SATELLITE IMAGERY STREAMING INTO SOUTHERN
ALASKA. THERE ARE NUMEROUS SHORTWAVES ROTATING AROUND THE UPPER
CENTER...THOUGH TWO MAIN SHORTWAVES ARE DOMINATING THE WEATHER
AROUND THE REGION TODAY. THE FIRST SHORTWAVE HAS PUSHED INTO
SOUTHCENTRAL THIS MORNING...AND CONTINUES TO BRING WIDESPREAD RAIN
AND A GALE-FORCE BARRIER JET TO THE NORTH GULF COAST AND PRINCE
WILLIAM SOUND. THIS PATTERN IS SO MOISTURE-LADEN THAT EVEN THE
USUAL DOWNSLOPE AREAS LIKE ANCHORAGE ARE SEEING RAIN...THOUGH NOT
NEARLY AS MUCH AS COASTAL SITES. THE SECOND SIGNIFICANT SHORTWAVE
IS APPARENT ON SATELLITE IMAGERY MOVING INTO THE SOUTHERN GULF.
THIS SECOND FEATURE IS RAPIDLY CATCHING UP TO THE FIRST...AND THE
NET EFFECT WILL BE A BRIEF PLATEAU OR WEAK LULL IN WINDS AND RAIN
ALONG THE COAST BEFORE RE-INTENSIFICATION THIS EVENING. PERIODS
OF RAIN ARE ALSO ROTATING THROUGH SOUTHWEST ALASKA...THOUGH WINDS
ARE MUCH WEAKER AS THE STRONG PRESSURE GRADIENTS REMAIN WELL TO
THE EAST. MEANWHILE...NORTHERLY FLOW AND WEAK COLD ADVECTION
CONTINUES ACROSS THE BERING SEA. CLOUDINESS IS VERY WIDESPREAD BUT
PRECIPITATION REMAINS ISOLATED AND SHOWER IN NATURE AT MOST
LOCATIONS.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT THROUGHOUT THE SHORT
TERM PERIOD...AND ARE COMING INTO BETTER AGREEMENT WITH THE
DETAILS FOR THE REMAINDER OF THE CURRENT STORM. THERE HAD BEEN
SOME ISSUE ABOUT WHETHER A SECONDARY SURFACE LOW CENTER WOULD FORM
UNDER THE AFOREMENTIONED SECONDARY UPPER SHORTWAVE...WITH SMALL
BUT SIGNIFICANT RAMIFICATIONS FOR THE STRENGTH OF COOK INLET WINDS
AND THE BARRIER JET ALONG THE NORTH GULF COAST. IT NOW LOOKS LIKE
THE SOLUTION FIRST ADVERTISED BY THE ECMWF WILL BE THE MOST
CORRECT...WITH ONLY A VERY BRIEF LULL IN THE STRENGTH OF THE
BARRIER JET BETWEEN SYSTEMS AND WEAKER COOK INLET WINDS
TONIGHT. ADDITIONALLY...THE ECMWF AND CANADIAN RDPS TRY TO KEEP
WEAK LOW PRESSURE AROUND COOK INLET TOMORROW DURING THE
DAY...KEEPING FLOW DOWN-INLET AND GUSTY WINDS OUT OF ANCHORAGE.
THIS SOLUTION DOES NOT MATCH CONCEPTUAL MODEL AND HISTORICAL
BEHAVIOR...AND WILL THUS ELECT TO STICK CLOSER TO THE GFS/NAM
SOLUTION THAT DOES BRING SOME WINDS INTO ANCHORAGE BY TOMORROW
MORNING.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
THE SECOND SHORTWAVE AND ASSOCIATED INCREASE IN WINDS AND RAIN IS
QUICKLY MOVING TOWARD THE COAST. THE COMBINATION OF UPPER FLOW
REMAINING MORE SOUTHERLY (RATHER THAN SOUTHEASTERLY) AND THE
MOISTURE-LADEN NATURE OF THIS STORM (OVER 1 INCH OF PRECIPITABLE
WATER ON THE ANCHORAGE MORNING SOUNDING) WILL CONTINUE TO SUPPORT
RAIN FALLING EVEN IN MOST OF THE USUAL DOWNSLOPE AREAS ON THE LEE
SIDES OF THE MOUNTAIN RANGES. AS MENTIONED IN THE MODEL
DISCUSSION...THERE IS SOME QUESTION ON WHEN (OR IF) THE TURNAGAIN
ARM WINDS SPREAD INTO PORTIONS OF ANCHORAGE TOMORROW. THE FORECAST
REASONING IS LARGELY UNCHANGED FROM OVERNIGHT...WITH WINDS LIKELY
TO BEGIN AFFECTING SOUTH AND WEST ANCHORAGE DURING THE MORNING
HOURS. WHILE THESE WINDS WILL NOT BE SEVERE OR DAMAGING...THEY
WILL BECOME NOTICEABLY GUSTY AND MAY LINGER UNTIL THE DAYTIME ON
SATURDAY.

SOUTHWEST ALASKA...
WHILE THE REGION WILL STAY OUT OF THE MOST SIGNIFICANT WEATHER
IMPACTS...UNSETTLED WEATHER WILL CONTINUE THROUGH AT LEAST THE
FIRST HALF OF THE WEEKEND AS THE LARGE UPPER LOW IN THE EASTERN
BERING SLOWLY MIGRATES INTO THE PACIFIC. NUMEROUS SHORTWAVES WILL
KEEP PERIODS OF RAIN LIKELY ACROSS MOST OF THE AREA...THOUGH CONFIDENCE
IN INDIVIDUAL TIMING AND PLACEMENT OF RAIN BANDS WILL LIKELY
REMAIN FAIRLY LOW.

BERING SEA/ALEUTIANS...
WEATHER ACROSS THE EASTERN BERING WILL REMAIN UNSETTLED AS THE
UPPER LOW LINGERS. CONDITIONS WILL MOSTLY BE SHOWERY IN NATURE
WITH LOCALIZED GUSTY WINDS AS OPPOSED TO WIDESPREAD SIGNIFICANT
IMPACTS. BY THE LATTER HALF OF THE WEEKEND HIGH PRESSURE WILL
BUILD INTO THE WESTERN AND CENTRAL BERING...DROPPING WINDS EVEN
MORE BUT LIKELY LEADING INTO ANOTHER ROUND OF WIDESPREAD MARINE
FOG/STRATUS.

&&

.AVIATION...
STRONG TURNAGAIN ARM WINDS ARE CURRENTLY TURNING STRONGLY
SOUTH/DOWN-INLET AND AS A RESULT WIND SHEAR CONDITIONS ARE STAYING
OUT OF THE ANCHORAGE AREA. THIS WILL CHANGE TOWARD FRIDAY MORNING
AS THE NORTHERLY PRESSURE GRADIENT WEAKENS AND THE CORE OF
TURNAGAIN ARM WINDS BEGIN TO BEND MORE NORTHERLY. THERE WILL
LIKELY BE A MULTI-HOUR PERIOD SOMETIME FRIDAY MORNING WHERE WIND
SHEAR IS EXPECTED TO MOVE INTO THE AREA. LATER FRIDAY MORNING GUSTY
SOUTHEAST WINDS WILL REACH ALL THE WAY DOWN TO THE SURFACE AND
END THE WIND SHEAR THREAT.

&&

.LONG TERM FORECAST (SUN JULY 13 - WED JULY 16)...

THE REMNANTS OF A LARGE UPPER LEVEL TROUGH WILL BE IMPACTING
SOUTHERN ALASKA SUNDAY...WITH SHOWERS MAINLY CONFINED TO THE
MOUNTAINS. TEMPERATURES WILL REMAIN NEAR NORMAL THEN SLOWLY RISE
TOWARDS MIDWEEK AS WEAK RIDGING BUILDS IN ACROSS THE MAINLAND. THE
BERING SEA WILL ALSO REMAIN QUIET WEATHER WISE THROUGH THIS
PERIOD...WITH THE A CONTINUATION OF TYPICAL SEA STRATUS AND FOG.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 119
         GALE 125 129
FIRE WEATHER...NONE.

&&

$$

AMD/JA JUL 14


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