Freezing Rain Advisory 7, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
528 AM AKDT WED MAR 23 2016

.ANALYSIS AND UPPER LEVELS...

UPPER LEVEL HIGH PRESSURE EXTENDING OUT OF NORTHWEST CANADA IS
PRODUCING VERY SPRING-LIKE WEATHER ACROSS MUCH OF MAINLAND ALASKA.
THE JET STREAM REMAINS LARGELY SOUTH OF THE STATE...WHICH IS
KEEPING THE ACTIVE STORM TRACK ALONG AND SOUTH OF THE ALEUTIANS
AND INTO THE SOUTHERN GULF. A MATURE AND VERTICALLY STACKED STORM
IN THE NORTHEAST PACIFIC/SOUTHERN GULF IS THE MAIN FEATURE EVIDENT
ON SATELLITE IMAGERY THIS MORNING. ASSOCIATED MID AND HIGH LEVEL
CLOUDINESS HAS MOVED INTO SOUTHWEST ALASKA...WITH SOUTHCENTRAL
LARGELY PROTECTED FROM SIGNIFICANT CLOUDS AND MOISTURE BY THE
AFOREMENTIONED HIGH PRESSURE FROM CANADA. A WEAKER MIDLEVEL LOW
PRESSURE CENTER IS STALLING NEAR DUTCH HARBOR...AND SHOULD START
TO DRIFT NORTHWARD BY LATER THIS MORNING. MEANWHILE...WAY OUT
WEST...AN ADDITIONAL 998 MB LOW IS APPROACHING THE AREA SOUTH OF
THE WESTERN-MOST ALEUTIAN ISLANDS. THIS LOW IS FOLLOWING A ZONAL
JET STREAM AND MOST IMPACTS ARE REMAINING SOUTH OF THE ALEUTIANS.

&&

.MODEL DISCUSSION...

THE MAJOR MODELS ARE IN EXCELLENT OVERALL AGREEMENT. THE NAM WAS
PRIMARILY UTILIZED FOR THE MORNING FORECAST...DUE TO SUPERIOR
DEPICTION OF WINDS THROUGH THE COMPLEX TERRAIN OF SOUTHERN ALASKA.

&&

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

A FRONT THAT STRETCHES ACROSS THE GULF OF ALASKA IS BRINGING
GUSTY WINDS ACROSS THE CENTRAL AND WESTERN GULF THIS MORNING.
WHILE SATELLITE IMAGERY INDICATES THE FRONT IS GRADUALLY
WEAKENING...GUSTY WINDS ARE STILL POSSIBLE THROUGH LOCAL GAPS IN
COASTAL REGIONS UNTIL THE FRONT DISSIPATES THIS EVENING. ACROSS
THE SOUTHCENTRAL MAINLAND THIS MORNING...GENERALLY CLEAR SKIES AND
LIGHT WINDS DOMINATE...WHICH HAS ALLOWED TEMPERATURES TO DROP
APPRECIABLY. ALTHOUGH A FRONT IS APPROACHING THE GULF COAST
TODAY...A RIDGE REMAINS STUBBORNLY IN PLACE AND WILL PREVENT IT
FROM PUSHING ONSHORE. WITH ANOTHER MOSTLY SUNNY DAY
EXPECTED...TEMPERATURES ARE EXPECTED TO REBOUND QUICKLY AND ONCE
MORE APPROACH RECORD LEVELS. HOWEVER...BY THURSDAY EVENING A WAVE
WILL APPROACH THE SOUTHCENTRAL MAINLAND AND INCREASE CLOUD COVER
AND THE CHANCE FOR WIDESPREAD SHOWERS.

&&

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

THE SOUTHWEST MAINLAND WILL REMAIN IN A RATHER BENIGN SHOWERY
PATTERN THROUGH TONIGHT ON THE NORTHERN PERIPHERY OF THE UPPER
LOW NEAR THE ALASKA PENINSULA. STEADIER PRECIPITATION WILL RETURN
TO THE REGION LATE TONIGHT INTO THURSDAY AS THE AKPEN LOW LIFTS
NORTHWARD AS A SHORTWAVE TROUGH. THE MAIN FORECAST CHALLENGE WITH
THIS FEATURE WILL BE PRECIPITATION TYPE OVER THE KUSKOKWIM DELTA
WHERE A WARM LAYER WILL PERSIST ALOFT AS SURFACE TEMPERATURES
HOVER NEAR OR JUST BELOW FREEZING THROUGH THURSDAY MORNING. THIS
WILL LEAD TO MARGINAL POTENTIAL FOR FREEZING RAIN AT THE ONSET OF
PRECIPITATION BEFORE COLD ADVECTION COMMENCES FROM THE SOUTHWEST
AND ERODES THE WARM LAYER DURING THE AFTERNOON. THE PASSAGE OF THE
SHORTWAVE WILL SIGNAL A RETURN TO A MORE SHOWERY REGIME FOR THE
END OF THE WEEK IN CYCLONIC FLOW BENEATH A SPRAWLING LONGWAVE
TROUGH.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

THE BULK OF THE SHOWER ACTIVITY WILL REMAIN FOCUSED OVER THE
EASTERN BERING THROUGH THURSDAY NIGHT IN THE VICINITY OF THE LOW
NEAR THE ALASKA PENINSULA...WITH SHOWERS GRADUALLY DIMINISHING IN
COVERAGE ACROSS THE AKPEN AND EASTERN ALEUTIANS ON THURSDAY AS THE
LOW LIFTS NORTHWARD TOWARD THE MAINLAND. THE WESTERN BERING WILL
REMAIN IN A BENIGN PATTERN CHARACTERIZED BY WEAK UPPER LEVEL FLOW
IN THE ABSENCE OF ANY WELL DEFINED FEATURES.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

BY FRIDAY AN UPPER LEVEL TROUGH WILL BE CENTERED SOUTH OF THE
ALASKA PENINSULA WITH A SECOND BROAD TROUGH STRETCHING ACROSS
WESTERN MAINLAND ALASKA. A LARGE RIDGE WILL EXTEND FROM THE
EASTERN PACIFIC UP OVER THE SOUTHEAST ALASKA PANHANDLE AND ACROSS
THE YUKON TERRITORY. A SURFACE LOW IN THE SOUTHERN GULF WILL TRACK
NORTH THROUGH THE CENTRAL GULF FRIDAY NIGHT AND TOWARDS PRINCE
WILLIAM SOUND SATURDAY. MEANWHILE A STRONG LOW SOUTH OF THE
WESTERN ALEUTIANS WILL TRACK EAST AS ITS ASSOCIATED FRONTAL
SYSTEM SPREADS ACROSS THE ALEUTIAN CHAIN SATURDAY AND THE SOUTHERN
BERING AND ALASKA PENINSULA SATURDAY NIGHT. A TRIPLE POINT FEATURE
WILL LIFT NORTH ACROSS SOUTHWEST ALASKA AND THE WESTERN GULF
SUNDAY AND INTO SOUTH CENTRAL ALASKA SUNDAY NIGHT.

THIS TREND OF INCREASINGLY WET WEATHER WILL CONTINUE INTO THE
FIRST HALF OF NEXT WEEK AS A BIG UPPER LEVEL RIDGE BUILDS NORTH
ACROSS THE EASTERN GULF AND A LARGE UPPER LOW BECOMES ESTABLISHED
SOUTH OF THE CENTRAL ALEUTIANS. THE RESULT OF THESE TWO HIGH
AMPLITUDE FEATURES WILL BE A DEEP TAP OF SOUTHERLY FLOW PUMPING
WARM AIR AND MOISTURE UP INTO SOUTHERN ALASKA. WITH A SERIES OF
FRONTAL WAVES RIPPLING UP THROUGH THIS SOUTHERLY FLOW...PERSISTENT
AND POTENTIALLY HEAVY RAINS ARE LOOKING INCREASINGLY LIKELY WITH
THE HIGHEST AMOUNTS ALONG SOUTHERLY FACING SLOPES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 120 131 138 351.
         HEAVY FREEZING SPRAY WARNING 185.

&&

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...JER