Freezing Rain Advisory 8, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
428 PM AKDT TUE MAR 29 2016

.ANALYSIS AND UPPER LEVELS...
WATER VAPOR SATELLITE IMAGERY SHOWS A CLASSIC OMEGA BLOCKING
RIDGE CENTERED NEAR THE DIXON ENTRANCE. ABUNDANT MOISTURE IS
STREAMING INTO SOUTHERN ALASKA AS LOW PRESSURE SPINS ON THE WEST
SIDE OF THE RIDGE IN THE PACIFIC. AT THE SURFACE A WEAK FRONT
REMAINS ALONG THE COPPER RIVER AND THE GULF WITH A DIFFUSE
BOUNDARY ALONG THE KENAI TO SUSITNA VALLEY. PATCHY FOG IS SLOW TO
CLEAR ALONG THE WEAK BOUNDARY KEEPING LOW VISIBILITIES ALONG THE
COOK INLET AND SUSITNA VALLEY. RAIN IS DEVELOPING ALONG THE FRONT
IN THE CENTRAL AND NORTHERN GULF WITH OCCASIONAL LIGHT SHOWERS
AROUND THE WEAK BOUNDARY INLAND.

ACROSS THE SOUTHWEST...THE SURFACE FLOW IS LIGHT AND VARIABLE
EXCEPT ALONG THE KUSKOKWIM DELTA WHERE FLOW REMAINS FROM THE
NORTHEAST. A LOW SOUTH OF THE ALASKA PENINSULA IS MOVING A WARM
FRONT TOWARD BRISTOL BAY. LIGHT SNOW AND RAIN IS CONFINED MAINLY
TO THE WESTERN CAPES EARLY AFTERNOON AS THE WARMER AIR MASS SLOWLY
OVERRUNS THE COOLER AIR OF THE SOUTHWEST. A SURFACE RIDGE IS THE
DOMINANT PATTERN ACROSS THE BERING KEEPING LOW CLOUDS ACROSS MUCH
OF THE BERING EXCEPT FOR SOME CLEARING ALONG AND JUST SOUTH OF
THE BERING STRAIT.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN
THROUGH THURSDAY NIGHT. HOWEVER THERE ARE DIFFERENCES BETWEEN THE
MODELS WITH HOW THE FRONT ACROSS THE GULF SHIFTS WEST THROUGH
THIS TIME PERIOD. IT IS NOT UNUSUAL TO SEE THESE DIFFERENCES AS
THE SURFACE TROUGH STRETCHES OVER 500 MILES AWAY FROM THE LOW
CENTER IN THE NORTH PACIFIC. UPPER LEVEL WAVES MOVING BETWEEN THE
BLOCKING RIDGE AND THE LOW SOUTH OF THE ALASKA PENINSULA WILL SET
THE FRONT INTO MOTION THIS EVENING. LOCAL WINDS ACROSS SOUTHCENTRAL
WERE UPDATED WITH THE USE OF THE HIRES MODEL DATA WITH A BLEND OF
ALL OPERATIONAL MODELS FOR PRECIPITATION TYPES AND AND FRONTAL
PROGRESSION.

&&

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

THE FRONTAL SYSTEM CURRENTLY DRAPED ACROSS THE NORTHEASTERN GULF
COAST WILL SWING BACK TO THE NORTHWEST TONIGHT THROUGH WEDNESDAY
MORNING AS THE UPPER LEVEL RIDGE OVER THE SOUTHEASTERN GULF AND
BRITISH COLUMBIA AMPLIFIES. ADDITIONALLY A FRONTAL WAVE
DEVELOPING IN THE VICINITY OF 45N 155W ALONG THE JET PUMPING UP
MOISTURE FROM THE SOUTH WILL LIFT TO THE NORTHWEST ALSO HELPING TO
SWING THE FRONT INTO THE SOUTHWEST GULF TONIGHT AND SOUTH CENTRAL
ALASKA EARLY WEDNESDAY MORNING. AN ADDITIONAL WAVE DEVELOPING
ALONG THE FRONT WILL STALL THE WESTWARD PROGRESS OF THE FRONT ON
WEDNESDAY PROLONGING PRECIPITATION ACROSS THE WESTERN HALF OF
SOUTH CENTRAL ALASKA THROUGH WEDNESDAY EVENING. SHARP RIDGING WILL
BUILD FROM SOUTHEAST ALASKA ALONG THE NORTHERN GULF COAST RAPIDLY
ENDED PRECIPITATION AND CLEARING SKIES FOR A RATHER SUNNY DAY
THURSDAY.

IN ADDITION TO BRINGING WIDESPREAD RAIN TO SOUTH CENTRAL ALASKA
STRONG PRESSURE RISES BEHIND THE FRONT WILL RAPIDLY INCREASE EAST
TO SOUTHEASTERLY GAP WINDS FOLLOWING FRONTAL PASSAGE ON WEDNESDAY.
STRONG EAST TO SOUTHEAST WINDS ARE LIKELY THROUGH PORTAGE
VALLEY...TURNAGAIN ARM AND ALONG THE ANCHORAGE HILLSIDE WITH WINDS
INCREASING THROUGH KNIK ARM AND THE EAGLE RIVER VALLEY AS WELL.
THE COPPER RIVER BASIN WILL ALSO SEE STRONG DOWNSLOPING
SOUTHEASTERLY WINDS DEVELOP AS SOON AS THE FRONT LIFTS BY MID TO
LATE WEDNESDAY MORNING. NOT ONLY WILL THIS RAPIDLY SHUT OFF
PRECIPITATION OVER THE COPPER RIVER BASIN LOWLANDS BUT ALSO
EXPECT TO SEE THE DOWNSLOPING WARM TEMPERATURES INTO THE MID TO
UPPER 50S THROUGH WEDNESDAY AFTERNOON.

&&

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

THE MAIN CHALLENGE FOR THE SHORT TERM REMAINS PRECIPITATION TYPE.
AN IMPRESSIVE WARM FRONT IS CURRENTLY ALONG THE WEST GULF OF
ALASKA...BUT IS POISED TO PUSH INLAND BEGINNING THIS EVENING. AS
TEMPERATURES ARE ALREADY HOVERING NEAR FREEZING ACROSS THE
BRISTOL BAY ZONE...MAINLY A RAIN SNOW MIX IS ANTICIPATED
TONIGHT...TRANSITIONING TO ALL RAIN BY WEDNESDAY AS WARMER AIR
SURGES IN BEHIND THE FRONT. MEANWHILE...WITH MORE COLD AIR IN
PLACE...MAINLY SNOW IS EXPECTED ACROSS THE KUSKOKWIM
VALLEY UNTIL WEDNESDAY NIGHT. SOME ISOLATED FREEZING RAIN IS
POSSIBLE LATE WEDNESDAY INTO EARLY THURSDAY MORNING...AS WARM AIR
PUSHES OVER THE COLD AIR IN PLACE. THE GREATEST CONCERN IS FOR THE
KUSKOKWIM DELTA...WHERE PERSISTENT NORTHERLY FLOW IS EXPECTED TO
SUSTAIN COLD AIR NEAR THE SURFACE AS THE WARM FRONT APPROACHES.

&&

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

WITH BROAD NORTHEASTERLY FLOW IN PLACE ACROSS THE
BERING...RELATIVELY CLEAR CONDITIONS ARE EXPECTED TO REMAIN ALONG
THE ICE EDGE DOWN TO THE PRIBILOFS. MEANWHILE...STRATUS ARE
EXPECTED TO CONTINUE TO LINGER ALONG THE NORTHERN EDGE OF THE
ALEUTIANS. A FRONT WILL APPROACH THE EASTERN ALEUTIANS BY
WEDNESDAY EVENING...AND BRING GUSTY WINDS AND RAIN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE WET PATTERN WILL RETURN TO SOUTHCENTRAL THURSDAY NIGHT AFTER
A BRIEF PERIOD OF DRIER WEATHER AS A FRONT PUSHES THROUGH THE GULF
AND THE WEAKENING UPPER LEVEL RIDGE IS DISPLACED NORTH AND
EASTWARD. THIS WILL ALLOW ONSHORE FLOW TO BECOME RE-ESTABLISHED
AND SUPPORT ENHANCED PRECIPITATION ALONG THE GULF COAST AND MORE
SPORADIC ACTIVITY INLAND DUE TO DOWNSLOPE FLOW IN THE LEE OF THE
COASTAL MOUNTAIN RANGES. THIS SHIFT IN THE PATTERN WILL ALSO BRING
A COOLING TREND STARTING THIS WEEKEND AS COLDER AIR FILTERS INTO
THE REGION FROM THE SOUTHWEST AHEAD OF A BROAD UPPER TROUGH OVER
THE EASTERN BERING. DESPITE THE COOLING TREND...TEMPERATURES ARE
STILL EXPECTED TO REMAIN ABOVE SEASONAL NORMAL VALUES THROUGH
EARLY NEXT WEEK ACROSS MUCH OF THE SOUTHERN MAINLAND. THE BERING
SEA AND AREAS ALONG THE SOUTHWEST COAST WILL ALSO REMAIN IN A
FAIRLY WET PATTERN INTO THE EARLY PART OF NEXT WEEK BENEATH THE
PERSISTENT UPPER TROUGH.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 150 155 170 172 173 174 175 176 179 180 181 185 411
412 413 414.

&&

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