Heavy Freezing Spray Warning 29, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
434 PM AKST MON FEB 1 2016

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVEL PATTERN IS SHIFTING OVER THE AREA TODAY AS THE
UPPER LEVEL RIDGE THAT HAS BEEN OVER THE STATE IS WEAKENING AND
MOVING NORTHWARD INTO THE ARCTIC. THE UPPER LEVEL LOW IS CENTERED
OVER THE KAMCHATKA PENINSULA WITH A TROUGH EXTENDING THROUGH THE
WESTERN BERING SEA AND SOUTH OF THE GULF OF ALASKA. THE JET
STREAM IS SOUTH OF THIS LOW RUNNING ZONALLY FROM JAPAN TO JUST
NORTH OF HAWAII. THERE IS A FRONT FROM THE PREVIOUS SET OF WEAK
LOWS THAT STRETCHES FROM NEAR THE BERING STRAIT THROUGH THE GULF
OF ALASKA. THIS FRONT IS WEAKENING IN PLACE WITH THE MAIN
DEFORMATION AREA OVER INLAND PORTIONS OF THE BRISTOL BAY ZONE AND
INTO THE LOWER KUSKOKWIM VALLEY. THE STRONG SURFACE LOW THAT IS
SOUTH OF THE ALASKA PENINSULA IS LOCATED IN THE LEFT FRONT EXIT
REGION OF THE JET STREAM WHERE IT HAS BEEN STRENGTHENED BY THE
UPPER LEVEL FLOW. AS AS IT MOVES NORTHWARD IT WILL DECOUPLE FROM
THE UPPER LEVEL SUPPORT AND THAT IS A LARGE REASON WHY THE LOW
SHOULD NOT STRENGTHEN MUCH IF AT ALL AS IT HEADS TOWARD ALASKA.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT. WHAT IS A LITTLE
SURPRISING IS THE WAY THE MODELS ARE STRUGGLING SOME WITH THE
LARGE LOW MOVING TOWARD THE GULF OF ALASKA. SPECIFICALLY THE ISSUE
IS WITH THE SECONDARY LOW THAT DEVELOPS IN THE LEFT FRONT EXIT
REGION OF THE JET STREAM TOMORROW. THIS SECONDARY LOW WILL GET
ENTRAINED INTO THE MAIN LOW ON WEDNESDAY AND MODELS DIVERGE ON THE
WAY IT INTERACTS WITH THE FIRST LOW...WHICH IS STALLING AS IT HITS
THE RIDGE OVER MAINLAND ALASKA AS WELL. WHAT LOOKS LIKELY IS THAT
THE SECOND LOW WILL CAUSE THE MAIN ONE TO ELONGATE WITH THE WHOLE
SYSTEM BECOMING A LARGE COMPLEX LOW IN THE GULF OF ALASKA.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE STALLED FRONTAL BOUNDARY OVER THE NORTHERN GULF COAST WILL
SLOWLY DISSIPATE THROUGH TUESDAY EVENING...KEEPING A CHANCE OF
PRECIPITATION IN THE FORECAST MAINLY FOR COASTAL AREAS ALONG THE
NORTHERN GULF AND THE SOUTHERN ALASKA RANGE. WINDS ALONG THE
BARREN ISLANDS WILL BEGIN TO DIMINISH THIS EVENING TO BELOW GALE
FORCE AS THE GRADIENT BEGINS TO WEAKEN. FOG IS EXPECTED TO
CONTINUE OVERNIGHT IN THE COPPER RIVER BASIN AS THE LOW LEVEL
INVERSION WILL KEEP LOW CLOUDS AND FOG IN THE REGION THROUGH
TOMORROW EVENING.

THE NEXT SYSTEM TO IMPACT THE REGION WILL BE THE STRONG FRONT
ASSOCIATED WITH THE LOW NEAR 43N 160W WHICH IS EXPECTED TO MOVE
THE SOUTHWEST OF KODIAK ISLAND BY WEDNESDAY EVENING. WINDS WILL
INCREASE TO GALE FORCE OVER THE SOUTHERN GULF TOMORROW AFTERNOON
AND CONTINUE TO INCREASE GALE FORCE THROUGH LOWER COOK
INLET...SHELIKOF STRAIT...AND THE NORTHERN GULF COAST BY LATE
TUESDAY NIGHT. AS STATED IN THE PREVIOUS DISCUSSION...THE FRONT IS
NOT EXPECTED TO MAKE MUCH PROGRESS PAST THE NORTHERN GULF COAST AS
THE RIDGE WILL REMAIN IN PLACE OVER THE ALCAN BORDER. KODIAK
ISLAND WILL BEAR THE BRUNT OF THE WINDS AS THE FRONT MOVES
THROUGH. RAIN IS MOSTLY EXPECTED AT SEA LEVEL WITH THIS SYSTEM
WITH MODERATE RAINFALL TOTALS ALONG THE COAST THROUGH WEDNESDAY
AFTERNOON. THE UPPER COOK INLET REGION WILL SEE ISOLATED AREAS OF
LIGHT PRECIPITATION WITH THIS FRONT AS THE AREA WILL REMAIN
DOWNSLOPED.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE REMNANT FRONTAL BOUNDARY OVER INTERIOR SOUTHWEST AK WILL KEEP
A NARROW BAND OF SNOW FOCUSED ALONG A CORRIDOR FROM SOUTH OF ANIAK
TO NEAR ILIAMNA THROUGH THIS EVENING...WITH ADDITIONAL
ACCUMULATIONS OF AROUND AN INCH POSSIBLE BEFORE A SUPPORTING
UPPER LEVEL WAVE LIFTS TO THE NORTH AND ALLOWS SNOW TO TAPER OFF
TO SHOWERS AFTER MIDNIGHT. THIS WILL USHER IN COOLER AND DRIER
CONDITIONS THROUGH WEDNESDAY AS OFFSHORE FLOW DEVELOPS IN RESPONSE
TO A TIGHTENING PRESSURE GRADIENT AHEAD OF THE NORTH PACIFIC LOW
MOVING TOWARDS THE AKPEN.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE PRIMARY FOCUS THROUGH WEDNESDAY WILL BE OVER THE SOUTHEAST
BERING AS THE NEXT NORTH PACIFIC LOW APPROACHES THE REGION. AN
ASSOCIATED FRONT WILL ARRIVE ALONG THE AKPEN AND EASTERN ALEUTIANS
ON TUESDAY AFTERNOON ACCOMPANIED BY GALE FORCE WINDS AND A MIX OF
RAIN AND SNOW. STRONG NORTHEAST WINDS AND MIXED PRECIPITATION
WILL PERSIST THROUGH WEDNESDAY AFTERNOON AS THE LOW CENTER MAKES
SLOW NORTHWARD PROGRESS...WITH PRECIPITATION GRADUALLY CHANGING
OVER TO MAINLY RAIN AS WARMER NORTH PACIFIC AIR MOVES INTO THE
REGION. MEANWHILE...BROAD CYCLONIC FLOW WILL KEEP SHOWERY
CONDITIONS OVER THE WESTERN HALF OF THE BERING THROUGH WEDNESDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
ANOTHER DEEP BUT WEAKENING NORTH PACIFIC LOW AND ITS ASSOCIATED
ELONGATED FRONT STRETCHING FROM THE NORTHERN GULF AND INTO THE
EASTERN BERING SEA WILL KEEP PRECIPITATION MAINLY ALONG UPWIND
PORTIONS OF LARGE MOUNTAIN BARRIERS NEAR THE GULF COAST...AND
ACROSS THE BERING SEA AND KODIAK ISLAND. AN ARCTIC HIGH NORTH OF
THE NORTH SLOPE WILL TRY TO KEEP COLDER AIR FILTERING DOWN INTO
INTERIOR LOCATIONS...BUT MOST LOCATIONS AROUND THE SOUTHERN
MAINLAND (ESPECIALLY ALONG THE COAST) WILL EXPERIENCE ENOUGH OF
AN INFLUENCE FROM THE PACIFIC FRONT TO BECOME WARMER THAN
AVERAGE. THEREAFTER...THE SPRAWLING NORTH PACIFIC LOW WILL SLOWLY
WEAKEN AND DRIFT INTO THE EASTERN BERING SEA THROUGH LATE FRIDAY.
THIS WILL BRING SOME SHOWERY ACTIVITY INLAND...BUT KEEP A BULK OF
THE ACTIVITY ACROSS COASTAL LOCATIONS.

BY THE WEEKEND...THE ACTIVE NORTH PACIFIC JET PATTERN WILL SEND
ANOTHER STRONG LOW AND ASSOCIATED WARM FRONT INTO THE GULF OF
ALASKA AND EASTERN BERING...WITH THAT SURGE OF WARMER AIR POSSIBLY
PENETRATING INLAND SOMETIME LATE SUNDAY INTO MONDAY. THIS
POTENTIAL CHINOOK SCENARIO WOULD USHER IN DRASTICALLY WARMER THAN
AVERAGE TEMPERATURES OVER THE SOUTHERN MAINLAND FOR THE EARLY PART
OF NEXT WEEK. HOWEVER...THERE REMAINS SOME UNCERTAINTY IN THIS
SCENARIO WHICH WE WILL CONTINUE TO MONITOR CLOSELY. WE CAN SAY
WITH HIGHER CONFIDENCE THAT A WARMING TREND WILL BE UNDERWAY...
BRINGING WARMER THAN AVERAGE TEMPERATURES ACROSS LARGE PORTIONS OF
SOUTHERN ALASKA. THIS ACTIVE PACIFIC PATTERN WILL CONTINUE INTO
THE MIDDLE OF NEXT WEEK WITH NO RETURN OF WINTER IN SIGHT FOR MOST
OF SOUTHERN ALASKA...AS HIGH LATITUDE BLOCKING OVER THE ARCTIC
CONTINUES TO DOMINATE ALONG WITH THE VERY ACTIVE PACIFIC JET
STREAM.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...RF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...TP