Heavy Freezing Spray Warning 9, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
455 PM AKST THU DEC 31 2015

.ANALYSIS AND UPPER LEVELS...

AN ACTIVE WEATHER PATTERN CONTINUES TO DOMINATE THE SOUTHWEST
MAINLAND AND SOUTHCENTRAL ALASKA. AT THE UPPER LEVELS...A JET
CONTINUES TO STRETCH FROM THE NORTH PACIFIC TOWARDS THE EAST GULF
OF ALASKA COAST AND HAS BEEN SENDING COPIOUS MOISTURE NORTHWARD.
SNOWFALL HAS BEEN PARTICULARLY HEAVY ACROSS PRINCE WILLIAM SOUND
WHERE A FEW FEET OF SNOW HAVE FALLEN TODAY IN THOMPSON PASS. TO
THE WEST...A BROAD LOW PRESSURE SYSTEM DOMINATES THE BERING
SEA...WITH SEVERAL EMBEDDED SHORTWAVES. ONE SUCH WAVE HAS BEEN
BRINGING LIGHT SNOW TO THE SOUTHWEST MAINLAND THIS MORNING.
HOWEVER...AS IT IS NOT TAPPING INTO THE RICH MOISTURE SUPPLY FROM
THE JET...SNOWFALL HAS BEEN LIGHT.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GENERALLY GOOD AGREEMENT IN TERMS OF SYNOPTIC
FEATURES...AS A LOW PRESSURE SYSTEM IN THE NORTH PACIFIC
STRENGTHENS AND MOVES ACROSS THE ALASKA PENINSULA...AND TOWARDS
THE KUSKOKWIM DELTA THE NEXT SEVERAL DAYS. HOWEVER...MODELS ARE IN
MORE DISAGREEMENT ON THE PROGRESSION OF AN ASSOCIATED FRONT ALONG
THE GULF COAST. IN ADDITION...MODELS DISAGREE ON THE TOTAL AMOUNT
OF PRECIPITATION FOR PRINCE WILLIAM SOUND AS CONDITIONS ARE
FAVORABLE FOR ANOTHER INTENSE PRECIPITATION EVENT. CURRENTLY A
BLEND OF GFS AND NAM WERE FAVORED FOR THE FORECAST.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (FRIDAY AND SATURDAY)...

GENERALLY SPEAKING THE REGION WILL BE CATCHING ITS COLLECTIVE
BREATH TONIGHT BETWEEN STORM SYSTEMS. GUSTY SOUTHERLY WINDS ACROSS
THE AREA WILL REVERSE AND BECOME MORE NORTHERLY TONIGHT IN ADVANCE
OF THE NEXT STORM SYSTEM THAT WILL BE MOVING INTO KODIAK ISLAND
AFTER MIDNIGHT. THIS NEXT STORM LOOKS GENERALLY SIMILAR TO THE
PREVIOUS FEW...WITH A FEW KEY DIFFERENCES. THE LOW CENTER WILL BE
A BIT FURTHER WEST AND WILL ALSO HAVE REACHED MAXIMUM INTENSITY
BEFORE THE FRONT COMES THROUGH SOUTHCENTRAL ALASKA.
ADDITIONALLY...THE FORWARD SPEED OF THE NEXT STORM WILL NOT BE AS
FAST AS THE PREVIOUS FEW. ALL THIS ADDS UP TO ANOTHER ROUND OF
WIND ACROSS MOST OF THE AREA...THOUGH LOWER WIND SPEEDS AND
SIGNIFICANTLY LESS IMPACTS EXPECTED AS A WHOLE. HEAVY
PRECIPITATION WILL AGAIN FALL ALONG THE GULF COASTLINES FRIDAY
AFTERNOON THROUGH FRIDAY NIGHT. WITH FREEZING LEVELS ALSO SIMILAR
TO PREVIOUS STORMS...THOMPSON PASS IS THE MOST LIKELY TO STAY
ALL-SNOW...AND WITH STRONG WINDS AGAIN EXPECTED BLOWING SNOW IS
LIKELY TO BE AN ISSUE. A BLIZZARD WATCH IS NOW IN EFFECT FOR
THOMPSON PASS. WITH A FAIRLY IMPRESSIVE SUBTROPICAL "TAP" OF
MOISTURE AGAIN...MORE PRECIPITATION THAN NORMAL IS AGAIN EXPECTED
TO MAKE IT OVER THE CHUGACH MOUNTAINS AND INTO THE COPPER RIVER
BASIN. THIS AREA WILL NEED TO BE MONITORED FOR POTENTIAL FOR HEAVY
SNOW OR MIXED PRECIPITATION EARLY IN THE DAY ON SATURDAY. STAY
TUNED TO SUBSEQUENT FORECAST UPDATES FOR THE LATEST EXPECTED
IMPACTS.

THE WESTERN KENAI UP THROUGH ANCHORAGE AND THE MATANUSKA VALLEY
SHOULD STAY MOST DOWNSLOPED AND DRY AGAIN...WITH ONLY A BRIEF
PERIOD OF RAIN OR A RAIN/SNOW MIX AS THE FRONT PASSES THROUGH LATE
FRIDAY EVENING. ONCE THE STORM MOVES OFF INTO THE NORTHERN BERING
SEA ON SATURDAY...ANOTHER ROUND OF SOUTHERLY WINDS WILL MOVE UP
COOK INLET AND AGAIN BRING GUSTY CONDITIONS TO THE COOK INLET
POPULATION CENTERS.

&&

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

A SLOW MOVING NORTH PACIFIC LOW WILL BE THE MAIN STORY THE NEXT
TWO DAYS AS IT MOVES TOWARD THE ALASKA PENINSULA TONIGHT. THIS
WILL TIGHTEN THE PRESSURE GRADIENT AND INCREASE NORTHEAST OFFSHORE
FLOW...WITH EASTERLY WINDS CLOSER TO THE ALASKA AND ALEUTIAN
RANGES. THIS GENERAL PATTERN IS NOT OVERLY CONDUCIVE TO HEAVY
PRECIPITATION AS LONG AS THE LOW REMAINS TO THE SOUTH OF THE
ALASKA PENINSULA. RAIN AND SNOW WILL BE MORE WIDESPREAD AS THE LOW
LIFTS NORTH AND THE FLOW BECOMES MORE ONSHORE.

&&

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

A BROAD LOW OVER THE CENTRAL BERING WILL REMAIN...KEEPING THE
COLDEST AIR OVER THE WESTERN BERING SEA AND ALEUTIANS. SMALLER
LOWS ROTATING AROUND THIS WILL ENHANCE NORTHWEST WINDS AND SNOW
SHOWERS OVER THE WESTERN AND CENTRAL ALEUTIANS AND WILL PERSIST
THROUGH SATURDAY. A NORTH PACIFIC LOW WILL LIFT A MAX GALE FORCE
TO LOW END STORM FORCE FRONT INTO THE EASTERN BERING AND
ALEUTIANS...SPREADING RAIN AND SNOW THROUGH FRIDAY...THEN BACK END
SNOW SHOWERS AS THE LOW LIFTS NORTH ON SATURDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE DOMINATE FEATURES AT THE START OF THE MID TERM WILL BE THE
LOW ABOUT 700 NM SOUTH OF COLD BAY SATURDAY EVENING AND A RIDGE
LYING ALONG THE ALASKAN INTERIOR AND RUNNING SOUTHEASTWARD ALONG
THE WESTERN NORTH AMERICAN COAST. MODELS ARE IN REASONABLE
AGREEMENT WITH THE LOW ON SATURDAY EVENING WITH A PRESSURE IN THE
960-965MB RANGE. THIS LOW WILL SLOWLY MOVE TO THE NORTHEAST
THROUGH THE DAY AND INTO THE DAY 4 TIME FRAME BEFORE BEGINNING TO
WEAKEN AND ELONGATE ALONG BRISTOL BAY TO THE SOUTH CENTRAL GULF AS
RIDGE THE SHIFTS ONLY SLIGHTLY EASTWARD. WITH THIS SETUP...EXPECT
CONTINUED SOUTHERLY FLOW ALOFT OVER MOST OF THE SOUTHERN ALASKAN
MAINLAND WITH PRECIPITATION LIKELY ALONG THE GULF COAST AND THE
ALASKA RANGE EAST OF THE PARKS HIGHWAY.

FROM DAY 4 ONWARD...MODEL AGREEMENT ALOFT IS IN GROSS AGREEMENT
WITH A BROAD ELONGATED TROUGH OVER THE BERING SEA AND THE LARGE
RIDGE FROM BRITISH COLUMBIA TO THE BEAUFORT SEA REMAINING IN
PLACE. THE POLAR JET DURING THIS TIME WILL REMAIN WELL SOUTH OF
ALASKA AT AROUND 40N. WITHIN THE BROAD TROUGH...MODELS ARE
INDICATING MULTIPLE WEAKER SYSTEMS ROTATING AROUND A BROAD CLOSED
LOW ANCHORED OVER THE SEA OF OHKOSK. HOWEVER AS IS USUALLY THE
CASE IN THIS PATTERN...MODEL AGREEMENT ON THE CHARACTER AND
LOCATION OF THESE SYSTEMS IS POOR. TOWARDS DAY 6 AND 7 /WEDNESDAY
INTO THURSDAY/...BOTH THE GFS AND THE ECMWF ARE BRINGING AN MORE
CONSOLIDATED STACKED LOW IN THE 960-965 MB RANGE SOUTH OF THE
ALEUTIAN CHAIN THAT WILL MOVE EASTWARD WITH THE JET ALONG 45N.

ON DAY 3...THE NAM AND EC SOLUTIONS WERE USED TO CAPTURE HIGH
RESOLUTION FEATURES AND BEGIN A TREND TO THE DAY 4-7 FORECAST.
WITH THE LOW CONFIDENCE IN THE MODEL SOLUTIONS IN THE EXTENDED...
DAYS 4 THROUGH 7 LEANED HEAVY TO WPC WITH A BLEND OF THE EC EARLY
ON DAY 4.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WATCH THOMPSON PASS. FLOOD ADVISORY ANCHOR
POINT.
MARINE...STORM 130 131 150 352. GALES 119 120 125 132 139 155 160
165 170 172 178 180 181 185 351. .

&&

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