Gale Warning 870, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
426 PM AKST MON DEC 29 2014

.ANALYSIS AND UPPER LEVELS...
A FIREHOSE OF SORTS IS BRINGING PLENTIFUL MOISTURE NORTHWARD INTO
ALASKA FROM ABOUT 20N...JUST AHEAD OF A BROAD TROUGH OVER THE
BERING SEA. PRECIPITATION...MAINLY IN THE FORM OF RAIN...CONTINUES
TO FALL OVER THE WESTERN MAINLAND AND KODIAK ISLAND. THE MOISTURE
IS GRADUALLY MOVING EASTWARD...AS A LOW MOVES NORTHWARD OVER THE
EASTERN BERING SEA THROUGH TUESDAY AFTERNOON. THIS AFTERNOON
THOUGH...THE PRECIPITATION IS FOCUSED OVER THE SOUTHERN KENAI
PENINSULA...THROUGH THE SOUTHERN SUSITNA VALLEY...AND THROUGH THE
SOUTHWESTERN MAINLAND. WINDS HAVE BEEN GUSTY THROUGH THE CHANNELED
TERRAIN OF THE ALEUTIAN RANGE...AND ARE IN LINE WITH THE EXPECTED
INCREASE IN STRENGTH THIS AFTERNOON AND TONIGHT AS THE LOW
APPROACHES AND TIGHTENS THE GRADIENT. WINDS WILL ALSO INCREASE
THROUGH TURNAGAIN ARM TONIGHT. A HIGH WIND WARNING REMAINS IN
EFFECT FOR BOTH LOCATIONS.

&&

.MODEL DISCUSSION...
MODELS ARE IN VERY GOOD AGREEMENT THROUGH THE SHORT TERM. THE GFS
IS A BIT OF AN OUTLIER AT 60 HOURS...WITH A MUCH BROADER/WEAKER
LOW OVER THE GULF. THE OTHER OPERATIONAL MODELS SHOW SOME VERY
MINOR DIFFERENCES...BUT THEY HAVE LESSENED EVEN SINCE THE PREVIOUS
MODEL RUNS. OVERALL WE WILL BE FOCUSING ON THE NAM AND GEM-
REGIONAL FOR UPDATES TO THE GRIDS TODAY.

&&

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

THE FRONT MOVING INTO THE NORTHERN GULF COAST WILL BRING
SIGNIFICANT WIND TO MUCH OF SOUTH CENTRAL THROUGH TUE
MORNING...REACHING WARNING LEVELS ALONG WESTERN TURNAGAIN ARM AND
THE HIGHER ELEVATIONS NEAR ANCHORAGE. THIS FRONT WILL ALSO BRING
OVERNIGHT WARMING TO THE REGION TONIGHT...WITH WARMER
TEMPERATURES PERSISTING INTO TUE NIGHT BEFORE COLDER AIR RETURNS.
PRECIPITATION WITH THE FRONT WILL BE RAIN AT SEA LEVEL ALONG THE
COAST WITH SNOW AT HIGHER ELEVATIONS OF THE KENAI PENINSULA AND
ABOVE VALDEZ...BUT CROSS BARRIER FLOW SHOULD KEEP ANCHORAGE FAIRLY
DRY UNTIL LATER ON TUE. ON TUE AND TUE NIGHT SNOW WILL DIMINISH
OVER HIGHER ELEVATIONS AND MIX OR CHANGE OVER TO RAIN AT LOWER
LEVELS. OVER THE INTERIOR ZONES SNOW WILL TAPER OFF TO SHOWERS
OVER THE COPPER RIVER BASIN ON TUE...BUT WILL CONTINUE OVER THE
NORTHERN SUSITNA VALLEY WITH SUSTAINED UPSLOPE FLOW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...TUESDAY AND
WEDNESDAY)...WE ARE IN THE HEART OF THE STRONGEST WINDS THIS
EVENING. AFTER TONIGHT WE SHOULD GRADUALLY SEE AN IMPROVEMENT IN
CONDITIONS...BOTH CALMER WINDS AND LESS INTENSE PRECIPITATION.
WATER VAPOR IMAGERY AND MODELS ARE STILL ON TRACK IN DEVELOPING A
CLOSED LOW JUST WEST OF BRISTOL BAY LATER THIS EVENING AND THEN
MOVING IT QUICKLY NORTH TUESDAY. THIS SHOULD BRING JUST ENOUGH
INSTABILITY TO MIX DOWN SOME OF THE WINDS THAT REMAIN ELEVATED
THIS AFTERNOON. BY TUESDAY MORNING WINDS WILL GRADUALLY BEGIN TO
DIMINISH AND BEGIN TO TURN MORE SOUTHWESTERLY THROUGH THE DAY.

PRECIPITATION INTENSITY WILL ALSO START TO COME DOWN DURING THE
DAY TUESDAY. HOWEVER...THERE WILL STILL BE PLENTY OF SHOWERS
AROUND WITH A VERY MOIST AIRMASS IN PLACE AND SHORTWAVES
REMAINING THROUGHOUT THE BASE OF THE LONGWAVE TROUGH. WE WILL SEE
A SLOW TRANSITION FROM RAIN BACK TO SNOW LATE TUESDAY INTO
WEDNESDAY AS THE SOUTHWESTERLY FLOW STARTS TO USHER IN SOME COOLER
AIR. THE GOOD NEWS IS THAT THE FIREHOSE OF AN UPPER LEVEL JET
STARTS TO SLIDE OFF TO THE EAST WEDNESDAY. ONE LAST SHORTWAVE
MOVES FROM WEST TO EAST INLAND FROM THE BERING LATE WEDNESDAY...SO
WE WILL KEEP SOME RAIN AND SNOW SHOWERS IN THE FORECAST FOR NOW.
A SHORTWAVE RIDGE FOLLOWS CLOSELY ON ITS HEALS FOR THURSDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...THINGS
REMAIN VERY ACTIVE ACROSS THE EASTERN QUADRANT OF THE BERING...BUT
RELATIVELY QUIET ELSEWHERE. A SHORTWAVE RIDGE WILL MOVE INTO THE
CENTRAL BERING TUE INTO WED BRINGING ONLY A CHANCE FOR RAIN AND
SNOW SHOWERS AND SOME PATCHY FOG. THEN THE FOCUS SHIFTS TO A
DEVELOPING LOW APPROACHING THE WESTERN ALEUTIANS BY TUE. MODELS
TAKE THE CENTRAL PRESSURE OF THIS STORM DOWN TO RIGHT AROUND 950
MB...WHICH IS VERY SEASONABLE FOR LATE DECEMBER. THIS LOOKS TO BE
A FAIRLY CLASSIC SET-UP WITH A WARM FRONT/OCCLUSION BRINGING A
QUICK SHOT OF STORM FORCE WINDS TUE EVENING INTO WED MORNING FOR
SHEMYA AND ATKA AND ADAK. ALL MODELS AGREE THAT COLD AIR WILL
SPILL IN BEHIND THIS LOW. BUT NOW THE CANADIAN MODEL IS HINTING AT
THIS COLD AIR LEADING TO A SMALL BUT STRONG LOW DEVELOPING WITHIN
THIS COLD AIR. WE WILL MONITOR THE OTHER MODELS TO SEE IF
CONSENSUS MOVES IN THAT DIRECTION ENOUGH TO ADD IT TO THE
FORECAST.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A LONGWAVE TROUGH OVER THE EASTERN BERING WILL PUSH INTO THE GULF
THURSDAY...THEN TRACK OVER THE NORTHERN GULF COAST AS A CLOSED
UPPER LOW BY THURSDAY NIGHT. THE FLOW PATTERN WILL STEADILY
CHANGE FROM ONSHORE TO OFFSHORE FLOW AS THE ACCOMPANYING SURFACE
LOW TRACKS CLOSER TO THE NORTHERN GULF COAST BY THURSDAY. THE
OFFSHORE PRESSURE GRADIENT WILL REMAIN MODERATELY STRONG THROUGH
SATURDAY...AS THE LOW TRACKS BACK WESTWARD INTO THE NORTHERN GULF
WHILE WEAKENING AND EVENTUALLY BEING OVERTAKEN BY A PACIFIC LOW
TRACKING INTO SOUTHEASTERN ALASKA SUNDAY AFTERNOON. THERE IS ALSO
GOOD MODEL AGREEMENT ON THE DEVELOPMENT OF A BLOCKING HIGH OVER
THE BEAUFORT SEA THURSDAY...WHICH WILL AIDE IN FILTERING IN
COLDER AND DRIER AIR FROM NORTHWEST CANADA ACROSS THE SOUTHERN
MAINLAND. COLDER AND DRIER CONDITIONS ARE EXPECTED TO SET UP OVER
THE AREA THURSDAY AFTERNOON AS THIS PATTERN TAKES SHAPE...WITH THE
POTENTIAL FOR SNOW AND SNOW SHOWERS TO LINGER ACROSS SOUTHCENTRAL
THROUGH SUNDAY. HOWEVER...THE POTENTIAL FOR SNOW AND SNOW SHOWERS
OVER SOUTHCENTRAL REMAINS HIGHLY DEPENDENT ON WHICH SOLUTION OF
THE LOW TRACK VERIFIES. CURRENTLY THERE REMAINS LOW CONFIDENCE IN
THE FORECAST WITH THE MODELS NOT YET HAVING A GOOD HANDLE ON THE
LOW TRACKING THROUGH THE GULF THURSDAY. THE MOST RECENT RUN OF THE
GFS BROUGHT THE LOW FURTHER EAST OVER SOUTHEASTERN ALASKA BY
THURSDAY NIGHT...WHERE THE ECMWF KEEPS THE LOW FURTHER WEST AND
OVER THE NORTHERN GULF. THE CURRENT ECMWF SOLUTION WOULD BE THE
ONE THAT KEEPS SNOW AND SNOW SHOWERS LINGERING OVER PARTS OF
SOUTHCENTRAL THROUGH MUCH OF THE WEEKEND.

FURTHER WEST...A SERIES OF NORTH PACIFIC LOWS WILL DEEPEN WHILE
TRACKING JUST WEST OF THE WESTERN ALEUTIANS...OCCLUDING AS THEY
TRACK TOWARD/OVER THE KAMCHATKA PENINSULA BEFORE DISSIPATING. THE
ASSOCIATED FRONTS WILL CONTINUE TO RESUPPLY THE WESTERN AND
CENTRAL ALEUTIANS/BERING WITH PRECIPITATION AND GUSTY WINDS
THROUGH MUCH OF THE LONG TERM FORECAST...WITH SMALL BREAKS FROM
THE PRECIPITATION AND WINDS BETWEEN EACH SYSTEM. FORECAST
CONFIDENCE REMAINS ABOUT AVERAGE OUT WEST...AS THERE ARE STILL
SOME STRENGTH AND TIMING DIFFERENCES WITH EACH FRONTAL PASSAGE
THROUGH THE WESTERN AND CENTRAL ALEUTIANS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 101 161
MARINE...STORM 119 120 130 131 177 178
         GALE 125 129 132 138 139 175 180
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MBS
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
LONG TERM...TP