Small Craft Advisory 105, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
428 PM AKST MON FEB 2 2015

.ANALYSIS AND UPPER LEVELS...
A LARGE UPPER LEVEL RIDGE IS CENTERED OVER THE BERING SEA WHICH
ALSO EXTENDS ACROSS THE ALASKA PENINSULA AND INTO SOUTHCENTRAL
ALASKA AS WELL. THERE IS AN UPPER LEVEL LOW SOUTH OF THE ALASKA
PENINSULA. ACROSS THE INTERIOR AND SOUTHWEST MAINLAND PORTION OF
THE STATE THERE IS AN UPPER LEVEL TROUGH THAT EXTENDS OUT OF A
LOW IN THE ARCTIC WHICH IS WEAKENING AS IT HEADS TO THE
SOUTHEAST. THE SURFACE FEATURES ARE LARGELY UNCHANGED FROM
YESTERDAY WITH HIGH PRESSURE OVER THE CENTRAL BERING SEA EASTWARD
THROUGH THE YUKON. THE ONLY SURFACE LOW IMPACTING THE REGION IS
WELL SOUTH OF KODIAK ISLAND AND BRINGING IN A NORTH TO NORTHEAST
FLOW OVER SOUTHWEST AND SOUTHCENTRAL ALASKA.

&&

.MODEL DISCUSSION...
MODELS ARE IN EXCELLENT AGREEMENT WITH ONE ANOTHER AND ARE ALL
HANDLING THIS STABLE SITUATION VERY WELL THE NEXT FEW DAYS. THERE
ARE SOME MODEL DIFFERENCES IN THE UPPER LEVELS THAT WILL HAVE SOME
IMPACT ON THE WINDS IN SOUTHCENTRAL AND SOUTHWEST MAINLAND ALASKA
IN THE THURSDAY THROUGH SATURDAY TIME PERIOD. THE ECMWF IS MORE
AGGRESSIVE IN BRINGING IN AN UPPER LEVEL TROUGH FROM THE YUKON
INTO THE GULF OF ALASKA THURSDAY NIGHT WHICH CUTS OFF INTO AN
UPPER LEVEL LOW ON FRIDAY. THE GFS JUST HAS A TROUGH OVER THE
EASTERN INTERIOR THROUGH YUKON WITHOUT A STRONG SOUTHERLY PUSH
UNTIL SATURDAY. BY SATURDAY AFTERNOON THE TWO MODELS ARE ACTUALLY
VERY SIMILAR AGAIN IN THEIR PLACEMENT OF THE UPPER LEVEL LOWS AND
HIGHS BUT THE TIMING AND LOCATION THAT THE TROUGH DIGS INTO THE
AREA WILL HAVE A LARGE IMPACT ON THE THE WINDS AND TEMPERATURES
OVER THE REGION.

&&

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

SOUTHCENTRAL WILL BE CLEAR..COLD...AND DRY THROUGH WED...EXCEPT
FOR A WEAK DISTURBANCE BRINGING A CHANCE OF SNOW AND RAIN TO
KODIAK ISLAND ON TUE. HIGH PRESSURE BUILDING INTO INTERIOR AK WILL
BRING INCREASING WINDS TO CHANNELED TERRAIN OF SOUTH CENTRAL
THROUGH WED. THIS WILL BE SEEN WITH WINDS OF 20 TO AS MUCH AS 40
MPH OFF THE GLACIER IN WHITTIER...THROUGH THOMPSON PASS...AND
THROUGH THE COPPER RIVER DELTA. OTHERWISE SOME AREAS OF OVERNIGHT
FOG WILL REDEVELOP NEAR COOK INLET AS WELL AS KNIK AND TURNAGAIN
ARMS. LOW CLOUDS AND FOG WILL ALSO REDEVELOP ALONG THE COPPER
RIVER.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH WED)...

MODELS HAVE SHOWN A BIT OF A CHANGE OVER THE PAST 24 HOURS IN
REGARDS TO HOW MUCH COLD AIR FILTERS IN BEHIND THE ARCTIC TROUGH
ALREADY PUSHING THROUGH THE NORTHERN HALF OF ALASKA. THE BIGGEST
CHANGE IS THAT THE COLDEST 850 MB AND 500 MB TEMPERATURES HAVE
NOW BEEN SHUNTED OVER THE INTERIOR AND INTO THE YUKON (WITH SOME
OF THE COLDER AIR RETROGRADING AROUND THE HIGH IN THE BERING SEA).
WITH THE MAJORITY OF THE COLDER AIR NO LONGER EXPECTED TO MOVE IN
LATE TONIGHT INTO TOMORROW...A WEAK AND GRADUAL WARMING TREND IS
EXPECTED BEFORE ANOTHER ARCTIC TROUGH BEGINS TO DIVE SOUTH LATE
WEDNESDAY NIGHT.

IN THE MEAN TIME...THE FIRST ARCTIC TROUGH IS DIVING SOUTH AND IS
WELL DEPICTED ON WATER VAPOR IMAGERY THIS AFTERNOON. A POTENT
AREA OF UPWARD OMEGA IS LOCATED ALONG THE FORWARD FLANK OF THE
TROUGH AND HAS SPARKED AREAS OF LIGHT SNOW ACROSS THE KUSKOKWIM
DELTA AND THE WESTERN CAPES OF THE BRISTOL BAY AREA. THIS POCKET
OF LIGHT SNOW IS EXPECTED TO PUSH SOUTH OF THE KUSKOKWIM DELTA AND
BRING NUMEROUS RAIN AND SNOW SHOWERS TO THE ALASKA PENINSULA THIS
EVENING AND CONTINUE TO SLIDE TO THE SOUTH AND WEST THROUGH TUESDAY
AFTERNOON. SKIES OVER THE KUSKOKWIM DELTA WILL BEGIN TO CLEAR THIS
EVENING AND ALL OF SOUTHWEST ALASKA WILL REMAIN CLEAR THROUGH AT
LEAST WEDNESDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH WED)...

WITH A SMALL PIECE OF THE COLDER AIR ASSOCIATED WITH THE ARCTIC
TROUGH RETROGRADING AROUND THE HIGH IN THE BERING...A BRIEF PERIOD
OF LIGHT SNOW AND/OR RAIN SHOWERS WILL BE OBSERVED TONIGHT OVER
THE ALASKA PENINSULA AND SPREAD TO THE EASTERN ALEUTAINS BY
TOMORROW. LITTLE TO NO SNOW ACCUMULATION IS EXPECTED AS MOST
AREAS WILL REMAIN AT OR ABOVE FREEZING DURING THE OVERNIGHT HOURS.
RAIN AND SNOW CHANCES WILL REMAIN ACROSS THE ALEUTIAN ISLANDS
THROUGH WEDNESDAY AS A WEAKENING AREA OF LOW PRESSURE OVER THE
NORTH PACIFIC (AND ASSOCIATED DECAYING STATIONARY FRONT) RETROGRADES
AND INTERACTS WITH THE HIGH OVER THE BERING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...THU THROUGH MON)...SOME
SUBTLE YET SIGNIFICANT CHANGES WILL TAKE SHAPE IN THIS TIME
PERIOD. OVERALL THE PATTERN WILL STILL BE DOMINATED BY A REX-BLOCK
"ESQUE" PATTERN. THE DIFFERENCE WILL BE THAT RATHER THAN THE HIGH
CENTER BEING OVER THE MAINLAND WITH A LOW PRESSURE CENTER IN THE
GULF OF ALASKA...THE PATTERN IS GOING TO SHIFT SEVERAL HUNDRED
MILES TO THE WEST. THIS WILL PUT THE HIGH OVER THE BERING WITH THE
LOW SOUTH OF THE CENTRAL ALEUTIANS. WHAT THIS COULD SPELL FOR MUCH
OF THE MAINLAND IS PIECES OF ENERGY BREAKING OFF IN THE ARCTIC AND
DESCENDING QUICKLY AROUND THE EASTERN PERIPHERY OF THE RIDGE AXIS.
WITH COLD AIR FIRMLY ENTRENCHED OVER MUCH OF THE MAINLAND AND
STILL PLENTY OF WARM OPEN WATER OVER THE GULF FROM OUR ABOVE-
NORMAL TEMPERATURES FROM MUCH OF THE WINTER...A INHERENTLY TIGHT
THERMAL GRADIENT IS ALREADY IN PLACE. THESE PIECES OF ENERGY
DIVING FROM NORTH TO SOUTH COULD BE JUST WHAT THE PATTERN NEEDS TO
HELP STRENGTHEN THE GRADIENT JUST A BIT MORE AND MIX SOME OF THE
STRONGER WINDS ALOFT DOWN TOWARDS THE SURFACE. THE UPPER LEVEL
SUPPORT COULD ALSO SERVE TO ALIGN THINGS VERY NICELY FOR OUR
TYPICAL GAP WINDS TO REALLY TAKE OFF.

AS MENTIONED ABOVE IN THE MODEL DISCUSSION...THERE ARE SOME
CRITICAL DIFFERENCES THAT STILL NEED TO BE IRONED OUT TO INCREASE
CONFIDENCE IN THE TIMING AND STRENGTH OF ANY WIND EVENTS. RIGHT
NOW THE FIRST WAVE LOOKS TO MOVE THROUGH SOUTH CENTRAL THU
EVENING. THIS ONE DOES DOES NOT LOOK TOO STRONG...BUT WILL OPEN
THE GATES SO TO SPEAK FOR SUCCESSIVE WAVES. THE
NEXT...SIGNIFICANTLY MORE ROBUST WAVE PUSHES THROUGH MUCH OF SOUTH
CENTRAL EARLY SATURDAY. THIS ONE HAS MUCH BETTER UPPER LEVEL
SUPPORT AND ALSO BRINGS 850MB TEMPERATURES FALLING FROM -8C TO AS
LOW AS -20C BY EARLY SUNDAY. WITH THIS IN MIND...WE HAVE STARTED
TO INCREASE WINDS THROUGH MANY OF THE TYPICAL OUTFLOW AREAS. WITH
COLDER AIR AND GUSTY WINDS...WIND CHILLS COULD BECOME AN ISSUE
THIS WEEKEND FOR MANY POPULATION CENTERS FROM THE KENAI PENINSULA
TO ANCHORAGE TO THOMPSON PASS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 155 172 173 179 413. HEAVY FREEZNIG SPRAY 127 139
160 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...MO