Small Craft Advisory 49, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKST SAT JAN 16 2010

.ANALYSIS AND UPPER LEVELS...
A BROAD LONGWAVE TROUGH REMAINS ENTRENCHED ACROSS MUCH OF MAINLAND
ALASKA...WITH AN UPPER LEVEL RIDGE SITUATED OVER THE ALASKA PANHANDLE
AND BRITISH COLUMBIA. AN ELONGATED ZONAL HIGH PRESSURE RIDGE
STRETCHES ACROSS THE CENTRAL BERING SEA. MEANWHILE...A LARGE UPPER
LEVEL LOW PRESSURE SYSTEM AND SEVERAL ACCOMPANYING SHORTWAVES
CONTINUE THEIR EASTWARD JOURNEY SOUTH OF THE CENTRAL ALEUTIANS.

AT THE SURFACE...A MATURE 960 MB SURFACE LOW IS STACKED UNDER THE
UPPER LEVEL LOW SOUTH OF THE ALEUTIAN ISLANDS. MULTIPLE SURFACE
SHORTWAVES ARE ROTATING AROUND THIS LOW...WITH THE MOST PRONOUNCED
WAVE EXTENDING NORTH AND WEST. WHILE THIS SYSTEM IS NOT BRINGING ANY
SIGNIFICANT WEATHER TO THE ISLAND CHAIN...NORTHERLY FLOW ON THE
BACKSIDE OF THIS SYSTEM SHOULD USHER IN COLDER AIR FROM THE NORTH IN
THE COMING DAYS. FURTHER EAST...A COMPLEX SURFACE LOW PRESSURE SYSTEM
ENVELOPES MUCH OF THE GULF OF ALASKA. A BARBELL LOW IS PRESENT ON
SATELLITE IMAGERY ABOUT 100 MILES SOUTHEAST OF KODIAK ISLAND. THIS
SYSTEM IS BRINGING SHOWERS TO THE GULF COAST AND THE UPSLOPE SIDE OF
THE KENAI PENINSULA. AN ADDITIONAL MESOSCALE CIRCULATION APPEARED
BRIEFLY ON THE MIDDLETON ISLAND RADAR BETWEEN 10 AND 11AM AKST AS IT
PASSED SOUTH OF CORDOVA.

ELSEWHERE ACROSS THE STATE...A HIGH PRESSURE RIDGE IS SLOWLY POKING
ITS WAY INTO THE NORTHWEST CORNER OF THE STATE WHILE A LOW PRESSURE
TROUGH IS SKIRTING THE ARCTIC SEABOARD.

.MODEL DISCUSSION...
IN GENERAL THE MODELS DO A FAIR JOB IN DEPICTING THE CURRENT WEATHER
PATTERNS IN THE SHORT TERM...ESPECIALLY WITH THE ALEUTIAN ISLAND LOW.
HOWEVER...THE GULF LOW IS PROVING TO BE A HEADACHE FOR THE MODELS.
WHILE THE MODELS AGREE THAT THE LOW SHOULD TRACK NORTH TOWARD
THE KENAI PENINSULA...DIFFERENCES EXIST AS TO THE EXACT
STRUCTURE...STRENGTH...AND TIMING OF LOW WHEN IT MOVES ONSHORE. THE
GFS IS THE OUTLIER OF THE GROUP IN FORECASTING HOW THE BARBELL LOW
WILL CONSOLIDATE INTO ONE LOW. IT PREDICTS THAT THE SOUTHERN LOW
WILL DOMINATE RATHER THAN THE NORTHERN LOW...AS THE NAM AND EUROPEAN
DEPICT. AS A RESULT OF THIS DISCREPANCY...THE GFS LAGS 12 HOURS
BEHIND THE OTHER MODELS WITH RESPECT TO THE POSITION OF THE LOW.

TO FURTHER COMPLICATE MATTERS...THE MODELS ALL INITIALIZED THE LOW
TOO FAR TO THE WEST...REDUCING CONFIDENCE IN THE FORECAST TRACK
OF THE LOW. NOT SURPRISINGLY...THE MODELS ARE NOT PICKING UP ON ANY
OF THE SUB SYNOPTIC CIRCULATIONS WRAPPING AROUND THE SYSTEM SUCH AS
THE ONE SEEN ON THE MIDDLETON ISLAND RADAR. THUS CONFIDENCE WITH
REGARDS TO THIS SYSTEM IS LOWER THAN USUAL.

AS THE WEEKEND PROGRESSES...THE MODELS MOVE THE ALEUTIAN LOW SOUTH OF
THE ALASKA PENINSULA. THIS WILL HELP PUSH THE CURRENT GULF LOW
NORTHWARD INTO SOUTH CENTRAL ALASKA...WHERE IT WILL DEGENERATE
INTO AN OPEN WAVE ON MONDAY.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...RAIN AND SNOW MOVED INLAND ACROSS THE KENAI PENINSULA
EARLY THIS AFTERNOON WHILE SHOWERS ARE FILLING IN ON THE BACKSIDE OF
THE OCCLUSION. SNOWFALL TOTALS WILL REMAIN VERY LIGHT WITH THE
EXCEPTION OF THE UPSLOPE MOUNTAINS AND COPPER RIVER BASIN. STEADY
SNOW WILL TAPER OFF TO SHOWERS OVERNIGHT AS THE LOW SLOWLY FILLS
THROUGH THE WEEKEND AND MOVES INLAND. THE CHANCE OF LIGHT SNOW WILL
CONTINUE DUE TO THIS SURFACE FEATURE AS WELL AS THE CYCLONIC
CIRCULATION ALOFT. BROAD SOUTHEASTERLY FLOW WILL PERSIST THROUGH MID
WEEK AS THE UPPER LEVEL TROUGH AXIS SHIFTS TO THE EAST AND SETTLES
NEAR THE ALASKA PENINSULA TUESDAY AND WEDNESDAY.

.SOUTHWEST...ARCTIC AIRMASS WELL ESTABLISHED ACROSS THE NORTHERN AND
SOUTHWESTERN PORTION OF THE STATE TODAY. STRONG NORTHEASTERLY WINDS
CONTINUE AS A REINFORCING SHOT OF COLD AIR SPILLS OUT OF THE YUKON
RIVER VALLEY. THE STRONG WINDS COUPLED WITH THE BELOW AVERAGE
TEMPERATURES IS RESULTING IN ADVISORY LEVEL WIND CHILL ACROSS THE
KUSKOKWIM DELTA. WINDS SHOULD SLOWLY DIMINISH DURING THE NEXT 48
HOURS...BUT UNTIL THEN WIND CHILLS COULD REACH AS LOW AS 50 BELOW
ZERO.

.ALEUTIANS/BERING SEA...THE UPPER LEVEL LOW THAT HAS ANCHORED THE
WEATHER PATTERN FOR THE PAST WEEK WILL BEGIN TO SHIFT TO THE EAST
DURING THE REMAINDER OF THE WEEKEND. THE RESULT WILL BE THE ARCTIC
AIRMASS BEGINNING TO SPREAD SOUTH AND WEST ACROSS THE BERING SEA.
WIDESPREAD SHOWER ACTIVITY WILL ENSUE FROM THE ALASKA PENINSULA TO
THE WESTERN ALEUTIANS AS THE COLD AIR ENCOUNTERS THE RELATIVELY WARM
BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 170 172 175 176 179 180 185
         HEAVY FREEZING SPRAY...160 165 179 185
FIRE WEATHER...NONE

KS AB JAN 10