Small Craft Advisory 11, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKST THU JAN 2 2014

.ANALYSIS AND UPPER LEVELS...
THE REMNANTS OF A VERTICALLY STACKED LOW OVER SOUTHCENTRAL ARE
SLIDING EASTWARD AND ARE NOW BARELY DISCERNABLE ON SATELLITE
IMAGERY...WITH MULTIPLE WEAK SURFACE CIRCULATIONS NOTED OVER THE
NORTHERN GULF AND IN UPPER COOK INLET. RAIN AND SNOW SHOWER ACTIVITY
IS RAPIDLY DIMINISHING ACROSS THE NORTHERN GULF AS A WEAK RIDGE
BUILDS INTO SOUTHWEST AND SOUTHCENTRAL. THIS IS IN ADVANCE OF ANOTHER
VERTICALLY STACKED SYSTEM CURRENTLY OVER THE NORTHERN BERING. AN
ASSOCIATED FRONT HAS MADE LANDFALL OVER THE SOUTHWEST MAINLAND WITH
SNOW...BLOWING SNOW...AND STRONG WINDS ALONG THE COAST CURRENTLY
SPREADING INLAND. THERE IS ANOTHER SYSTEM WELL SOUTH OF THE ALASKA
PENINSULA NEAR 40N THAT HAS FORMED ON THE POLEWARD SIDE OF THE MAIN
JET. THIS SYSTEM IS DRIFTING NORTHWARD. FINALLY...OVER THE WESTERN
ALEUTIANS...A FRONT ASSOCIATED WITH A SYSTEM NEAR THE KAMCHATKA
PENINSULA IS SPREADING WIND AND RAIN SLOWLY EASTWARD ACROSS THE
ALEUTIANS.

.MODEL DISCUSSION...
THE UPPER LEVEL PATTERN IS BEGINNING TO TRANSITION. THE BULK OF THE
JET ENERGY REMAINS WELL SOUTH OF THE STATE...THOUGH A RIDGE OVER
WESTERN NORTH AMERICA IS BEGINNING TO AMPLIFY. THIS IS BEGINNING TO
CAUSE AMPLIFICATION OF THE UPSTREAM PATTERN OVER THE NORTH PACIFIC
AND ALASKA. AS A RESULT...THE CURRENT LOW OVER THE CENTRAL BERING
WILL BE THE LAST IN THE SERIES OF ATMOSPHERIC WAVES THAT TRACK TOWARD
THE MAINLAND. ALL AVAILABLE MODELS ARE PAINTING THE SAME GENERAL
PICTURE...WHICH FEATURES A LONGWAVE TROUGH AMPLIFYING OVER THE BERING
SEA WITH A LARGE AND COMPLEX LOW WITH MULTIPLE CENTERS SETTING UP
SHOP IN THE BASE OF THIS TROUGH. IN THE NEAR TERM...THERE IS GOOD
MODEL AGREEMENT THAT THE SYSTEM CURRENTLY MOVING INTO SOUTHWEST WILL
CLIP THE INTERIOR PORTIONS OF SOUTHCENTRAL WITH A QUICK SHOT OF SNOW
DURING THE DAY TOMORROW. THE HIGHEST RESOLUTION MODELS ARE THE MOST
AGGRESSIVE WITH SNOW AMOUNTS...LIKELY BECAUSE THERE WILL BE AN
UPSLOPE/OROGRAPHIC COMPONENT FROM ANCHORAGE TO THE MAT-SU. AM
INCLINED TO BITE OFF ON SOME OF THIS ENHANCEMENT...BUT NOT ALL THE
WAY GIVEN THAT LOW-LEVEL FLOW SHOULD HAVE A SOUTHERLY COMPONENT THAT
MAY KEEP SURFACE TEMPERATURES ELEVATED AND REDUCE ACCUMULATION. A
COMBINATION OF THE NAM AND GFS IS PREFERRED ACROSS THE EASTERN DOMAIN
FOR THIS REASON. MEANWHILE THE WESTERN DOMAIN FORECAST WILL TAKE
ADVANTAGE OF THE SUPERIOR RUN-TO-RUN CONSISTENCY OF THE
ECMWF...THOUGH NO MODELS WERE COMPLETELY REJECTED TODAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL...CLOUDS AND FOG ARE HAVING A DIFFICULT TIME SCOURING
OUT OF INLAND PORTIONS OF THE AREA AS A FAST-MOVING RIDGE HAS
REINFORCED PERSISTENT LOW-LEVEL TEMPERATURE INVERSIONS ACROSS THE
AREA. WITH WARM ADVECTION ALREADY BEGINNING OVER KODIAK ISLAND AND
LOWER COOK INLET IN ADVANCE OF THE NEXT SYSTEM...THINK CONTINUATION
OF AREAS OF FOG IS LIKELY THROUGH THE OVERNIGHT HOURS. THE
AFOREMENTIONED WEATHER FRONT MOVES THROUGH COOK INLET TOMORROW DURING
THE DAY...WHICH WILL BE A FAIRLY QUICK EVENT IN RELATIVE TERMS BUT
COULD FEATURE SOME IMPRESSIVE SNOWFALL INTENSITIES AS DEEP-LAYER
INSTABILITY IS UNLEASHED WITH AN ADDITIONAL UPSLOPE COMPONENT FROM
ANCHORAGE NORTHWARD. THIS FRONT WILL RAPIDLY WEAKEN AND MOVE TO THE
NORTHEAST EARLY FRIDAY EVENING...AS ANOTHER WEAK RIDGE OF HIGH
PRESSURE MOVES IN FOR THE FRIDAY NIGHT PERIOD. THIS WILL CONTINUE THE
THREAT OF FOG...PRIMARILY FOR PROTECTED INLAND AREAS.

SOUTHWEST MAINLAND...THE LOW CENTER HEADING TOWARD NORTON SOUND WILL
KEEP MUCH OF THE AREA IN SHOWERY PRECIP EVEN AS THE FRONT MOVES OFF
TO THE EAST THIS EVENING. THE THERMAL PROFILE WILL SLOWLY
COOL...ALLOWING MANY LOCATIONS NORTH OF THE PENINSULA THAT MAY HAVE
MIXED WITH RAIN TO CHANGE BACK TO ALL SNOW. ACCUMULATIONS WILL BE ON
THE ORDER OF SEVERAL INCHES ACROSS A FAIRLY WIDESPREAD AREA BEFORE
SNOW TAPERS OFF DURING THE DAY FRIDAY AS THE LOW CONTINUES TO WEAKEN
AND DEPART THE AREA.

BERING SEA AND ALEUTIANS...OVER THE COMING DAYS THE LOW CENTER
CURRENTLY WEST OF THE ALEUTIANS WILL DRIFT EASTWARD AND BECOME
STATIONARY OVER THE WESTERN BERING...WITH NUMEROUS UPPER WAVES AND
SURFACE LOWS PINWHEELING AROUND THROUGH THIS WEEKEND. TEMPERATURES
WILL REMAIN NEAR OR ABOVE FREEZING FOR MOST OF THE AREA...MEANING
THAT PERIODS OF RAIN OR A RAIN/SNOW MIX WILL ACCOMPANY GUSTY (THOUGH
SHORT-LIVED) WIND EVENTS.

.LONG TERM FORECAST FROM PREVIOUS DISCUSSION...

DEEP SOUTHERLY FLOW WILL HELP PUSH A STRONG CYCLONE AND WARM FRONT
NORTH INTO SOUTHERN ALASKA SUNDAY. WHILE PRECIPITATION IS LIKELY TO
BEGIN AS SNOW...WARM TEMPERATURES WILL PUSH INLAND BRINGING
PRECIPITATION-TYPE CONCERNS TO MANY AREAS...EVEN AS FAR NORTH AS
BETHEL AND POSSIBLY ANCHORAGE. THE REST OF THE EARLY TO MID WEEK
PERIOD NEXT WEEK WILL REMAIN STORMY WITH WARMER THAN NORMAL
TEMPERATURES ACROSS THE MAINLAND AND BERING AS WARM PACIFIC AIR
MASSES CONTINUE TO PUSH NORTH INTO THE STATE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 132 138 150 155 160 165 173 174 175 176 177 178 180 185
FIRE WEATHER...NONE

AMD JAN 14