Small Craft Advisory 143, NWS Fairbanks, AK

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
614 AM AKDT WED OCT 17 2012

.DISCUSSION...
THE LARGE AREA OF LOW PRESSURE ALOFT EXTENDING SOUTHWARD OVER THE
ALASKA MAINLAND FROM THE EASTERN CHUKCHI SEA IS FORECAST TO
CONTINUE SPLITTING INTO A WEAK ARCTIC PORTION AND A MODERATELY
STRONG GULF OF ALASKA PORTION. THE GFS AND NAM COMPUTER WEATHER
FORECAST MODELS PROJECT HIGH PRESSURE ALOFT NOW OVER THE WESTERN
BERING SEA TO BUILD OVER THE CENTRAL AND EASTERN BERING SEA
THURSDAY...AND THEN TO REMAIN OVER THAT AREA THROUGH THE WEEKEND
AND BEYOND. THE GFS MODEL FORECASTS A LARGE AREA OF HIGH PRESSURE
ALOFT TO REMAIN OVER WESTERN ALASKA THROUGH NEXT WEEK. CIRCULATION
ALOFT OVER ALASKA IS FORECAST TO SIGNIFICANTLY WEAKEN.

THE GFS MODEL FORECAST IS NOT CONSISTENT WITH EARLIER RUNS...WHICH
FORECAST THE BERING SEA HIGH PRESSURE SYSTEM TO WEAKEN IN THE
SECOND HALF OF THIS WEEK...AND FOR LOW PRESSURE FROM THE NORTHWEST
PACIFIC TO STRENGTHEN AS IT MOVED NORTHWARD OVER SIBERIA. THE MOST
RECENT NORTH PACIFIC SURFACE ANALYSES SUGGEST THAT THE LATEST GFS
MODEL RUN IS MORE REASONABLE THAN EARLIER RUNS. THIS IS BECAUSE
THE LOW PRESSURE SYSTEM NOW HEADED TOWARD SIBERIA CLEARLY LACKS
THE ENERGY REQUIRED TO BE IN LINE WITH EARLIER MODEL RUNS.

THERE ARE SEVERAL RELEVANT SHORTER TERM WEATHER FEATURES.
FIRST...THE THREE INBOUND SHORT WAVES ALOFT...WHICH WERE MOVING
SLOWLY NORTHWESTWARD OVER THE ALASKA MAINLAND 24 HOURS AGO...ARE
CONTINUING TO DRIFT WESTWARD. THE FIRST IS MUCH WEAKENED...AND NOW
EXTENDS FROM WAINWRIGHT DOWN TO ILIAMNA. THE SECOND EXTENDS FROM
CAPE HALKETT / ON THE NORTHERN ARCTIC COAST / DOWN TO THE WESTERN
ALASKA RANGE. THE THIRD IS NOW OVER THE SOUTHEASTERN INTERIOR.

ALL THREE OF THESE TROUGHS OF LOW PRESSURE ALOFT ARE CAUSING LIGHT
SNOW OVER INTERIOR ALASKA. SO FAR...SNOWFALL OVER THE PAST 2 DAYS
HAS BEEN FROM 1 TO 3 INCHES. ANOTHER SUCH TROUGH ALOFT COULD FORM
IN THE PATHS OF ITS PREDECESSORS LATER TODAY. THIS REMAINS TO
MATERIALIZE...BUT IS A POSSIBILITY.

THE PARENT LOW ALOFT...FROM WHICH THESE TROUGHS ALOFT HAVE
EMERGED...REMAINS JUST SOUTH OF PRINCE WILLIAM SOUND.

THE FLOW OF UNSTABLE ARCTIC AIR FROM THE CHUKCHI SEA SOUTHWARD
OVER ALASKAS CHUKCHI SEA AND WEST COASTS CONTINUES...AS DO THE
SNOW SHOWERS WHICH HAVE ACCOMPANIED IT FOR DAYS.

A SMALL LOW PRESSURE SYSTEM THAT FORMED JUST NORTH OF PRUDHOE BAY
HAS GAINED SOME STRENGTH IN THE PAST 12 HOURS. THERE IS A SMALL
AREA OF STRONG NORTH WINDS ON THE WEST SECTOR OF THIS LOW. BARROW
HAS HAD NORTH WINDS 20 TO 30 MPH WITH BLOWING SNOW SINCE LATE
YESTERDAY EVENING. THIS AREA OF STRONG NORTH WINDS IS LESS THAN
100 MILES WIDE...AND IS EXPECTED TO REMAIN THERE TODAY...AND THEN
TO WEAKEN TONIGHT AS THE LOW PRESSURE CENTER NOW ABOUT 100 MILES
NORTHWEST OF PRUDHOE BAY WEAKENS.

THE SHIFT IN THE WIND FROM NORTHWEST TO NORTH AT BARROW HAS
SIGNIFICANTLY CHANGED NEAR SHORE SEA CONDITIONS. SWELLS INBOUND
FROM THE NORTH ARE REFRACTED AROUND POINT BARROW...AND LOSE
STRENGTH IN THE PROCESS. WHEN THE WIND AND SWELLS WERE COMING IN
FROM THE NORTHWEST YESTERDAY AND THE DAY BEFORE...THE FULL FORCE
OF THE SWELLS WAS DELIVERED TO THE BEACH AT BARROW.

EARLY MORNING POLAR SATELLITE IMAGERY OVER THE MAINLAND OF ALASKA
SHOWS A COMPLEX ARRANGEMENT OF CLOUDS ALIGNED WITH THE TROUGHS
ALOFT. THE ENTIRE INTERIOR AND ARCTIC ARE OVERCAST. SKIES ARE
CLEAR OVER NORTON SOUND AND OFFSHORE KOTZEBUE SOUND...AND THERE
AREA SCATTERED SNOW SHOWERS OUT AT SEA BEYOND THE WESTERN ALASKA
COAST.

COASTAL HAZARD POTENTIAL DAYS 3 AND 4.../FRIDAY AND
SATURDAY/...NONE.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FOR AKZ206-AKZ218.

SMALL CRAFT ADVISORY FOR PKZ200-PKZ215-PKZ230-PKZ235-PKZ240.
&&

TF OCT 12