Small Craft Advisory 159, NWS Fairbanks, AK

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
434 PM AKDT MON OCT 31 2011

.SYNOPSIS...
ALOFT....
A VERY DEEP 578 DM 500 MB LOW NEAR 80N/150W WILL WEAKEN SLOWLY
THROUGH THE WEEKEND. A LONG WAVE TROUGH EXTENDING SOUTH FROM THIS
LOW OVER MAINLAND ALASKA WILL PROGRESS EAST TO NW CANADA BY WED.
A VERY COLD AIR MASS HAS NOW MOVED OVER THE STATE UNDER THIS LONG
WAVE TROUGH WITH THE BELOW SURFACE TEMPERATURES IN THE CLEAR
AREAS. TEMPERATURES WILL CONTINUE TO FALL UNDER THROUGH MID-WEEK
AS A LONG WAVE RIDGE BUILDS OVER MAINLAND ALASKA AND SKIES BECOME
MORE CLEAR.

SEVERAL STRONG SHORT WAVES ARE ROTATING E ACROSS THE ARCTIC SLOPE
OF ALASKA NOW THROUGH TUE AS THEY PASS THROUGH THIS DEEP TROUGH.

SURFACE...
A 985 MB LOW 600 NM NORTH OF PRUDHOE BAY WILL WEAKEN THROUGH
WEDNESDAY. A COLD FRONT FROM THIS LOW TO DEMARCATION POINT TO THE
BERING STRAIT WILL DISSIPATE TONIGHT. THIS IS NOW CAUSING LIGHT
SNOW BLOWING SNOW AND NORTH-WEST WINDS 25 MPH ALONG THE FRONT.

DEEP NORTHWEST FLOW ALOFT PARALLEL TO THE ICE EDGE COMBINED WITH
A MAINLY OPEN WATER OVER THE CHUKCHI SEA, A VERY COLD AIR MASS WITH
850 MB TEMPERATURES OF -20C, AND A STRONG SHORT WAVE ARE EXPECTED
TO CAUSE A POLAR LOW TO DEVELOP IN THE NORTHERN CHUKCHI SEA
TONIGHT WHICH WILL MOVE TO 100 NM NORTHWEST OF BARROW AS A 990 MB
LOW BY 4AM TUE AND TO 150 NM NORTHEAST OF BARTER ISLAND AS A 999
MB LOW BY 4PM TUE...THEN CONTINUE NORTHEAST. THIS IS AT LEAST 10
MB DEEPER THAN MODELS INDICATE, BUT MODELS DO VERY POORLY WITH
POLAR LOWS. PREVIOUS EXPERIENCE WITH THESE TYPE OF SYSTEMS LEADS
US TO EXPECT POLAR LOW DEVELOPMENT WITH A VERY TIGHT GRADIENT
CLOSE IN TO THE LOW CENTER. FOR THIS REASON WE ARE FORECASTING
WINDS 10KT STRONGER THAN ANY OF THE MODELS BUT HAVE GONE ALONG
WITH THE GFS STORM TRACK DUE TO THE FAST NW FLOW ALOFT. THIS IS
EXPECTED TO BRING NW WINDS 35-45KT TO THE WESTERN ARCTIC COAST BY
EARLY TUE AND W WINDS 40-50KT TO THE EASTERN ARCTIC COAST TUE PM.

DUE TO THE STRONG INSTABILITY WITH THIS STORM EXPECT "LAKE EFFECT"
TYPE SNOW FROM BARROW WEST WHERE THERE IS OPEN WATER AND ONSHORE FLOW.
HAVE ISSUED BLIZZARD WARNING FOR ALL OF THE ARCTIC COAST FOR TUE-
WED AS A RESULT. DUE TO THE UNCERTAINTY OF THE TRACK AND STRENGTH
OF THIS SYSTEM HAVE LEFT THE COASTAL FLOOD WATCH AS A WATCH FOR
TUE-TUE NIGHT FOR ZONES 201-202. EXPECT THAT EAST OF POINT BARROW
THE MORE SIGNIFICANT SHORE FAST ICE AND DENSER ICE COVER OFFSHORE
WILL PREVENT COASTAL FLOODING. THIS COULD ALSO RAISE SEA LEVELS IN
ZONES 207 209 AND 210 WHERE SEA LEVELS ARE ALREADY 1 FT ABOVE
NORMAL DUE TO NW FLOW SO HAVE ISSUE HIGH SURF FOR THOSE ZONES FOR TUE.
SURGE MODELS NOT MUCH HELP HERE DUE TO THE POOR GFS PERFORMANCE
WITH THE SURFACE LOW AND WINDS FIELDS AROUND THE POLAR LOW.
THIS POLAR WILL BE THE MAIN FEATURE TO MONITOR TONIGHT.

A STRONG LOW WILL MOVE INTO THE CENTRAL BERING SEA ON WED.
THIS WILL CAUSE STRONG E WINDS IN THE NORTHERN BERING SEA WED NIGHT.

&&

.DISCUSSION...
SEE DISCUSSION ABOUT POLAR LOW.

COASTAL HAZARD POTENTIAL DAYS 3 AND 4...NONE

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FOR AKZ207-AKZ209-AKZ210.

COASTAL FLOOD WATCH FOR AKZ201-AKZ202.

BLIZZARD WARNING FOR AKZ201-AKZ202-AKZ203-AKZ204.

WINTER WEATHER ADVISORY FOR AKZ207.

HEAVY FREEZING SPRAY WARNING FOR PKZ225-PKZ230-PKZ235.

GALE WARNING FOR PKZ220-PKZ225-PKZ230-PKZ235-PKZ240-PKZ245.

STORM WARNING FOR PKZ230-PKZ235.

SMALL CRAFT ADVISORY FOR PKZ210-PKZ215.

BRISK WIND ADVISORY FOR PKZ245.
&&

JB OCT 11