Brisk Wind Advisory 5, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1230 PM AKST MON JAN 12 2009

.ANALYSIS AND UPPER LEVELS...A STRONG SHORT-WAVE TROUGH EXTENDING
FROM A CLOSED UPPER LOW OVER THE NORTHWEST BERING SEA EASTWARD
ACROSS THE SOUTHERN MAINLAND IS A TEMPORARY KINK IN THE STRONG
EAST PACIFIC RIDGE. THE THROUGH IS LIFTING QUICKLY NORTHWARD ACROSS
THE STATE. A MODERATE SURFACE LOW OVER THE NORTH GULF SOUTH OF CAPE
SUCKLING IS WEAKENING AS IT HEADS TOWARD YAKUTAT AND THEN INLAND.
LIGHT SNOW CONTINUES AHEAD OF THE TROUGH FROM THE KUSKOKWIM VALLEY
TO PORTIONS OF SOUTHCENTRAL. HOWEVER THE MOST SIGNIFICANT SNOW IS
JUST OUT AHEAD OF THE LOW OVER THE EASTERN COPPER RIVER
BASIN...INCLUDING MCCARTHY...WHERE UP TO 6 INCHES OF SNOW IS
POSSIBLE.

THE UPPER RIDGE IS BUILDING BEHIND THE SHORT-WAVE TROUGH AHEAD OF
A DIGGING TROUGH OVER THE NORTH CENTRAL PACIFIC. THERE IS A DEEP
COLD CORE LOW EMBEDDED WITHIN THIS TROUGH WITH OCCLUDED FRONT
PUSHING TOWARD THE ALEUTIANS. AHEAD OF THE FRONT MAX GALE TO MIN
STORM FORCE WINDS COMBINED WITH SNOW ARE PRODUCING NEAR BLIZZARD
CONDITIONS ALONG THE CENTRAL TO WESTERN ALEUTIANS. SURFACE
TEMPERATURES ARE SLOWLY CREEPING UP AS THIS FRONT GETS CLOSER.

.MODEL DISCUSSION...MODEL AGREEMENT IS REASONABLE WITH LARGE SCALE
PATTERN...BUT THERE ARE DIFFERENCES IN MAIN LOW CENTER OUT WEST AS
WELL AS WITH SURFACE LOWS/UPPER WAVES MOVING UP THE WEST SIDE OF THE
EAST PACIFIC RIDGE. THESE DIFFERENCES WILL ONLY SIGNIFICANTLY AFFECT
THE FORECAST IN THE VICINITY OF THESE FEATURES...ESPECIALLY IN THE
CORRIDOR FROM THE ALASKA PENINSULA NORTHWARD ACROSS SOUTHWEST ALASKA.

DO NOT PARTICULARLY HAVE A FAVORED MODEL SOLUTION. WILL GENERALLY
STICK CLOSE TO CURRENT FORECAST WITH SOME MINOR CHANGES.

.SHORT TERM FORECAST...

SOUTHERN MAINLAND...THE UPPER RIDGE WILL BUILD TONIGHT AND TUESDAY
OVER MAINLAND ALASKA. A LONG FETCH OF SOUTHERLY FLOW ALOFT WILL
TRANSPORT TROPICAL AIR AND MOISTURE ORIGINATING DOWN AROUND 30N
NORTHWARD ACROSS MAINLAND ALASKA. THE WARM AIR WILL INITIALLY
OVERRUN THE COLD ARCTIC AIR CURRENTLY IN PLACE...BUT WILL GRADUALLY
ERODE THAT AIR AS WE HEAD THROUGH THE WEEK. INITIAL OVERRUNNING
PRECIPITATION WILL BEGIN DURING THE DAY TUESDAY SPREADING OVER THE
ENTIRE REGION BY TUESDAY NIGHT. PRECIPITATION TYPE WILL START AS
SNOW MOST PLACES...BUT QUICKLY CHANGE TO RAIN IN COASTAL AREAS BY
LATE TUESDAY. THE AIR ALOFT WILL BE SO WARM THAT FREEZING RAIN WILL
BECOME A THREAT STARTING TUESDAY NIGHT AND CONTINUING WEDNESDAY FOR
INLAND LOCATIONS WHERE THE ARCTIC AIR IS DEEPEST. MEANWHILE...AT THE
SURFACE LOWS WILL TRACK FROM THE PACIFIC NORTHWARD TO THE ALASKA
PENINSULA AND THEN UP ACROSS THE BRISTOL BAY AND SOUTHWEST ALASKA
REGION. AS EACH OF THESE MOVES NORTHWARD THE PRESSURE GRADIENT WILL
TIGHTEN SIGNIFICANTLY TO THE EAST RESULTING IN STRONG WINDS ACROSS
THE GULF WATERS AND GAP WINDS THROUGH THE CHUGACH...ALASKA...AND
ALEUTIAN RANGES. THIS WILL KEEP PRECIPITATION VERY LIGHT IN THE LEE
OF THE MOUNTAINS...BUT UPSLOPE AREAS SUCH AS THE SUSITNA VALLEY WILL
SEE ENHANCED SNOWFALL. A WINTER WEATHER ADVISORY FOR SNOW WILL HAVE
TO BE CONSIDERED FOR THE WESTERN SUSITNA TUESDAY NIGHT AND
WEDNESDAY...BUT THE TIMING OF CHANGE IN PRECIPITATION TYPE IS IN
QUESTION...SO WILL HOLD OFF FOR NOW UNTIL HAVE A BETTER IDEA OF
HOW FAST THE WARMING WILL OCCUR.

BERING SEA/ALEUTIANS...THE OCCLUDED FRONT SOUTH OF THE ALEUTIANS
WONT MAKE MUCH MORE NORTHWARD PROGRESSION. HOWEVER...TEMPS HAVE
WARMED TO 34 DEGREES AT BOTH ADAK AND ATKA AND VISIBILITIES ARE
STARTING TO IMPROVE. THEREFORE...WE WILL LIKELY BE ABLE TO CANCEL
THE BLIZZARD WARNING THIS AFTERNOON. THE FRONT WILL LIFT NORTHWARD
EAST OF THE REGION...TOWARD THE EASTERN ALEUTIANS AND ALASKA
PENINSULA...PUSHING WARMER AIR NORTHWARD AND CHANGING PRECIPITATION
TO RAIN. MEANWHILE...COLDER AIR WILL HEAD BACK SOUTHWARD ACROSS THE
CENTRAL TO WESTERN ALEUTIANS TUESDAY NIGHT AND WEDNESDAY. THERE IS
A CHANCE THAT BLIZZARD CONDITIONS COULD MOVE BACK IN...BUT
PRECIPITATION CHARACTER WILL BE SHOWERY SO LOW VISIBILITIES WOULD
NOT LAST LONG. IN AREAS FARTHER EAST WHERE THE PRECIPITATION WILL
BE STEADIER TEMPS SHOULD BE WARM ENOUGH TO PREVENT BLIZZARD
CONDITIONS. THE LOW SOUTH OF THE ALEUTIANS WILL TRACK TO TOWARD
THE ALASKA PENINSULA MID WEEK AND INTO THE EASTERN BERING BY WEEKS
END. ARCTIC AIR WILL USHER SOUTHWARD BEHIND THIS LOW PRODUCING THE
USUAL STRONG AND GUSTY WINDS AND SNOW SHOWERS.

.LONG TERM FORECAST...MEDIUM RANGE MODELS INDICATE THE STRONG
BLOCKING RIDGE PROGRESSING EASTWARD A BIT BY NEXT WEEKEND AND
ALLOWING A COLD TROUGH TO MOVE BACK INTO MAINLAND ALASKA.
HOWEVER...NOT READY TO BUY COMPLETELY INTO THIS YET SINCE MODEL
BIAS IS TO CHANGE A STABLE PATTERN SUCH AS THIS TOO QUICKLY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 187 191.
MARINE...GALE WARNING 120 130 150 155 160 165 170 171 172 175 176
                      179.
         HEAVY FREEZING SPRAY WARNING...165 179 185.
FIRE WEATHER...NONE.

SEB JAN 09