Brisk Wind Advisory 10, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM AKST SAT JAN 17 2009

.ANALYSIS AND UPPER LEVELS...THE POWERFUL SYSTEM WHICH STORMED
THROUGH SOUTHERN ALASKA YESTERDAY IS NOW EXITING OVER NORTHWEST
ALASKA. CONDITIONS HAVE GREATLY IMPROVED BEHIND THE SYSTEM WITH
SOME RESIDUAL STRONG WINDS HANGING ON OVER THE NORTHERN KUSKOKWIM
VALLEY. LOCALIZED FLOODING AND PONDING OF WATER CONTINUES ACROSS
SOUTHCENTRAL THIS MORNING DUE TO ALL OF THE RECENT RAINFALL AND
MELTING SNOW...AS WELL AS ICE CLOGGED STORM DRAINS...BUT CONDITIONS
ARE STEADILY IMPROVING. ARCTIC AIR HAS MOVED BACK INTO SOUTHWEST
ALASKA BEHIND THIS SYSTEM WITH TEMPERATURES NOW DOWN TO SINGLE
DIGITS ALONG THE KUSKOKWIM DELTA. THE EAST PACIFIC RIDGE HAS ALSO
BEEN NUDGED A BIT TO THE EAST. THE NEXT SYSTEM IN LINE ALONG THE
WEST EDGE OF THE RIDGE IS THEREFORE TRACKING FARTHER EAST ALONG 151W.
THE FIREHOUSE OF TROPICAL MOISTURE IS CURRENTLY POINTED TOWARD THE
YAKUTAT AREA. HOWEVER...AS THE NEXT LOW TRACKS NORTHWARD A WARM
FRONT OUT AHEAD OF IT IS PUSHING NORTHWESTWARD...DIRECTING A LOT
OF THAT MOISTURE BACK TOWARD SOUTHCENTRAL. MEANWHILE...OUT WEST A
SERIES OF LOWS ARE EMBEDDED WITHIN THE LONG-WAVE TROUGH IN THE
VICINITY OF THE ALEUTIANS. MOST NOTEWORTHY IS A LOW JUST WEST OF
ADAK TRACKING NORTHWARD INTO THE BERING WITH A WELL DEFINED OCCLUDED
FRONT EXTENDING TO THE SOUTH. A DEVELOPING LOW IS ALSO TRACKING
EASTWARD ALONG THE NORTH PACIFIC JET DOWN AROUND 40N 170W.

.MODEL DISCUSSION...MODELS ALL INDICATE SIMILAR IDEAS...BUT DETAILS
IN LOW POSITIONS AND TRACKS DO DIFFER. WITH NEXT LOW MOVING INTO THE
GULF PREFER A CONSENSUS POSITION OF ECMWF/NAM. OUT WEST WILL STICK
WITH BLEND OF GFS/CURRENT GRIDS FOR THE SHORT-TERM...SO NO MAJOR
CHANGES FROM CURRENT FORECAST. BY MID WEEK MORE SIGNIFICANT MODEL
DIFFERENCES SHOW UP WITH POSITION OF UPPER RIDGE...SO WILL STICK
CLOSE TO CURRENT FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL...THE FORECAST PROBLEM OF THE DAY ACROSS SOUTHCENTRAL
IS PRECIPITATION TYPE. COOLER AIR IS CURRENTLY WORKING ITS WAY BACK
IN TO WESTERN PORTIONS OF SOUTHCENTRAL ALASKA. THE WARM FRONT MOVING
ACROSS THE GULF WILL OCCLUDE TONIGHT AND SUNDAY AS IT REACHES
SOUTHCENTRAL. LOCATIONS ACROSS THE NORTH GULF COAST WILL LIKELY SEE
SOME ADDITIONAL WARMING AS THIS FRONT NEARS. HOWEVER...FOR LOCATIONS
ON THE INLAND SIDE OF THE COASTAL RANGE...THERMAL ADVECTION WILL BE
NEUTRAL TO WEAK WARM. SO THE QUESTION IS WHETHER ENOUGH COOLING WILL
TAKE PLACE FOR PRECIPITATION TO FALL AS SNOW WHEN IT ARRIVES. THE
FREEZING LEVEL ON THE ANCHORAGE SOUNDING WAS 4156 FEET THIS MORNING.
THE AFTERNOON SOUNDING WILL BE A KEY INDICATOR TO HOW MUCH COOLING
HAS OCCURRED. THE CURRENT THINKING IS THAT AS PRECIPITATION BEGINS
LATE TONIGHT INTO TOMORROW MORNING IT WILL INITIALLY BE MAINLY
RAIN...AND MAY MIX WITH OR CHANGE TO SNOW AS MELTING HELPS COOL THE
COLUMN A BIT. HOWEVER...ANY SNOW WILL BE VERY WET AND WILL NOT
ACCUMULATE MUCH. SO...UNLESS NEW INFORMATION SHOWS
OTHERWISE...FORECAST WILL BE CONSERVATIVE WITH SNOW AMOUNTS. RAIN
ALONG THE COAST MAY CAUSE FURTHER LOCALIZED FLOODING OR PONDING OF
WATER ON ROADWAYS...SO FLOOD ADVISORIES MAY HAVE TO BE RE-ISSUED.
MODELS INDICATE A LOW TRACK TO PRINCE WILLIAM SOUND SUNDAY NIGHT
AND MONDAY...SO COLD AIR WILL THEN MOVE BACK IN FROM THE WEST AND
GRADUALLY CHANGE PRECIPITATION TO ALL SNOW. THIS SYSTEM IS EXPECTED
TO MOVE OFF TO THE EAST BY TUESDAY...BRINGING A DRYING TREND BACK
TO THE REGION.

SOUTHWEST ALASKA...A NARROW BAND OF SNOW HAS DEVELOPED IN BRISTOL
BAY THIS MORNING AHEAD OF A VERY WEAK UPPER LEVEL SHORT-WAVE. SNOW
WILL LIKELY SPREAD UP TO THE KUSKOKWIM VALLEY THIS AFTERNOON OR
EVENING AND THEN END BY SUNDAY MORNING AS THE LOW LEVEL FLOW SHIFT
TO THE NORTH AHEAD OF THE GULF SYSTEM. MOISTURE ASSOCIATED WITH THE
GULF LOW WILL BE PUSHED OVER THE ALASKA RANGE SUNDAY AND
MONDAY...BRINGING SNOW TO PORTIONS OF THE KUSKOKWIM VALLEY WHILE THE
REST OF SOUTHWEST ALASKA STAYS DRY AND COLD DUE TO A BUILDING
SHORT-WAVE RIDGE AHEAD OF DEVELOPING NORTH PACIFIC LOW.

BERING SEA/ALEUTIANS...THE MULTIPLE LOWS ALONG THE ALEUTIANS WILL
ALL TRACK NORTHWARD UP THE EASTERN SIDE OF THE LONG-WAVE
TROUGH...WITH THE LOW WEST OF ADAK BEING THE MOST SIGNIFICANT WEATHER
MAKER. MEANWHILE THE LOW DEVELOPING UNDERNEATH THE UPPER JET WILL
DEEPEN...WITH UPPER TROUGH DIGGING AND INDUCING AMPLIFICATION OF
THE PATTERN HEADING INTO THE NEW WEEK. THE RESULT WILL BE A HIGH
AMPLITUDE RIDGE BUILDING OVER THE ALASKA PENINSULA AND SOUTHWEST
ALASKA...WITH A TROUGH OVER SOUTHCENTRAL...AND THE BLOCKING RIDGE
PUSHED FARTHER EAST OVER MAINLAND LOWER 48 AND CANADA. MOISTURE WILL
BE PUSHED NORTHWARD UP THE WEST SIDE OF THIS NEW RIDGE ACROSS THE
CENTRAL AND EASTERN ALEUTIANS AND INTO THE BERING SEA.

.LONG TERM FORECAST...THE GFS/ECMWF BOTH SHOW THE NEWLY BUILT RIDGE
CUTTING OFF OVER WESTERN ALASKA MID WEEK AND BUILDING OVER NORTHERN
ALASKA. THERE IS THEN DISAGREEMENT ON WHETHER THIS RIDGE QUICKLY
JOINS BACK WITH BLOCKING RIDGE OVER WESTERN CANADA OR HOLDS AS A
CUT-OFF OVER NORTHERN ALASKA. IN EITHER CASE...THE RIDGE WILL BRING
QUIETER AND COOLER (NEAR NORMAL TEMPERATURES) WEATHER TO MAINLAND
ALASKA MID TO LATE WEEK. DEPENDING ON EVOLUTION OF THIS
RIDGE...STORMS MAY START AFFECTING THE SOUTHERN MAINLAND AGAIN BY
NEXT WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...FLOOD WARNING 101 CHESTER CREEK AT ARCTIC BLVD.
MARINE...GALE WARNING...120 170 172 175 179 185.
         HEAVY FREEZING SPRAY...130.
FIRE WEATHER...NONE.

SEB JAN 09