Brisk Wind Advisory 17, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM AST TUE MAR 4 2008

.ANALYSIS AND UPPER LEVELS...A DEEP ANCHOR LOW EMBEDDED WITHIN A
LONG-WAVE HIGH AMPLITUDE TROUGH IS CENTERED JUST SOUTHWEST OF ADAK.
DOWNSTREAM HIGH AMPLITUDE RIDGE LIES FROM THE EAST PACIFIC NORTHWARD
ACROSS THE EASTERN GULF OF ALASKA AND ACROSS MAINLAND ALASKA. A ZONAL
JET EXTENDS EASTWARD OUT OF ASIA ALONG 30N LATITUDE AND THEN CURVES
NORTHWARD AROUND 150W LONGITUDE. LOWS HAVE BEEN DEVELOPING IN THE
CURVE OF THE JET WHERE THERE IS GOOD UPPER LEVEL DIVERGENCE.
SATELLITE IMAGERY SHOWS ONE SUCH LOW SOUTH OF THE ALASKA PENINSULA
NEAR 49N 161W...DRIFTING OFF THE NORTH AND EAST. A SURFACER TROUGH
EXTENDS NORTHEAST FROM THE LOW TO BRISTOL BAY. THERE IS A VERY TIGHT
PRESSURE GRADIENT EAST OF THIS TROUGH AXIS...ACROSS THE GULF AND
SOUTHCENTRAL ALASKA. THE SURFACE RIDGE AXIS EXTENDS FROM SOUTHEAST
ALASKA TO ALONG THE NORTH GULF COAST..AIDING IN TIGHTENING THE
PRESSURE GRADIENT EVEN MORE. THUS...THERE ARE STRONG SOUTHEAST WINDS
ACROSS THE REGION WITH GUSTS UP TO 65 MPH ALONG TURNAGAIN ARM. GUSTY
WINDS HAVE CAUSED TEMPERATURES TO RISE INTO THE UPPER 30S FOR MANY
AREAS IN SOUTHCENTRAL AND ALONG THE ALASKA AND ALEUTIAN RANGES IN
SOUTHWEST ALASKA. SOUTHERLY FLOW ALOFT IS COUNTERACTING SOME OF THE
SOUTHEASTERLY DOWNSLOPE FLOW...BUT MOST SIGNIFICANT PRECIPITATION
REMAINS IN UPSLOPE AREAS...MOST NOTABLY OVER THE SUSITNA VALLEY
WHERE STEADY SNOW HAS BEEN FALLING ALL MORNING. CONDITIONS ARE
FAIRLY QUIET OUT WEST. NO SIGNIFICANT WINDS TO SPEAK OF. SNOW SHOWERS
ARE CONCENTRATED AROUND ANCHOR LOW NEAR ADAK AND AHEAD OF A TROUGH
AXIS THAT EXTENDS NORTHWARD ACROSS THE CENTRAL BERING.

.MODEL DISCUSSION...MODELS WERE FAIR IN THEIR INITIALIZATION OF LOW
POSITIONS. THERE ARE SMALL DIFFERENCES IN STRENGTH AND TRACK OF LOW
THAT MOVES FROM SOUTH OF THE ALASKA PENINSULA TO SOUTHWEST ALASKA
WEDNESDAY. HOWEVER...SOLUTIONS ALL ALL GROUPED TOGETHER AND THE
RUN-TO-RUN CONSISTENCY IS OKAY. WITH SOMEWHAT MORE CONFIDENCE THAN
PREVIOUS SHIFTS WILL WORK TO FINE-TUNE THE FORECASTS FOR WHEN THIS
LOW MOVES THROUGH. THE MODELS HAVE BEEN ALL OVER THE PLACE WITH THE
NEXT BIG LOW SOMING UP FROM THE PACIFIC LATER THIS WEEK.
HOWEVER...THE GFS HAS SHOWN DECENT RUN-TU-RUN CONSISTENCY BETWEEN
THE 00Z AND 12Z RUNS AND OPERATION RUN MATCHES UP WELL WITH ENSEMBLE
MEAN. THEREFORE...FORECAST WILL TREND TOWARD THE GFS SOLUTION.

.SHORT TERM FORECAST...LOW SOUTH OF THE ALASKA PENINSULA WILL BE
FORCED NORTHWARD AS COMBINATION OF UPPER JET DRIVING EASTWARD AND
MULTIPLE EMBEDDED WAVES HELP TO AMPLIFY TROUGH TO THE SOUTH AND
CAUSE IT TO BECOME NEGATIVELY TILTED. THE LOW TRACK WILL TAKE IT
SOUTH OF KODIAK ISLAND TONIGHT AND THEN NORTHWESTWARD ALONG THE
SOUTHWEST ALASKA COAST ON WEDNESDAY. THIS WILL PUSH A FRONT INTO
THE GULF TONIGHT WHICH WILL THEN TRACK TO THE NORTH GULF WEDNESDAY
AFTERNOON AND INLAND WEDNESDAY NIGHT. MEAN FLOW WILL SHIFT TO
SOUTHEAST AHEAD OF THE STORM SYSTEM ALLOWING CLASSICAL DOWNSLOPE
DRYING TO INITIATE. WITH A STRONG RIDGE TO THE EAST AND A DEEPENING
LOW WINDS AHEAD OF THE FRONT WILL BE VERY STRONG. HIGH WIND WATCHES
ARE IN EFFECT FOR TURNAGAIN ARM AND PORTAGE VALLEY BEGINNING AROUND
MIDNIGHT TONIGHT AND CONTINUING THROUGH TOMORROW. ANOTHER ROUND OF
WARM ADVECTION WILL ACCOMPANY THE SYSTEM SO THAT PRECIPITATION WILL
BE MAINLY IN THE FORM OF RAIN OVER SOUTHCENTRAL AND EASTERN PORTIONS
OF SOUTHEAST ALASKA. THE KUSKOKWIM DELTA WILL REMAIN AHEAD OF WARM
FRONT MOVING ACROSS SOUTHWEST ALASKA...SO PRECIPITATION WILL REMAIN
ALL SNOW AND WILL BE ACCOMPANIED BY NORTHERLY WINDS. THERE IS AN
OUTSIDE CHANCE OF BLIZZARD CONDITIONS WEDNESDAY AFTERNOON...BUT DO
NOT HAVE CONFIDENCE IN DETAILS OF TRACK OF THIS SYSTEM TO ISSUE
ONE...SO WILL WAIT ANOTHER MODEL AND REEVALUATE THE THREAT. RAPID
PRESSURE RISES BEHIND THE LOW WILL BRING GUSTY SOUTH TO SOUTHEAST
WINDS ACROSS SOUTHCENTRAL AND SOUTHWEST ALASKA WEDNESDAY NIGHT INTO
THURSDAY. THIS WILL RESULT IN WIDESPREAD BALMY TEMPERATURES ACROSS
THE SOUTHERN MAINLAND. OUT WEST...QUIET CONDITIONS WILL CONTINUE AS
ANCHOR LOW DRIFTS SOUTHEASTWARD THROUGH THE SHORT-TERM.

.LONG TERM FORECAST...AS THE NEXT DEEP LOW MOVES UP FROM THE PACIFIC
LATER THIS WEEK THE ANCHOR LOW WILL MERGE INTO THE NEW LOWS
CIRCULATION AND THE UPPER TROUGH WILL RE-CENTER FARTHER EAST. THUS
THE PATTERN WILL TEMPORARILY CHANGE AND MAINLAND ALASKA WILL LIKELY
COOL BACK TO NEAR NORMAL. AS IS TYPICAL THIS TIME OF YEAR...THE
PATTERN LOOKS LIKE IT WILL CONTINUE TO EVOLVE THROUGH THE EXTENDED
PERIOD...SO WEATHER WILL REMAIN CHANGEABLE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WATCH ZONE 101 AND 125.
MARINE...STORM WARNING...120 130.
         GALE WARNING 125 129 132 138 140.
         HEAVY FREEZING SPRAY WARNING 185.
FIRE WEATHER...NONE.

SEB MAR 08