Gale Warning 308, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKDT TUE APR 13 2010

.ANALYSIS AND UPPER LEVELS...
AMPLIFIED PATTERN CONTINUES TODAY WITH LONG WAVE TROUGH CENTERED
BETWEEN 170W AND 180W AND DOWNSTREAM RIDGE CENTERED NEAR THE ALASKA
PANHANDLE. A 125 KT JET FLOWING AROUND THE BASE OF THE TROUGH
CONTINUES TO TAP THE SUBTROPICAL MOISTURE AND TRANSPORT IT NORTH
TOWARD THE NORTHEASTERN GULF COAST.

VERY FEW SURFACE FEATURES TO SPEAK OF...BROAD SOUTHWESTERLY FLOW
BRINGING GUSTY WINDS TO THE REGION. THE MAIN AREA OF LOW PRESSURE IS
CENTERED NEAR KOTZEBUE SOUND WITH A WEAK FRONTAL BOUNDARY EXTENDING
SOUTH AND WEST THROUGH THE CENTRAL BERING SEA. SATELLITE IMAGERY
INDICATING THE INITIAL SIGNS OF A SHORTWAVE EMBEDDED WITHIN THE
SOUTHWESTERLY JET HELPING TO DEVELOP A WEAK AREA OF LOW PRESSURE THAT
WILL BRING SOUTHCENTRAL ANOTHER CHANCE OF RAIN AND SNOW WEDNESDAY.

.MODEL DISCUSSION...
MODELS IN EXCELLENT AGREEMENT THIS MORNING. THE MOST SIGNIFICANT
FEATURE IS THE LOW DEVELOPING ALONG THE FRONTAL BOUNDARY IN THE NORTH
PACIFIC. MODELS HAVE FINALLY COME INTO AGREEMENT ON THE TIME AND NOW
THE ECMWF...WHICH WAS THE OUTLIER...IS ALSO ADVERTISING A SIMILAR
TRACK OF THE LOW WHICH IS JUST EAST OF KODIAK ISLAND BEFORE MOVING
INLAND NEAR SEWARD. THE OTHER FEATURE OF INTEREST IS A STRONG GALE
FORCE FRONT MARCHING ACROSS THE ALEUTIANS AND BERING SEA WEDNESDAY
THROUGH THURSDAY. MODELS ARE VERY CONSISTENT WITH THE TIMING AND
STRENGTH OF THIS FEATURE. ONLY MINOR CHANGES ARE EXPECTED WITH THIS
FORECAST PACKAGE.

.SHORT TERM FORECAST...
.SOUTH CENTRAL ALASKA...PARTLY CLOUDY TO MOSTLY SUNNY SKIES
PREVAILING THIS AFTERNOON OVER MUCH OF SOUTHCENTRAL ALASKA. SHOWERS
DEVELOPING ALONG THE EASTERN PRINCE WILLIAM SOUND COAST THANKS TO THE
MOIST SOUTHWESTERLY FLOW BUTTING UP AGAINST THE MOUNTAINS. SHOWERS
WILL TURN INTO STEADY RAIN AND SNOW LATE TONIGHT INTO WEDNESDAY
MORNING AS THE WAVE APPROACHES THE REGION. THE WESTERN EXTENT OF THE
PRECIPITATION IS STILL UP IN THE AIR AS THE LAST TWO MODEL RUNS HAVE
BACKED OFF SIGNIFICANTLY ON PRECIPITATION FOR THE ANCHORAGE BOWL.
THERE IS A LACK OF SOUTHEASTERLY FLOW ALOFT AT ANY LEVEL TO THROW THE
PRECIPITATION OVER THE MOUNTAINS BACK TOWARD ANCHORAGE. TEMPERATURE
ADVECTION IS NEUTRAL WHILE THERE IS MOISTURE AVAILABLE. BY THE TIME
COOLER AIR ARRIVE...IT IS AFTER THE MOISTURE HAS EXITED THE REGION.
STILL...THE POSITION OF THE LOW NEAR SEWARD AND WESTERN PRINCE
WILLIAM SOUND COUPLED WITH THE SOUTHWESTERLY SUBTROPICAL FETCH OF
MOISTURE ALOFT IS HISTORICALLY A FAVORABLE SCENARIO FOR PRECIPITATION
IN ANCHORAGE. AGAIN...TEMPERATURES WILL BE AT OR ABOVE FREEZING AT
SEA LEVEL WHICH WILL EITHER LIMIT ACCUMULATION OR RESULT IN A MIX OF
RAIN AND FALL. THE HILLSIDE HAS THE BEST CHANCE AT ACCUMULATING
SNOWFALL WHERE TEMPERATURES WILL BE NEAR FREEZING. THE SPEED OF THE
SYSTEM WILL LIMIT ACCUMULATION TO A FEW INCHES.

ANOTHER AREA OF CONCERN WITH THIS SYSTEM IS THE COPPER RIVER BASIN
WHERE A BOUNDARY BETWEEN THE WARMER AIR TO THE SOUTH AND EAST AND THE
COLDER AIR OVER THE NORTHWESTERN HALF OF THE ZONE WILL SET UP. THE
PRESSURE GRADIENT WILL RELAX OVERNIGHT AS THE LOW APPROACHES AND
MOISTURE AND WARMER AIR BEGINS TO OVERRUN THE COLDER AIR TO THE
NORTH. THE RESULT WILL BE LIGHT TO MODERATE SNOW THROUGHOUT THE
BASIN. WILL FINE TUNE SNOW AMOUNTS BUT EXPECTING RESPECTABLE
TOTALS...JUST BELOW ADVISORY CRITERIA.

.SOUTHWEST ALASKA...SOUTHWESTERLY ONSHORE FLOW CONTINUES WITH
SCATTERED SHOWERS AND NEAR NORMAL TEMPERATURES EXPECTED THROUGH MID
WEEK. A SURFACE TROUGH AXIS ROTATES INLAND WEDNESDAY AFTERNOON
ENHANCING THE SHOWER ACTIVITY ACROSS THE LOWER KUSKOKWIM VALLEY.
BEHIND THAT TROUGH...HIGH PRESSURE BUILDS BRIEFLY AHEAD OF THE NEXT
FRONTAL BOUNDARY THAT WILL AFFECT THE COAST THURSDAY AND MOVE INLAND
THURSDAY NIGHT.

.ALEUTIANS AND BERING SEA...SHOWER ACTIVITY WILL SLOWLY DISSIPATE AS
MINIMUM GALES GIVE WAY TO SMALL CRAFT ADVISORY WINDS. THIS IS ALL
RELATED TO AN AREA OF HIGH PRESSURE BUILDING BUILDING BRIEFLY TONIGHT
AND TOMORROW AHEAD OF THE APPROACHING FRONTAL BOUNDARY. THE FRONT
WILL AFFECT THE WESTERN ALEUTIANS EARLY WEDNESDAY MORNING BRINGING
STRONG GALE FORCE WINDS AND ABUNDANT MOISTURE TO THE REGION. BY THE
WEEKEND...THE FRONT WILL HAVE WEAKENED AS IT MOVES INLAND AND INTO
THE NORTHERN GULF AND THE PARENT LOW POSITIONS ITSELF IN THE CENTRAL
GULF.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...170 172 175 176 179 185
FIRE WEATHER...NONE.

AB APR 10