Blizzard Watch 22, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 PM AKST THU MAR 5 2009

.ANALYSIS AND UPPER LEVELS...
AT THE SURFACE...THE PRIMARY FEATURE OF INTEREST IS A WEAKENING 977
MB LOW LOCATED OVER THE SEWARD PENINSULA. AN ASSOCIATED WARM FRONT
STRETCHES THROUGH INTERIOR ALASKA AND INTO THE YUKON TERRITORY...WITH
DEEP MOISTURE TRANSPORT EVIDENT ON WATER VAPOR IMAGERY. A WEAK
SURFACE TROUGH IS LOCATED OVER THE NORTHERN GULF OF ALASKA...WITH
SOUTHERLY FLOW CONTINUING ACROSS SOUTHCENTRAL. ELSEWHERE...A COLD
FRONT EXTENDING FROM THE LOW IS MOVING INTO SOUTHCENTRAL FROM THE
WEST. THE NEXT FEATURE OF INTEREST IS A DEVELOPING NORTH PACIFIC
LOW...CURRENTLY LOCATED WELL SOUTHWEST OF SHEMYA.

IN THE UPPER LEVELS...A HIGHLY AMPLIFIED RIDGE CENTERED OVER THE
YUKON TERRITORY CONTINUES TO TRANSLATE EASTWARD. A BROAD TROUGH OVER
THE BERING SEA CONTAINS VARIOUS EMBEDDED WAVES. ONE SUCH POTENT
SHORTWAVE IS BEGINNING TO MOVE OVER THE WESTERN MAINLAND. BETWEEN
THESE TWO SYSTEMS...A STRONG JET IS TRANSPORTING WARM AND MOIST AIR
INTO ALASKA FROM THE SUBTROPICS.

.MODEL DISCUSSION...
THE GFS CONTINUES TO BE THE MODEL OF CHOICE DUE TO RUN TO RUN
CONSISTENCY. GENERAL MODEL AGREEMENT IS GOOD THROUGH 00Z
SUNDAY...BEFORE MODELS BEGIN TO DIVERGE ON THE EVOLUTION OF THE NEXT
NORTH PACIFIC LOW MOVING INTO THE BERING SEA OVER THE WEEKEND.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...
THE COLD FRONT IS BEGINNING TO PUSH INTO THE AREA THIS
AFTERNOON...WITH MOST LOCATIONS TRANSITIONING BACK TO ALL SNOW.
UPSLOPE SNOW WILL BE WANING THROUGH TONIGHT ALONG THE SUSITNA
VALLEY...WITH SNOW SHOWERS PERSISTING THROUGH THE NIGHT ACROSS MOST
OF SOUTHCENTRAL. A LOW EXPECTED TO FORM IN THE COPPER RIVER BASIN
TONIGHT WILL LEAD TO ENHANCED SNOWFALL IN THAT AREA...WITH SNOWFALL
EXPECTED TO REACH CRITERIA LEVELS MAINLY NORTH AND EAST OF GLENALLEN.
OTHERWISE...AN UPPER TROUGH WILL SWING THROUGH TONIGHT...HELPING TO
SCOUR OUT REMAINING PRECIPITATION. HIGH PRESSURE WILL BEGIN BUILDING
INTO SOUTHCENTRAL TOMORROW...WITH IMPROVING CONDITIONS AS WE HEAD
INTO THE WEEKEND.

.SOUTHWEST...
THE COLD FRONT HAS MOVED THROUGH SOUTHWEST EARLY THIS AFTERNOON...AND
ANY REMNANT PRECIPITATION WILL BE SWITCHING BACK TO SNOW AS COLD AIR
FILTERS BACK INTO THE REGION. GUSTY SOUTHERLY WINDS WILL CONTINUE
THROUGH TONIGHT AS COLD AIR ADVECTION CONTINUES BEHIND THE FRONT.
BLIZZARD CONDITIONS ARE POSSIBLE ALONG THE KUSKOKWIM DELTA
TONIGHT...WITH CONDITIONS IMPROVING AS SNOW MOVES OUT OF THE AREA BY
EARLY TOMORROW MORNING. CONDITIONS WILL BE QUIETING DOWN
TOMORROW...AS HIGH PRESSURE BRIEFLY MOVES THROUGH THE AREA. BY FRIDAY
NIGHT...SOUTHERLY WINDS ALONG COASTAL LOCATIONS AND THE AK PENINSULA
WILL BE INCREASING AGAIN IN RESPONSE TO A TIGHTENING GRADIENT AHEAD
OF THE NORTH PACIFIC LOW APPROACHING THE ALEUTIANS.

.BERING SEA AND ALEUTIANS...
COLD AIR ADVECTION SNOW SHOWERS WILL BE COMING TO AN END TONIGHT AS
HIGH PRESSURE NOSES INTO THE CENTRAL AND EASTERN ALEUTIANS. HIGH
PRESSURE RIDGING WILL BE SHORT LIVED...AS THE CENTER MOVES EASTWARD
INTO THE GULF OF ALASKA TOMORROW. PRECIPITATION AND WINDS WILL BE ON
THE INCREASE OVERNIGHT AND INTO TOMORROW AS THE AFOREMENTIONED NORTH
PACIFIC LOW MOVES NORTHWARD. WIDESPREAD STORM FORCE WINDS WILL
ACCOMPANY THIS LOW...PARTICULARLY OVER THE CENTRAL AND EASTERN
ALEUTIANS. THIS IS MAINLY IN RESPONSE TO A VERY STRONG PRESSURE
GRADIENT EXISTING BETWEEN THE HIGH AND LOW PRESSURE SYSTEMS. THE
POSSIBILITY FOR HIGH WIND WARNINGS WILL HAVE TO BE CONSIDERED AS THE
SITUATION EVOLVES.

.LONG TERM FORECAST...
AS MENTIONED IN THE PREVIOUS DISCUSSION...SURFACE HIGH PRESSURE WILL
BUILD ACROSS THE INTERIOR THIS WEEKEND AHEAD OF ANOTHER STRONG NORTH
PACIFIC LOW. THIS LOW WILL MOVE INTO THE BERING SEA SATURDAY...WITH
STRONG WINDS LIKELY CREATING BLIZZARD CONDITIONS OVER THE WESTERN
ALEUTIANS ON THE BACKSIDE. STRONG SOUTHERLY FLOW WILL DEVELOP ACROSS
THE EASTERN ALEUTIANS AND SOUTHWEST MAINLAND...AS THE PRESSURE
GRADIENT TIGHTENS BETWEEN THE HIGH OVER THE MAINLAND AND THE
DEEPENING LOW IN THE BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER WEATHER ADVISORY...141 145
         BLIZZARD WARNING...155
MARINE...GALE WARNING...130 132 140 141 150 155 160 165 170 171 176
                        180 412 413 414
         STORM WARNING...120 172 175 179 185 351 352 411
         HEAVY FREEZING SPRAY WARNING...121 129 141 185
FIRE WEATHER...NONE

NRH MAR 09