Gale Warning 386, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKDT SAT MAY 5 2012

.ANALYSIS AND UPPER LEVELS...
A DEEP UPPER TROUGH/CLOSED LOW PRESSURE CONTINUES TO DIG INTO THE
NORTHERN PACIFIC THIS AFTERNOON. A DECENT 135KT JET SUPPORTS THE
TROUGH AND LOOKS TO ROUND THE BASE OF THE TROUGH AXIS THIS AFTERNOON.
ALONG WITH THE AFOREMENTIONED JET SUPPORT...AN INFUSION OF COLD
NORTHERLIES AND 850MB TEMPS OF -18C HAVE SUPPORTED ROBUST DEVELOPMENT
OF A COMPACT SURFACE CYCLONE STEMMING FROM THE COLD FRONT/SURFACE
TROUGH THAT MOVED OVER THE ALEUTIANS YESTERDAY. OVER THE
MAINLAND...CLOUD COVER FROM THE SHORTWAVE TROUGH IN THE GULF HAS
SPREAD OVER MUCH OF THE SOUTHCENTRAL SO WOULD EXPECT SIMILAR HIGH
TEMPERATURES TO YESTERDAY. LACK OF STRATIFORM CLOUDS OVER THE COPPER
RIVER BASIN HAS ALLOWED THEM TO CONVECT A NICE CUMULUS FIELD ALREADY
IN THE EARLY AFTERNOON. VERTICALLY...THE ATMOSPHERE LOOKS MUCH THE
SAME OVER THE ANCHORAGE BOWL AS YESTERDAY WITH COLD AIR ALOFT AND
STEEP LOW LEVEL LAPSE RATES.

.MODEL DISCUSSION...
YESTERDAY THE CONSENSUS AMONG GUIDANCE WAS A CLUSTER OF SOLUTIONS
SHOWING SURFACE LOW PRESSURE DEVELOPMENT TOWARD THE END OF THE
ALASKAN PENINSULA WITH THE ECMWF BEING THE CLEAR OUTLIER TO THE WEST.
VISIBLE/IR IMAGERY TODAY INDICATES THAT THE ECMWF IS CLOSEST TO
VERIFYING WITH THE POSITION OF THE SURFACE LOW APPEARING TO BE NEAR
PADU EVEN A TAD FARTHER WEST THAN EVEN THE ECMWF IS INDICATING. THE
MODEL SPREAD TODAY IS MUCH THE SAME WITH THE ECMWF BEING THE
STRONGEST AND FURTHEST WEST BUT HAS GAINED SUPPORT FROM THE
GEM/UKMET/SREF. FURTHER EAST MODELS ARE IN MUCH BETTER AGREEMENT IN A
DEVELOPING SURFACE LOW IN THE GULF BY THE END OF THE WEEKEND.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...PERSISTENCE WOULD SEEM TO BE PRUDENT TODAY AS
CONDITIONS HAVE NOT CHANGED OVER THE SOUTHCENTRAL THAT MUCH. THE ONLY
CAVEAT BEING THE INCREASE IN SOUTHEASTERLY LOW LEVEL WINDS WHICH
WOULD TEND TO DOWNSLOPE AND DRY THE AIR AS WELL AS INCREASED MID
LEVEL CLOUDS AHEAD OF THE TROUGH IN THE GULF. WOULD STILL EXPECT AN
INCREASE IN SHOWER ACTIVITY MAINLY OVER THE CHUGACH FRONT RANGE AS
THE UPPER LEVEL SHORTWAVE APPROACHES THIS EVENING. MORE WIDESPREAD
RAIN WILL AFFECT THE GULF AND WESTERN PORTIONS OF PRINCE WILLIAM
SOUND. A STRONGER UPPER TROUGH/SURFACE LOW WILL MOVE INTO THE
NORTHERN GULF ON SUNDAY AFTERNOON BRINGING MORE WIDESPREAD RAIN
MAINLY TO COASTAL LOCATIONS. SUBSIDENCE/GEOPOTENTIAL HEIGHT RISES
BEHIND THAT TROUGH SHOULD KEEP THE WEATHER ON MONDAY
AFTERNOON/EVENING FAIRLY BENIGN OVER MUCH OF THE AREA.

SOUTHWEST ALASKA...SCATTERED SNOW SHOWERS OVER THE BRISTOL BAY AREA
AND ASSOCIATED WITH THE COLD AIR ALOFT AND UPPER LEVEL LOW LOOK TO
CONTINUE THIS EVENING. RAIN SHOWERS OVER THE KUSKOKWIM VALLEY WILL
ALSO LINGER THROUGH THE EVENING HOURS BEFORE TAPERING OFF. SUNDAY AND
MONDAY A TROUGH WILL MOVE OVER THE ALASKA RANGE FROM THE GULF OF
ALASKA KEEPING SCATTERED SNOW SHOWERS IN THE FORECAST. THE KUSKOKWIM
DELTA WILL BE FAIRLY QUIET IN TERMS OF PRECIPITATION BUT THE CHANCE
FOR FOG AND LOW STRATUS IS POSSIBLE IN THE OVERNIGHT/EARLY MORNING
HOURS.

BERING SEA AND ALEUTIANS...COLDER NORTHERLY FLOW CONTINUES THIS
EVENING AS THE UPPER LOW MOVE TOWARD THE NORTH PACIFIC. COLD AIR
MOVING OVER THE RELATIVELY WARM WATER WILL FOSTER INSTABILITY SNOW
SHOWERS BEHIND THE MAIN BAND OF COLD ADVECTION OVER THE CENTRAL
ALEUTIANS. A RAPIDLY DEVELOPING SURFACE LOW WILL TIGHTEN THE SURFACE
PRESSURE GRADIENT AND BRING GALE FORCE WINDS REACHING STORM FORCE AT
TIMES OVER THE EASTERN ALEUTIANS WEST OF DUTCH HARBOR. SNOW
ASSOCIATED WITH THIS LOW WILL LINGER THROUGH THE EVENING BEFORE
TAPERING OFF TO SHOWERS ON SUNDAY. ANOTHER SHOT OF STEADIER SNOW WILL
AFFECT THE EASTERN BERING ON LATE SUNDAY MORNING/EARLY AFTERNOON.
ISOLATED SHOWERS WILL WANE ON MONDAY AS THE LOW PRESSURE MOVES INTO
THE GULF.

.LONG TERM FORECAST...
EXTENDED FORECAST WILL BEGIN WITH UPPER LOW DRIFTING FROM THE
NORTHERN PACIFIC INTO THE GULF OF ALASKA. A BIT MORE OF A PROGRESSIVE
PATTERN IS IN STORE FOR MID WEEK THOUGH. A QUICK MOVING SYSTEM WILL
SKIRT OVER THE ALEUTIANS INTO THE GULF PROVIDING A QUICK BREAK FROM
THE PERSISTENT TROUGHING...BUT WILL EVENTUALLY ESTABLISH A NEW TROUGH
IN THE GULF AGAIN BY LATE WEEK KEEPING THE PATTERN AMPLIFIED.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC... FLOOD WATCH 152
MARINE...GALE 120 170 171 172
FIRE WEATHER...NONE

MTL MAY 12