Gale Warning 105, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKST WED FEB 17 2010

.ANALYSIS AND UPPER LEVELS...
A STRONG UPPER LEVEL RIDGE OFF THE US NORTHWEST PACIFIC COAST
CONTINUES TO DEVELOP AND EXPAND NORTHWARD TOWARDS THE PANHANDLE AND
WESTERN CANADA. A SHARP UPPER LEVEL SHORTWAVE TROUGH DIGGING
SOUTHEASTWARD EXTENDING SOUTH FROM THE AKPEN TO THE 40 N PARALLEL IS
HELPING TO AMPLIFY AND STRENGTHEN THIS RIDGE. A SEEMINGLY PERMANENT
UPPER LEVEL RIDGE EXTENDS OUT OF RUSSIA AND INTO THE WESTERN BERING.
AT THE SURFACE...AN ELONGATED LOW AND ASSOCIATED OCCLUDED FRONT IN
THE NORTHERN GULF OF ALASKA ARE SPREADING RAIN ACROSS MUCH OF THE
NORTH GULF COAST...WITH SNOW AT HIGHER ELEVATIONS. A WEAKENING 954 MB
LOW NEAR THE WESTERN TIP OF THE ALEUTIANS IS STILL BRINGING STORM
FORCE WINDS TO THE WESTERN BERING SEA.

.MODEL DISCUSSION...
MODELS IS GOOD AGREEMENT THROUGH FRIDAY MORNING WITH REGARDS TO THE
SYSTEMS IN BOTH THE GULF AND THE ALEUTIANS. WHILE SOLUTIONS AGREE ON
THE SYNOPTIC SCALE SYSTEMS...THEY ARE HAVING A HARDER TIME PICKING UP
ON SMALLER SCALE FEATURES...WHICH SLOWLY ERODES FORECAST CONFIDENCE
THROUGH THE FORECAST PERIOD. FOR EXAMPLE...MODELS ARE HAVING A HARD
TIME PICKING UP ON A WEAK SHORTWAVE ROTATING INTO THE NORTH GULF ON
THE BACKSIDE OF THE CURRENT LOW ON FRIDAY AFTERNOON. STARK TIMING
DIFFERENCES ARISE DURING THE WEEKEND WITH THE NEXT SHORTWAVE THAT
TAKES AIM AT THE AKPEN...WITH THE ECMWF A GOOD 12 HOURS AHEAD OF THE
GFS.

.SHORT TERM FORECAST...
.SOUTHCENTRAL ALASKA...THE CURRENT LOW IN THE GULF WEAKENS THROUGHOUT
THE NIGHT...BUT REBUILDS TOMORROW NEAR ITS PRESENT LOCATION AS ITS
REMNANTS INTERACT WITH A NEW LOW TO THE SOUTH. THUS EXPECT A QUICK
SERIES OF WAVES TO MOVE OVER SOUTHCENTRAL ALASKA FOR THE REST OF THE
WORK WEEK. A CONTINUOUS SUPPLY OF MOIST ONSHORE FLOW WILL HELP
INTENSIFY RAIN ACROSS PRINCE WILLIAM SOUND AND THE UPSLOPE REGIONS OF
THE KENAI PENINSULA THROUGHOUT THE DAY TODAY. THE QUICK SUCCESSION OF
SHORTWAVES MEANS THAT MODERATE TO HEAVY PRECIPITATION CAN BE EXPECTED
TO PERSIST ALONG THE GULF COAST FOR THE NEXT FEW DAYS. THIS INFLUX OF
WARM AIR WILL ALSO RAISE FREEZING LEVELS AND HELP MAINTAIN THE
PRECIPITATION AS RAIN OVER COASTAL REGIONS OF THE GULF COAST FOR THE
COURSE OF THE EVENT. DUE TO THE COMBINED POSSIBILITY OF TWO TO THREE
INCHES OF NEW RAIN AND RAPID SNOW MELT...AN URBAN AND SMALL STREAM
FLOOD ADVISORY HAS BEEN ISSUED FOR THE EASTERN KENAI PENINSULA AND
PRINCE WILLIAM SOUND THROUGH FRIDAY MORNING. THE MAIN THREAT WILL BE
LOCALIZED PONDING OF WATER IN AREAS OF POOR DRAINAGE...SUCH AS SEWERS
THAT MAY BE CLOGGED BY THE CURRENT SNOW PACK. SOME OF THESE SHOWERS
MAY SNEAK OVER THE KENAI MOUNTAINS DURING THIS TIME FRAME AND AFFECT
THE ANCHORAGE BOWL...BUT FOR THE MOST PART THE AREA REMAINS
DOWNSLOPED FOR THIS EVENT. WINDS ALSO INCREASE THROUGH TURNAGAIN ARM
AND OTHER FAVORABLE MOUNTAIN GAPS TODAY THROUGH FRIDAY MORNING. A
BUILDING RIDGE OF HIGH PRESSURE OVER THE PANHANDLE WILL FORCE LOWS TO
TRACK OVER THE AKPEN AND BRING CLEARING SKIES FOR SOUTH CENTRAL FOR
THE WEEKEND.

.SOUTHWEST ALASKA...LIGHT SHOWERS WILL PERSIST ACROSS SOUTHWEST
ALASKA THROUGH THE WEEKEND AS DISTURBANCES TRACK ACROSS THE WESTERN
GULF AND INTO BRISTOL BAY. SOUTHEASTERLY FLOW WILL CONTINUE TO PUMP
GULF AIR NORTHWARD AND MAINTAIN MARCH-LIKE TEMPERATURES FOR AT LEAST
THE NEXT FEW DAYS.

.ALEUTIANS...CURRENT SYSTEM JUST WEST OF THE ALEUTIANS WILL GRADUALLY
WEAKEN OVER THE NEXT FEW DAYS AS IT MEANDERS AROUND THE WESTERN
ALEUTIANS. A SERIES OF RESIDUAL MID-LEVEL SHORTWAVES AND SURFACE LOWS
ROTATE INTO THE ALEUTIANS DURING THE NEXT FEW DAYS...BUT FORECAST
CONFIDENCE IS LOW PAST THE NEAR SHORT-TERM WITH MODELS POORLY
HANDLING THE EVOLUTION AND INTERACTION BETWEEN THESE SYSTEMS. THUS A
CHANCE OF RAIN AND SNOW WAS HELD IN THE FORECAST FOR THE ALEUTIANS
FOR THE DURATION OF THE FORECAST PERIOD.

.LONG TERM FORECAST...
THE UPPER LEVEL RIDGE OVER THE PANHANDLE WILL SLOWLY DISSIPATE EARLY
NEXT WEEK..ALLOWING A LOW OVER NORTHWESTERN CANADA AND A HIGH OVER
FAR EASTERN RUSSIA TO TAKE CONTROL OF THE UPPER LEVEL WIND PATTERN.
THUS EXPECT A RETURN TO MORE NORMAL TEMPERATURES AS WINDS SWITCH TO
THE NORTH ACROSS MOST OF THE STATE. THE OFFSHORE FLOW SHOULD ALSO
USHER IN A DRIER WEATHER PATTERN FOR THE MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...URBAN AND SMALL STREAM FLOOD ADVISORY...125 131 135.
MARINE...STORM 176. GALES 120 125 130 132 138 140 AND 175.
FIRE WEATHER...NONE.

KS FEB 10