Gale Warning 168, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
125 PM AKST MON FEB 11 2013

.ANALYSIS AND UPPER LEVELS...A HIGH AMPLITUDE TROUGH IS CENTERED
OVER THE BERING SEA WITH A NEARLY STATIONARY CLOSED LOW EMBEDDED
OVER THE NORTHERN BERING. A SERIES OF WEAK MESO-SCALE WAVES ARE
TRANSITING THE EASTERN SIDE OF THE TROUGH FROM THE EASTERN
ALEUTIANS NORTHEASTWARD ACROSS MAINLAND ALASKA. THE MOST SIGNIFICANT
OF THESE WAVES IS HEADING INLAND ACROSS SOUTHCENTRAL ALASKA THIS
MORNING PRODUCING WIDESPREAD AREAS OF SNOW. THE WEAKER AND SMALLER
WAVES UPSTREAM ARE PRODUCING BRIEF PERIODS OF SNOW AS THEY CROSS
THE EASTERN BERING AND SOUTHWEST ALASKA. THERE IS A CONVECTIVE
CHARACTER TO SOME OF THIS SNOW AS SEEN IN RADAR AND SATELLITE
IMAGERY AND INDICATED BY STEEP LAPSE RATES IN THE LOWER TO MID
LEVELS ON AREA SOUNDINGS.

THE SUBTROPICAL JET IS CENTERED OVER THE NORTH PACIFIC BETWEEN
30N AND 40N LATITUDE. AN AMPLIFYING WAVE CROSSING THE NORTHWEST
PACIFIC IS INITIATING SURFACE LOW DEVELOPMENT. THIS LOW WILL
BECOME THE MAJOR FORECAST PROBLEM FOR MID WEEK.

.MODEL DISCUSSION...MODELS ARE STRUGGLING WITH THE TIMING AND
PLACEMENT OF THE MANY WEAK WAVES MOVING THROUGH THE TROUGH. WILL
MAKE USE OF RADAR AND SATELLITE IMAGERY TO PROVIDE DETAILS FOR THE
FIRST PERIOD OF THE FORECAST THEN EMPLOY A MORE BROAD-BRUSH FORECAST
FOR TIMING OF PRECIP AFTER THIS. A NOTABLY STRONGER WAVE SOUTH OF
THE ALASKA PENINSULA ALONG WITH A WEAK SURFACE REFLECTION ARE KEY
TO A MORE SIGNIFICANT PRECIP EVENT OVER SOUTHCENTRAL IN THE
TUESDAY/WEDNESDAY TIME FRAME. GFS IS THE OUTLIER IN TRACKING THE
SURFACE LOW FURTHER SOUTH AND EAST...SO WILL GO STRONGLY WITH THE
REST OF THE MODELS WHICH TRACK THE LOW TO WESTERN PRINCE WILLIAM
SOUND. MORE SIGNIFICANT DIFFERENCES DEVELOP WITH EVOLUTION OF
DEVELOPING SYSTEM OVER THE NORTH PACIFIC...ESPECIALLY WITH
SECONDARY WAVE WHICH DEVELOPS ON THE EAST SIDE OF THE LOW. BASED
ON THE LARGE DEGREE OF UNCERTAINTY WITH THIS SYSTEM WILL MAKE
LITTLE CHANGE TO EXISTING FORECAST UNTIL MODELS BETTER LOCK ON
TO A SOLUTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...AS ONE UPPER WAVE EXITS TO THE NORTH TONIGHT
ANOTHER ONE CURRENTLY NEAR KODIAK ISLAND WILL MOVE IN. EXPECT LIGHT
ACCUMULATION AS THIS WEAK FEATURE MOVES QUICKLY THROUGH TONIGHT INTO
TUESDAY MORNING. A STRONGER UPPER WAVE WON'T BE FAR BEHIND - MOVING
THROUGH TUESDAY NIGHT THROUGH WEDNESDAY MORNING. MOST OF THE ENERGY
(AND STRONGEST VERTICAL MOTION) WILL CROSS THE NORTHERN GULF BRINGING
THE HIGHEST PRECIP AMOUNTS TO PRINCE WILLIAM SOUND. A WEAK SURFACE
LOW WILL TRACK TO WESTERN PRINCE WILLIAM SOUND TUE NIGHT. IN MANY
CASES THIS IS A GOOD SET-UP TO ADVECT MOISTURE OVER THE KENAI
MOUNTAINS TO ANCHORAGE. HOWEVER...THE LOW LOOKS TOO WEAK WITH VERY
LITTLE IN THE WAY OF ADVECTION OVER THE MOUNTAINS. IN ADDITION
TEMPERATURE ADVECTION BEHIND THIS SHORT-WAVE AND LOW IS NEUTRAL.
ALL OF THIS POINTS TOWARD ANOTHER LIGHT SNOW EVENT FROM THE WESTERN
KENAI TO ANCHORAGE AND THE MAT-SU. THERE IS MUCH MORE UNCERTAINTY
WITH LARGER STORM SYSTEM MOVING INTO THE AREA WEDNESDAY NIGHT AND
THURSDAY. AT THIS POINT IN TIME IT IS LOOKING LIKE A CLASSIC STRONG
WARM SECTOR SOUTHEASTERLY FLOW WITH DOWNSLOPE DRYING IN THE LEE OF
THE KENAI AND CHUGACH MOUNTAINS.

SOUTHWEST ALASKA...WEAK AND SMALL SCALE FEATURES WILL CONTINUE TO
TRACK OVERHEAD OF SOUTHWEST ALASKA OVER THE NEW COUPLE DAYS. EXPECT
GENERALLY BRIEF PERIODS OF SNOW AS THESE MOVE THROUGH...WITH VERY
LOCALIZED HEAVY SNOW THANKS TO AN UNSTABLE AIR MASS. THERE WILL BE
A SLIGHT COOLING TREND IN TEMPERATURES AS THE TROUGH CENTERED OVER
THE CENTRAL BERING ROTATES INTO SOUTHWEST ALASKA. A DEVELOPING
PACIFIC SYSTEM WILL PUSH A FRONT NORTHWARD ACROSS SOUTHWEST ALASKA
LATE WEDNESDAY OR WEDNESDAY NIGHT. THERE IS QUITE A BIT OF
UNCERTAINTY WITH THE DETAILS OF THIS SYSTEM...BUT BASED ON THE
CURRENT SUITE OF MODEL SOLUTIONS LOOKS LIKE THE HIGHEST IMPACT
WEATHER MAY BE BLOWING SNOW ISSUES ALONG THE KUSKOKWIM DELTA.

BERING SEA/ALEUTIANS...A SHOWERY REGIME WILL PERSIST OVER THE BERING
SEA AND ALEUTIANS AS UPPER LEVEL SHORT-WAVE TROUGH SWINGS EASTWARD
TOWARD SOUTHWEST ALASKA AND ANOTHER DROPS DOWN OVER THE CENTRAL
BERING. THIS WILL LEAD TO PERSISTENT COLD AIR ADVECTION ACROSS
MUCH OF THE REGION THROUGH TUESDAY NIGHT. THE DEVELOPING NORTH
PACIFIC LOW WILL PUSH A FRONT NORTHWARD ACROSS INTO THE EASTERN
BERING ON WEDNESDAY. CONDITIONS WILL BE FAVORABLE FOR BLOWING SNOW
OR EVEN A BLIZZARD RIGHT OUT AHEAD OF THIS FRONT. AT THIS TIME
THERE IS TOO MUCH UNCERTAINTY IN WHERE THE FRONT WILL ULTIMATELY
SET UP TO DETERMINE WHERE THE HIGHEST THREAT AREA WILL BE.

.LONG TERM FORECAST...THE UPPER TROUGH WILL SHIFT FROM THE BERING
SEA TO MAINLAND ALASKA AS SYSTEM MOVES OUT OF THE PACIFIC THE
MIDDLE OF THIS WEEK. MODELS THEN INDICATE A BLOCKING RIDGE SETTING
UP SHOP FROM THE BERING TO SIBERIA AND HOLDING THROUGH THE WEEKEND.
THE PRIMARY STORM TRACK WILL BE UNDERNEATH THIS RIDGE SOUTH OF THE
ALEUTIAN CHAIN AND THEN NORTHEASTWARD INTO THE GULF...MAINTAINING
FAIRLY ACTIVE WEATHER ALONG THE SOUTHERN TIER OF THE FORECAST AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...172.
FIRE WEATHER...NONE.

SEB FEB 13