Small Craft Advisory 329, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
120 PM ADT SAT APR 12 2008

.ANALYSIS AND UPPER LEVELS...IN THE UPPER LEVELS WE ARE UNDER THE
INFLUENCE OF A FAIRLY HIGH AMPLITUDE BUT PROGRESSIVE PATTERN. THERE
ARE RIDGES OVER WESTERN NORTH AMERICA AND ALONG 170W FROM THE NORTH
PACIFIC TO BERING SEA WITH TROUGHS FROM MAINLAND ALASKA SOUTHWARD
ACROSS THE GULF INTO THE PACIFIC AND ANOTHER FAR TO THE WEST ALONG
160E(NEAR THE KAMCHATKA PENINSULA). THE GULF TROUGH...WHICH IS
NEGATIVELY TILTED IS LIFTING UP THE WEST SIDE OF THE WESTERN N.A.
RIDGE...DRIVING A MATURE LOW JUST SOUTH OF THE GULF NORTHEASTWARD
TOWARD SOUTHEAST ALASKA. A TROUGH EXTENDS NORTHWARD ACROSS THE
EASTERN GULF AND TIGHT PRESSURE GRADIENT ACROSS THE NORTHERN TO
WESTERN GULF IS PRODUCING STRONG GAP WINDS IN THE USUAL PLACES.
MOISTURE IS ALSO BEING PUSHED WESTWARD INTO THE EASTERN COPPER
RIVER BASIN AND TOWARD EASTERN PRINCE WILLIAM SOUND...BUT WITH
TROUGH LIFTING EXPECT THE WESTWARD PROGRESSION TO COME TO A HALT
LATER TODAY. DRY AND CLEAR CONDITIONS DOMINATE WESTERN SOUTHCENTRAL
AND INTERIOR SOUTHWEST ALASKA...BUT TEMPERATURES ARE SLOW TO
REBOUND AFTER A COLD MORNING ACROSS THE REGION THIS MORNING. OUT
WEST THERE IS A DEEP LOW SOUTH OF KAMCHATKA TRACKING NORTHEASTWARD
TOWARD THE WESTERN ALEUTIANS. SATELLITE IMAGERY SHOWS A LOT OF
MOISTURE MOVING ACROSS THE BERING OVER THE TOP OF THE NORTH PACIFIC
RIDGE. THERE IS ALSO A LOT OF WARM AIR ADVECTION RESULTING IN
OVERRUNNING PRECIPITATION AND AND AREAS OF STRATUS AND FOG.

.MODEL DISCUSSION...MODELS HAVE A VERY GOOD HANDLE ON CURRENT SYSTEMS
AND CONTINUE TO BE IN EXCELLENT AGREEMENT THROUGH THE SHORT-TERM
PERIOD. THERE ARE SOME MINOR DIFFERENCES IN THE SPEED OF UPPER TROUGH
AS IT MOVES ACROSS MAINLAND ALASKA MONDAY NIGHT AND TUESDAY. THE
UKMET/ECMWF/GFS ENSEMBLE MEAN ARE ALL SLIGHTLY SLOWER THAN THE
OPERATIONAL GFS SO HAVE A PREFERENCE FOR THIS SLOWER SOLUTION. SINCE
THE TROUGH SPEED IS QUITE FAST ANYWAY...THIS WILL HAVE LITTLE IMPACT
ON THE RESULTING FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL...THE NORTHEAST PACIFIC LOW WILL TRACK NORTHWARD ACROSS
THE EASTERN GULF TONIGHT AND DISSIPATE SUNDAY...SO ONGOING GUSTY GAP
WINDS ALONG THE GULF COAST WILL GRADUALLY DIMINISH BEGINNING TONIGHT.

THE SNOW OVER THE EASTERN COPPER RIVER BASIN MAY MAKE IT TO THE
MOUNTAINS OF EASTERN PRINCE WILLIAM SOUND THIS AFTERNOON AND
EVENING...BUT WITH LOW LEVEL OFFSHORE FLOW EXPECT VALDEZ AND CORDOVA
TO REMAIN MAINLY DRY. SNOW WILL TAPER OFF SUNDAY AS THE SYSTEM EXITS
TO THE EAST. A SURFACE LOW WILL MOVE ACROSS THE BERING TONIGHT AND
SUNDAY AND THEN TRACK TO INTERIOR ALASKA SUNDAY NIGHT. WITH NEAR
ZONAL FLOW ALOFT THERE WILL NOT BE MUCH SYNOPTIC LIFT ASSOCIATED
WITH THIS AND MUCH OF MOISTURE WILL GET STUCK WEST AND NORTH OF THE
ALASKA RANGE...SO ONLY EXPECT A CHANCE OF SHOWERS ACROSS SOUTHCENTRAL
SUNDAY NIGHT INTO MONDAY. MONDAY NIGHT AND TUESDAY WILL BE A
DIFFERENT STORY AS A VERY SHARP UPPER TROUGH MOVES ACROSS THE REGION.

A SURFACE LOW WILL LIKELY FORM OVER THE NORTHERN GULF AS THE TROUGH
APPROACHES...BUT TROUGH WILL MOVE THROUGH VERY QUICKLY AND DRY COLD
AIR WILL MOVE IN...SO EXPECT CHANCE OF SNOW TO BE BRIEF WITH ONLY
MINOR AMOUNTS. STRONG COLD ADVECTION BEHIND THE TROUGH WILL PRODUCE
WINTER LIKE WINDS ACROSS MUCH OF THE REGION ON TUESDAY.

SOUTHWEST ALASKA...WARM FRONT OVER THE BERING WILL MOVE TO SOUTHWEST
ALASKA TONIGHT...SPREADING SNOW ONSHORE. AS THE BERING LOW TRACKS
INLAND SUNDAY AFTERNOON MOISTURE WILL SPREAD INLAND. THERE WILL
INITIALLY BE SOME AREAS OF BLOWING SNOW...BUT FLOW WILL QUICKLY
SHIFTING TO SOUTHWEST AS THE FRONT MOVES ONSHORE HELPING TEMPERATURES
TO RISE TO AROUND FREEZING. WARMING WILL CONTINUE SUNDAY AND CHANGE
PRECIPITATION ALONG THE COAST TO MAINLY RAIN. PRECIPITATION WILL
DIMINISH SUNDAY NIGHT...BUT MORE IS LIKELY MONDAY AS A SHARP UPPER
TROUGH APPROACHES. STRONG COLD AND DRY ADVECTION WILL BEGIN MONDAY
NIGHT AND CONTINUE THROUGH TUESDAY MAINTAINING BELOW NORMAL
TEMPERATURES ACROSS THE REGION.

BERING SEA/ALEUTIANS/ALASKA PENINSULA...WARM AND MOIST AIR WILL
CONTINUE TO SPREAD ACROSS THE BERING REGION THROUGH
SUNDAY...RESULTING IN AREAS OF RAIN AND FOG. THE UPPER TROUGH BACK
OVER THE KAMCHATKA PENINSULA WILL THEN MARCH EASTWARD ACROSS THE
BERING SUNDAY NIGHT THROUGH MONDAY NIGHT WITH A RIDGE BUILDING IN
BEHIND. A BRIEF PERIOD OF GUSTY WINDS AND COLD ADVECTION SNOW SHOWERS
WILL ACCOMPANY THE TROUGH.

.LONG TERM FORECAST...MODELS ARE ALSO SHOWING VERY GOOD AGREEMENT
THROUGH THE BEGINNING OF THE EXTENDED FORECAST PERIOD WITH
UNCERTAINTY INCREASING BY DAY 7. THE PATTERN LOOKS TO REMAIN
PROGRESSIVE INITIALLY WITH SHARP UPPER TROUGH EXITING SOUTHCENTRAL
WEDNESDAY AND A SHORT-WAVE DROPPING SOUTHEASTWARD ACROSS THE STATE.
WITH DRY AIR IN PLACE AND THE TYPICALLY DRY NATURE OF SYSTEMS
TRACKING FROM THE NORTHWEST...EXPECT MAIN IMPACT TO BE CLOUDS WITH
PRECIPITATION MOST LIKELY IN UPSLOPE LOCATIONS ON THE NORTH AND WEST
SIDE OF THE ALASKA RANGE. THERE WILL BE YET ANOTHER SURGE OF COLDER
AIR WITH THIS...SO TEMPERATURES WILL REMAIN BELOW NORMAL. THE RIDGE
IN PLACE OVER THE BERING WEDNESDAY WILL GRADUALLY MOVE EASTWARD
THROUGH THE REST OF NEXT WEEK. EXPECT A SYSTEM TO MOVE INTO THE
WESTERN BERING BY THE END OF THE WEEK...BUT NOT MUCH CONFIDENCE IN
DETAILS THAT FAR OUT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...121 129 130 150 155 160 165 170 171 172 175
                        176 179.
         HEAVY FREEZING SPRAY...121 129 130.
FIRE WEATHER...NONE.

SEB APR 08