Small Craft Advisory 45, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM AKST SAT JAN 10 2009

.ANALYSIS AND UPPER LEVELS...A HIGH AMPLITUDE PATTERN IS IN PLACE
WITH A NEUTRALLY TILTED TROUGH CENTERED OVER THE BERING/NORTH
CENTRAL PACIFIC AND A RIDGE OVER THE EAST PACIFIC EXTENDING
NORTHWARD TO THE EASTERN GULF. THERE ARE SEVERAL SYSTEMS OF
INTEREST EMBEDDED WITHIN THE LONG-WAVE TROUGH. A MATURE LOW SOUTH
OF THE EASTERN ALEUTIANS/AKPENN IS SLOWLY LIFTING NORTHEASTWARD
TOWARD THE AKPENN. AN OCCLUDED FRONT EXTENDS EASTWARD TO THE
SOUTHERN GULF WHERE SOME ROTATION IS EVIDENT IN SATELLITE IMAGERY.
EXPECT A SURFACE LOW TO DEVELOP OVER THE CENTRAL GULF THIS AFTERNOON.
MOISTURE IS SPREADING NORTHWARD TOWARD SOUTHCENTRAL WITH SNOW
FALLING FROM KODIAK ISLAND TO THE SOUTHERN KENAI PENINSULA. ARCTIC
AIR REMAINS ENTRENCHED ACROSS THE REST OF THE SOUTHERN MAINLAND
THIS MORNING.

A DEVELOPING LOW NEAR THE BASE OF THE TROUGH AT 35N 167W IS THE
PRECURSOR TO A MAJOR STORM EXPECTED TO AFFECT SOUTHCENTRAL LATER
THIS WEEKEND. MEANWHILE...A MAJOR LOW IS MOVING OUT OF ASIA INTO
THE NORTHWEST PACIFIC...WHICH WILL HELP MAINTAIN THE THE LONG-WAVE
TROUGH OUT WEST.

.MODEL DISCUSSION...MODELS CONTINUE TO STRUGGLE IN THE
SHORT-TERM...ALTHOUGH UNLIKE THE PAST COUPLE DAYS SOLUTIONS ARE
NOW GROUPED TOGETHER. ALL MODELS INITIALIZED WELL...BUT DIFFERENCES
SHOW UP IN THE 18Z FORECAST WITH DEVELOPMENTS OF WEAK LOWS ALONG THE
OCCLUDED FRONT. A RECENT QUICKSCAT IMAGE FROM THIS REGION DOES NOT
INDICATE THE PRESENCE OF ANY LOWS ALONG THIS FRONT...BUT WITH A
SHARP WIND SHIFT THERE LIKELY IS A SURFACE WAVE IN THERE SOMEWHERE.
THE KEY IS THE DEVELOPMENT OF A LOW OVER CENTRAL GULF THIS AFTERNOON
AND GFS/UKMET/ECMWF ARE ALL IN DECENT AGREEMENT WITH THE LOCATION
AND TRACK OF THIS LOW SO WILL GO WITH AN AVERAGE POSITION. THE
UKMET/ECMWF SOLUTIONS ARE PREFERRED WITH HANDLING OF THE MAIN LOW
SOUTH OF THE EASTERN ALEUTIANS. THE GFS IS AN OUTLIER IN DEVELOPING
AND MAINTAINING TWO DISTINCT LOWS WHILE THE NAM IS JUST A BIT OFF
FROM THE PREFERRED SOLUTION. THE EAST PACIFIC RIDGE WILL AMPLIFY
FURTHER AS THE UPPER TROUGH PUSHES UP AGAINST IT...HELPING TO
STRENGTHEN THE UPPER JET AND QUICKLY DRIVE THE SURFACE LOW NORTHWARD.
ALL MODELS INDICATE A TRIPLE POINT DEVELOPING AND BECOMING THE
DOMINANT LOW...BUT TIMING AND TRACK OF THIS LOW IS IN DISAGREEMENT.
THE GFS LOOKS TOO LOW CONSIDERING THE STRENGTH OF THE UPPER JET. NAM
IS MUCH FARTHER EAST THAN THE OTHER SOLUTIONS. THE UKMET/ECMWF ARE A
NICE MIDDLE GROUND OF FASTER SPEED AND A TRACK OVER THE WESTERN GULF.
BEYOND THIS SYSTEM MODELS HAVE BEEN MORE CONSISTENT AND PLAN TO STICK
WITH CURRENT FORECAST.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE SURFACE LOW EXPECTED TO DEVELOP OVER THE
CENTRAL GULF THIS AFTERNOON ALONG WITH ASSOCIATED UPPER WAVE WILL
TRACK TO THE NORTHEAST GULF TONIGHT AND THEN QUICKLY WEAKEN AS THEY
MOVE OVER TOP OF THE RIDGE SUNDAY. WITH THIS TRACK EXPECT SNOW WILL
BE LIMITED TO THE IMMEDIATE GULF COAST...MAINLY OVER SOUTHERN KENAI
PENINSULA AND WESTERN PRINCE WILLIAM SOUND. THE REMNANT MOISTURE WILL
PUSH INLAND SUNDAY AS THE UPPER RIDGE AMPLIFIES...MAINLY BRINGING
LOWERING CLOUDS TO THE REGION. LIGHT OVERRUNNING OUT AHEAD OF THE
NEXT MAJOR SYSTEM WILL BEGIN LATE SUNDAY AFTERNOON OR EVENING. ON
MONDAY STRONG LOW WILL TRACK INTO THE GULF...DEEP MOISTURE AND STRONG
VERTICAL MOTION WILL MOVE OVER SOUTHCENTRAL...BRINING WIDESPREAD SNOW
TO THE REGION. UPSLOPE AREAS SUCH AS THE WESTERN SUSITNA MAY NEED A
SNOW ADVISORY...BUT SINCE DETAILS OF THE TRACK OF THE SURFACE LOW ARE
STILL IN QUESTION...WILL HOLD OFF ON THIS FOR NOW. WITH A LOW TRACK
TO NEAR CORDOVA...BULK OF WARM AIR WILL BE PUSHED OFF TO THE EAST OF
THE REGION...SO PRECIP WILL REMAIN SNOW MOST EVERYWHERE WITH THE
EXCEPTION OF PERHAPS SOUTHEAST PRINCE WILLIAM SOUND.  THIS SYSTEM
WILL EXIT QUICKLY MONDAY NIGHT AS UPPER TROUGH PUSHES THROUGH AND
EXPECT RAPID END TO PRECIP. TEMPERATURES DURING THE NEXT FEW DAYS
WILL STEADILY HEAD UPWARD AS CLOUDS AND PRECIPITATION MOVE INTO THE
REGION.

SOUTHWEST ALASKA...WINDS ARE INCREASING OVER SOUTHWEST ALASKA AS THE
OCCLUDED FRONT DRIFTS NORTHWARD TOWARD THE ALASKA PENINSULA. A WIND
CHILL ADVISORY WAS SET TO BEGIN THIS EVENING ACROSS THE KUSKOKWIM
DELTA...BUT CONDITIONS ARE ALREADY BEING MET...SO WENT AHEAD AND
RE-ISSUED IT TO START IMMEDIATELY. AS THE LOW SOUTH OF AKPENN AND
ASSOCIATED UPPER SHORT-WAVE TRACKS TOWARD BRISTOL BAY SUNDAY AND
SUNDAY NIGHT SNOW WILL SPREAD NORTHWARD ACROSS SOUTHWEST
ALASKA...HELPING TO MODERATE TEMPERATURES ALONG THE WAY. THE UPPER
TROUGH WILL EXIT THE REGION MONDAY WITH DRYING CONDITIONS BEHIND IT.

BERING SEA/ALEUTIANS...SNOW WILL PERSIST IN THE VICINITY OF THE
EASTERN ALEUTIANS AND SOUTHERN ALASKA PENINSULA THROUGH SUNDAY AND
THEN TAPER TO SCATTERED SNOW SHOWERS BY MONDAY AS THE SURFACE LOW
AND UPPER TROUGH EXIT TO SOUTHWEST ALASKA. THE NEXT MAJOR LOW
CURRENTLY OVER THE FAR NORTHWEST PACIFIC WILL TRACK SOUTH OF THE
ALEUTIANS SUNDAY AND MONDAY...FAR ENOUGH SOUTH THAT IMPACT WILL BE
LIMITED TO STRONGER WINDS ALONG THE ALEUTIANS.

.LONG TERM FORECAST...MODELS STILL INCONSISTENT IN EXACTLY HOW
AMPLIFIED EAST PACIFIC RIDGE WILL BECOME AND WHERE JET WILL SET
UP...HELPING TO DIVIDE COOL AIR FROM REALLY WARM AIR. BOTTOM LINE
THOUGH...LOOK FOR WARMER AND WETTER CONDITIONS FOR MAINLAND ALASKA
BEGINNING BY THE MIDDLE OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 130 132 138 140 172 175 176.
         HEAVY FREEZING SPRAY WARNING...130 140 141 165 179 185.
FIRE WEATHER...NONE.

SEB JAN 09