Small Craft Advisory 903, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1250 PM AKST FRI NOV 15 2013

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVELS HAVE BEGUN A TRANSITION
TO A NEW PATTERN. A LARGE UPPER LEVEL CLOSED LOW OVER THE TROPICAL
PACIFIC IS TRACKING NORTHWARD INTO THE HEART OF THE RIDGE WHICH HAS
BEEN SITTING OVER THE NORTH-CENTRAL PACIFIC THE PAST WEEK OR MORE.
THIS IS CAUSING THE RIDGE TO RETREAT EASTWARD AND CONNECT UP WITH
ANOTHER RIDGE OVER THE EAST PACIFIC. MEANWHILE...A RIDGE IS
BEGINNING TO BUILD IN THE VICINITY OF THE KAMCHATKA PENINSULA AND
EASTERN RUSSIA.

IN BETWEEN THESE FEATURES THE LAST VESTIGES OF THE OLD PATTERN ARE
IN PLACE WITH WARM MOIST AIR FLOWING NORTHWARD TO THE WESTERN
ALEUTIANS AND THEN EASTWARD ACROSS THE SOUTHERN BERING AND INTO
BRISTOL BAY. A WEAK SURFACE LOW OFF THE KUSKOKWIM DELTA COAST IS
DISSIPATING AS IT GETS PUSHED QUICKLY SOUTHWARD BY A SHORT-WAVE
OVER THE NORTHERN BERING SEA. LIGHT PRECIPITATION HAS OVERSPREAD
MUCH OF SOUTHWEST ALASKA...MOSTLY SNOW WITH THE EXCEPTION OF THE
IMMEDIATE COASTLINE WHERE RAIN IS FALLING. PRECIPITATION RETURNS
IN RADAR IMAGERY ARE UNIMPRESSIVE AND SHOWING SIGNS OF BEGINNING
TO BREAK UP AND BECOME LESS ORGANIZED. A SHORT-WAVE TROUGH AND
VERY WEAK SURFACE LOW ON THE WEST SIDE OF WHAT REMAINS OF THE
NORTH PACIFIC RIDGE ARE BRINGING ANOTHER BATCH OF RAIN TO THE
WESTERN ALEUTIANS.

DOWNSTREAM OVER SOUTHCENTRAL ALASKA CONDITIONS ARE MOSTLY DRY BUT
CLOUDY AS MID TO UPPER LEVEL MOISTURE STREAMS IN FROM THE WEST.
MOST OF THE PRECIP WITH THE SOUTHWEST ALASKA SYSTEM IS HANGING
UP IN THE MOUNTAINS BUT RADAR IMAGERY SHOWS SOME VERY LIGHT PRECIP
MAY BE AFFECTING PORTIONS OF THE WESTERN GULF AND THE SOUTHERN
TIP OF THE KENAI PENINSULA.

.MODEL DISCUSSION...MODELS ALL HAVE A SIMILAR DEPICTION OF THE
PATTERN CHANGE. THE AREA WHERE SOLUTIONS SIGNIFICANTLY DIVERGE
IS WITH TRACK OF LOW SOUTH OF THE WESTERN ALEUTIANS. THE LOW
BECOMES VERTICALLY STACKED AND CAUGHT BETWEEN THE NEW RIDGE TO
THE NORTHWEST AND THE RECEDING NORTH PACIFIC RIDGE. WILL CONTINUE
TO GO WITH A MIDDLE GROUND SOLUTION.

THERE ARE ALSO DIFFERENCES WITH TRACK OF AN UPPER LEVEL
SHORT-WAVE/WEAK SURFACE LOW WHICH DROPS OUT OF RUSSIA AND TRACKS
SOUTHWARD ALONG THE WESTERN ALASKA COAST EARLY NEXT WEEK. IMPACTS
WILL BE MINOR AND ANY PRECIP THAT DOES FALL WILL BE BRIEF IN
DURATION BECAUSE OF THE RAPID MOVEMENT OF THIS SYSTEM.

.SHORT TERM FORECAST...PRECIP WILL RAPIDLY END THIS AFTERNOON AND
EVENING AS REMNANTS OF SOUTHWEST ALASKA LOW DROP QUICKLY SOUTHWARD
INTO THE PACIFIC. THE UPPER LEVEL SHORT-WAVE OVER THE NORTHERN
BERING WILL TRACK SOUTHEASTWARD TO SOUTHCENTRAL...AMPLIFYING AS
IT MOVES THROUGH LATE TONIGHT AND SATURDAY MORNING THANKS TO RISING
HEIGHTS UPSTREAM WITH THE BUILDING RIDGE. ARCTIC AIR WILL ADVECT
SOUTHWARD WITH AND BEHIND THE SHORT-WAVE CONTINUING SOUTHWARD ACROSS
THE GULF OF ALASKA AND INTO THE PACIFIC. THIS WILL CLEAR MOST OF
THE CLOUDS OUT OF THE SOUTHERN MAINLAND AND LEAD TO PLUNGING
TEMPERATURES AS WE HEAD THROUGH THE WEEKEND. THE PASSAGE OF THE
SHORT-WAVE COMBINED WITH THE LOW LEVEL COLD ADVECTION WILL LEAD
TO THE TYPICAL STRONG GAP WINDS ALONG THE GULF COAST. THE SURFACE
PRESSURE GRADIENT IS THE WEAKEST COMPONENT OF THIS EVENT (WITH A
LACK OF A LOW CENTER OVER THE GULF). THUS...DOES NOT LOOK LIKE
ENOUGH FORCING TO PRODUCE WARNING LEVEL WINDS ANYWHERE...ALTHOUGH
PEAK WIND GUSTS IN THE VALDEZ AREA WILL NOT BE TOO FAR FROM THOSE
LEVELS.

ANOTHER UPPER LEVEL SHORT-WAVE WILL DROP SOUTHWARD ACROSS MAINLAND
ALASKA SATURDAY NIGHT AND SUNDAY FOLLOWED BY AN UPPER LEVEL LOW
ON MONDAY. THIS WILL PROVIDE A NEARLY STEADY STREAM OF COLD AIR
ADVECTION. THEREFORE...EXPECT A PROLONGED PERIOD OF GUSTY GAP WINDS
ALONG THE NORTH GULF COAST AND PRINCE WILLIAM SOUND. MEANWHILE
TEMPERATURES WILL CONTINUE THE DOWNWARD TREND AS WE HEAD INTO
EARLY NEXT WEEK.

THE VERTICALLY STACKED LOW WHICH TAKES SHAPE JUST SOUTH OF THE
WESTERN ALEUTIANS TONIGHT AND SATURDAY WILL REMAIN IN THE REGION
THROUGH SUNDAY NIGHT AND THEN FINALLY EXIT TO THE SOUTH MONDAY AND
TUESDAY AS THE RIDGE OVER EASTERN RUSSIA BUILDS INTO THE BERING SEA.
THIS WILL BRING NOTICEABLY COLDER AIR SOUTHWARD ACROSS THE ALEUTIAN
CHAIN EARLY NEXT WEEK AND LEAD TO BENIGN WEATHER ACROSS THE REGION.

.LONG TERM FORECAST...THERE IS HIGH CONFIDENCE IN A DRY AND COLD
FORECAST FOR NEXT WEEK ACROSS MOST OF THE FORECAST AREA. THE
EXCEPTION TO THE DRY FORECAST WILL BE A WEAK DISTURBANCE MOVING
THROUGH SOUTHWEST ALASKA MONDAY NIGHT AND TUESDAY WHICH MAY BRING
A QUICK SHOT OF LIGHT SNOW. COLD ADVECTION ACROSS THE OPEN WATERS
OF THE BERING SEA AND GULF OF ALASKA WILL ALSO INITIATE SNOW SHOWER
ACTIVITY. WITH ALL OF THE COLD AIR POURING OVER THE COASTAL RANGE
ALONG THE NORTH GULF COAST A LOW WILL EVENTUALLY FORM. MODELS
SOLUTIONS ARE GROUPED OVER THE EASTERN GULF WITH THE LOW
POSITION...SO EXPECT SOUTHCENTRAL WILL REMAIN DRY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...119 120 121 127 128 130 131 132 178.
FIRE WEATHER...NONE.

SEB NOV 13