Small Craft Advisory 291, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
521 AM AKDT TUE APR 8 2014

.ANALYSIS AND UPPER LEVELS...
THE SOUTHCENTRAL ALASKA AREA HAS AN UPPER LEVEL TROUGH DROPPING
DOWN THROUGH THE ALASKA RANGE EXTENDING INTO KODIAK ISLAND REGION.
THE COLD AIR ADVECTION IS STARTING TO FILTER INTO THE SUSITNA
VALLEY EXTENDING SOUTH ALONG THE WEST SIDE OF THE COOK INLET WITH
SURFACE DEWPOINTS IN THE TEENS AND WINDS OUT OF THE WEST/NORTHWEST
DIRECTION. THE PRECIPITATION IS PREDOMINATELY ALL SNOW SHOWERS IN
THE SUSITNA/MATANUSKA VALLEY AND THE WESTERN KENAI AREA. THERE IS
AN MERIDIONAL 110 KNOT NORTHWEST JET STREAK OVER THE KUSKOKWIM
BAY EXTENDING JUST SOUTH OF KODIAK ISLAND. AN AMPLIFIED UPPER
LEVEL RIDGE EXTENDING THROUGH THE EASTERN ALEUTIANS NORTHWARD JUST
WEST OF SAINT LAWRENCE ISLAND. THE COMBINATION OF THE UPPER LEVEL
TROUGH AND AMPLIFIED RIDGE IS STRENGTHENING THE PRESSURE GRADIENT
AND PRODUCING GUSTY NORTHWESTERLY WINDS THROUGH THE ALASKA
PENINSULA NORTHWARD ALONG THE ALASKA RANGE. THE SATELLITE IMAGERY
HAS CLEAR SKIES FOR THE SOUTHWEST ALASKA AND THE EASTERN BERING
SEA. THE CENTRAL/WESTERN BERING SEA HAS A LARGE SWATH OF MOISTURE
ASSOCIATED WITH THE SURFACE FRONTAL BOUNDARY.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD AGREEMENT WITH THE LOW PRESSURE OVER PRINCE
WILLIAM SOUND THIS MORNING. THIS LOW PRESSURE WILL GET PUSHED OUT
OF THE PRINCE WILLIAM SOUND DUE TO AN UPPER LEVEL TROUGH PUSHING
DOWN INTO THE REGION. THE LOW PRESSURE WILL DISSIPATE BY WEDNESDAY
WITH A TROUGH IN THE NORTHERN GULF REPLACING THE LOW PRESSURE. THE
MODELS HANDLED WELL THE WARM FRONTAL BOUNDARY PUSHING THROUGH THE
BERING SEA AND CENTRAL/EASTERN ALEUTIANS. THE LOW PRESSURE
ASSOCIATED WITH THIS WARM FRONT THE ECMWF/GFS/NAM MODELS HANDLED
THE TRACKING AND STRENGTH OF THE LOW PRETTY WELL. IT TRACKS
ACROSS THE WESTERN ALEUTAINS NEAR ADAK BY WEDNESDAY MORNING. THE
ECMWF WAS THE PREFERRED MODEL OF CHOICE DUE TO ITS CONSISTENCY
OVER THE LAST FEW DAYS. THE FORECAST CONFIDENCE REMAINS HIGH
THROUGH THE SHORT TERM.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
THE FIRST DYNAMIC FEATURE EFFECTING THE AREA IS AN UPPER LEVEL
TROUGH WILL CONTINUE TO DROP DOWN IN THE SOUTHCENTRAL AREA THIS
MORNING. THIS WILL BRING SNOW SHOWERS THROUGH THE
SUSITNA/MATANUSKA VALLEY EXTENDING SOUTHWARD INTO THE ANCHORAGE
BOWL THIS MORNING CONTINUING INTO THE EVENING. LOOK FOR SNOWFALL
AMOUNTS RANGING FROM 1 TO 2 INCHES WITH HEAVIEST SNOWFALL AMOUNTS
IN THE HIGHER ELEVATIONS. THE SECOND FEATURE IS THE WEAK SURFACE
LOW PRESSURE TRACKING THROUGH THE PRINCE WILLIAM SOUND. THIS LOW
WILL WEAKEN INTO A TROUGH IN THE NORTHERN GULF BY WEDNESDAY
AFTERNOON. THIS FEATURE WILL BRING SNOW SHOWERS TO THE EASTERN
KENAI PENINSULA FROM MOOSE PASS EXTENDING NORTHWARD THROUGH THE
WRANGELL MOUNTAINS WITH SNOWFALL AMOUNTS RANGING FROM 1 TO 2
INCHES FOR TODAY GOING INTO THE EVENING. THE WINDS AT WHITTIER
WILL BE GUSTY THROUGH WEDNESDAY DUE TO THE COMBINATION OF THE
TROUGH APPROACHING AND THE SURFACE LOW TRACKING INTO THE AREA.

SOUTHWEST ALASKA...
THE UPPER LEVEL TROUGH THAT WILL MOVE THROUGH THE SOUTHCENTRAL
TODAY IS WORKING WITH THE SHARP RIDGE OVER THE EASTERN BERING TO
HELP TO KEEP THE GRADIENT PINCHED OVER THE SOUTHWEST. THIS HAS
KEPT MODERATE WINDS AT MANY SITES DURING THE OVERNIGHT HOURS. THE
RIDGE WILL SLIDE VERY SLOWLY EAST TOWARDS THE COAST TODAY. THIS
WILL SERVE TO RELAX THE GRADIENT SLIGHTLY AND REINFORCE THE DRY
NORTHERLY FLOW ACROSS THE AREA. THE RIDGE WILL REMAIN NEARLY
STATIONARY THROUGH THE REST OF THE WEEK AND KEEP ANY FRONTS OVER
THE BERING FROM BEING ABLE TO AFFECT THE MAINLAND. NOT UNTIL THIS
FEATURE BREAKS DOWN CLOSER TO THE WEEKEND WILL WE INTRODUCE ANY
CHANCE FOR PRECIPITATION.

BERING SEA/ALEUTIANS...
A BROAD FRONT IS BEING STRETCHED OUT ACROSS THE CENTRAL BERING
THIS MORNING. AHEAD OF IT ARE LOW-END SOUTHEASTERLY GALES WHILE ON
THE BACKSIDE ARE SOME SMALL-CRAFT SOUTHWEST WINDS. PRECIPITATION
IS FALLING AS A MIX ACROSS THE ALEUTIANS WITH SHEMYA HANGING IN
THE MID 30'S WHILE COLD BAY REMAINS IN THE MID 20'S. THIS FRONT
WILL MAKE LITTLE EASTWARD PROGRESS AS THE PREVIOUSLY MENTIONED
SHORTWAVE RIDGE STARTS TO ASSERT ITS INFLUENCE. IN FACT...THE
PRIBILOFS WILL REMAIN RIGHT ON THE EDGE OF THE PRECIPITATION
SHIELD AND WILL LIKELY ONLY SEE SOME OCCASIONAL SNOW SHOWERS. THE
PARENT UPPER LEVEL LOW WELL SOUTHWEST OF SHEMYA WILL CONTROL THE
WEATHER THROUGH THE WEEK. AS TODAY'S FRONT WEAKENS AND FALLS
APART, IT PUSHES SEVERAL MORE VERY SIMILAR FRONTS ACROSS MANY OF
THE SAME AREAS WEDNESDAY AND THURSDAY. HOWEVER, IT WON'T BE UNTIL
EARLY FRIDAY WHEN A TRIPLE POINT LOW TRIES TO FORM NEAR COLD BAY
THAT THE RIDGE WILL FINALLY GIVE WAY AND ALLOW PRECIPITATION
CHANCES TO SPREAD TOWARDS THE MAINLAND.

&&

.LONG TERM FORECAST...
MODELS AGREE THAT THE WEEKEND WILL START WITH RIDGING HOLDING
STRONG BASICALLY FROM THE ALEUTIAN RANGE EASTWARD. A
BROAD...NEGATIVELY TILTED TROUGH OVER THE BERING WILL FEATURE AN
UPPER LEVEL LOW CENTERED NEAR DUTCH HARBOR. THIS WILL KEEP
PRECIPITATION CHANCES FAIRLY HIGH FOR THE EASTERN ALEUTIANS AND
BRISTOL BAY AREAS...WITH DRY AND RELATIVELY WARM CONDITIONS FOR
MUCH OF SOUTHCENTRAL. INTO SUNDAY...SOME MORE SIGNIFICANT
DIFFERENCES BEGIN TO DEVELOP IN THE MODELS. THEY ALL PUSH A FRONT
INTO THE SOUTHWEST COAST...BUT THE GFS SHIFTS THE UPPER LEVEL LOW
MUCH FURTHER INLAND EFFECTIVELY DISPLACING THE RIDGE TOWARDS THE
CANADIAN BORDER. THE EC BRINGS THE FRONT AS WELL...BUT HOLDS THE
UPPER LEVEL LOW AND THUS THE BROAD TROUGH OVER THE BERING. THIS
WOULD RESULT IN THE MORE ACTIVE PORTION OF THE STORM TRACK
REMAINING OVER THE BERING AND THEN HEADING SOUTH THROUGH THE GULF
TOWARDS THE PANHANDLE. THIS FORECAST PACKAGE WAS HEDGED TOWARDS
THE DRIER EC SOLUTION AS MODELS HAVE BEEN TOO FAST IN BREAKING
DOWN THESE RIDGES THE PAST FEW WEEKS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...130 179 411 412 413 414
         HEAVY FREEZING SPRAY WARNING...160 180 185 412 414
FIRE WEATHER...NONE.

&&

MSO/PLD APR 14