Small Craft Advisory 211, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
408 PM AKDT SUN MAR 8 2015

.ANALYSIS AND UPPER LEVELS...
BASICALLY A BROAD TROUGH ACROSS MUCH OF THE FORECAST AREA WITH A
LONG WAVE TROUGH TO DEVELOP OVER THE STATE LATER THIS WEEK.
CURRENTLY...THERE IS A STRONG CLOSED LOW/VORT MAX ROTATING INTO
WEST COAST THIS MORNING. THIS FEATURE IS ASSOCIATED WITH A JET
CORE OF 110 KT WHICH IS MAKING IT RATHER VIGOROUS. A SECOND
STRONG SURFACE LOW/UPPER LEVEL CLOSED LOW SOUTH OF SHEMYA WITH A
JET CORE OF 120 KT. A WEAK SHORT WAVE RIDGE IS PRESENT AS WELL IN
THE SOUTHERN BERING SEA AHEAD OF THE WESTERN ALEUTIAN LOW. A THIRD
FEATURE IS A SHORT WAVE TROUGH MOVING INTO THE SEA OF OKHOTSK
WHICH WILL FEED SOME ENERGY TOMORROW TO THE NORTH PACIFIC LOW
NEAR THE WESTERN ALEUTIANS.

AT THE SURFACE...THE UPPER LOW OVER THE WEST COAST PRODUCING
STRONG SNOW SHOWERS REDUCING VISIBILITIES TO LESS THAN A MILE AT
TIMES. THESE SHOWERS WILL SPREAD ACROSS SOUTHWEST ALASKA THIS
AFTERNOON/EVENING. THIS LOW WILL MOVE OVER SOUTHCENTRAL LATE
TONIGHT WITH CONVECTIVE SNOW SHOWERS ACROSS SOUTH CENTRAL. THIS
FEATURE WILL ALSO REINFORCE THE TROUGH OF LOW PRESSURE OVER THE
NORTHERN GULF COAST. AS A RESULT...STRONG TO VERY STRONG GAP
(WEST TO EAST AND NORTH TO SOUTH) WINDS WILL STRENGTHEN TONIGHT.
THE WESTERN ALEUTIAN LOW PUSHED A WARM FRONT TO THE CHAIN THIS
MORNING WITH SNOW AND WIND. TEMPERATURES ARE WARM ENOUGH THAT
BLIZZARD CONDITIONS ARE NOT APPEARING. THE SURFACE LOW WRAPS UP
TONIGHT AS COLDER AIR IS PUSHED INTO THE SYSTEM TONIGHT AND
TOMORROW.

&&

.MODEL DISCUSSION...
ONCE AGAIN THE MODELS ARE IN EXCELLENT AGREEMENT FOR THE NEXT
COUPLE DAYS. THE COLD AIR HAS FILTERED OVER THE MAINLAND WITH THE
FIRST WAVE YESTERDAY. THE SECOND SURGE OF COLD AIR ARRIVING WITH
THE STRONG CLOSED LOW CURRENTLY PUSHING THROUGH SOUTHWEST ALASKA.
ANOTHER WAVE WILL BE MOVING OUT OF THE ARCTIC WEDNESDAY FOR
ANOTHER SHOVE OF COLD AIR OVER THE BERING AND WESTERN ALASKA.
SUFFICE TO SAY...A COLD TROUGH WILL REMAIN OVER THE STATE THROUGH
MUCH OF THE WEEK. THERE IS NOT MUCH SPREAD IN THE FORECAST THROUGH
WEDNESDAY WITH THE EUROPEAN AND NORTH AMERICAN MODEL GUIDANCE.

OVERALL...THE STRONG CLOSED LOW MOVES THROUGH THE MAINLAND TO THE
YUKON BY TUESDAY MORNING. THIS IS WHEN THE GRADIENT AND STRONG GAP
WINDS WILL DIMINISH. A TROUGH WILL REMAIN OVER THE MAINLAND WITH
DRY AND COLD CONDITIONS PERSISTING TUESDAY AND WEDNESDAY. THE
STACKED LOW NEAR THE WESTERN ALEUTIANS TO BE REINFORCED BY A
COUPLE UPPER LEVEL DISTURBANCES AND DIG THE CLOSED LOW INTO THE
NORTH PACIFIC. AS THIS CLOSED LOW FLOWS TO NEAR 40N 160W
TUESDAY...IT WILL PHASE SOMEWHAT WITH A LOW CURRENTLY NEAR 35N
150W. THE RESULTANT SURFACE FEATURE WILL BE AN ELONGATED LOW
STRETCHING FROM 40N 160W TO THE SOUTHERN PANHANDLE OF ALASKA. AT
THIS TIME...HIGH PRESSURE AT THE SURFACE WILL BE PREVALENT OVER
THE MAINLAND TO THE BERING SEA WITH A FRONT APPROACHING THE FAR
WESTERN ALEUTIANS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
WITH THE PASSAGE OF THE SYSTEM YESTERDAY...THE AIR MASS IS
UNSTABLE FOR SOME CONVECTIVE SHOWERS OVER SOUTHCENTRAL AS EVIDENT
BY RADAR AND SATELLITE AND WEB CAMS. IN ADDITION...THE FEATURE
YESTERDAY DEVELOPED A TROUGH OF LOW PRESSURE OVER THE NORTHERN
GULF COAST ALLOWING FOR GAP WINDS TO INITIATE. THE STRONGER GAP
FLOW ARE FROM THE WEST TO EAST ORIENTATION. HOWEVER...NORTH TO
SOUTH GAPS ARE DOING WELL TOO. THE UPPER CLOSED LOW OVER SOUTHWEST
ALASKA WILL PASS THROUGH THE AREA TONIGHT. THIS FEATURE WILL
INCREASE SHOWER ACTIVITY AND GAP WINDS OVER THE AREA. DUE TO THE
GAP WIND THROUGH THE BARREN ISLANDS...THERE COULD BE A NICE LAKE
EFFECT EVENT OVER THE BARREN ISLANDS TO KACHEMAK BAY TONIGHT.
COMBINED WITH THE WINDS...THE KACHEMAK BAY AREA COULD EXPERIENCE
BLOWING SNOW AND REDUCED VISIBILITIES AT TIMES. AS THE CLOSED LOW
PASSES...PRESSURE GRADIENTS WILL CONTINUE TO BE MODERATE OVER THE
NORTHERN GULF COAST AREAS. THEREFORE...MODERATE TO STRONG GAP
WINDS WILL BE PREVALENT. SOME BLOWING SNOW WILL BE PRESENT THROUGH
MOUNTAIN PASSES AS WELL. WITH THE THOMPSON PASS GAP FLOW...WIND
CHILLS COULD REACH NEAR 30 BELOW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A STRONG UPPER LEVEL LOW WILL MOVE OVERHEAD OF SOUTHWEST ALASKA
LATE THIS AFTERNOON THROUGH THIS EVENING BRINGING ANOTHER SHOT
OF COLD AIR ADVECTION...GUSTY WINDS...AND SNOW SHOWERS. AREA
SOUNDINGS SHOW VERY UNSTABLE CONDITIONS IN THE NEAR SURFACE
LAYER...SO SOME OF THESE SHOWERS MAY BE HEAVY. THIS WILL ALSO
ALLOW STRONGER WINDS TO MIX DOWN FROM ALOFT. THE AXIS OF STRONGEST
COLD AIR ADVECTION HEADS RIGHT ACROSS THE ALASKA PENINSULA WHICH
WILL PRODUCE VERY STRONG GAP WINDS. UP TO THIS POINT CLOUD COVER
AND GUSTY WINDS HAVE KEPT SURFACE TEMPERATURES FROM DROPPING VERY
FAR. THAT WILL CHANGE IN THE WAKE OF THE UPPER LOW TONIGHT INTO
MONDAY AS CLOUDS DECREASE AND THE AIR MASS STABILIZES. TEMPERATURES
WILL FALL QUICKLY WHERE SKIES CLEAR AND WINDS LIGHTEN AND THERE
WILL BE LITTLE RECOVERY IN TEMPERATURES ON MONDAY. THE COOLING
TREND WILL CONTINUE THROUGH MONDAY NIGHT...ALTHOUGH A LITTLE BIT
OF WIND WILL PERSIST IN COASTAL AREAS KEEPING TEMPS A LITTLE
WARMER THAN INLAND LOCALES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A MATURE LOW HEADING TOWARD THE ALEUTIANS WILL STALL SOUTH OF THE
CHAIN TONIGHT THEN REMAIN NEARLY STATIONARY THROUGH MONDAY NIGHT
BEFORE HEADING BACK SOUTH. A WET SNOW HAS BEEN FALLING ACROSS
MUCH OF THE CENTRAL ALEUTIAN ISLANDS...BUT WARM AIR WILL PUSH
JUST FAR ENOUGH NORTHWARD TO CHANGE PRECIP TO RAIN. A SHORT-WAVE
MOVING OUT OF RUSSIA WILL DROP INTO THE BACK SIDE OF THIS
SYSTEM...HELPING TO STRENGTHEN THE BAROCLINICITY WHICH WILL
STRENGTHEN WINDS AND INTENSIFY PRECIP. THE WORST CONDITIONS ARE
EXPECTED OVER THE UNINHABITED ISLANDS OF THE WESTERN ALEUTIANS
BETWEEN SHEMYA AND ADAK. AS THIS SYSTEM EXITS ON TUESDAY COLDER
AIR WILL MOVE BACK SOUTH WITH WIDESPREAD SNOW OR SNOW SHOWERS
ACROSS THE SOUTHERN BERING AND AND CENTRAL ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MOSTLY CLEAR SKIES...OFFSHORE FLOW...AND OUTFLOW WINDS WILL
CONTINUE OVER MUCH OF THE SOUTH MAINLAND THROUGH THURSDAY. OVER
THE BERING...A LOW SKIRTING THE CENTRAL ALEUTIANS WILL MOVE INTO
THE NORTH PACIFIC ON WEDNESDAY...DRAGGING COLD AIR AND SNOW
SHOWERS TO MUCH OF THE REGION THAT SHOULD PERSIST INTO THURSDAY.

ANOTHER SYSTEM LOOKS TO ENTER THE WESTERN ALEUTIANS ON THURSDAY
AS AN UPPER LEVEL TROUGH BECOMES NEARLY STATIONARY OVER THE
WESTERN BERING. THIS WILL BRING A PERIOD OF STORMY AND MORE ACTIVE
WEATHER TO THE BERING SEA REGION THAT WILL LIKELY CONTINUE INTO
NEXT WEEK. OVER THE GULF THERE CONTINUES TO BE DISCREPANCIES IN
THE MODELS WITH THE STRENGTH OF AN ARCTIC TROUGH OVER THE MAINLAND
AND RESULT LOW OVER THE GULF. THE GFS CONTINUES TO BE
EXTRAORDINARILY CONSISTENT WITH A MUCH DEEPER AND WARMER SYSTEM
APPROACHING THE NORTH GULF COAST ON FRIDAY...WHILE THE EC AND GEM
BRING A MUCH WEAKER AND (IMPORTANTLY) COOLER SYSTEM TOWARDS THE
NORTHERN PANHANDLE. AFTER COORDINATION WITH WPC AND WFO JUNEAU
THIS MORNING...IT WAS DECIDED TO CONTINUE TO TREAT THE GFS AS AN
OUTLIER AND INSTEAD THE EXTENDED FORECAST USED AN EC/GEM BLEND ON
FRIDAY. CONFIDENCE HOWEVER CONTINUES TO BE FAIRLY LOW...AND MODEL
TRENDS WILL NEED TO BE CLOSELY WATCHED OVER THE COMING DAYS.

BY LATE NEXT WEEKEND...THERE IS VERY GOOD AGREEMENT THAT A
FAMILIAR PATTERN WILL RETURN TO MAINLAND ALASKA AS A BUILDING
NORTHEAST PACIFIC RIDGE MAKES ITS RETURN. BECAUSE OF THIS IT NOW
APPEARS THAT THE MAINLAND WILL RETURN TO THE WARM AND STORMY
PATTERN SEEN FOR MOST OF THIS WINTER BY EARLY NEXT WEEK (IF NOT
BEFORE AS THE GFS HAS BEEN INDICATING).

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 130 131 177 178.
 GALE WARNING 119 120 125 127 128 129 132 137 139 150 160 170 173
174 175 176.
 HEAVY FREEZING SPRAY 121 126 127 129 130 131 138 139 140 141 150
160 165 179 180 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JN
SOUTHCENTRAL ALASKA...JN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SB
LONG TERM...DEK