Small Craft Advisory 260, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
507 PM AKDT MON MAR 23 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW CENTERED OVER THE EASTERN AND CENTRAL
ALEUTIANS. AN ASSOCIATED HORSESHOE SHAPED FRONT STRETCHES FROM THE
ALASKA PENINSULA UP TO THE PRIBILOFS...THEN SOUTH TO UNALASKA. AT
THE SURFACE THIS FRONT IS AN INVERTED TROUGH...BUT THE SIGNAL
ALOFT IS VERY WEAK. HIGH PRESSURE AND STRONG SUBSIDENCE IS OVER
THE SOUTHERN ALASKA MAINLAND WITH A WEAK WESTWARD EXTENSION ACROSS
THE BERING (NORTH OF THE PRIBILOFS) TO ANOTHER RIDGE OVER THE
SOUTHWEST BERING.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN VERY GOOD AGREEMENT THROUGH THE SHORT
TERM ONCE AGAIN. FORECAST CONFIDENCE IS THUS ABOVE NORMAL TODAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2 - TUESDAY
AND WEDNESDAY)...
STRONG HIGH PRESSURE OVER THE SOUTHERN MAINLAND WITH THE
RESULTING SUBSIDENCE INVERSION ALOFT HAS PRODUCED ANOTHER SUNNY
WARM DAY FOR THE REGION. THE REMNANTS OF AN OCCLUSION ACROSS THE
GULF OF ALASKA IS RESULTING IN CLOUDS PERSISTING OVER KODIAK
ISLAND. SOUTH OF THIS IS AN INCOMING INTENSIFYING LOW ABOUT 600
MILES SOUTH OF KODIAK ISLAND. THE UPPER LEVEL LOW SUPPORTING THIS
LOW WILL MERGE INTO THE UPPER LEVEL TROUGH FROM THE ALEUTIANS INTO
THE GULF OF ALASKA THROUGH WEDNESDAY.

FOG WAS NOT AN ISSUE LAST NIGHT IN SOUTH CENTRAL ALASKA PRIMARILY
DUE TO THE LACK OF SIGNIFICANT LOW LEVEL MOISTURE AND THE
INVERSION BEING SLOW TO FORM. TONIGHT WE SHOULD SEE THE INVERSION
FORM MORE RAPIDLY HOWEVER WE STILL HAVE A VERY DRY LOWER LAYER.
THUS WE EXPECT THE FOG TO BE PATCHY AT WORST.

THE MORE SIGNIFICANT CONCERN IS THE STRONG WIND EXPECTED IN THE
MATANUSKA VALLEY BEGINNING WEDNESDAY MORNING. THIS COUPLED WITH
THE DRY CHINOOK FLOW HAS ELEVATED CONCERNS ABOUT FIRE WEATHER FOR
STRONG WIND WITH LOW RELATIVE HUMIDITY WEDNESDAY AFTERNOON.

THE INCOMING LOW AND ASSOCIATED FRONT MOVING INTO THE GULF
OF ALASKA WILL SPREAD RAIN INTO KODIAK ISLAND BY TUESDAY MORNING.
AS THE FRONT APPROACHES THE COAST WE EXPECTED HIGH END GALE FORCE
TO MINIMUM STORM FORCE WINDS TO IMPACT THE SOUTH SIDE OF KODIAK
ISLAND BEGINNING TUE AFTERNOON...AND PUSH TO THE NORTH GULF COAST
AND THE LOWER COOK INLET REGIONS TUESDAY NIGHT. ALONG WITH THE
STRONG WIND WILL BE MODERATE RAIN ALONG THE GULF COAST SIDE OF THE
MOUNTAINS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2 - TUESDAY
AND WEDNESDAY)...
SKIES CONTINUE TO CLEAR OVER MUCH OF THE SOUTHWEST MAINLAND...AS
HIGH PRESSURE AND DRIER OFFSHORE FLOW PERSISTS OVER THE AREA
THROUGH LATER THIS EVENING. AN UPPER LEVEL DISTURBANCE SOUTH OF
THE AKPEN WILL BEGIN TO TRACK NORTHWARD THROUGH THE BRISTOL BAY
AREA OVER NIGHT. THIS WILL BRING A QUICK SHOT OF RAIN SHOWERS TO
THE COASTAL AREAS OF BRISTOL BAY AND THE AREAS ALONG THE ALEUTIAN
RANGE THROUGH TOMORROW AFTERNOON. THIS QUICK SHOT OF RAIN SHOWERS
WILL BE QUICKLY FOLLOWED BY MORE STEADIER PRECIPITATION ASSOCIATED
WITH A NORTH PACIFIC LOW TRACKING NORTHWARD TOWARD THE ALASKA
PENINSULA WEDNESDAY. GUSTY WINDS ARE EXPECTED TO PICK UP OVER
PARTS OF THE BRISTOL BAY AREA TOMORROW MORNING AND STRENGTHEN
THROUGH WEDNESDAY...AS THE AFOREMENTIONED LOW APPROACHES THE AKPEN
AND CONTINUES TO TIGHTEN THE GRADIENT OVER THE AREA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2 - TUESDAY
AND WEDNESDAY)...
A LOW LEVEL TROUGH/FRONTAL BOUNDARY WILL CONTINUE TO WORK
WESTWARD THROUGH THE BERING THIS EVENING...IMPACTING THE
CENTRAL/EASTERN ALEUTIANS AND THE PRIBILOF ISLANDS. THE EASTERN
CHAIN AND ALASKA PENINSULA WILL CONTINUE TO SEE RAIN SHOWERS AS
A SERIES OF DISTURBANCES TRACK THROUGH THE AREA THROUGH TOMORROW
NIGHT. SNOW AND SOME AREAS OF BLOWING SNOW WILL CONTINUE OVER THE
PRIBILOF ISLANDS...WITH 20 TO 35 MPH WINDS PERSISTING THROUGH
TOMORROW AFTERNOON WHEN WARMER SURFACE TEMPERATURES BEGIN TO
MITIGATE THE THREAT SOMEWHAT. GUSTY WINDS WILL BEGIN TO DEVELOP
OVER THE CENTRAL BERING TOMORROW MORNING WITH COLDER NORTHERLY
FLOW SETTING UP OVER THE AREA. THESE GUSTY WINDS WILL INCREASE
OVER THE EASTERN/CENTRAL BERING AND ALEUTIANS THROUGH MIDWEEK...AS
THE NORTH PACIFIC LOW TRACKS CLOSER TO THE AKPEN WEDNESDAY AND
CONTINUES TO TIGHTEN THE GRADIENT FURTHER OVER THE AREA. WITH
THESE INCREASED GUSTY WINDS AND SNOW SHOWERS APPROACHING THE
PRIBILOF ISLANDS WEDNESDAY...THERE IS AN INCREASED POTENTIAL FOR
THE AREAS OF BLOWING SNOW TO REDUCE VISIBILITIES TO ONE QUARTER
MILE OR LESS AT TIMES OVER THE AREA. THEREFOR...A BLIZZARD WATCH
WAS ISSUED FOR WEDNESDAY MORNING THROUGH LATE WEDNESDAY NIGHT FOR
THE PRIBILOF ISLANDS.

&&

.LONG TERM FORECAST (WEDNESDAY NIGHT THROUGH SUNDAY NIGHT)...
WEDNESDAY NIGHT THE STACKED LOW NEAR KODIAK ISLAND PUSHES A
SHORTWAVE NORTH TO SOUTHCENTRAL. AT THE SAME TIME...AN ASSOCIATED
FRONT MOVES TOWARD THE SOUTHERN COOK INLET AND STRETCHES EAST INTO
THE NORTHERN GULF. GUSTY WINDS INCREASE ALONG THE TIGHT PRESSURE
GRADIENT ALONG THE BOUNDARY...WITH NORTHERLY FLOW ALONG THE COOK
INLET AND EASTERLY FLOW ACROSS THE GULF AND SURROUNDING COAST. IN
ADDITION...RAIN DEVELOPS ALONG THE FRONT WHICH STALLS ALONG THE
WESTERN AND NORTHERN GULF. WITH EASTERLY FLOW MUCH OF THE SOUTHERN
MAINLAND AND WESTERN KENAI STAYS DRY DUE TO DOWNSLOPE AFFECTS FROM
THE MOUNTAINS...HOWEVER THE UPPER WAVE WILL BE STRONG ENOUGH TO
BRING SHOWERS TO THE EASTERN KENAI WEDNESDAY EVENING AND THEN
ACROSS INLAND AREAS AFTER MIDNIGHT.

TO THE WEST ON WEDNESDAY NIGHT...NORTHERLY FLOW INCREASES ALONG
THE BERING WITH WRAP AROUND PRECIPITATION MOVING BEHIND THE
STACKED LOW. GUSTY WINDS MAY CAUSE BLOWING SNOW TO REDUCE
VISIBILITIES ACROSS THE PRIBILOFS AND THEN IS EXPECTED TO IMPROVE
FOR THURSDAY AS PRECIPITATION DIMINISHES. HOWEVER...THIS STORM
SYSTEM WILL NEED TO BE MONITORED AS THERE IS STILL UNCERTAINTY IN
MODEL OUTCOMES.

THE NEXT SHORT WAVE MOVES INTO THE SOUTHERN GULF THURSDAY MORNING
BRINGING ANOTHER RAIN BAND TO THE NORTHERN GULF THURSDAY EVENING.
WINDS WITH THIS NEXT WAVE ARE EXPECTED TO BE MORE INTENSE
AS THE STACKED LOW PRESSURE SYSTEM MOVES FROM JUST SOUTH OF
KODIAK ISLAND TO THE SOUTHERN COOK INLET THURSDAY MORNING. WINDS
WILL HAVE THE MOST IMPACT ACROSS CHANNELED TERRAIN ALONG WESTERN
PRINCE WILLIAM SOUND...TURNAGAIN ARM AND THE HILLSIDE AREA.

AN ACTIVE WEATHER PATTERN REMAINS ON TAP THROUGH THE BEGINNING TO
NEXT WEEK AS LOW PRESSURE REMAINS DOMINANT THROUGH THE EXTENDED
FORECAST.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WATCH 195.
MARINE...STORMS 131 138.
         GALES 119 120 130 132 136 137 139 150 351 352.
         HEAVY FREEZING SPRAY 179 412.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...SA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...KH