Small Craft Advisory 183, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
443 AM AKST THU FEB 26 2015

.ANALYSIS AND UPPER LEVELS...RIDGING IS STARTING TO BUILD OVER THE
STATE FROM THE SOUTHWEST. THIS IS LEADING TO SOME LOW STRATUS OVER
THE KUSKOKWIM DELTA AND CONTINUED LOW STRATUS AND POCKETS OF DENSE
FOG STRETCHING FROM THE KNIK ARM THROUGH THE COPPER RIVER BASIN.
NASA NIGHTTIME SATELLITE IMAGERY CLEARLY SHOWS THE ISOLATED LOW
STRATUS AND FOG STRETCHING FROM THE MATANUSKA VALLEY THROUGH THE
KNIK ARM AND THEN ANOTHER AREA IN THE COPPER RIVER BASIN JUST
SOUTH AND EAST OF GLENNALLEN. MUCH FURTHER WEST...A SHARP UPPER
LEVEL TROUGH OVER THE WESTERN BERING CONTINUES TO GIVE SUPPORT TO
A VERY SLOW MOVING FRONT NEAR ATKA AND ADAK. A 100-110KT JET FROM
THE NORTH PACIFIC IS AIDING THIS FEATURE AND HELPING TO STRETCH
THE ENERGY THROUGH THE BERING STRAIT. THE RAPIDLY WEAKENING
SURFACE LOW THAT TRANSITIONED THROUGH THE GULF WEDNESDAY IS NOW
CENTERED JUST WEST OF HAIDA GWAII. IT WILL CONTINUE TO MOVE AWAY
FROM THE MAINLAND...BUT IT IS WORKING IN TANDEM WITH A SURFACE
HIGH BUILDING UNDER THE AFORE MENTIONED RIDGE TO CREATE SOME GUSTY
OUTFLOW WINDS. FINALLY...SATELLITE SHOWS A WEAK SYSTEM TRYING TO
DEVELOP NEAR 42N 163W ALONG A 120KT PORTION OF THE JET. WHILE
STILL WELL SOUTH OF THE EASTERN ALEUTIANS FOR NOW...THIS ENERGY
WILL BE A PRIMARY FOCUS LOOKING AT THE FORECAST INTO THE WEEKEND.

&&

.MODEL DISCUSSION...MODELS REMAIN TIGHTLY CLUSTERED IN THE FIRST
24 HOURS...SO ONLY MINOR CHANGES WERE MADE TO CURRENT FORECAST.
THAT SAID...NONE OF THE MODELS WERE DEPICTING THE FOG THAT IS
DEVELOPING ACROSS MUCH OF SOUTH CENTRAL THIS MORNING. SO WHILE
OVERALL FORECAST CONFIDENCE REMAINS HIGH IN THE SHORT TERM...THE
FOG COULD THROW A SIGNIFICANT WRENCH INTO THINGS. BEYOND THE FIRST
24 HOURS...THE BIGGEST MODEL DISCREPANCY THAT DEVELOPS IS THE
HANDLING OF THE LOW RIDING UP THE JET TOWARD SAND POINT. THIS WILL
BE THE "SURGE" OF MOISTURE MOVING NORTH TOWARD SOUTH CENTRAL
HEADING INTO THE WEEKEND. FORECASTERS MAINLY RELIED ON THE GLOBAL
MODELS (GEM/EC/GFS) WITH THIS SYSTEM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

PRESSURE GRADIENTS ALONG THE GULF COAST WILL SLACKEN TODAY AS A
LOW NEAR HAIDA GWAII EXITS INTO BRITISH COLUMBIA. THIS WILL ALLOW
GAP WINDS TO WEAKEN SIGNIFICANTLY. GRADIENTS WILL TIGHTEN BACK UP
JUST A BIT TONIGHT AS AN UPPER WAVE MOVES THROUGH SO WINDS WILL
INCREASE AGAIN...BUT NOT NEARLY AS STRONG AS THIS MORNING. THE
COMBINATION OF SUBSIDENCE WARMING FROM THE UPPER LEVEL RIDGE AND
WARMING FROM DOWNSLOPE FLOW OFF THE COASTAL MOUNTAINS WILL MAINTAIN
SOME FAIRLY BALMY TEMPERATURES ALONG THE COAST.

OTHER THAN THE LOCALIZED GAP WINDS THE MAIN FORECAST CHALLENGE IS
FOG AS INVERSIONS STRENGTHEN UNDERNEATH A STRONG UPPER LEVEL RIDGE.
LOCALLY DENSE FOG WHICH FORMED IN THE PALMER AREA HAS DRIFTED
SOUTH TO ANCHORAGE UNDER A VERY LIGHT NORTH WIND. EXPECT THE FOG
TO CONTINUE TO DRIFT SOUTHWARD TO THE WESTERN KENAI AND EASTWARD
ALONG TURNAGAIN ARM. CONDITIONS REMAIN FAVORABLE FOR FOG UNTIL AT
LEAST FRIDAY MORNING AS CLOUDS APPROACH. THERE MAY BE SOME
IMPROVEMENTS DURING THE DAY WITH AN INCREASINGLY HIGHER SUN
ANGLE...BUT THE FOG WILL LIKELY HOVER IN THE NORTHERN COOK INLET
REGION AS WELL AS IN PORTIONS OF THE COPPER RIVER BASIN.

AS THE UPPER RIDGE SLIDES EASTWARD FRIDAY AND FRIDAY NIGHT ALL
MODELS INDICATE A WEAK UPPER WAVE AND WEAK SURFACE LOW MOVING
UP THE WEST SIDE OF THE RIDGE TOWARD THE GULF AND SOUTHCENTRAL.
FORECAST CONFIDENCE IN THE DETAILS IS FAIRLY LOW AT THIS
POINT...BUT ANY PRECIP ASSOCIATED WITH THESE FEATURES WILL BE
LIGHT. THE AIR MASS IN PLACE OVER SOUTHCENTRAL WILL ALSO BE QUITE
DRY WHICH MAY PREVENT PRECIP FROM REACHING THE GROUND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

A RIDGE OF HIGH PRESSURE ALOFT WILL GIVE WAY TO A NORTH PACIFIC
LOW LATE FRIDAY AFTERNOON INTO FRIDAY NIGHT. CLOUDS AND MOISTURE
WILL STREAM IN FROM THE SOUTH...WITH RAIN AND SNOW DEVELOPING
ACROSS BRISTOL BAY BEFORE RAPIDLY SPREADING NORTHWARD. ALL SNOW IS
EXPECTED ACROSS THE KUSKOKWIM DELTA AND LOWER KUSKOKWIM
VALLEY...WITH RAIN ALONG THE ALASKA PENINSULA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

A SLOW MOVING GALE FORCE FRONT WILL REMAIN OVER THE CENTRAL
ALEUTIANS BEFORE WEAKENING AND MOVING EAST. COLDER AIR WILL FILTER
INTO THE CENTRAL BERING SEA ALONG WITH WEST NORTHWEST WINDS. RAIN
AND SNOW SHOWERS WILL MOVE INTO THE PRIBILOF ISLANDS AND EASTERN
ALEUTIANS AS THE FRONT MOVES EAST...AND A WEAK NORTH PACIFIC LOW
MOVES TOWARD THE ALASKA PENINSULA. A NEAR STORM FORCE LOW WILL
MOVE INTO THE FAR WESTERN ALEUTIANS LATE FRIDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

ALL IS STILL LOOKING GOOD FOR A QUICK SHOT OF SNOW FOR SOUTHWEST
AND SOUTH CENTRAL ALASKA ON SATURDAY. MOISTURE WILL BE IN GOOD
SUPPLY FROM THE WEAK FRONTAL SYSTEM LIFTING UP FRIDAY NIGHT...THEN
A FAST MOVING SHORT WAVE FROM THE WEST WILL BRING COLDER AIR IN
ALOFT AND A BURST OF LIFT WITH IT AS IT RAPIDLY CROSSES THE AREA
SATURDAY. THE SHORTWAVE WILL REACH THE WEST COAST OF ALASKA EARLY
SATURDAY MORNING...CROSS THE ALASKA RANGE EARLY TO MID AFTERNOON
AND THEN SWING OVER SOUTH CENTRAL ALASKA IN THE EVENING. FOR THE
ANCHORAGE AREA...MATSU VALLEY AND KENAI PENINSULA THE CHANCES FOR
LIGHT SNOW WILL INCREASE THROUGH THE DAY SATURDAY WITH A QUICK
COUPLE HOURS OF HEAVIER SNOW LIKELY IN THE LATE AFTERNOON AND
EARLY EVENING AS THE SHORTWAVE APPROACHES AND PASSES OVERHEAD.

OUT IN THE NORTH PACIFIC AND BERING SEA A STRONG FRONTAL SYSTEM
WILL PUSH INTO THE THE WESTERN ALEUTIAN ON SATURDAY BRINGING A
SWATH OF STORM FORCE WINDS AND A BROAD AREA OF GALES WITH IT. THE
ASSOCIATED BROAD VERTICALLY STACKED LOW SUPPORTING IT WILL LIFT
NORTH THROUGH THE WESTERN BERING ON SUNDAY AS THE FRONTAL SYSTEM
TRACKS TOWARDS THE CENTRAL ALEUTIANS AND GRADUALLY WEAKENS. THE
LARGE LOW WILL ALSO ACT TO RAPIDLY AMPLIFY AN UPPER LEVEL RIDGE
OVER THE EASTERN BERING AND WESTERN ALASKA SATURDAY NIGHT. THE
RIDGE WILL CONTINUE TO STRENGTHEN SUNDAY AS IT IS PUSHED EAST OVER
MAINLAND ALASKA SUNDAY QUICKLY CLEARING OUT THE REMNANTS OF THE
EARLIER TROUGH.

RIDGING AND DRIER WEATHER WILL PERSIST OVER MAINLAND ALASKA THROUGH
MONDAY. A LARGE LOW PRESSURE COMPLEX WILL ESTABLISH ITSELF SOUTH
OF THE ALEUTIANS AND ALASKA PENINSULA SUNDAY AND MONDAY THEN SPIN
THE NEXT FRONTAL SYSTEM UP TO SOUTHWEST ALASKA MONDAY NIGHT AND
SOUTH CENTRAL ALASKA ON TUESDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 175 177 185 412 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...JER