Small Craft Advisory 410, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
429 PM AKDT WED MAY 13 2015

.ANALYSIS AND UPPER LEVELS...
A HIGH AMPLITUDE TROUGH IS CENTERED OVER THE BERING SEA AND
NORTH-CENTRAL PACIFIC WITH A CLOSED LOW JUST SOUTH OF THE CENTRAL
ALEUTIANS. A CORRESPONDING HIGH AMPLITUDE RIDGE JUST DOWNSTREAM IS
BUILDING NORTHWARD INTO MAINLAND ALASKA AS THE TROUGH CONTINUES TO
DIG OVER THE PACIFIC. AN OCCLUDED FRONT EXTENDING FROM A WEAKENING
SURFACE LOW OVER THE CENTRAL BERING IS PUSHING INLAND ACROSS
SOUTHWEST ALASKA TODAY PRODUCING WIDESPREAD RAIN ACROSS THE REGION.
THE HEAVIEST RAIN IS COINCIDENT WITH AN UPPER LEVEL SHORT-WAVE
MOVING NORTHWARD ALONG THE WESTERN ALASKA COAST AND A STRONG
SOUTHERLY JET WHICH EXTENDS UP THE EAST SIDE OF THE TROUGH. EVEN
MORE IMPRESSIVE IS THE MOISTURE OUT AHEAD OF A SHORT-WAVE ROUNDING
THE BASE OF THE TROUGH...WITH A LARGE AREA OF GREATER THAN 200%
OF NORMAL PRECIPITABLE WATER (AS DERIVED FROM SATELLITE IMAGERY)
STREAMING NORTHWARD TOWARD THE ALASKA PENINSULA AND BRISTOL BAY.

MEANWHILE...AN UPPER RIDGE IS BUILDING TOWARD SOUTHCENTRAL ALASKA
PRODUCING A WARM AND SUNNY DAY ACROSS MOST OF THE REGION. WITH THE
SURFACE HIGH CENTERED OVER THE GULF OF ALASKA AND WARMEST
TEMPERATURES INLAND IT WILL BE A GOOD DAY FOR SEA BREEZES. THESE
WILL HELP MODERATE TEMPERATURES ALONG THE COAST LATER THIS
AFTERNOON AND EVENING.

&&

.MODEL DISCUSSION...
MODELS CONTINUE TO DIFFER A BIT IN SOME OF THE DETAILS OF BOTH
UPPER LEVEL FEATURES AND THE TRACK OF SURFACE LOWS....BUT
SOLUTIONS ARE GENERALLY GROUPED TOGETHER IN THE SAME REGION.
ONE CONSISTENT TREND IN RECENT DAYS IS TO SHIFT THE LONG-WAVE
PATTERN EASTWARD. MORE SPECIFICALLY...PRIOR MODEL SOLUTIONS
INDICATED THE UPPER RIDGE WOULD REMAIN SOLIDLY OVER THE EASTERN
PORTION OF MAINLAND ALASKA...WHILE GUIDANCE NOW INDICATES THERE
WILL BE PERIODS OF TIME WHERE THIS RIDGE MAY IS MOMENTARILY
PUSHED EASTWARD...WHICH WILL ALLOW MOISTURE TO PENETRATE
FARTHER INTO SOUTHCENTRAL.

THE MOST SIGNIFICANT MODEL DIFFERENCE OVER THE NEXT FEW DAYS IS
THE TRACK OF THE UPPER LEVEL TROUGH AS IT LIFTS NORTHWARD UP THE
WEST SIDE OF THE RIDGE THURSDAY NIGHT THROUGH SATURDAY. THE GFS IS
THE OUTLIER IN TRACKING THIS RIGHT OVER SOUTHCENTRAL...WITH ALL
OTHER SOLUTIONS FARTHER WEST. CAN NOT COMPLETELY DISCOUNT THE GFS
SOLUTION THOUGH BASED ON THE EASTWARD TREND OF FEATURES OVER THE
PAST COUPLE DAYS. THE TRACK OF THIS TROUGH WILL MAKE A HUGE
DIFFERENCE IN THE THE FORECAST FOR SOUTHCENTRAL AND SOUTHWEST
ALASKA. FORECAST CONFIDENCE FOR THE FIRST COUPLE DAYS OF THE
FORECAST IS AVERAGE TO A LITTLE ABOVE AVERAGE...BUT DROPS
SIGNIFICANTLY SATURDAY DUE TO THE UNCERTAINTY IN TRACK OF THE
UPPER TROUGH.

&&

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

UPPER LEVEL RIDGING ALOFT WILL REMAIN OVER SOUTHEAST ALASKA
THROUGH FRIDAY...WITH A SLOW MOVING TROUGH OVER SOUTHWEST ALASKA.
MOISTURE AND CLOUDS FROM THAT SYSTEM WILL SLOWLY SPREAD
EAST...WITH RAIN ACROSS KODIAK ISLAND INTO THE COASTAL AREAS OF
THE KENAI PENINSULA. A BUILDING COASTAL RIDGE WILL STRENGTHEN EAST
TO WEST GAP WINDS...AS WELL AS SOUTHERLY WINDS ACROSS THE COPPER
BASIN. THIS PATTERN WILL ALSO SUPPORT GUSTY AFTERNOON WINDS ACROSS
ANCHORAGE ON THURSDAY...ESPECIALLY ACROSS THE SOUTH AND WEST PARTS
OF TOWN AND UP INTO THE HILLSIDE.

&&

.FIRE WEATHER...

CRITICAL FIRE WEATHER CONDITIONS WILL CONTINUE INTO THE EARLY
EVENING ACROSS THE COPPER BASIN AS HUMIDITY VALUES HAVE DROPPED
INTO THE LOW 20S. WINDS WILL DIMINISH TONIGHT...WITH RECOVERING RH
VALUES...BEFORE REDEVELOPING AGAIN ON THURSDAY. WITH A BUILDING
COASTAL RIDGE...WINDS TOMORROW WILL BE STRONGER FROM THE SOUTH
WITH GUSTS AS HIGH AS 35 MPH. FRIDAY WILL REMAIN ON THE DRIER SIDE
ACROSS THE BASIN...BUT WINDS ARE NOT CURRENTLY EXPECTED TO REACH
CRITICAL THRESHOLDS.

FOR THE LONG TERM...MODELS ARE NOW INDICATING A FAIRLY STRONG
UPPER LEVEL DISTURBANCE CLIPPING THE KENAI PENINSULA SATURDAY
MORNING...LEAVING THE POTENTIAL FOR DRIER AND GUSTIER WINDS TO MIX
DOWN FROM ALOFT IN ITS WAKE. HIGHLY DEPENDENT ON WHICH MODEL
SOLUTION VERIFIES...THIS COULD LEAD TO WIDESPREAD LOWER RELATIVE
HUMIDITIES AND STRONGER GUSTS OVER THE SOUTHCENTRAL INTERIOR. WE
WILL CONTINUE TO MONITOR TRENDS AS WE MOVE CLOSER TO THE WEEKEND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A FRONT HAS STALLED ACROSS THE KUSKOKWIM VALLEY AND DELTA AND
WILL BE A FOCUS FOR CONTINUED RAIN THROUGH THE NIGHT ALONG WITH
DEEP SOUTHERLY FLOW ADVECTING MOISTURE UP FROM THE PACIFIC. THE
SURFACE PRESSURE GRADIENT TIGHTENS TONIGHT ACROSS BRISTOL BAY AND
THEN REMAINS STEADY THROUGH THURSDAY AS SURFACE RIDGING HOLDS
ACROSS THE EASTERN GULF AND A WEAK TROUGH MOVES EAST ACROSS THE
ALASKA PENINSULA. GUSTY WINDS WILL MAINLY IMPACT BRISTOL BAY
THROUGH FRIDAY...HOWEVER LOCAL GUSTS CAN BE EXPECTED ELSEWHERE AS
AN UNSETTLED PATTERN CONTINUES THROUGH THE END OF THE WEEK.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
LOW CLOUDS...RAIN AND PATCHY FOG CONTINUE THROUGH THE END OF THE
WEEK ACROSS THE BERING/ALEUTIANS. THE FRONT ALONG THE NORTHERN
BERING SLOWLY DIMINISHES THROUGH THURSDAY AND IS FOLLOWED BY THE
NEXT FRONT MOVING UP FROM THE PACIFIC FRIDAY MORNING. THIS FRONT
INITIALLY PROGRESSES SLOWLY ACROSS THE WESTERN AND CENTRAL
ALEUTIANS AND THEN PICKS UP MOMENTUM FRIDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE GENERAL PATTERN THROUGH MUCH OF THE LONG TERM FORECAST
REMAINS UNCHANGED...AND LOOKS TO CONTINUE THROUGH THE MIDDLE OF NEXT
WEEK. MODELS CONTINUE TO INDICATE A PERSISTENT BLOCKING NORTH
AMERICAN RIDGE STANDING FAST OVER THE GULF AND SOUTHCENTRAL ALASKA
THROUGH MID NEXT WEEK...WITH A DEEP TROUGH OVER THE BERING AND
NORTH PACIFIC PRODUCING MULTIPLE DISTURBANCES THAT RIDE UP ALONG
THE RIDGE FROM THE NORTH PACIFIC. WITH THIS PATTERN WE ARE
EXPECTING RELATIVELY WARM AND MOIST SOUTHERLY FLOW OVER MUCH OF
THE MAINLAND...ALONG WITH ROUND AFTER ROUND OF RAIN AND GUSTY
WINDS AS EACH SYSTEM TRACKS THROUGH THE EASTERN ALEUTIANS AND INTO
THE SOUTHWEST MAINLAND AND WESTERN GULF. HOWEVER...THE PLACEMENT AND
STRENGTH OF THESE SYSTEMS IS NOT YET SOLIDIFIED BETWEEN THE
CURRENT MODEL SOLUTIONS. THE CURRENT SPREAD BETWEEN MODEL
SOLUTIONS HAS LED TO LOWER FORECAST CONFIDENCE IN WHERE THE
SIGNIFICANT WEATHER WILL SET UP OVER THE MAINLAND...AND THE
TIMING OF GAP FLOWS ALONG THE ALASKA PENINSULA AND AROUND
SOUTHCENTRAL ALASKA.

THE PREFERRED SOLUTION FOR THE LONG TERM FORECAST PACKAGE WAS THE
ECMWF AND WPC...WHICH HAS BEEN CONSISTENTLY SHOWING A SLIGHTLY
MORE RESILIENT/STRONGER RIDGE BUILDING OVER THE GULF AND
SOUTHCENTRAL. THE THOUGHT PROCESS BEHIND THIS WAS WITH MORE
DIURNAL HEATING RESULTING IN WARMER LOW LEVEL TEMPERATURES...AND
WARMER AIR BEING ADVECTED UP FROM THE NORTH PACIFIC...THAT THE
RIDGE WILL LIKELY STRENGTHEN. THE CHALLENGE REMAINS TO THE WEST
OF THE AMPLIFIED RIDGE OVER THE GULF AND SOUTHCENTRAL...WHERE
MODEL AGREEMENT ON THE VARIOUS SYSTEMS OUT WEST KEEPS FORECAST
CONFIDENCE LOWER THAN NORMAL.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...RED FLAG WARNING...141.

&&

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