Small Craft Advisory 564, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT WED JUL 15 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL TROUGH STRETCHING FROM BRISTOL BAY ACROSS THE
ALASKA PENINSULA AND GULF TO SOUTHEAST ALASKA WILL SHEAR APART
TODAY AS THE NEXT INCOMING LOW SOUTH OF THE CENTRAL ALEUTIANS
TRACKS TO THE EAST NORTHEAST TOWARDS THE SOUTHWESTERN GULF. THE
EASTERN PART OF THE UPPER TROUGH WILL BREAK OFF AND MOVE INTO
BRITISH COLUMBIA ALLOWING RIDGING TO STRENGTHEN OVER THE EASTERN
GULF AND NORTHERN GULF COAST. THE WESTERN PORTIONS OF THE TROUGH
WILL LIFT NORTH AND INLAND TO BE PULLED BACK TOWARDS BRISTOL BAY
WHERE IT WILL MERGE WITH THE NEW MAIN LOW CENTER.

&&

.MODEL DISCUSSION...
MODEL DIFFERENCE REMAIN FAIRLY MINOR THROUGH THE END OF THE WEEK.
THE GEM REGIONAL AND THEN ECMWF WERE PREFERRED ON THE EAST DOMAIN
AND THE GFS FOR THE WEST. CONFIDENCE IN THE PLACEMENT AND TIMING
OF THE SYNOPTIC SCALE FEATURES SUCH AS THE UNSEASONABLY STRONG
FRONT APPROACHING THE SOUTHWESTERN GULF THIS AFTERNOON AND EVENING
IS HIGH.

&&

.FIRE WEATHER...
A MODERATELY UNSTABLE ATMOSPHERE COMBINED WITH A SHORTWAVE TROUGH
SWINGING OVER SOUTHWEST ALASKA TODAY WILL BRING ONE MORE
AFTERNOON AND EVENING OF SCATTERED SHOWERS AND ISOLATED WET
THUNDERSTORMS. ADDITIONALLY ISOLATED WET THUNDERSTORMS ARE
POSSIBLE OVER THE PORTIONS OF THE SUSITNA VALLEY AND TALKEETNA
MOUNTAINS THIS AFTERNOON AND EVENING. AN INCOMING PACIFIC FRONTAL
SYSTEM WILL BRING WIDESPREAD WETTING RAIN TO SOUTHWEST ALASKA AND
THE GULF COAST THURSDAY AND THURSDAY NIGHT AND TO SOUTHCENTRAL
ALASKA THURSDAY NIGHT AND FRIDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
SOUTH CENTRAL ALASKA WILL BE IN BETWEEN WEATHER SYSTEMS TODAY AS
THE LOW THAT HAS BEEN OVER THE GULF BREAKS APART AND A STRONGER
SYSTEM PUSHES EASTWARD ACROSS THE ALEUTIANS. THEREFORE A BIT OF A
BREAK IS IN STORE FOR TODAY INTO TONIGHT...ALTHOUGH SOME SHOWERS
ARE POSSIBLE DUE TO LINGERING MOISTURE. BY LATER TONIGHT THE
NEXT UPPER LOW WILL BE OVER THE EASTERN ALEUTIANS AND ALASKA
PENINSULA. THIS WILL OPEN UP STRONG SOUTHWESTERLY FLOW ALOFT AND
USHER IN A FAIRLY WET PERIOD. FAIRLY STRONG WINDS ARE EXPECTED
WITH THIS SYSTEM (FOR THIS TIME OF YEAR). GALE WARNINGS HAVE BEEN
ISSUED FOR SOME OF THE MARINE AREAS...AND WINDS IN EXCESS OF 50
MPH ARE POSSIBLE ALONG TURNAGAIN ARM BY LATE THURSDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH THURSDAY)...
A WETTER PATTERN SETS UP FOR THE END OF THE WEEK AS A STORM
SYSTEM MOVES UP FROM THE NORTH PACIFIC. THE FRONT CURRENTLY OVER
THE EASTERN ALEUTIANS MOVES INTO THE ALASKA PENINSULA THIS
MORNING. GUSTY WINDS ALONG THE FRONTAL BOUNDARY WILL BE OUT THE
EAST BETWEEN 25 TO 35 MPH. ACROSS THE SOUTHWEST MAINLAND
TODAY...IT WILL BE RELATIVELY QUIET WITH PATCHY FOG ALONG THE
COAST IN THE MORNING AND MOSTLY CLOUDY CONDITIONS ELSEWHERE.
DURING THE AFTERNOON A FEW BREAKS IN THE CLOUDS WILL HELP MAXIMIZE
SURFACE HEATING AND TRIGGER ISOLATED THUNDERSTORMS IN THE
AFTERNOON AND EVENING...HOWEVER COVERAGE WILL BE MINIMAL AS THE
UPPER LEVEL LOW OVER THE SOUTHWEST SHEARS APART WITH THE APPROACH
OF THE NEXT STORM SYSTEM.

THE FRONTAL BOUNDARY ADVANCES TONIGHT MAKING INTO THE CENTRAL
BERING AND BRISTOL BAY THURSDAY MORNING. THE FRONT THEN SLOWS
ON THURSDAY AS THE SURFACE LOW CROSSES FROM THE NORTH PACIFIC
INTO THE EASTERN BERING...HOWEVER RAIN CONTINUES TO SPREAD ACROSS
KUSKOKWIM DELTA AND VALLEY BY THE AFTERNOON. WINDS ACROSS THE
SOUTHWEST MAINLAND PEAK THURSDAY MORNING WITH THE STRONGEST WINDS
ALONG THE ALEUTIAN RANGE. RAIN DIMINISHES THURSDAY NIGHT INTO
FRIDAY AS THE SURFACE LOW LIFTS NORTH AND WEAKENS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH THURSDAY)...
THE UPPER LEVEL LOW SPINNING SOUTH OF KISKA MAKES EASTWARD
PROGRESS TODAY. AN EXPANSIVE RAIN BAND DEVELOPS THIS MORNING
ACROSS THE CENTRAL ALEUTIANS TO THE ALASKA PENINSULA. THE STORM
SYSTEM WILL NOT MAKE MUCH PROGRESS NORTH UNTIL TONIGHT. RAIN
SPREADS TO THE CENTRAL BERING OVERNIGHT WITH GUSTY EAST WINDS
INCREASING ALONG THE BOUNDARY. THE WESTERN BERING WILL SEE
NORTHERLY WINDS ON THE BACKSIDE OF THE LOW WITH PATCHY FOG AND
CLOUDS. A RIDGE BUILDS ACROSS THE BERING AS THE STORM SYSTEM LIFTS
NORTH ON FRIDAY. A WEAK DISTURBANCE EARLY FRIDAY MORNING WILL
BRING INCREASED RAIN CHANCES ACROSS THE WESTERN BERING AND
ALEUTIANS THROUGH THE DAY WITH A STRONGER FRONT MOVING IN FRIDAY
NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A LOW PRESSURE SYSTEM TRACKING THROUGH THE EASTERN ALEUTIANS
EARLY THURSDAY WILL QUICKLY SHIFT NORTHWARD INTO THE EASTERN
BERING BY THE AFTERNOON...AS A STRONG JET STREAK SETS UP OVER
THE AKPEN. MODELS HAVE CONTINUED TO TREND TOWARD A MUCH LESS
AGGRESSIVE PHASING OF THE UPPER LEVEL ENERGY COMING OFF EASTERN
RUSSIA WITH THE UPPER LOW TRACKING INTO THE WESTERN COAST OF
ALASKA BY THE END OF THE WEEK. MODERATE TO HEAVY RAINFALL
ASSOCIATED WITH THIS SYSTEM WILL BEGIN TO BLANKET THE SOUTHERN
MAINLAND...WITH SOME AREAS ALONG THE KENAI/CHUGACH MOUNTAINS
EXPERIENCING SOME DOWNSLOPING DUE TO STRONGER CROSS BARRIER FLOW
ON THURSDAY. HOWEVER...WITH MODELS NOW SHOWING THE WAVE OVER THE
SOUTHWESTERN COAST ON THURSDAY SHIFTING SLIGHTLY TO THE
EAST...BROAD SOUTHWEST FLOW WILL QUICKLY BUILD OVER THE AREA. AS A
RESULT...DOWNSLOPING WILL QUICKLY FADE AND STEADIER RAINFALL WILL
BUILD OVER THE KENAI/CHUGACH MOUNTAINS BY FRIDAY. IT IS WORTH
NOTING THAT RUN TO RUN MODEL CONSISTENCY HAS NOT BEEN GOOD OVER
THE PAST FEW DAYS. THERE HAS BEEN IMPROVEMENT THOUGH WITH THE
MODEL RUNS TODAY...SO THERE IS NOW MODERATE CONFIDENCE IN THIS
SOLUTION.

MODELS THEN COME INTO FAIR AGREEMENT WITH THE PARENT TROUGH
SHIFTING NORTHWARD OVER THE NORTHERN INTERIOR BY SATURDAY
AFTERNOON...GIVING WAY TO AN AMPLIFYING RIDGE BUILDING OVER THE
EASTERN BERING AND MUCH OF THE MAINLAND BY TUESDAY MORNING.
HOWEVER...THE FINER DETAILS SUCH AS STRENGTH AND POSITIONING STILL
NEED TO BE WORKED OUT...AS WELL AS HOW EACH MODEL IS HANDLING THE
WEAKER WAVES CIRCULATING AROUND THE TOP OF THE RIDGE DIFFERENTLY.
THUS THE FORECAST LEANED HEAVIER ON THE WPC ENSEMBLE APPROACH.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

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