Small Craft Advisory 512, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
458 AM AKDT FRI JUN 19 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL HIGH REMAINS IN AN OMEGA BLOCK PATTERN OVER THE
NORTHERN BERING SEA...WITH THE UPPER LEVEL LOW OVER SOUTHEAST
ALASKA. THIS HAS KEPT THE GENERAL NORTH TO SOUTH FLOW OVER MUCH OF
THE MAINLAND FOR THE PAST FEW DAYS. UNLIKE YESTERDAY WHERE THERE
WAS LINGERING INSTABILITY AND A LACK OF MOISTURE OR TRIGGER TO
INITIATE STRONG CONVECTION...TODAY SOME MOISTURE BEGINS TO ADVECT
INTO THE AREA ALONG WITH INCREASED INSTABILITY. THIS PRIMES THE
ATMOSPHERE OVER SOUTHCENTRAL AND PARTS OF THE SOUTHWEST MAINLAND
FOR STRONGER CONVECTION...KICKING OFF SHOWERS AND THUNDERSTORMS
BOTH TODAY AND SATURDAY. THE ISOLATED THUNDERSTORMS CURRENTLY SEEN
ON RADAR TRACKING ALONG THE TALKEETNA AND CHUGACH MOUNTAINS THIS
MORNING IS A PRECURSOR TO HOW MUCH INSTABILITY IS STILL LINGERING
AROUND...AND HOW STRONG THE INSTABILITY WILL BE TODAY WHEN WE
START TO PICK UP SOME DAYTIME HEATING.

AT THE SURFACE...THE THERMAL TROUGH IS DEVELOPING IN THE INTERIOR
OF THE STATE AND EXTENDING TOWARD BRISTOL BAY. MARINE STRATUS HAS
REMAINED OVER A LARGE PART OF THE GULF OF ALASKA AND ALEUTIAN
CHAIN UNDERNEATH HIGH PRESSURE OVERNIGHT. THE MARINE LAYER OVER
THE GULF WILL LIKELY START TO PUSH NORTHWARD UP COOK INLET THIS
EVENING...DRIVEN BY THE THERMAL TROUGH OVER THE INTERIOR.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT THROUGH THE WEEKEND. THE
GFS AND NAM ARE BOTH IN GOOD AGREEMENT WITH THE AREAS OF MOISTURE
AND INSTABILITY SETTING UP OVER THE SOUTHERN MAINLAND TODAY AND
THROUGH THE WEEKEND. BOTH SHOW THE STRONGER INSTABILITY
STRETCHING FROM THE TALKEETNA MOUNTAINS THROUGH KUSKOKWIM
MOUNTAINS AND SOUTHWARD OVER THE KENAI PENINSULA TODAY AND
SATURDAY. THE NAM CONTINUES TO PERFORM WELL WITH PICKING UP THE
LOW LEVEL MARINE LAYER...AND IS CONTINUING TO SHOW A STRONG PUSH
UP COOK INLET FRIDAY NIGHT THROUGH SUNDAY MORNING. HOWEVER...THIS
REMAINS A DIFFICULT FEATURE TO RESOLVE AND THE NAM DOES THE BEST
JOB OF IT. THE GFS IS ALSO SHOWING THIS OCCURRING BUT IS LIMITED
IN ITS RESOLUTION.

&&

.FIRE WEATHER...
CRITICAL FIRE WEATHER CONDITIONS ARE NOT EXPECTED OVER THE NEXT
COUPLE OF DAYS. INCREASING MOISTURE AND INSTABILITY WILL BRING
ISOLATED TO SCATTERED THUNDERSTORMS OVER PARTS OF SOUTHCENTRAL
DURING THE AFTERNOON AND EVENING HOURS TODAY. THESE THUNDERSTORMS
WILL BE MAINLY WET. SOME WIND IS EXPECTED TODAY IN THE COPPER
RIVER BASIN...BUT SHOULD REMAIN BELOW CRITICAL LEVELS.

OUT WEST...WINDS AND HUMIDITY VALUES WILL REMAIN BELOW CRITICAL
FIRE WEATHER THRESHOLDS...WITH THE LOWEST HUMIDITY VALUES OVER
THE MIDDLE KUSKOKWIM VALLEY AND WESTERN ALASKA RANGE TODAY.
HOWEVER...THESE VALUES WILL MODERATE QUICKLY THIS EVENING WITH
DEVELOPMENT OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS MAINLY
OVER THE MOUNTAINS...WITH THE BEGINNING OF A WEAK SOUTHWEST WIND
WITH MOISTURE ADVECTION. A GENERAL MODERATING TREND WILL CONTINUE
THROUGH THE WEEKEND WITH ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS DEVELOPING EACH AFTERNOON AND EVENING MAINLY TOWARD
THE ALASKA RANGE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (TODAY THROUGH SUNDAY)...
UPPER LEVEL HIGH PRESSURE OVER SOUTH CENTRAL ALASKA WILL WEAKEN
TODAY AND SATURDAY. THIS WILL ALLOW AN INCREASE IN MOISTURE AND
INSTABILITY OVER THE AREA. EXPECTING SOME DIURNAL SHOWERS AND
THUNDERSTORMS OVER MUCH OF THE AREA TODAY...MAINLY OVER THE
MOUNTAINS AND INLAND AREAS. ON SATURDAY THESE SHOWERS WILL PUSH
FURTHER INLAND. THE LOW LEVEL THERMAL TROUGH WILL PUSH NORTH OF
THE ALASKA RANGE TODAY. THIS WILL USHER IN COOLER MARINE AIR.
MAXIMUM TEMPERATURES WILL BE COOLER THAN THEY HAVE BEEN...THOUGH
STILL ABOVE NORMAL IN MOST AREAS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TODAY THROUGH SUNDAY)...
HIGH PRESSURE ALOFT WILL CONTINUE OVER WESTERN AND CENTRAL
ALASKA...WITH A WEAK UPPER LEVEL TROUGH/LOW OVER THE BRISTOL BAY
COAST EVENTUALLY MOVING NORTH AND WEST INTO THE BERING BY LATE
TONIGHT INTO SATURDAY. WINDS WILL CONTINUE TO BE FROM THE NORTH
AND WEST ON THE WEST SIDE OF THE THERMAL TROUGH AND GENERALLY FROM
THE SOUTH ON THE EAST SIDE. THIS WILL MEAN GOOD MOISTURE ADVECTION
PRIMARILY DURING THE OVERNIGHT HOURS...ESPECIALLY FOR GREATER
BRISTOL BAY. ISOLATED SHOWERS AND THUNDERSTORMS WILL DEVELOP WITH
INCREASING INSTABILITY OVER THE REGION...ESPECIALLY TOWARD THE
ALASKA AND ALEUTIAN RANGES THROUGH THE WEEKEND BUT PERHAPS
EXTENDING SOUTH TOWARD BRISTOL BAY AND TO THE WEST TOWARD THE
KILBUCK MOUNTAINS AT TIMES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TODAY THROUGH SUNDAY)...
THE HIGH PRESSURE THAT HAD BEEN SO DOMINANT THIS WEEK LOOKS TO
SHIFT NORTH AND WEST AS IT BEGINS TO WEAKEN ON FRIDAY. CONDITIONS
STILL APPEAR QUITE FAVORABLE TO HAVE FOG RE-DEVELOP ALONG THE
BERING SIDE OF THE ALASKA PENINSULA AND ALONG THE ALEUTIAN CHAIN
AS WELL AS THE NORTHERN AND WESTERN BERING SEA. AN AREA OF LOW
PRESSURE IN THE NORTHWESTERN PACIFIC CONTINUES TO INCH CLOSER TO
THE WESTERN ALEUTIANS AND WILL PUSH A FRONT ACROSS THE WESTERN
ALEUTIANS ON TODAY. THIS WILL BRING GALE FORCE WINDS TO THE
COASTAL MARINES ZONES SURROUNDING THE CENTRAL ALEUTIANS AS WELL AS
NEAR STRONG-WIND HEADLINE CRITERIA OVER ADAK AND ATKA. THESE WINDS
WILL BE SHORT-LIVED AS THE FRONT QUICKLY SLIDES EASTWARD AND
OCCLUDES THROUGH THE WEEKEND.

&&

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

THE UPPER LEVEL BLOCKING RIDGE CENTERS NEAR THE BERING STRAIT
TOWARD THE END OF THE WEEKEND AND BECOMES STATIONARY THROUGH THE
NEXT WEEK. THERE IS A PATTERN CHANGE THAT COMMENCES SLOWLY WITH
LOW PRESSURE SLOWLY BREAKING DOWN THE RIDGE INFLUENCE ACROSS THE
MAINLAND THROUGH NEXT WEDNESDAY. MODELS ARE STILL NOT IN GOOD
AGREEMENT WITH THE EVOLVING WEATHER PATTERN ON THE LATEST 12Z RUN.
HOWEVER...THE ECMWF AND GFS WERE IN BETTER AGREEMENT TODAY THEREFORE
A BLEND TOWARD BOTH SOLUTIONS WERE INCORPORATED IN THE EXTENDED
FORECAST.

THE FORECAST CONTINUES TO ADVERTISE DIURNALLY DRIVEN PRECIPITATION
CHANCES ACROSS THE MOUNTAIN RANGES OF THE SOUTHERN MAINLAND. A
STRONG SHORTWAVE THAT IS EXPECTED TO MOVE FROM THE EASTERN GULF ON
SATURDAY NIGHT MAY BRING ENHANCED CONVECTION AS IT TRACKS WEST THROUGH
THE GULF INTO THE BEGINNING OF NEXT WEEK. THE MOST ORGANIZED
SYSTEM TO WATCH THIS WEEK IS THE LOW THAT CENTERS SOUTH OF THE
EASTERN ALEUTIANS SATURDAY NIGHT. THIS STACKED SYSTEM WILL BRING A
NOTABLE WETTER CHANGE TO THE GULF WATERS BY MID WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 174 176.
FIRE WEATHER...NONE.

&&

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