Small Craft Advisory 579, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
130 PM AKDT SUN AUG 3 2014

.ANALYSIS AND UPPER LEVELS...
THE LARGE UPPER LOW IN THE NORTHEAST PACIFIC CONTINUES TO INCH
INTO THE SOUTHERN GULF...AND WITH IT HAS BROUGHT A RETURN TO
ACTIVE WEATHER ACROSS MUCH OF SOUTHERN ALASKA. A SHORTWAVE AND
ASSOCIATED BAND OF PRECIP SWEPT THROUGH PORTIONS OF SOUTH CENTRAL
THIS MORNING WITH A FAIRLY BRIEF SHOT OF RAIN. DEEP MOISTURE IS
NOW DIMINISHING GIVING WAY TO MUCH MORE SHOWERY PRECIPITATION FROM
THE COPPER BASIN INTO THE NORTHERN GULF AND COOK INLET AREA. THE
NEXT SHORTWAVE AND ASSOCIATED PRECIP IS QUICKLY RACING INTO THE
NORTHERN GULF AND LOOKS EVEN MORE IMPRESSIVE THAN THE FIRST...WITH
OVER-WATER THUNDERSTORM ACTIVITY CONTINUING ALONG A LINE OF
IMPRESSIVE CONVECTION ALONG 140W. A POOL OF COLD AIR ALOFT IS
HELPING TO STEEPEN LAPSE RATES AND INCREASE INSTABILITY ACROSS
MUCH OF THE AREA...WHICH WILL BE THE PREVAILING CONDITION ACROSS
VIRTUALLY ALL OF SOUTHERN ALASKA OVER THE NEXT FEW DAYS. LOW-LEVEL
MOISTURE REMAINS TRAPPED ACROSS THE Y-K DELTA...WHERE DENSE FOG
AGAIN FORMED THIS MORNING. THE AFOREMENTIONED INSTABILITY ALOFT IS
ALREADY PRODUCING SHOWER ACTIVITY ROLLING OVER THE TOP OF THIS FOG
LAYER...AND IF SKIES ARE ABLE TO CLEAR AT ALL THIS AFTERNOON THERE
IS A POTENTIAL FOR THUNDERSTORM ACTIVITY ALONG THE KILBUCK
MOUNTAINS AND LOWER KUSKOKWIM VALLEY. IN THE BERING SEA...STRATUS
AND WEAK PRESSURE GRADIENTS REMAIN THE OVERALL PATTERN...THOUGH
CHANGE IS JUST BEGINNING TO PEAK INTO THE WESTERN ALEUTIANS AS A
FRONT APPROACHES FROM THE NORTHWEST PACIFIC.

&&

.MODEL DISCUSSION...
THE MODELS ARE STILL STRUGGLING WITH THE PLACEMENT AND STRENGTH OF
THE SURFACE LOW ASSOCIATED WITH THE SHORTWAVE CURRENTLY ROARING UP
THE EAST SIDE OF THE UPPER LOW IN THE GULF. THE ECMWF WAS THE
FIRST TO DEPICT A SIGNIFICANTLY STRONGER CENTER DEVELOPING
TOMORROW...AND OVERNIGHT ALL MODELS HAVE CONTINUED TO GENERALLY
TREND THIS DIRECTION. WILL NOT GO AS WHOLE-HOG STRONG AS THE ECMWF
OR GEM-REGIONAL...BUT WILL CONTINUE TO INCREASE WINDS ABOVE WHERE
THE AMERICAN MODELS HAVE THEM. THIS WILL MEAN HOISTING A GALE
WARNING FOR THE NORTHERN GULF FOR TOMORROW AFTERNOON AND EVENING.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
DEEP MOISTURE ASSOCIATED WITH THE FIRST FRONT THAT ROLLED THROUGH
THIS MORNING IS NOW MOVING OFF TO THE WEST. CONVECTIVE CLOUDS HAVE
FILLED IN QUICKLY OVER THE COPPER BASIN AND INTERIOR KENAI
PENINSULA AS EVEN SMALL AMOUNTS OF SUNSHINE AND HEATING HAVE
TAKEN ADVANTAGE OF STEEP ATMOSPHERIC LAPSE RATES. IT DOES STILL
SEEM LIKELY THAT SOME LIMITED DIURNAL HEATING IN THE SUSITNA
VALLEY AND A SLACKING DOWN-INLET GRADIENT WILL ALLOW SOME OF THE
WINDS BLOWING THROUGH TURNAGAIN ARM TO BEND INTO WEST ANCHORAGE
THIS EVENING...BUT THIS SHOULD END QUICKLY BY LATE EVENING AS THE
DOWN-INLET GRADIENT QUICKLY STRENGTHENS ONCE AGAIN.

CLOUD-TOP TEMPERATURES ARE QUICKLY FALLING AS LIFT ASSOCIATED
WITH THE VIGOROUS WAVING MOVING NORTH INTO THE GULF ARE ALREADY
SPREADING INTO THE EASTERN COPPER RIVER BASIN. THE BIORKA ISLAND
RADAR SHOWS PRECIP ALREADY SURGING TOWARD THE COAST...ALL
INDICATIONS THAT THIS NEXT ROUND OF RAIN IS MOVING AHEAD OF
SCHEDULE JUST LIKE THE ONE LAST NIGHT. HI- RESOLUTION MODELS ARE
TRYING TO DEPICT SOME CONVECTIVE SHOWER ACTIVITY IMMEDIATELY AHEAD
OF THE BAND OF FRONTAL PRECIP MOVING INTO PRINCE WILLIAM SOUND AND
COOK INLET DURING THE MORNING HOURS TOMORROW. SINCE THIS IS THE
SAME TYPE OF EVOLUTION AS HAPPENED THIS MORNING...A "RINSE AND
REPEAT" SCENARIO LOOKS LIKELY OVER BOTH COASTAL AND INLAND AREAS
OF SOUTHCENTRAL THROUGH TOMORROW.

SOUTHWEST ALASKA...
IN GENERAL THE SOUTHWEST MAINLAND WILL REMAIN ON THE PERIPHERY OF
THE LARGE LOW EXPECTED TO TAKE UP RESIDENCE IN THE GULF FOR THE
NEXT FEW DAYS. AS MENTIONED ABOVE...INCREASING MID-LEVEL
INSTABILITY WILL SET THE STAGE FOR MORE AND MORE CONVECTIVE
ACTIVITY OVER THE COMING DAYS. THE LARGEST QUESTION MARK REMAINS
HOW MUCH CLEARING WILL OCCUR AND ALLOW DIURNAL HEATING TO WORK IN
TANDEM WITH THIS MID-LEVEL INSTABILITY. WITH DECENT SURFACE
HEATING SOME DIURNAL THUNDERSTORMS ARE LIKELY THROUGH MIDWEEK
ALONG THE KILBUCK AND AHKLUN MOUNTAINS. HOWEVER...LOW STRATUS IS
HAVING A VERY HARD TIME BURNING OFF TODAY...AND A THERMAL TROUGH
STRENGTHENING NORTH OF THE DELTA WILL HELP TO KEEP PERIODS OF
STABLE SOUTHWEST SURFACE WINDS PUSHING MORE OF THIS FOG/STRATUS
BACK ONSHORE. WILL KEEP THE GOING FORECAST AS-IS FOR NOW AND SEE
HOW THINGS PLAY OUT LATER THIS EVENING. FURTHER EAST OVER MOST OF
BRISTOL BAY AND THE LOWER KUSKOKWIM VALLEY...SYNOPTIC CLOUDS WILL
GENERALLY BE MORE SUBSTANTIAL AND THUS LIMIT POTENTIAL FOR
THUNDERSTORM DEVELOPMENT...ALTHOUGH REGULAR RAIN SHOWER ACTIVITY
IS STILL A GOOD BET FOR EACH OF THE NEXT FEW DAYS.

BERING SEA/ALEUTIANS...
THE REGION WILL REMAIN UNDER THE STABILIZING INFLUENCE OF THE
WEAKENING HIGH PRESSURE FOR A FEW MORE DAYS...MEANING FOG AND
STRATUS WILL CONTINUE BUT BEGIN TO SLOWLY TREND TOWARD IMPROVEMENT
BY EARLY IN THE WEEK. MORE ACTIVE WEATHER WILL MOVE IN FROM THE
WEST STARTING MONDAY NIGHT IN THE FORM OF A WARM FRONT. THIS WILL
GRADUALLY SPREAD RAIN AND GUSTY SOUTHERLY WINDS ACROSS THE WESTERN
BERING AND ALEUTIANS BY MIDWEEK.

&&

.LONG TERM FORECAST (THU AUG 7TH - SUN AUG 10TH)...

A SUBSTANTIAL PATTERN CHANGE ACROSS THE REGION WILL BE IN FULL
SWING BY THURSDAY...WITH A HIGH LATITUDE BLOCK CENTERED OVER THE
CHUKCHI SEA FORCING A REINVIGORATED NORTH PACIFIC JET STREAM
OVER THE ALEUTIAN CHAIN...UNDERCUTTING WHAT HAD BEEN A PERSISTENT
BERING RIDGE. OVER SOUTHERN ALASKA...MOISTURE LEFT OVER FROM THE
REMNANTS OF THE GULF LOW WILL SUPPORT DIURNAL DRIVEN SHOWERS AND
CLOUDS...AND NEAR CLIMATOLOGICAL TEMPERATURES. EVENTUALLY...A
LARGE LOW WILL FORM ALONG THE PERIPHERY OF THE UPPER LEVEL JET
STREAM IN THE VICINITY OF THE EASTERN ALEUTIANS AND DUTCH
HARBOR...WITH A LARGE WARM FRONT TRACKING INTO THE GULF FRIDAY AND
SATURDAY. THIS SYSTEM HAS ALL THE TRAITS OF A TYPICAL LATE
SUMMER/EARLY FALL LOW...WITH SOUTHEAST FLOW SPREADING RAIN AND
CLOUDS ACROSS COASTAL LOCATIONS. INLAND LOCATIONS WILL GENERALLY SEE
SIGNIFICANT DOWNSLOPE DRYING WITH THE EXCEPTION OF THE SOUTHWEST
(BRISTOL BAY AND KUSKOKWIM DELTA) COASTLINES. THE FRONT WILL STALL
ALONG THE NORTH GULF COAST SUNDAY...WITH CLOUDINESS OVERSPREADING
SOUTHCENTRAL...AND CONTINUED RAIN ACROSS COASTAL AREAS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119.
FIRE WEATHER...NONE.

&&

DIXON/AHSENMACHER AUG 14