Small Craft Advisory 586, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
433 PM AKDT TUE JUL 21 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS A LARGE EASTWARD MOVING LOW OVER THE CENTRAL BERING SEA.
AN ASSOCIATED FRONT IS CURRENTLY DISSIPATING OVER SOUTHWEST
ALASKA AS IT MOVES INTO A RIDGE OVER SOUTHERN ALASKA. THIS RIDGE
IS IN THE PROCESS OF FLATTENING. A WEATHER SYSTEM ASSOCIATED WITH
THE BERING LOW IS DEVELOPING JUST SOUTH OF THE EASTERN ALEUTIANS
AND IS MOVING TOWARD THE NORTHEAST. AT THE LOWER LEVELS THE FLOW
HAS BECOME SLACK OR SLIGHTLY ONSHORE...THE OFFSHORE FLOW THAT HAS
BEEN SEEN THE LAST COUPLE OF DAYS HAS ENDED.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN REASONABLE AGREEMENT FOR THE SHORT
TERM PORTION OF THE FORECAST (THROUGH THURSDAY AFTERNOON). THERE
ARE SOME DIFFERENCES IN HOW FAR NORTH THEY BRING THE DEEPER
MOISTURE AND DECENT RAINS INTO SOUTH CENTRAL ALASKA WEDNESDAY
NIGHT INTO EARLY THURSDAY. THE NAM IS KEEPING IT JUST TO THE SOUTH
OF ANCHORAGE. THE CANADIAN MODEL IS SIMILAR THOUGH NOT QUITE AS
EXTREME. THE GFS AND ECMWF PUT ANCHORAGE FULLY UNDER THE GUN (GFS
GOING FOR AROUND A QUARTER INCH). THE CURRENT PREFERENCE IS FOR
THE GFS/ECMWF SOLUTION...BUT WITH CONFIDENCE NOT SUPER HIGH WILL
STAY WITH THE "LIKELY" POPS.

&&

.FIRE WEATHER...
NOT MUCH IN THE WAY OF FIRE WEATHER CONCERNS FOR THE NEXT FEW DAYS.
HUMIDITIES AND RAIN CHANCES WILL INCREASE THROUGH WEDNESDAY NIGHT
AS THE BERING LOW MOVES ACROSS SOUTHWEST ALASKA AND KODIAK ISLAND.
THURSDAY NIGHT AND FRIDAY WILL SEE A DECREASE IN MOISTURE. WINDS
ARE EXPECTED TO BE FAIRLY LIGHT TONIGHT INTO THURSDAY. AS THE
NEXT RIDGE BUILDS IN FROM THE NORTH OFFSHORE FLOW WILL DEVELOP
AGAIN THURSDAY NIGHT AND FRIDAY. THESE WINDS SHOULD BE OF SIMILAR
MAGNITUDE TO THE PREVIOUS EVENT (SUNDAY/MONDAY) THAT JUST ENDED. A
BRIEF PERIOD OF GUSTY SOUTHERLY WINDS WILL DEVELOP ALONG THE
COPPER RIVER LATE WEDNESDAY AFTERNOON AS THE SURFACE RIDGE ALONG
THE COAST INTENSIFIES. HOWEVER...BOTH WIND SPEEDS AND RH VALUES
WILL BE MARGINAL FOR RED FLAG CONDITIONS...SO NO WARNING WILL BE
ISSUED. HOWEVER...CONFIDENCE THAT CONDITIONS GET CLOSE IS FAIRLY
HIGH.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
CLOUD COVER AND SHOWER COVERAGE WILL INCREASE ACROSS THE REGION
THROUGH WEDNESDAY AS WEAK RIDGING IS REPLACED BY SOUTHWEST FLOW
ALOFT AHEAD OF THE BERING LOW. INSTABILITY WILL REMAIN SUFFICIENT
TO GENERATE A FEW THUNDERSTORMS ALONG THE ALASKA RANGE THROUGH
WEDNESDAY EVENING. WIDESPREAD RAIN WILL MOVE IN ON WEDNESDAY
NIGHT AS THE LOW PUSHES INTO THE WESTERN GULF. THE LOW WILL THEN
QUICKLY DEPART TO THE EAST ON THURSDAY LEAVING SCATTERED SHOWERS
IN ITS WAKE WITH GUSTY NORTHWEST WINDS ALONG THE GULF COAST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE REMNANTS OF THE WEATHER FRONT CONTINUE TO PUSH FARTHER INTO
THE UPPER KUSKOKWIM VALLEY THROUGH FAIRBANKS REGION THIS EVENING.
THIS WILL BRING SCATTERED SHOWERS WITH ONSHORE FLOW. BY WEDNESDAY
MORNING AN UPPER LEVEL CLOSED LOW WILL BE APPROACHING THE WESTERN
BRISTOL BAY WITH ABUNDANT MOISTURE STREAMING INTO THE SOUTHWEST
REGION. THERE WILL BE WIDESPREAD WETTING RAINS THROUGH LATE
WEDNESDAY EVENING WITH THE POTENTIAL FOR LOCALLY HEAVY RAINFALL
ALONG THE ALEUTIAN RANGE. THIS WILL BE ENHANCED BY THE UPSLOPE
OROGRAPHIC LIFT COMBINED WITH THE UPPER LEVEL LOW TRACKING ACROSS
THE ALEUTIAN RANGE INTO THE SOUTHWESTERN GULF BY THURSDAY MORNING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE LOW LOCATED JUST WEST OF SAINT MATTHEW ISLAND WILL CONTINUE TO
TRACK INTO THE NORTHERN BERING SEA BY WEDNESDAY...PUSHED ALONG BY
AN IMPRESSIVE 120 KT SOUTHWESTERLY JET STREAK. THIS WILL PRODUCE
SMALL CRAFT SOUTHWESTERLY WINDS THROUGH WEDNESDAY. NUMEROUS
SHORTWAVES ROTATING AROUND THE ASSOCIATED UPPER LEVEL LOW WILL
CONTINUE TO PRODUCE A SHOWERY WEATHER REGIME. THERE WILL BE
WIDESPREAD STRATUS WITH PATCHY FOG AS WE HEAD INTO THE MIDWEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A CLOSED UPPER LOW OVER THE GULF OF ALASKA THURSDAY WILL CONTINUE
TO TRACK EASTWARD INTO THE EASTERN GULF BY FRIDAY MORNING. A
SURFACE LOW ASSOCIATED WITH THIS SYSTEM WILL TRACK A FRONT ALONG
THE NORTHERN GULF COAST...AND STRETCHING DOWN TO THE SOUTHEASTERN
COAST. THIS WILL BRING INCREASED RAINFALL AMOUNTS...WITH HIGHER
AMOUNTS ALONG THE SOUTHERN KENAI AND WESTERN PRINCE WILLIAM SOUND.
SOME SCATTERED SHOWERS WILL LINGER OVER THE INLAND AREAS INTO THE
WEEKEND ACROSS SOUTHCENTRAL...HOWEVER RAIN AMOUNTS WILL BE
ON THE RELATIVELY LIGHT SIDE FOR THE COASTAL AREAS AS THE SURFACE
LOW QUICKLY SLIDES SOUTH TO THE EASTERN PACIFIC.

A PROGRESSIVE PATTERN SETS UP ACROSS THE BERING HEADING INTO THE
WEEKEND WITH SEVERAL WEAK DISTURBANCES MOVING AHEAD OF A
DEVELOPING TROUGH OVER KAMCHATKA. MODELS ARE STARTING TO COME INTO
AGREEMENT WITH REGARDS TO HOW THE UPPER LOW DEVELOPS AND TRACKS.
HOWEVER THERE ARE STILL ENOUGH MODEL DISCREPANCIES TO NOT HAVE
HIGH CONFIDENCE IN THE TRACK OF THIS SYSTEM. ENDED UP SIDING WITH
GLOBAL MODELS AND WPC WHICH WERE DEPICTING A SIMILAR SOLUTION OF
A LOW TRACKING THROUGH THE EASTERN BERING SATURDAY...THEN
REFORMING OVER THE GULF MONDAY WITH A RIDGE BUILDING TO THE WEST.
THE BERING AND ALEUTIANS WOULD CONTINUE WITH MARINE FOG/STRATUS UNDER
THE BUILDING RIDGE.

&&

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

&&

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