Small Craft Advisory 619, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
502 AM AKDT SAT AUG 8 2015

.ANALYSIS AND UPPER LEVELS...
THE PROGRESSIVE SOUTHWESTERLY FLOW ALOFT IS BEGINNING TO SET UP
ACROSS THE MAINLAND THIS MORNING. TWO PROMINENT SHORTWAVE TROUGHS
ARE APPARENT ON WATER VAPOR IMAGERY...ONE WEAKER AND BEGINNING TO
ENTER THE COOK INLET REGION AND ANOTHER BEEFIER WAVE APPROACHING
THE ALASKA PENINSULA...THE LATTER WILL BE THE MAIN WEATHER MAKER
OVER THE WEEKEND. THE TWO MAIN LOW PRESSURE SYSTEMS ALOFT
CONTROLLING THE SOUTHWEST FLOW SIT OVER THE THE CHUKCHI/BEAUFORT
SEA...AND ANOTHER OVER THE WESTERN ALEUTIANS. THE SOUTHERN SYSTEM
BRINGS A NICE FETCH OF HIGHER PRECIPITABLE WATER FROM THE
SUBTROPICAL PACIFIC AS WELL AS A 100 KT JET UP IN TO THE BERING
SEA WHERE SOME NOCTURNAL THUNDERSTORMS ARE CURRENTLY FIRING SOUTH
OF THE PRIBILOF ISLANDS.

&&

.MODEL DISCUSSION...
NO HUGE DISCREPANCIES BETWEEN MODEL GUIDANCE WITH THIS PACKAGE.
FRONTAL PROGRESSION...MOISTURE...AND WINDS ARE ALL VERY SIMILAR AS
WELL AS SURFACE LOW TRACK. THE GFS WAS USED ON THE WESTERN DOMAIN
AND A CONSENSUS BLEND WAS USED IN THE EASTERN DOMAIN.

&&

.FIRE WEATHER...
FIRE WEATHER CONCERNS WILL BE MITIGATED BY CLOUD COVER AHEAD OF A
MOIST SYSTEM APPROACHING THE MAINLAND TODAY. THE COPPER RIVER WILL
GET RELATIVE HUMIDITY VALUES DOWN INTO THE 30S THIS AFTERNOON
ALONG WITH SOME GUSTY SOUTHERLY WINDS BUT SHOULD STAY ABOVE RED
FLAG CRITERIA. THE NEXT SYSTEM ON SUNDAY WILL BRING A WIDESPREAD
WETTING RAIN TO MOST AREAS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL SHORT-WAVE RIDGE WHICH PROVIDED WARM AND DRY
CONDITIONS OVER SOUTHCENTRAL WILL QUICKLY EXIT TO THE EAST TODAY.
A VERY WEAK SHORT-WAVE WILL THEN QUICKLY TRANSIT THE AREA.
CONDITIONS ACROSS SOUTHCENTRAL REMAIN FAIRLY DRY AND STABLE THANKS
TO THE UPPER RIDGE. THUS...EXPECT NO MORE THAN SOME SCATTERED
CONVECTION FOCUSED ALONG INTERIOR MOUNTAINS.

ALL THE INGREDIENTS ARE COMING TOGETHER FOR A WIDESPREAD SOAKING
RAIN SUNDAY THROUGH MONDAY AS A TROUGH DIGGING OUT OF THE ARCTIC
INTERACTS WITH JUICY AIR BEING TRANSPORTED FROM THE NORTHWEST
PACIFIC VIA A 90 KT+ SUBTROPICAL JET. THIS WILL BE A CONTINUOUS
RAIN OF 24 HOURS OR LONGER FOR MOST AREAS WITH WIDESPREAD RAINFALL
AMOUNTS OF ONE QUARTER TO THREE QUARTERS OF AN INCH. STRONG
SOUTHERLY FLOW THROUGHOUT MUCH OF THE EVENT WILL PRODUCE HEAVIER
RAIN OVER THE NORTHERN SUSITNA VALLEY AND PRINCE WILLIAM SOUND
WHERE STORM TOTAL AMOUNTS OF ONE TO THREE INCHES ARE LIKELY BY
MONDAY AFTERNOON.

&&

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

A SYSTEM APPROACHING THE SOUTHWEST COAST FROM THE BERING SEA WILL
USHER IN A PERIOD OF COOL AND WET WEATHER THAT WILL PERSIST OVER
THE TO THE SOUTHWEST MAINLAND THROUGH THE WEEKEND. RAIN SHOWERS CAN
ALREADY BE SEEN STARTING ALONG THE KUSKOKWIM DELTA COAST...AND
THIS WILL CONTINUE TO DEVELOP AND SPREAD INLAND OVER THE COURSE OF
THE DAY. AN ARCTIC TROUGH DIVING INTO THE NORTHWEST COAST WILL
PROVIDE THE COLD AIR THAT WILL CAUSE TEMPERATURES TO FALL BELOW
NORMAL THROUGH MONDAY...AND MAY EVEN SUPPLY ENOUGH COLD AIR TO
BRING A FRESH DUSTING OF SNOWFALL TO THE WESTERN ALASKA RANGE BY
MONDAY MORNING AS TEMPERATURES ALOFT FALL BELOW FREEZING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

THE LOW CURRENTLY OVER THE CENTRAL BERING WILL BE THE FOCAL POINT
FOR THE WEATHER THROUGHOUT THE REGION THIS WEEKEND. OF PARTICULAR CONCERN
IN THE FORECAST THIS MORNING SURROUND THE DEVELOPMENT OF ISOLATED
THUNDERSTORMS JUST TO THE SOUTH OF THE PRIBILOF ISLANDS. THESE
THUNDERSTORMS ARE DEVELOPING ALONG THE BACK EDGE OF THE
RAINFALL...WHERE DRY AIR ENTRAINMENT ALOFT AND AN APPROACHING JET
STREAK ARE CREATING ENOUGH INSTABILITY AND DYNAMICS TO SUPPORT
THUNDERSTORMS. THESE STORMS ARE EXPECTED TO CONTINUE IN THE
PRIBILOF ISLANDS AREA INTO THE MID MORNING...AND THEN PERSIST OVER
THE OFFSHORE WATERS TO THE EAST INTO THIS AFTERNOON. GUSTY
SOUTHEASTERLY WINDS ARE ALSO OCCURRING FROM THE EASTERN ALEUTIANS
INTO THE AKPEN IN ADVANCE OF THE APPROACHING LOW AND RESULTANT
PRESSURE FALLS OVER THE BERING. THESE WINDS ARE EXPECTED TO
PERSIST WITH RAIN IN THE AREA THROUGH THIS EVENING WHEN THEY WILL
BEGIN TO DIMINISH. RAIN WILL THEN CONTINUE OVER MUCH OF THE REGION
THROUGH SUNDAY...BUT WITH DIMINISHING WINDS.

&&

.LONG TERM FORECAST (MONDAY THROUGH FRIDAY)...

AS THE LARGE RAINMAKER THIS WEEKEND MOVES OUT OF THE AREA ON
MONDAY...THE BERING SEA/ALEUTIANS AS WELL AS THE MAINLAND WILL
COME UNDER THE GENERAL INFLUENCE OF A BROAD LONGWAVE TROUGH
CENTERED OVER THE FAR WESTERN BERING. THIS WILL SET THE AREA UP
UNDER WESTERLY OR WEST/SOUTHWESTERLY FLOW FOR NEXT WEEK. THIS IS
USUALLY A PRETTY PROGRESSIVE PATTERN OVERALL...WHICH MEANS THAT
INDIVIDUAL STORMS/WAVES TEND TO BE ON ON THE FASTER AND WEAKER END
OF THE SCALE (RELATIVELY) FOR THE VOLATILE NORTH PACIFIC. THE
UPCOMING WEEK LOOKS LIKE IT WILL FOLLOW THIS GENERAL
TEMPLATE...WITH SENSIBLE WEATHER DICTATED LARGELY BY AN
ALTERNATING SEQUENCE OF SHORTWAVE TROUGHS AND SHORTWAVE RIDGES.
THE BIGGEST AREA OF UNCERTAINTY IS THE EVENTUAL FATE OF A TROPICAL
DISTURBANCE CURRENTLY SOUTHEAST OF JAPAN. GLOBAL MODELS HAVE BEEN
STRUGGLING WITH WHETHER TO BRING THE REMNANTS INTO THE ALEUTIAN
REGION OR KEEP IT SOUTH...WITH THE LATEST AND GREATEST GUIDANCE
SUGGESTING IT WILL STAY SOUTH AND OUT OF OUR AREA. THERE SHOULD BE
SOME BREAKS OF SUN BY MIDWEEK ACROSS THE MAINLAND...BUT NO
HEATWAVES OR HUGE RAIN-OUTS ANTICIPATED AT THIS TIME.
OVERALL...CONSIDERING THAT AUGUST IS HISTORICALLY THE RAINIEST
MONTH FOR MOST LOCATIONS IN SOUTHERN ALASKA...NEXT WEEK SHOULD BE
NICER THAN NORMAL ACROSS MAINLAND LOCATIONS.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...AMD

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1105 AM AKDT SAT AUG 8 2015

AKZ141-100100-
COPPER RIVER BASIN-
INCLUDING THE CITIES OF...GLENNALLEN...EUREKA...MCCARTHY...
PAXSON...SLANA
1105 AM AKDT SAT AUG 8 2015

...RIVER LEVELS ON THE TAZLINA RIVER CONTINUE TO RISE DUE TO A
GLACIER DAMMED LAKE RELEASE...

THE RELEASE OF WATER FROM ICEBERG LAKE...A GLACIER DAMMED LAKE ON
THE NELCHINA GLACIER...HAS STOPPED. WATER LEVELS IN THE NELCHINA RIVER
AND TAZLINA LAKE HAVE RISEN ABOUT 2 TO 3 FEET AND ARE NOW RECEDING.
RIVER LEVELS ON THE TAZLINA RIVER AT THE RICHARDSON HIGHWAY BRIDGE
CONTINUE TO RISE AS A RESULT OF THIS RELEASE AND ARE EXPECTED TO CREST BY
MONDAY MORNING THEN RECEDE.

FLOOD STAGE ON THE TAZLINA RIVER AT THE RICHARDSON HIGHWAY BRIDGE
IS 31 FEET BUT WATER LEVELS ARE NOT EXPECTED TO REACH FLOOD STAGE.
ALL PERSONS WITH INTERESTS NEAR THESE AREAS SHOULD MONITOR THE
WATER LEVELS OVER THE NEXT SEVERAL DAYS. RIVER STAGE DATA FOR THE
TAZLINA RIVER AT THE GLENN HIGHWAY BRIDGE ARE AVAILABLE AT THE WEB
SITE: APRFC.ARH.NOAA.GOV

THIS STATEMENT WILL BE UPDATED AS CONDITIONS WARRANT.