Small Craft Advisory 564, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1119 AM AKDT SAT JUL 26 2014

.ANALYSIS AND UPPER LEVELS...

THE REGIONAL UPPER AIR PATTERN CONSISTS OF A HIGH AMPLITUDE NORTH
CENTRAL PACIFIC RIDGE EXTENDING THROUGH THE BERING SEA INTO
EASTERN SIBERIA...WITH TWO LARGE LOWS BOOKENDING THE RIDGE. THE
WESTERN LOW COMPLEX IS SITUATED NEAR THE DATELINE AND 43N...THE
OTHER ACROSS THE GULF OF ALASKA. THE UPPER AIR PATTERN OVER THE
MAINLAND IS A BIT MORE CONVOLUTED...BUT CONSISTS OF A LARGE
CLOSED LOW OVER THE EASTERN GULF OF ALASKA...AND ANOTHER UPPER LOW
OVER CENTRAL ALASKA NEAR THE BROOKS RANGE. ALONG THE PERIPHERY OF
THE RIDGE/TROUGH OVER WESTERN ALASKA IS A 100 KT NORTHERLY JET
STREAK...EXTENDING FROM THE NORTH SLOPE TO KODIAK ISLAND. VISIBLE
AND SATELLITE IMAGERY IS CAPTURING A WEAK UPPER LEVEL ANOMALY
ALONG THE PERIPHERY OF THE JET STREAK AS EVIDENCED BY A DECK OF
HIGH CLOUDS AND DIFFLUENT FLOW. WITH TIME...UPPER LEVEL HEIGHTS
WILL BEGIN TO FALL ACROSS THE WESTERN PORTION OF THE
UPPER LOW OVER CENTRAL ALASKA...WITH THE LOW RETROGRADING
WESTWARD BEFORE PROPAGATING INTO THE GULF OF ALASKA SUNDAY. THIS
RETROGRESSION WILL DRIVE SENSIBLE WEATHER ACROSS THE MAINLAND FOR
THE NEXT TWO DAYS...AND WILL INFLUENCE THE TRACK OF A SYSTEM (AND
ASSOCIATED MID AND UPPER LEVEL FRONTOGENESIS) MOVING INTO
SOUTHWEST ALASKA LATE MONDAY INTO TUESDAY.

&&

.MODEL DISCUSSION...

THE NUMERICAL GUIDANCE IS IN EXCELLENT AGREEMENT WITH THE HIGH
AMPLITUDE NATURE OF THE SYNOPTIC FLOW PATTERN DEEP INTO NEXT WEEK.
WITH THE SMALLER SHORT WAVELENGTH FEATURES...THERE ARE SOME
DISCREPANCIES...BUT THE LARGE UNCERTAINTY FROM PREVIOUS DAYS HAS
BEEN ERASED. AS A WHOLE...CONFIDENCE IS MODERATE TO HIGH THROUGH
THE SHORT TERM PERIOD...WITH CONFIDENCE DIMINISHING BY LATE
TUESDAY INTO WEDNESDAY. WITH THAT SAID...THE ECMWF...CANADIAN
GDPS...AND GFS CONTINUE TO HINT AT A POTENTIAL EASTERLY WAVE
TRACKING THROUGH THE COPPER BASIN INTO SOUTHCENTRAL TUESDAY AND
WEDNESDAY...BUT TIMING AND TRACK REMAINS UNCERTAIN (SEE EXTENDED
DISCUSSION).

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
A LOW IN THE GULF WILL TRACK INTO THE COPPER BASIN AND NORTH GULF
COAST THIS EVENING...WITH INCREASING SHOWERS SPREADING THROUGH
THE EASTERN BASIN AND ALONG THE COAST. SHOWERS ACROSS THE BASIN
WILL CONTINUE INTO THE OVERNIGHT AS THE GULF DISTURBANCE TRACKS
INLAND. ACROSS THE WESTERN BASIN...SHOWERS AND ISOLATED
THUNDERSTORMS WILL FORM ALONG THE TALKEETNA MOUNTAINS AND PARTS OF
THE EASTERN ALASKA RANGE...CONTINUING INTO THE EVENING. SHOWERS
WILL ALSO FORM ALONG THE CHUGACH...BUT WEAK STORM MOTIONS FROM THE
WEST WILL KEEP SHOWER ACTIVITY LARGELY RELEGATED TO THE MOUNTAINS.
SHOWERS WILL BE MORE PREVALENT ACROSS THE KENAI MOUNTAINS...AND
WILL ALSO FORM ACROSS THE SOUTHERN KENAI. ON SUNDAY...SHOWERS WILL
REMAIN MOST PREVALENT ACROSS THE BASIN AS EXTENSIVE CLOUDS MOVE IN
FROM THE GULF...WITH ISOLATED TO SCATTERED MOUNTAIN SHOWERS
FARTHER EAST ACROSS THE CHUGACH...KENAI MOUNTAINS...AND TALKEETNA
MOUNTAINS. WEAK WESTERLY STORM MOTIONS WILL HELP TO PUSH SOME
SHOWERS INTO INLAND LOCATIONS...ESPECIALLY WEST OFF THE TALKEETNA
MOUNTAINS. WEAK RIDGING ALOFT WILL BUILD IN MONDAY...WITH DRIER
CONDITIONS FOR MUCH OF SOUTHCENTRAL.

SOUTHWEST ALASKA...
NORTHERLY OFFSHORE FLOW WILL KEEP SOUTHWEST DRY THROUGH SUNDAY
BEFORE A LOW TRACKS INTO THE REGION FROM THE NORTHWEST. WESTERLY
FLOW AHEAD OF THE LOW WILL SPREAD SUBSTANTIAL LOW LEVEL MOISTURE
INTO THE KUSKOKWIM DELTA SUNDAY NIGHT THROUGH MONDAY...WITH THE
THREAT FOR INLAND FOG AND DRIZZLE...AND SUBSTANTIALLY COOLER
TEMPERATURES BY MONDAY. INCREASING RAIN AND SHOWERS WILL
OVERSPREAD THE LOWER KUSKOKWIM DELTA AND BRISTOL BAY LATE MONDAY
INTO TUESDAY MORNING AS THE LOW TRACKS INTO THE EASTERN BERING.

LAKE CLARK AND INTERIOR ALASKA RANGE...
DRY NORTHERLY FLOW WILL CONTINUE INTO SUNDAY...WITH AN INCREASING
PRESSURE GRADIENT DEVELOPING BY SUNDAY AFTERNOON. NORTHERLY WINDS
WILL BECOME GUSTY BEFORE WEAKENING SUNDAY NIGHT. A LOW MOVING IN
FROM THE NORTHWEST WILL INCREASE WESTERLY FLOW MONDAY...WITH
INCREASING CLOUDS AND WIDESPREAD RAIN IMPACTING THE WINDWARD
SLOPES OF THE ALASKA RANGE INTO THE INTERIOR MOUNTAINS. SHOWERS
WILL LINGER INTO TUESDAY WITH AFTERNOON DIURNAL SHOWER THREATS
WEDNESDAY AND THURSDAY.

BERING SEA/ALEUTIANS...
HIGH PRESSURE WILL DOMINATE THE BERING THROUGH MID WEEK...WITH
INCREASING RAIN CHANCES ACROSS THE FAR WESTERN ALEUTIANS TONIGHT
THROUGH WEDNESDAY AS A FRONT STALLS OVER THE WESTERN BERING.
STAGNANT AND MOIST AIR OVER THE REMAINDER OF THE BERING AND
ALEUTIANS WILL SUPPORT WIDESPREAD SEA STRATUS...WITH PERIODS OF
LIGHT DRIZZLE AND PATCHY FOG PERSISTING THROUGH LATE WEEK.

&&

.LONG TERM FORECAST (WED JULY 30 - SAT 2 AUG)...

THE HIGH AMPLITUDE PATTERN WILL BE TRANSITIONING TO A HIGH
LATITUDE BLOCKING PATTERN...WITH A CLASSIC OMEGA BLOCK CENTERED
OVER THE NORTHERN BERING SEA. PERSISTENT LOWS WILL REMAIN OVER THE
SOUTHWEST ALEUTIANS AND THE GULF OF ALASKA...WITH RIDGING OVER
NORTHERN ALASKA. THIS PATTERN IS FAVORABLE FOR EASTERLY SHORTWAVE
TROUGHS ROTATING INTO SOUTHERN ALASKA FROM THE YUKON AND NORTH
GULF COAST. THERE IS INCREASING CONFIDENCE IN SUCH A WAVE TRACKING
INTO SOUTHCENTRAL LATE TUESDAY INTO WEDNESDAY...BUT THE
TRACK..TIMING...AND STRENGTH REMAIN UNCERTAIN. EVENTUALLY...THE
GULF LOW WILL SLOWLY TRACK SOUTH...WITH WEAK RIDGING BUILDING INTO
SOUTHERN ALASKA LATE THURSDAY AND FRIDAY...AND A RETURN TO
DRIER AND SLIGHTLY WARMER WEATHER.

&&

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

&&

AHSENMACHER JUL 14