Small Craft Advisory 569, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
436 PM AKDT THU JUL 16 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVELS HAVE BECOME MORE AMPLIFIED AS THE BROAD LONG
WAVE TROUGH OVER THE EASTERN BERING SEA DUG SOUTH TO OVER THE
NORTH PACIFIC. THIS SET UP A DEEP SOUTHWESTERLY JET AND MOISTURE
PLUME WHICH IS EXPANDING NORTH TOWARD SOUTHCENTRAL/NORTH GULF. AT
THE SURFACE...A COUPLE OF MINOR LOWS ROTATE AROUND THE MAIN CENTER
NEAR THE AK PEN. THE SURFACE OCCLUDED AND WARM SECTIONS OF THE
FRONTAL TROUGH ARE PRODUCING RAIN ACROSS THE SOUTHWEST AND THE
NORTHERN GULF AND KENAI PENINSULA. RAIN IS ALSO SPREADING NORTH
OVER THE WESTERN SUSITNA VALLEY. THE TRAILING COLD FRONT IS STILL
WEST OF KODIAK. GAP WINDS ARE INCREASING ACROSS THE SOUTHCENTRAL
WITH THE MOST NOTABLE...COPPER RIVER...TURNAGAIN ARM/PORTAGE...AND
KNIK VALLEY. SMALL CRAFT TO GALE FORCE WINDS WERE EVIDENT AHEAD OF
THE FRONT OVER THE NORTHERN GULF. BRISK NORTH WINDS WERE EVIDENT
ACROSS THE CENTRAL AND EASTERN ALEUTIANS WITH FAIRLY LIGHT WINDS
UNDER HIGH PRESSURE OVER THE WESTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
MODELS ARE IN GENERALLY FAIR AGREEMENT WITH THE SYNOPTIC FEATURES
THOUGH DIFFERENCES IN THE INTENSITY AND TIMING OF SHORT WAVES
BEHIND THE FRONTAL TROUGH EXIST. THESE DIFFERENCES WILL LIKELY
AFFECT THE POST FRONTAL PRECIPITATION PATTERN THROUGH FRI. MODELS
HOWEVER ARE IN GOOD AGREEMENT ON THE POSITIONING OF THE
SOUTHWESTERLY JET OVER THE THE GULF. THOUGH NOT PERFECT...MODELS
DO FOCUS THE BRUNT OF ASSOCIATED PRECIPITATION ALONG THE NORTHERN
GULF COAST. AFTERNOON FORECAST PACKAGES IN THE EAST WILL BE A
BLEND OF OFFICIAL/NAM AND IN THE WEST A NAM/ECMWF BLEND.

&&

.FIRE WEATHER...
THE WEATHER FRONT WILL CONTINUE TO MOVE INTO THE SOUTHCENTRAL AND
THE SOUTHWEST ALASKA REGION THIS EVENING. THIS WILL CONTINUE TO
BRING WIDESPREAD WETTING RAINS AND GUSTY WINDS AS THE WEATHER
FRONT MOVES INLAND TONIGHT. THIS WET AND COOLER WEATHER PATTERN
WILL CONTINUE RESULTING IN NO FIRE WEATHER CONCERNS AS WE HEAD
INTO THE WEEKEND.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A STRONG FRONTAL SYSTEM TRACKING OVER THE AREA WILL CONTINUE TO
BRING STRONG WINDS AND MODERATE TO HEAVY RAINFALL TO MUCH OF
SOUTHCENTRAL THROUGH FRIDAY. THE GUSTY WINDS WILL PEAK EARLY THIS
EVENING AS THE FRONTAL BOUNDARY TRACKS ONSHORE ALONG THE NORTH
GULF COAST. SOME OF THE GUSTY WINDS OVER TURNAGAIN ARM WILL BEND
INTO PARTS OF ANCHORAGE AS THE FRONT PASSES OVER...WITH GUSTY
WINDS ALSO EXPECTED ALONG THE KNIK RIVER VALLEY AND COPPER RIVER.
WINDS WILL THEN DIMINISH A BIT...BUT GUSTY SOUTHERLIES WILL
DOMINATE THROUGH FRIDAY EVENING WITH PRESSURE RISES IN A WELL
MIXED BOUNDARY LAYER.

AS FOR PRECIPITATION OVER SOUTHCENTRAL...WIDESPREAD MODERATE TO
HEAVY RAINS ARE EXPECTED TO DOMINATE MUCH OF SOUTHCENTRAL THROUGH
TOMORROW...AS SOUTHERLY FLOW TRANSPORTS TROPICAL MOISTURE OVER
THE AREA AND A RELATIVELY STRONG UPPER LEVEL WAVE TRACKS UP COOK
INLET TONIGHT. HOWEVER...SOME AREAS ALONG THE WESTERN
KENAI/CHUGACH MOUNTAINS MAY CONTINUE TO EXPERIENCE SOME
DOWNSLOPING DUE TO STRONG CROSS-BARRIER FLOW IN THE EARLY EVENING.
IN THE WAKE OF THE STRONG UPPER LEVEL DISTURBANCE...THE MEAN FLOW
WILL BECOME MORE FAVORABLE (SOUTH/SOUTHWEST) FOR UPSLOPING ALONG
THE MOUNTAINS OF THE SUSITNA VALLEY AND SURROUNDING PRINCE
WILLIAM. THIS CAN RESULT IN PERIODS OF HEAVY RAIN ALONG THE ALASKA
RANGE...TALKEETNA MOUNTAINS...AND MOUNTAINS SURROUNDING PRINCE
WILLIAM SOUND. CONDITIONS AROUND SOUTHCENTRAL WILL BEGIN TO
IMPROVE AND DRY OUT SATURDAY MORNING...AS HIGHER PRESSURE BEGINS
TO BUILD IN FROM THE WEST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
AS THE MAIN LOW PUSHES CLOSER TO BRISTOL BAY IT WILL CONTINUE TO
BRING RAIN THROUGHOUT SOUTHWEST ALASKA. THE RAIN WILL BEGIN TO
LIGHTEN UP FRIDAY AFTERNOON BUT SHOWERS WILL LINGER INTO THE
WEEKEND. THE STRONGER SOUTHEAST WINDS WILL DIMINISH OVERNIGHT AS
THE LOW CENTER MOVES THROUGH THE AREA BUT WILL THEN PICK BACK UP
OUT OF THE SOUTHWEST BEHIND THE LOW FRIDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
NORTH TO WEST FLOW WILL STAY OVER THE AREA INTO FRIDAY WITH WEAK
RIDGING MOVING THROUGH THE BERING. THIS WILL ALLOW FOR LIGHT
SHOWERS AND FOG THROUGHOUT THE BERING AND ALEUTIANS. THEN FRIDAY
NIGHT A FRONT WILL MOVE IN OVER THE WESTERN ALEUTIANS BRINGING
STRONGER WINDS AND RAIN TO THE AREA. THE FRONT WILL THEN SLOWLY
PUSH EAST THROUGH THE WEEKEND STALLING OUT OVER THE CENTRAL
ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...SUN THROUGH THU)...THIS
PERIOD WILL LARGELY FEATURE A RIDGE OVER MUCH OF THE MAINLAND WITH
A CLOSED UPPER LEVEL LOW EMBEDDED IN A BROAD TROUGH OVER THE
WESTERN ALEUTIANS. THERE WILL BE ENOUGH RESIDUAL ENERGY SLIDING
THROUGH SOUTH CENTRAL BEFORE THE RIDGE BUILDS IN TO TRIGGER SOME
THUNDERSTORMS SUNDAY AFTERNOON IN THE EASTERN COPPER RIVER BASIN.
OTHER THAN THAT...MOST PLACES WILL SEE DRYING CONDITIONS WITH
JUST SOME ISOLATED MOUNTAIN SHOWERS. OUT WEST...THE LOW OVER THE
WESTERN ALEUTIANS WILL HAVE A NEARLY STATIONARY FRONT DRAPED
THROUGH THE CENTRAL ALEUTIANS. THIS WILL KEEP PRECIPITATION IN THE
FORECAST AS WELL AS SOUTHERLY SMALL CRAFT WINDS. HIGH PRESSURE AT
THE SURFACE BUILDS OVER SOUTHWEST ALASKA THROUGH THE EARLY PART OF
NEXT WEEK. THIS WILL BRING A SHORT STRETCH OF DRIER AND SUNNIER
WEATHER THAN WE HAVE EXPERIENCED OVER THE PAST FEW WEEKS.

BY TUESDAY...THE SUBTROPICAL JET WILL ACCELERATE OVER THE NORTH
PACIFIC AND HELP TO MAKE OUR PATTERN MORE PROGRESSIVE ONCE AGAIN.
IT WILL SERVE TO FERRY THE WESTERN ALEUTIAN LOW ACROSS THE BERING
TOWARD THE MAINLAND BY WEDNESDAY. MODELS ARE IN SOLID AGREEMENT
THROUGH THIS TIME IN THE SYNOPTIC PATTERN. HOWEVER...THERE ARE
SOME SMALL FEATURES THAT ARE HANDLED DIFFERENTLY. THESE SMALL
FEATURES...WHEN EXTRAPOLATED OUT TO DAYS 6-8 IN THE FORECAST...CAN
LEAD TO KEY DIFFERENCES IN THE OVERALL PATTERN. SOME OF THOSE
DIFFERENCES ARE IN HOW THE ENERGY SLIDING THROUGH COOK INLET ON
SUNDAY INTERACTS WITH A CUT-OFF LOW IN THE SOUTHERN GULF OF
ALASKA. ANOTHER DIFFERENCE IS HANDLING A CUT-OFF LOW SPINNING OVER
NORTH CENTRAL CANADA. BECAUSE OF THESE DIFFERENCES...FORECAST
CONFIDENCE SUBSIDES LATER IN THE PERIOD. BUT THE BOTTOM LINE IS
THAT IT DOES APPEAR THE RIDGE BREAKS DOWN BY THE MIDDLE OF THE
WEEK AND ONCE AGAIN OPENS THE DOOR FOR PRECIPITATION TO RETURN TO
THE MAINLAND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 125 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...MO