Small Craft Advisory 459, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
209 PM AKDT MON JUN 9 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS A SLOW-MOVING UPPER LOW CURRENTLY IN PLACE OVER THE WEST
COAST OF ALASKA. THIS FEATURE IS CREATING SOUTHWEST FLOW ACROSS
THE SOUTHERN MAINLAND...WITH EMBEDDED SHORTWAVE TROUGHS
PINWHEELING AROUND THE MAIN CENTER AND PRODUCING SHOWERY
CONDITIONS ACROSS MOST OF THE AREA. A MORE SIGNIFICANT TROUGH IS
CURRENTLY PUSHING NORTHWARD THROUGH COOK INLET...WHICH HAS
COMBINED WITH MODEST DIURNAL WARMING TO PRODUCE MORE WIDESPREAD
SHOWER ACTIVITY AHEAD OF THIS FEATURE OVER UPPER COOK INLET. THIS
WEAKENING WEST COAST LOW IS SLOWLY TAKING ON A MORE NEGATIVE
TILT...ALLOWING SOME WEAK PRESSURE RISES AT THE SURFACE TO SPREAD
INTO THE NORTHERN GULF. FURTHER WEST...A FAIRLY GARDEN-VARIETY
VERTICALLY STACKED LOW IS SLOWLY MAKING ITS WAY INTO THE WESTERN
BERING...WITH AN ASSOCIATED FRONT PRODUCING RAIN AND GUSTY WINDS
TO THE WESTERN AND CENTRAL ALEUTIANS.

&&

.MODEL DISCUSSION...
ALL MODELS ARE IN SIMILAR SYNOPTIC AGREEMENT...DEPICTING A
WEAKENING OF THE CURRENT WEST COAST LOW AS IT LIFTS NORTHWARD BY
MIDWEEK. AFTER A BRIEF BREAK...THE SYSTEM CURRENTLY APPROACHING
THE WESTERN BERING WILL THEN SLIDE INTO THE LONGWAVE TROUGH AND
BECOME THE NEW ANCHOR LOW OVER THE WEST COAST BY LATE IN THE
WEEK. THE NAM IS A BIT MORE AGGRESSIVE DIGGING THE CURRENT WEST
COAST LOW INTO THE BRISTOL BAY ZONE DURING THE DAY TOMORROW...AND
AS A RESULT IS A BIT SLOWER WITH THE STRONG TROUGH PASSING THROUGH
COOK INLET TOMORROW AFTERNOON/EVENING. SIMILARLY...THE NAM IS
NOTABLY SLOWER THAN ALL OTHER MODELS PROGRESSING THE WEAK WEATHER
FRONT EASTWARD ACROSS THE BERING TONIGHT AND TOMORROW. CURRENTLY
FAVOR THE EC/GFS/GEM SOLUTIONS THAT BRING THE COOK INLET TROUGH
THROUGH A FEW HOURS QUICKER (AND TAKE FULL ADVANTAGE OF DIURNAL
PEAK HEATING)...AND ALSO SPREAD RAIN INTO THE PRIBILOF ISLANDS FASTER
AND CLOSER TO THE MODEL CONSENSUS TIMING.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
SHOWERS BLOSSOMED EARLY THIS AFTERNOON ACROSS COOK INLET AND THE
SUSITNA VALLEY AS THE WEAK UPPER TROUGH AND DIFLUENCE ALOFT
COMBINED WITH THE FIRST VESTIGES OF DIURNAL HEATING. WIDESPREAD
SHOWERS SHOULD TAPER OFF QUICKLY FROM SOUTH TO NORTH AS THE UPPER
TROUGH MOVES THROUGH THE REGION. IT WILL TAKE THE TROUGH LONGER TO
FULLY IMPACT THE WESTERN COPPER RIVER BASIN...WHERE ENOUGH
INSTABILITY MAY BE ABLE TO BUILD UP TO PRODUCE A FEW LIGHTNING
STRIKES LATER THIS EVENING. AS MENTIONED EARLIER (IN THE MODEL
DISCUSSION)...THE MAIN AXIS OF THE UPPER TROUGH ITSELF WILL
FOLLOW A SIMILAR TRACK UP COOK INLET TOMORROW AFTERNOON. COLDER
AIR ALOFT (AND RESULTING STRONGER INSTABILITY) WILL LIKELY MAKE
THE SHOWERS TOMORROW STRONGER AND MORE WIDESPREAD THAN TODAY.
ISOLATED THUNDERSTORMS ARE ALSO POSSIBLE AGAIN TOMORROW OVER THE
TALKEETNA MOUNTAINS AND WESTERN COPPER RIVER BASIN. BY
WEDNESDAY...WEAK HIGH PRESSURE BETWEEN SYNOPTIC-SCALE SYSTEMS WILL
ALLOW A RETURN OF THE SUN TO MUCH OF SOUTHCENTRAL ALASKA.

SOUTHWEST ALASKA...
THE PRESENCE OF THE UPPER LOW WILL KEEP ROUNDS OF SHOWERY
CONDITIONS PRESENT THROUGH TOMORROW AFTERNOON ACROSS MUCH OF THE
REGION. THE STRONGEST INSTABILITY TOMORROW WILL BE ACROSS THE
EASTERN KUSKOKWIM VALLEY...AND WILL PLAN TO INCLUDE MENTION OF
THUNDERSTORMS WITH THE AFTERNOON FORECAST. THE BREAK BETWEEN
WEATHER SYSTEMS WILL OCCUR TUESDAY NIGHT AND WEDNESDAY
MORNING...BEFORE CLOUDS AND STEADY RAIN ARRIVE AGAIN WEDNESDAY
EVENING.

BERING SEA/ALEUTIANS...
HIGH PRESSURE OVER THE CENTRAL BERING IS PRESERVING GENERALLY
STABLE CONDITIONS ACROSS MUCH OF THE AREA...WITH MARINE FOG AND
STRATUS LOITERING AROUND. THIS FOG/STRATUS SHOULD BECOME MORE
WIDESPREAD AS SOUTHERLY FLOW AND WARM AIR ADVECTION MOVE INTO THE
AREA TONIGHT. PRECIPITATION AND WINDS ASSOCIATED WITH THE
ADVANCING WEATHER FRONT WILL BE ON THE LIGHT END OF THE SPECTRUM
FOR THIS PART OF THE WORLD...AND WILL STRUGGLE TO EXCEED 30 MPH AT
MOST PLACES OVER THE COMING DAYS.

&&

.LONG TERM FORECAST...
BY THE END OF THE WEEK...THE WESTERN BERING SYSTEM WILL MOVE INTO
PLACE OVER THE WEST COAST OF THE MAINLAND...AND WITH A STRONGER
REPRESENTATION IN THE LOWER LEVELS SHOULD RESULT IN A FAIRLY
WIDESPREAD SWATH OF RAIN IMPACTING MUCH OF THE SOUTHWEST MAINLAND
THURSDAY AFTERNOON/EVENING AND THE SOUTHCENTRAL MAINLAND ON
FRIDAY. MODEL AGREEMENT GOES DOWNHILL QUICKLY BEGINNING THIS
WEEKEND...AS MODELS ARE STRUGGLING WITH POSSIBLE TRIPLE POINT
DEVELOPMENT IN THE GULF. WE CAN SAY WITH CONFIDENCE THAT MOST OF
THE STATE WILL REMAIN SQUARELY UNDER THE INFLUENCE OF A BROAD
UPPER LEVEL TROUGH...WHICH WILL KEEP CLOUDY...COOL...AND GENERALLY
SHOWERY WEATHER ACROSS LARGE PORTIONS OF THE SOUTHERN MAINLAND
THROUGH EARLY NEXT WEEK.

&&

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

AMD JUN 14