Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 122145
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKDT SAT JUL 12 2014

.ANALYSIS AND UPPER LEVELS...
A LARGE AND COMPLEX UPPER LOW NEAR THE ALASKA PENINSULA IS
DOMINATING SENSIBLE WEATHER ACROSS THE MAINLAND. THIS LOW
CONTINUES TO SPIN MULTIPLE SHORTWAVES THROUGH SOUTHERN ALASKA. ONE
OF THESE SHORTWAVES MOVED THROUGH THE COOK INLET REGION
OVERNIGHT...INITIATING RARE NOCTURNAL THUNDERSTORMS MAINLY OVER
THE SUSITNA VALLEY. BEHIND THIS DEPARTING FEATURE...SOME BREAKS OF
SUN HAVE DEVELOPED ACROSS INLAND LOCATIONS AROUND SOUTH CENTRAL
AND TO A LESSER EXTENT SOUTHWEST ALASKA. COLD AIR ALOFT REMAINS IN
PLACE...WITH STEEP LAPSE RATES SETTING THE STAGE FOR MORE
CONVECTION. THE NEXT NOTABLE SHORTWAVE IS MOVING NORTHWARD TOWARD
KODIAK ISLAND AND WILL ARRIVE IN SOUTHERN ALASKA EARLY THIS
EVENING. AT THE SURFACE...WEAK HIGH PRESSURE IS BUILDING INTO THE
GULF OF ALASKA AND SOUTHERN MAINLAND...WITH OFFSHORE PRESSURE
RISES KEEPING SOME GAP WIND ACTIVITY GOING PRIMARILY THROUGH
TURNAGAIN ARM AND ALONG THE COPPER RIVER DELTA INTO THE COPPER
RIVER VALLEY. ELSEWHERE...A HIGH AMPLITUDE RIDGE OVER THE
NORTHWEST PACIFIC IS CLIPPING THE FAR WESTERN BERING...WITH
NORTHERLY FLOW AND WARM ADVECTION HELPING TO BUILD AN IMPRESSIVE
SHIELD OF MARINE FOG/STRATUS THAT IS SLOWLY INVADING THE CENTRAL
BERING.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN EXCELLENT OVERALL AGREEMENT. NO UNUSUALLY STRONG
SURFACE FEATURES WILL BE IN PLAY DURING THE SHORT TERM PERIOD...AS
THE FORECAST OVER THE NEXT FEW DAYS WILL CONSIST OF THE LARGE
UPPER LOW SLOWLY DRIFTING SOUTHWEST INTO THE NORTH PACIFIC. IN ITS
WAKE WEAK HIGH PRESSURE WILL BUILD IN ACROSS MUCH OF THE SOUTHERN
ALASKA AOR...BUT WILL NOT BE STRONG ENOUGH TO MITIGATE CLOUDS AND
SHOWERS IN THE USUAL PLACES. THE TRICKY PART OF THE FORECAST WILL
BE IN NAILING DOWN THE TIMING AND STRENGTH OF TWO MAIN SHORTWAVES
THAT WILL BE IMPACTING THE SOUTHERN MAINLAND IN THE NEXT 24-30
HOURS. THE FIRST COMES THROUGH THIS EVENING...AND THERE IS GOOD
MODEL AGREEMENT THAT THE CENTROID OF THIS DISTURBANCE WILL PASS
LOOSELY THROUGH ANCHORAGE. THE LATTER SHORTWAVE COMES THROUGH
TOMORROW DURING THE DAY AND WILL TAKE A MORE NORTHEAST TRAJECTORY
OVER THE COPPER RIVER BASIN. THE GFS IS LAGGING THE FASTER
NAM/GFS/ECMWF SOLUTION...THUS WILL GO WITH THE FASTER SOLUTION
FOR THE AFTERNOON FORECAST.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
AS MENTIONED ABOVE...SOME THUNDERSTORMS FIRED IN THE SUSITNA
VALLEY OVERNIGHT AS SUFFICIENT MID-LEVEL INSTABILITY AND A
DYNAMIC BOOST WORKED TOGETHER. WITH THESE FACTORS REMAINING IN
PLACE FOR THIS EVENING...WITH SOME BREAKS OF SUN THROWN IN FOR
ADDITIONAL INSTABILITY...DO NOT SEE A REASON WHY A FEW ISOLATED
THUNDERSTORMS WILL NOT KICK OFF AGAIN THIS EVENING AS THE
SHORTWAVE CURRENTLY NEAR KODIAK MOVES UP INTO THE MAINLAND. THE
FINAL IN THE SERIES OF SHORTWAVES PINWHEELING AROUND THE MAIN LOW
WILL MOVE THROUGH TOMORROW...PASSING MORE OFF TO THE EAST AND
PRIMARILY AFFECTING THE COPPER RIVER BASIN WITH MORE SHOWERS AND
THUNDERSTORMS. MEANWHILE...AS BROAD HIGH PRESSURE CONTINUES TO
SLOWLY INTENSIFY IN THE GULF...SOUTHERLY FLOW UP COOK INLET WILL
CONTINUE TO KEEP TEMPERATURES MODERATED EVEN AS THE THERMAL TROUGH
ATTEMPTS TO BECOME A BIT MORE RE-ESTABLISHED OVER THE COMING DAYS.

SOUTHWEST ALASKA...
THE BATCH OF STEADY RAIN THAT MOVED THROUGH THE DELTA OVERNIGHT
HAS NOW HEADED SOUTHWEST AND OUT INTO THE BERING SEA. PARTLY
SUNNY SKIES HAVE NOW BROKEN OUT ACROSS MUCH OF THE AREA AS
COLD AIR ALOFT CONTINUES TO SET THE STAGE FOR SHOWERS AND LIKELY
SOME THUNDERSTORMS BY LATER THIS AFTERNOON. BRISTOL BAY SHOULD SEE
THE MOST VIGOROUS CONVECTIVE ACTIVITY...BUT AN OVERALL WESTWARD
STORM MOTION WILL MAKE BETHEL ALSO VULNERABLE TO ANYTHING THAT
DEVELOPS ALONG THE KILBUCK MOUNTAINS THIS EVENING. THE REGION THEN
SLIPS INTO A FAIRLY TYPICAL PATTERN OF DIURNAL SHOWER ACTIVITY
THROUGH THE START OF NEXT WEEK AS LOW-LEVEL TEMPERATURES SLOWLY
RECOVER BACK TO SEASONAL NORMS. THE EXCEPTION WILL BE OVER THE
NORTHERN SECTIONS OF THE KUSKOKWIM VALLEY WHERE A FRONT SAGGING
DOWN FROM THE INTERIOR ON MONDAY MAY BRING A PERIOD OF STEADY
RAIN...WITH HIGHEST AMOUNTS LIKELY FOUND ALONG THE WESTERN SLOPES
OF THE ALASKA RANGE.

BERING SEA/ALEUTIANS...
SURFACE LOW PRESSURE NORTH OF THE ALASKA PENINSULA WILL CROSS INTO
THE PACIFIC TONIGHT. RAIN WILL GRADUALLY TAPER OFF ALONG THE
BERING SIDE...WITH THE SOUTH/PACIFIC SIDE LIKELY SEEING RAIN
CONTINUE THROUGH TOMORROW MIDDAY. MEANWHILE...HIGH PRESSURE AND AN
ASSOCIATED LARGE AREA OF FOG/STRATUS ARE SETTING UP SHOP OVER THE
WESTERN BERING. THIS AREA WILL CONTINUE TO EXPAND TO THE EAST AS
THE AFOREMENTIONED LOW DROPS DOWN INTO THE PACIFIC AND BECOME THE
MOST SIGNIFICANT WEATHER FEATURE ACROSS THE AREA THROUGH EARLY
NEXT WEEK.

&&

.LONG TERM FORECAST...
A WETTER PATTERN ONCE AGAIN SETS UP FOR SOUTHERN ALASKA AT THE END
OF NEXT WEEK. THE UPPER LEVEL LOW IN THE NORTH PACIFIC MEANDERS
TO THE EASTERN ALEUTIANS WEDNESDAY INTO THURSDAY. BY
THURSDAY...THIS CLOSED LOW BEGINS TO LIFT AND PICKS UP MOMENTUM AS
IT OPENS INTO A LONGWAVE TROUGH OVER THE EASTERN ALEUTIANS/BERING.
RAIN CHANCES WILL INCREASE ACROSS THE EASTERN ALEUTIANS AND THEN
EASTWARD THROUGH THE SOUTHERN MAINLAND AND SURROUNDING WATERS AS
THE SYSTEM TRACKS NORTH. MODELS ARE IN AGREEMENT WITH THE GENERAL
NORTHERLY TRACK...HOWEVER THERE IS STILL A BIT OF UNCERTAINTY IN
TIMING AND PLACEMENT. THE LONG RANGE FORECAST IS ABOUT AVERAGE FOR
THIS TIME OF YEAR AND WILL NEED TO BE MONITORED FOR DETAILS ON
THIS UPCOMING STORM SYSTEM.

&&

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

$$

AMD/KH JUL 14



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