Gale Warning 551, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
325 PM AKDT SAT AUG 31 2013

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL LOW OVER THE BEAUFORT SEA WITH A DEVELOPING LOW OVER
THE WESTERN BERING PROVIDING FOR A ZONAL FLOW OVER THE MAINLAND. IN
THE ZONAL FLOW...THERE ARE PLENTY OF FEATURES TO FOLLOW THROUGH THE
EASTERN BERING INTO THE MAINLAND. A DECENT WAVE IS MOVING THROUGH
SOUTH CENTRAL CURRENTLY CREATING AN UNSTABLE ENVIRONMENT AND RAIN.
THERE IS A GOOD BACK EDGE TO THIS FEATURE. HOWEVER...THE AIR MASS IS
UNSTABLE ENOUGH OVER SOUTHWEST ALASKA FOR ISOLATED SHOWERS. SOME MID
LEVEL WARMING IS STARTING TO SHUT OFF SHOWERS ALONG THE WEST COAST.
HOWEVER...ENOUGH STRATUS OVER THE BERING FOR CONTINUED CLOUDINESS.
THIS MID LEVEL WARMING TO MOVE THROUGH THE SOUTHERN MAINLAND TONIGHT
AND EFFECTIVELY CUT OFF SHOWERS OVER SOUTH CENTRAL TONIGHT WEST OF
THE CHUGACH. A GOOD VORT MAX ASSOCIATED WITH A DEVELOPING WARM FRONT
IS PUSHING THROUGH THE CENTRAL BERING THIS AFTERNOON AS THE LOW IN
THE WESTERN BERING CONTINUES TO CONSOLIDATE. A VERY STRONG JET CORE
IS DIGGING BEHIND THE WESTERN BERING LOW AT 150 KT.

.MODEL DISCUSSION...
MOST MODELS YESTERDAY DID NOT HANDLE THE STRENGTH AND SPEED OF THE
WAVE MOVING THROUGH SOUTH CENTRAL THIS MORNING AND AFTERNOON VERY
WELL. AS A RESULT...THE FEATURES ARE SPED UP ABOUT 12 HOURS FROM
YESTERDAYS FORECAST. AS IT STANDS...THE MODELS ARE GETTING CLOSER TO
THE SITUATION. WITH THE OVERALL PATTERN DEFINITELY BECOMING MORE LONG
WAVE/MERIDIONAL...THE CONVERGENCE OF THE MODELS IS BETTER THROUGH
MONDAY. THE ENERGIES ROTATING IN AND OUT OF THE LONG WAVE TROUGH ARE
DIFFERING BETWEEN MODELS RIGHT NOW. SO...THE EXACT POSITIONING OF
FEATURES WILL BE DIFFICULT PAST MONDAY INTO WEDNESDAY. AFTER
WEDNESDAY...A SHORT WAVE TROUGH MOVING INTO THE LONG WAVE TROUGH FROM
THE KAMCHATKA AREA IS HANDLED MUCH DIFFERENT BETWEEN THE HEMISPHERIC
MODELS. THEREFORE...THERE IS A LOT OF UNCERTAINTY IN THE LATTER PART
OF THE WEEK INTO NEXT WEEK. RIGHT NOW...THE BEST BET IS A EC SOLUTION
THROUGH THE NEXT FEW DAYS...THEN ENSEMBLE MEANS VIA WPC FORECASTS.

.SHORT TERM FORECAST...
SOUTHCENTRAL/GULF...
MODERATE SHORT WAVE TROUGH MOVING THROUGH SOUTH CENTRAL AREA THIS
AFTERNOON WITH SOME SHOWERS. HELPING WITH THE PRECIPITATION PROCESS
IS THE FACT WE HAVE DESTABILIZED A BIT FROM YESTERDAY WITH THE UPPER
LOW SWINGING THROUGH THE NORTHERN HALF OF THE STATE. THE INSTABILITY
WILL WANE BEHIND THE WAVE TONIGHT IN A SHORT WAVE RIDGE AND MID LEVEL
WARMING RESULTING IN ISOLATED SHOWERS THROUGH TONIGHT INTO TOMORROW.
THE SHORT WAVE RIDGE IS IN CONCERT WITH THE LOW IN THE BERING
CONSOLIDATING AND STRENGTHENING. HOWEVER...AHEAD OF THE RIDGE...A MID
LEVEL WARM FRONT WILL PUSH THROUGH THE WESTERN GULF INTO SOUTH
CENTRAL TOMORROW AFTERNOON AND EVENING. AS THE LOW MOVES CLOSER ON
SUNDAY NIGHT INTO MONDAY...RAIN WILL BECOME WIDESPREAD WITH A DEEPER
TAP OF MOISTURE AS THE FLOW TURNS MORE SOUTHERLY AT ALL LEVELS.
STRONGER WINDS ESPECIALLY THROUGH THE TYPICAL GAPS ARE EXPECTED AS
WELL. A STRONG JET PUSHES INTO THE REGION WITH THE FRONTAL WAVE
MOVING THROUGH MONDAY EVENING ENHANCING THE WINDS THROUGH THE GAPS TO
DEFINITE STRONG WIND HEADLINES. DO NOT EXPECT WIND WARNING CRITERIA
AS OF YET. THE WAVE MOVES TUESDAY MORNING WITH RAIN TAPERING OFF OVER
THE REGION TUESDAY EXCEPT ALONG THE COASTAL AREAS EAST OF THE
ANCHORAGE AREA WHERE ONSHORE FLOW AT ALL LEVELS AND THE DEEPER
MOISTURE IS POINTED.

SOUTHWEST/AKPEN...
A MID LEVEL FRONT IS MOVING THROUGH SOUTHWEST ALASKA THIS AFTERNOON
WITH SOME ISOLATED SHOWERS DIRECTLY BEHIND IN A SOMEWHAT STABILIZING
ENVIRONMENT DUE TO MID LEVEL WARMING. THE LOW IN THE WESTERN BERING
WRAPS UP TONIGHT INTO SUNDAY WITH ANOTHER FRONT MOVING TO THE COAST
BY SUNDAY MORNING. THE UPPER LEVEL TROUGH DIGS IN THE BERING INTO THE
NORTH PACIFIC SUNDAY BRINGING DEEPER MOISTURE TO THE COAST SUNDAY
NIGHT. THE FRONT ASSOCIATED WITH THIS MOISTURE TAP IS BEING SUPPORTED
BY A MODERATE JET AND GOOD BAROCLINICITY. GALE FORCE WINDS AND
MODERATE TO HEAVY PRECIP TO HIT THE COAST SUNDAY NIGHT. THE FRONT
BREAKS UP MONDAY AS IT HITS THE COAST AND THE STRONGER JET CORE MOVES
SOUTH OF THE AKPEN INTO THE GULF. THE MODERATE TO HEAVY PRECIP TO
CONTINUE INTO MONDAY MORNING BEFORE VENTURING INTO THE GULF MONDAY
EVENING. THE WINDS WILL DIMINISH MONDAY NIGHT WITH SHOWERS AND AT
TIMES MODERATE RAIN INTO TUESDAY.

BERING SEA/ALEUTIANS...
THE LOW IS DEEPENING IN THE WESTERN BERING THIS AFTERNOON WITH A GOOD
FRONT DEVELOPING. BY LATER TONIGHT...A WARM FRONT WILL BE NEAR THE
WEST COAST WITH AN OCCLUDED FRONT WRAPPING THROUGH THE NORTH CENTRAL
BERING BACK TO THE PARENT LOW IN THE WESTERN BERING. THE TRAILING
COLD/COOL FRONT IN THE SOUTHERN AND CENTRAL BERING IS WELL SUPPORTED.
GALE FORCE WINDS AND MODERATE TO HEAVY PRECIP WILL MOVE WITH THIS
FRONT. THE FRONT WILL REACH THE COAST SUNDAY NIGHT AS THE MOVES TO
THE CENTRAL BERING SEA. STRONG JET IN THE BASE OF THE LONG WAVE
TROUGH WITH A DISTURBANCE MOVING DOWN FROM EASTERN RUSSIA WILL
ENHANCE WINDS ON THE BACK SIDE OF THE LOW SUNDAY NIGHT INTO MONDAY TO
STORM FORCE. THE LOW WRAPS UP IN THE EASTERN BERING AND BEGINS TO
FILL AS THE JET CORE PUNCHES INTO THE GULF AND REMAINS WELL SOUTH OF
THE LOW IN THE EASTERN BERING.

.LONG TERM FORECAST...
THE MODELS HAVE A GOOD OVERALL HANDLE ON A LONG WAVE TROUGH IN THE
EASTERN BERING REMAINING THROUGH LATE NEXT WEEK WITH A RIDGE OVER THE
YUKON AND ALBERTA/BC. THE ENERGY FLOWING AROUND THE TROUGH IS
SOMEWHAT AT DEBATE FOR SURFACE FEATURES. OVERALL...MILD AND WET FOR
THE MAINLAND WITH SOME WIND. COOLER AND SHOWERY OVER THE BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM 185 411
         GALE 155 160 165 170 172 175 176 180 412 413 414
FIRE WEATHER...NONE.

NELSON AUG 13

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1155 PM AKDT SAT AUG 31 2013

AKZ181-011500

...MINOR ASH FALL REMAINS POSSIBLE BETWEEN PERRYVILLE AND CHIGNIK...

SATELLITE IMAGERY AND INSTRUMENTATION NEAR VENIAMINOF VOLCANO
CONTINUE TO INDICATE ELEVATED LEVELS OF ACTIVITY AT THE VOLCANO.
WINDS WILL CONTINUE TO TRANSPORT THE ASH TO THE EAST WHICH COULD
STILL BRING SOME VERY LIGHT ASHFALL TO AREAS ALONG THE ALASKA
PENINSULA BETWEEN PERRYVILLE AND CHIGNIK THROUGH EARLY SUNDAY
MORNING.