Area Forecast Discussion - SouthCentral and SouthWest


FXAK68 PAFC 042348
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
348 PM AKDT WED MAY 4 2016
.ANALYSIS AND UPPER LEVELS...
THE DOMINANT FEATURE ON SATELLITE IMAGERY TODAY IS A HIGH
AMPLITUDE DIGGING TROUGH OVER THE NORTH CENTRAL PACIFIC WITH
STRENGTHENING SURFACE LOW. THIS IS INDUCING DOWNSTREAM RIDGING
WHICH IS LEADING TO DEVELOPMENT OF A STRONG SOUTHERLY JET...WITH 
A STREAM OF WARMER AIR AND MOISTURE POINTED TOWARD THE GULF OF
ALASKA. THIS WILL BE THE PRIMARY SYSTEM OF CONCERN FOR THE GULF
AND SOUTHERN MAINLAND OF ALASKA THURSDAY THROUGH FRIDAY.

OUT AHEAD OF THIS SYSTEM A MUCH SMALLER BUT POTENT SHORT-WAVE IS
DIGGING EAST-NORTHEASTWARD ACROSS THE GULF OF ALASKA RE-INVIGORATING
WHAT HAD BEEN A VERY WEAK OCCLUDED FRONT. THE UPPER WAVE HAS ALSO
INDUCED FORMATION OF A SURFACE LOW OVER THE WEST-CENTRAL GULF.
THE COMBINATION OF THE LOW AND AND APPROACH OF THE FRONT ARE
LEADING TO STRENGTHENING WINDS ALONG THE NORTH TO NORTHWEST GULF
COAST AND INTO COOK INLET. A BAND OF STEADY RAIN...WITH EMBEDDED
MODERATE TO HEAVY AREAS (AS SEEN IN MIDDLETON ISLAND RADAR
IMAGERY) IS MAKING ITS WAY TOWARD THE NORTH GULF COAST AND PRINCE
WILLIAM SOUND.

AREA SOUNDINGS FROM THIS MORNING SHOW A GENERALLY MOIST AND WEAKLY 
UNSTABLE ATMOSPHERE ACROSS INLAND PORTIONS OF SOUTHCENTRAL AND
MUCH OF SOUTHWEST ALASKA. THIS IS QUITE EVIDENT IN THE EARLY
DEVELOPMENT OF CUMULUS AND LIGHT SHOWERS DURING THE LATE MORNING
HOURS. WEAK AND DIFFUSE WAVES EMBEDDED IN THE FLOW ALOFT ARE
MOVING OVERHEAD...BUT THEY ARE NOT PROVIDING ALL THAT MUCH
VERTICAL MOTION. THUS...THE RECENT DAYS OCCURRENCE OF ISOLATED 
TO SCATTERED CONVECTION SEEMS LIKE IT WILL BE THE PREVAILING
CONDITION FOR TODAY.

LASTLY...CONDITIONS ARE QUITE BENIGN ACROSS THE BERING SEA AND
ALEUTIANS WITH A STRONG RIDGE BUILDING IN FROM THE WEST. 

&&
.MODEL DISCUSSION...
MODEL GUIDANCE CONTINUES TO DIVERGE WITH HANDLING OF TRIPLE POINT
LOW DEVELOPMENT SOUTH OF THE ALASKA PENINSULA/KODIAK ISLAND
THURSDAY MORNING ALONG WITH THE PROGRESSION OF THE FRONTAL SYSTEM
OUT AHEAD OF THE TRIPLE POINT AS IT CROSSES THE GULF AND ROTATES
WESTWARD TOWARD BRISTOL BAY. THERE IS NO CLEAR PREFERENCE WITH THE
TRIPLE POINT LOCATION AND DEPTH. GENERALLY PREFER THE FRONTAL
TIMING OF THE GFS/ECMWF WHICH REPRESENTS THE MIDDLE GROUND BETWEEN
THE NAM AND CANADIAN SOLUTIONS...AND IS CLOSE TO TIMING OF
INHERITED GRIDS. THE NAM IS QUITE A BIT OF AN OUTLIER WITH ITS
FURTHER EAST LOCATION OF TRIPLE POINT...BUT HAS THE BEST
REPRESENTATION OF PRE-FRONTAL WINDS ALONG THE GULF COAST...SO
WILL MAKE HEAVY USE OF IT. ALL IN ALL THE DIFFERENCES LARGELY
AFFECT A VERY SMALL AREA AND RESULT IN A MINOR DIFFERENCE IN
FRONTAL TIMING. THUS...FORECAST CONFIDENCE IS AVERAGE TO ABOVE
AVERAGE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE FRONT ALONG THE NORTHERN GULF WEAKENS LATER THIS EVENING AS
IT STALLS ACROSS PRINCE WILLIAM SOUND AND THE NORTHEAST GULF.
GUSTY WINDS ACROSS EAST TO WEST GAPS WILL DEVELOP THIS
EVENING...HOWEVER THE DURATION AND STRENGTH WILL BE SHORTER AND
WEAKER THAN THE PREVIOUS FEW DAYS. THE NEXT FRONT IS DEVELOPING IN
THE NORTH PACIFIC AND MOVES INTO THE SOUTHERN GULF EARLY THURSDAY.
GUSTY WINDS AND RAIN ACCOMPANY THIS SYSTEM AS IT MOVES QUICKLY TO
THE NORTHERN GULF. MAX GALE WINDS ARE EXPECTED ACROSS MUCH OF THE
GULF ALONG THE FRONTAL PASSAGE. STRONG DOWN INLET FLOW WILL
INCREASE DURING THE DAY ALONG WITH GUSTY FLOW THROUGH FAVORABLE
GAPS. THE UPPER LEVEL LOW DRIVING THE FRONT ORIENTS SOUTH OF
KODIAK ISLAND THURSDAY NIGHT AND MOVES A STRONGER SHORTWAVE INLAND
THURSDAY NIGHT. AT THE SAME TIME...LOW LEVEL FLOW BACKS TO THE
SOUTH WITH ADEQUATE GULF MOISTURE STREAMING INLAND. THIS
COMBINATION ALONG WITH THE WEAK FRONT MOVING INLAND SHOULD ALLOW
FOR LIGHT RAIN TO DEVELOP ACROSS MUCH OF SOUTHCENTRAL THROUGH
EARLY FRIDAY. ISOLATED TO SCATTERED RAIN SHOWERS ARE POSSIBLE
THROUGH FRIDAY AFTERNOON AS THE SURFACE LOW MOVES SLOWLY ACROSS
THE SOUTHERN GULF.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE SHORTWAVE OVER THE ALASKA PENINSULA WILL SLOWLY PUSH NORTH
THROUGH SOUTHWEST ALASKA THROUGH THURSDAY BEFORE STALLING AND
EVENTUALLY GETTING PUSHED TO THE EAST ON FRIDAY BY RIDGING COMING
IN FROM THE BERING. THIS EVENING AHEAD OF THE SHORTWAVE AN
UNSTABLE ENVIRONMENT DOMINATES. HOWEVER...WITH WEAK CAPPING AND
LOW CAPE VALUES THUNDERSTORMS DEVELOPMENT WILL BE INHIBITED. THE
OTHER CONCERN IS FOG DEVELOPMENT OVERNIGHT FOR THE KUSKOKWIM
DELTA. THE SETUP LOOKS TO BE SIMILAR TO LAST NIGHT WITH THE
ATMOSPHERE DECOUPLING OVERNIGHT AND ENOUGH LOW LEVEL MOISTURE TO
SEE MORE FOG.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
RIDGING OUT WEST LOOKS TO CONTINUE TO TRACK EAST AND MAKE IT OVER
THE EASTERN ALEUTIANS THURSDAY AFTERNOON. BEHIND THE RIDGE ANOTHER
LOW WILL MOVE IN FROM THE WEST BRINGING ITS FRONT OVER THE WESTERN
ALEUTIANS THURSDAY EVENING. THE FRONT WILL CONTINUE EAST AND MAKE
IT TO THE EASTERN ALEUTIANS FRIDAY NIGHT. THE SYSTEM IS PULLING UP
WARM AIR FROM THE SOUTH SO THE PRECIPITATION FROM IT SHOULD FALL
AS RAIN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
RESIDUAL SHOWERS WILL LINGER OVER THE SOUTHERN MAINLAND IN THE
WAKE OF A DECAYING WARM FRONT PUSHING FURTHER INLAND FRIDAY NIGHT
INTO SATURDAY MORNING. GUSTY GAP WINDS ALONG THE NORTHERN GULF
COAST AND PRINCE WILLIAM SOUND WILL ALSO BE ON THE DOWN TREND AS
HIGHER PRESSURE BEGINS TO BUILD INTO THE AREA. THE LOW THEN
QUICKLY EXITS THE AREA OVER THE WEEKEND GIVING WAY TO SOME
RIDGING TO BUILD IN ITS PLACE. THE INCREASING HIGHER PRESSURE
OVER THE AREA WILL BRING CLEARING SKIES AND WARMER TEMPERATURES
OVER SOUTHCENTRAL ALASKA THROUGH SUNDAY. A SERIES OF FRONTS WILL
WORK THEIR WAY INTO THE SOUTHERN MAINLAND SUNDAY NIGHT THROUGH THE
MIDDLE OF NEXT WEEK...BRINGING ANOTHER ROUND OF PRECIPITATION TO
THE AREA.

MODELS ARE IN MUCH BETTER AGREEMENT IN HANDLING THE SERIES OF LOWS
AND FRONTS PUSHING OFF THE KAMCHATKA PENINSULA AND INTO THE
WESTERN BERING OVER THE WEEKEND. PREVIOUS MODELS HAVE STRUGGLED
WITH HOW FAR EAST THESE SYSTEMS WOULD PROGRESS...BUT WITH THE MOST
RECENT MODEL RUNS THEY HAVE ALL BACKED OFF TOWARD A SLOWER AND
MORE WESTERLY SOLUTION. MODELS HAVE ALSO COME INTO BETTER
AGREEMENT WITH THE STRENGTH AND POSITIONING OF THE RIDGE AHEAD OF
THESE SYSTEMS. BOTH THE GFS AND EC ARE NOW SHOWING A RIDGE SETTING
UP OVER THE GULF AND SOUTHCENTRAL BY SUNDAY MORNING...AND
CONTINUING TO STRENGTHEN INTO THE EARLY PART OF NEXT WEEK. THIS
BUILDS HIGHER CONFIDENCE IN THE POTENTIAL FOR SOME CLEAR SKIES AND
WARMER WEATHER FOR GULF COAST AND SOUTHCENTRAL ALASKA BY THE END
OF THE WEEKEND AND INTO EARLY NEXT WEEK. HOWEVER...THE MODELS ARE
STRUGGLING WITH THE POSITIONING OF THE SECOND LOW OVER THE BERING
MID WEEK NEXT WEEK...AND THE STRONG ROGUE NORTH PACIFIC LOW THAT
THE EC IS TRACKING TOWARD THE CENTRAL ALEUTIANS WEDNESDAY
AFTERNOON. GIVEN THE SPREAD BETWEEN THE GFS AND EC AT THIS TIME
FRAME...CONFIDENCE IS MUCH LOWER REGARDING THESE FEATURES.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 119 120 130 131 132 136 137 138 150 155 172.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...PEPE