Area Forecast Discussion - SouthCentral and SouthWest


FXAK68 PAFC 060134
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
434 PM AKST FRI FEB 5 2016
.ANALYSIS AND UPPER LEVELS...
THE ATMOSPHERE ALOFT OVER THE GREAT LAND TODAY LOOKS MUCH THE SAME
AS THE MAJORITY OF WINTER SO FAR...WEAK TROUGHING/CYCLONIC
CIRCULATION CENTERED OVER THE BERING SEA AND EXTENDING OVER THE
MAINLAND. LOOKING AT WATER VAPOR SATELLITE EARLY THIS
AFTERNOON...A COUPLE THINGS STAND OUT. THE FIRST IS THE CONVECTIVE
NATURE OF THE TROUGH...MAINLY OVER THE NORTHERN GULF. THE OPEN-
CELLED STRUCTURE SPEAKS TO THE INSTABILITY PRESENT ALOFT. THE
SECOND IS THE NUMBER OF EMBEDDED VORTICITY MAXIMA WITHIN THE FLOW.
NO LESS THAN FOUR ARE EVIDENT...MOVING TOWARD SOUTHCENTRAL ALASKA.
LOTS OF SHOWERS ARE POPPING UP ON THE RADAR ALONG THE NORTH GULF
WITH MORE ACTIVITY FOCUSING ALONG A LOW/MID LEVEL TROUGH
DEVELOPING ON THE SOUTHERN KENAI PENINSULA AND EASTWARD INTO THE
GULF. CURRENTLY...WEAK CROSS BARRIER FLOW KEEPS THE COOK INLET
REGION DRY WITH DOWNSLOPE FLOW...HOWEVER IT LOOKS LIKE THE FLOW
SLACKENS BEHIND THE TROUGH.

&&
.MODEL DISCUSSION...
ON THE LARGE SCALE...MODELS ARE IN GOOD AGREEMENT WITH THE
EVOLUTION OF THE PATTERN FOR THE NEXT FEW DAYS. THE MAIN
DEVELOPING FEATURE WILL BE AN UPPER LEVEL LOW TAKING SHAPE SOUTH
OF THE GULF...THAT WILL SEND A GALE FORCE FRONT INTO THE GULF ON
EARLY SUNDAY. 

ON THE MESO-SCALE...MORE DISAGREEMENTS ARE EVIDENT...CONCERNING A
MID-LEVEL TROUGH AND ANY SURFACE REFLECTION THAT WILL BE SPINNING
UP IN THE WESTERN GULF. THIS CIRCULATION WILL HAVE RAMIFICATIONS
ON WHEN THE TURNAGAIN/DOWNSLOPE WINDS WANE AND PRECIPITATION
STARTS AROUND ANCHORAGE. WITH THE PRECIPITATION ITSELF...HIGHER
RESOLUTION MODELS HAVE MORE OF A CONSOLIDATED BAND OF
PRECIPITATION WHILE THE COARSER MODELS ARE SIGNIFICANTLY LIGHTER
IN THE QPF.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

PRECIPITATION TYPE CONTINUES TO PLAGUE THE FORECAST FOR THIS
EVENING AS SUBTLE CHANGES IN SEVERAL SMALL VARIABLES WILL END UP
DETERMINING WHETHER IT RAINS OR SNOWS (OR BOTH!). LET US START OFF
WITH THE SHORTWAVE PASSING ACROSS THE ANCHORAGE AREA THIS EVENING
PRECEDING THE UPPER LEVEL TROUGH TOMORROW. RECENT GUIDANCE AS WELL
AS HIGH-RES GUIDANCE IS STARTING TO SUGGEST THAT THIS WAVE ENDS
UP FRAGMENTING. SHOULD THIS OCCUR...TWO SEPARATE VORT MAXES OVER
THE SUSITNA VALLEY AND EASTERN TURNAGAIN ARM WOULD DEVELOP. THIS
WOULD END UP KEEPING ANCHORAGE MAINLY ON THE DRY SIDE WITH WEAK
SUBSIDENCE BETWEEN THE TWO VORT MAXES. NOW...TURNAGAIN ARM WINDS
AND GAP WINDS HAVE BEEN PERFORMING A BIT STRONGER THAN ORIGINALLY
ANTICIPATED WHICH MAY PLAY A ROLE IN PRECIPITATION TYPE AS WELL.
THE GRADIENT IN TURNAGAIN ARM WILL BRIEFLY BECOME UP INLET RIGHT
AROUND WHEN PRECIPITATION BEGINS. THIS WOULD BE FAVORABLE FOR A
TINY PIECE OF THE TURNAGAIN ARM WINDS TO MOVE INTO SOUTH ANCHORAGE
AND WARM TEMPERATURES AND DEW POINTS INTO THE UPPER 30S. SHOULD
THIS OCCUR...THE PRECIPITATION THAT FALLS ACROSS SOUTH ANCHORAGE
WOULD FALL AS RAIN WITH AREAS IN EAST ANCHORAGE AND DOWNTOWN
SEEING A MIX OF RAIN AND SNOW. THE LAST DRIVING FACTOR FOR
PRECIPITATION TYPE WILL BE THE INTENSITY THAT THE PRECIPITATION
FALLS. WITH WEAK COLD AIR ADVECTION FILTERING IN RIGHT AROUND THE
ONSET OF PRECIPITATION...A FAIRLY UNSTABLE MID-LEVEL AND UPPER-
LEVEL ENVIRONMENT WILL SET UP. SOME CONVECTIVE SHOWERS MAY BE
EMBEDDED WITHIN THE MAIN BAND OF PRECIPITATION WHICH WOULD LIKELY
CHANGE ANY RAIN CURRENTLY FALLING TO SNOW BUT WOULD LIKELY REVERT
BACK TO RAIN AFTER THE INTENSITY DIMINISHES. SO AFTER ALL OF
THAT...THE BEST ANSWER FOR PRECIPITATION TYPE LOOKS TO BE A MIX OF
RAIN. A FEW LOCATIONS MAY LUCK OUT AND SEE UP TO 1 INCH OF SNOW
ACCUMULATION IN ANCHORAGE BUT OVERALL MOST LOCATIONS WILL SEE
LITTLE ACCUMULATION (IF THAT).

LOOKING BACK AT THE BIG PICTURE...AN UPPER LEVEL TROUGH WILL PUSH
THROUGH THE REGION ON SATURDAY WHICH WILL INTERACT WITH SOME
RESIDUAL LOW LEVEL MOISTURE. THIS MAY SPARK SOME ISOLATED TO
SCATTERED SNOW SHOWERS ACROSS THE COOK INLET REGION WITH MORE
WIDESPREAD UPSLOPE SHOWERS ALONG THE NORTHERN GULF COAST. A FRONT
ASSOCIATED WITH A LOW MOVING INTO THE SOUTHERN GULF WITH PUSH
ACROSS THE GULF ON SUNDAY WHICH WILL HELP INCREASE RAIN/SNOW
CHANCES ACROSS THE NORTHERN GULF COAST. IT LOOKS LIKE A BIT OF THE
COLD AIR THAT GETS ADVECTED BEHIND THE SYSTEM TONIGHT WILL BE
ERODED BY THIS AIR MASS AND TEMPERATURES WILL LIKELY REMAIN ABOVE
NORMAL.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
MOST OF THE ACTIVE WEATHER OVER THE SOUTHWEST MAINLAND WILL CENTER
AROUND THE UPPER LEVEL TROUGH OVER THE AREA. THIS TROUGH WILL
CAUSE SNOW TO DEVELOP FROM NORTHERN BRISTOL BAY INTO THE
KUSKOKWIM DELTA THIS EVENING...AND PERSIST INTO SATURDAY MORNING.
THE HEAVIEST ACCUMULATIONS WILL LIKELY OCCUR OVER THE HIGHER
ELEVATIONS NORTH OF DILLINGHAM AS THEY WILL EXPERIENCE DEEP
UPSLOPE FLOW...WITH LOWER ELEVATIONS RECEIVING JUST A FEW INCHES
OF SNOW BY SATURDAY MORNING. SNOW ACCUMULATIONS OVER THE KUSKOKWIM
DELTA WILL BE LIMITED A BIT BY DOWNSLOPING FROM THE KILBUCK
MOUNTAINS...HOWEVER THIS IS RELATIVELY WEAK SO MOST AREAS SHOULD
RECEIVE AN INCH OR SO OF SNOW OVERNIGHT. RIDGING MOVING IN BEHIND
THIS TROUGH ON SATURDAY THEN CAUSE THE SNOW THROUGHOUT THE AREA TO
DIMINISH BY SATURDAY AFTERNOON. THIS RIDGING WILL THEN DIMINISH
OVER BRISTOL BAY SUNDAY AS A STORM FORCE FRONT FROM THE NORTH
PACIFIC APPROACHES KODIAK ISLAND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE WEATHER OVER THE BERING WILL REMAIN FAIRLY BENIGN FOR THIS
TIME OF YEAR THROUGH THE WEEKEND. THE WEAK LOW CENTERED SOUTH OF
THE CENTRAL ALEUTIANS WILL APPROACH UNALASKA LATE
TONIGHT...BRINGING SNOW MIXED WITH RAIN ALONG WITH GUSTY
SOUTH EASTERLY WINDS TO THE AREA BEFORE SLOWLY WEAKENING ON
SATURDAY. MORE ACTIVE WEATHER WILL THEN MOVE INTO THE WESTERN
BERING/ALEUTIANS LATE SUNDAY AS A GALE TO STORM FORCE NORTH
PACIFIC LOW MOVES INTO THE AREA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN ACTIVE WEATHER PATTERN WILL CONTINUE ACROSS THE GULF AND BERING
THROUGH NEXT FRIDAY...WITH DRIER CONDITIONS FOR INLAND LOCATIONS.
SUNDAY NIGHT...LOW PRESSURE LIFTS TOWARD KODIAK BRINGING A REINFORCING
WAVE TO THE NORTHERN GULF WHICH SPREADS SCATTERED RAIN AND SNOW
SHOWERS FURTHER INLAND INTO MONDAY. AT THE SAME TIME...ANOTHER LOW
ORGANIZES SOUTH OF THE CENTRAL ALEUTIANS AND TRACKS EASTWARD
THROUGH TUESDAY. THE SURFACE LOW ASSOCIATED WITH THIS SYSTEM IS
EXPECTED TO BRING A STORM FORCE FRONT AS IT DEEPENS TO 950 MB.
THIS SYSTEM LOSES MOMENTUM INTO WEDNESDAY AS A RIDGE BUILDS OVER
SOUTHERN ALASKA. THIS RIDGE CURRENTLY LOOKS TO SHUNT PROGRESS OF
THIS LOW AND ANOTHER LOW TRACKING IN FROM THE EASTERN BEAUFORT
SEA. THIS KEEPS TEMPERATURE TRENDS ABOVE NORMAL IN THE EXTENDED
FORECAST. ANOTHER DEVELOPING LOW SOUTH OF THE CENTRAL ALEUTIANS
SPINS UP AND FOLLOWS A SIMILAR PATTERN AS THE JET STREAMS REMAINS
NEARLY ZONAL ALONG 40N AT THE END OF THE NEXT WEEK.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 131 136 137 138 155 172.
		 STORM 130 150.
		 HEAVY FREEZING SPRAY 185.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...MC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...KH