Area Forecast Discussion
Issued by NWS Anchorage, AK

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
000
FXAK68 PAFC 041248
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
448 AM AKDT WED MAY 4 2016

.ANALYSIS AND UPPER LEVELS...
THE SYNOPTIC PATTERN OVER THE NORTH PACIFIC AND ALASKA HAS BECOME
MUCH MORE PROGRESSIVE OVER THE LAST 24 HOURS WITH STRONG RIDGES IN
PLACE OVER WESTERN NORTH AMERICAN COAST AND THE KAMCHATKA
PENINSULA WITH A BROAD LONGWAVE TROUGH IN BETWEEN. IN
BETWEEN...TWO HIGHER AMPLITUDE SHORTWAVES /ONE ALONG 130W AND A
SECOND ALONG 180/ CONTINUE TO PROGRESS EASTWARD WITH A FLAT RIDGE
ALONG 155W. AN ELONGATED BROAD UPPER LOW LIES ALONG THE ALEUTIAN
CHAIN WITH A CENTER NEAR DUTCH HARBOR WITH MULTIPLE WEAK
SHORTWAVES ROTATING AROUND THE LOW. THE POLAR JET HAS RESPONDED
WITH THE CHANGE IN PATTERN TO A MORE MERIDIONAL SHAPE WITH A
130KT JET ALONG THE EASTERN SIDE OF THE KAMCHATKA RIDGE AND A
140KT JET ON THE EASTERN SIDE OF THE TROUGH NEAR 180.

AT THE SURFACE...A BROAD 1003 MB LOW LIES ALONG THE ALEUTIAN
CHAIN UNDER THE ABOVE MENTIONED UPPER CLOSED LOW. A 1005 MB LOW IS
EVIDENT FROM SURFACE OBSERVATIONS OVER THE KUSKOKWIM DELTA THIS
MORNING. A 996 MB LOW IS RAPIDLY DEVELOPING NEAR 44N 172W UNDER
THE SHORTWAVE NEAR 180. THE LOW HAS AMPLE UPPER LEVEL SUPPORT WITH
ITS DEVELOPMENT NEAR THE LEFT EXIT REGION OF THE 140KT MENTIONED
ABOVE. FINALLY...A 1024 MB HIGH IS COUPLED WITH THE KAMCHATKA
RIDGE OVER THE NORTHWEST PACIFIC OCEAN.

&&

.MODEL DISCUSSION...
FOR THE 00Z MODEL RUNS...MODELS SEEMED TO HAVE INITIALIZED
ACCEPTABLY. THROUGH DAY 1...GUIDANCE SEEMS TO BE IN REASONABLE
AGREEMENT ON THE HANDLING OF THE DEVELOPING LOW SOUTH OF THE
ALEUTIANS. STARTING EARLY THURSDAY MORNING...THE MODELS BEGIN TO
DEVIATE WITH THEIR PROGRESSION OF THE LOW. ALL OF THE MODELS BEGIN
A SOUTHWEST TO NORTHEAST ELONGATION OF THE LOW...BUT THE NAM IS
GENERALLY FASTER WITH THIS PROCESS AND DEVELOPS A TRIPLE POINT
LOW ALONG THE SURFACE FRONT SOUTH OF KODIAK BY MID-DAY TUESDAY.
WHILE THE NAM DOES HAVE A HINT OF SUPPORT FOR THIS SOLUTION FROM
THE OTHER MODELS...THE NAM IS FASTER...DEEPER...AND FURTHER WEST
WITH THIS SOLUTION AND FOR THIS FORECAST PACKAGE IS CONSIDERED THE
OUTLIER SOLUTION. THE DAY 1 THROUGH 3 FORECAST FOR THIS PACKAGE IS
GENERALLY BASED ON A GFS/ECWMF BLEND WITH THE GEM- REGIONAL USED
HEAVY IN THE FIRST 36 HOURS ON THE EASTERN DOMAIN FOR SPATIAL
DETAIL IN THE MARINE AREAS.

&&

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

A WEAK OCCLUDED FRONT WILL MOVE NORTHWARD TO THE NORTH GULF COAST
THIS AFTERNOON. UPPER LEVEL FORCING WITH THIS LOOKS MUCH MORE
IMPRESSIVE WITH AMPLIFICATION OF A SHORT-WAVE TROUGH AS IT CROSSES
THE GULF. THUS...EXPECT AREA AND INTENSITY OF RAIN TO INCREASE AS
THE FRONT AND TROUGH REACH THE NORTHERN GULF. THE TROUGH WILL THEN
ELONGATE AND WEAKEN AS IT HEADS INLAND...SO EXPECT A REPEAT OF THE
ISOLATED TO SCATTERED CONVECTION THIS AFTERNOON THROUGH TONIGHT.
A COUPLE OF THUNDERSTORMS DEVELOPED ACROSS THE SOUTHERN AND
WESTERN SUSITNA VALLEY YESTERDAY AFTERNOON AND EARLY
EVENING. WITH NEARLY IDENTICAL THERMODYNAMIC PROFILE FOR THIS
AFTERNOON AND TIMING OF A DISTURBANCE MOVING ACROSS THE
AREA...WILL INCLUDE ISOLATED THUNDERSTORMS FOR LATE THIS AFTERNOON
INTO EARLY THIS EVENING.

GUIDANCE HINTS AT A WEAK LOW FORMING OVER THE NORTHWEST GULF
WEDNESDAY AFTERNOON IN RESPONSE TO THE AMPLIFYING UPPER TROUGH.
THIS WILL RESULT IN STRONGER NORTHERLY FLOW DOWN COOK INLET.
HOWEVER...WITH A VERY LOW STABILITY ENVIRONMENT DEPICTED ON THE
12Z ANCHORAGE SOUNDING AND EAST TO SOUTHEAST WINDS
ALOFT...GUSTY SOUTHEAST WINDS WILL BE INCLUDED FOR LOCATIONS SUCH
AS SOUTH AND WEST ANCHORAGE THIS AFTERNOON AND EARLY
EVENING...WHILE MOST OTHER PARTS OF ANCHORAGE WILL LIKELY SEE
LIGHT AND VARIABLE WINDS...BUT IT IS NOT OUT OF THE QUESTION A FEW
ISOLATED SOUTHEAST GUSTS OCCUR. THIS NORTHERLY PRESSURE GRADIENT
WILL ALSO LEAD TO MARGINALLY WEAKER GAP WINDS THROUGH THE KNIK
RIVER VALLEY COMPARED WITH THE PAST FEW DAYS.

THE LOW LEVEL FLOW...WHICH HAS BEEN PREDOMINANTLY OUT OF THE
EAST TO SOUTHEAST FOR QUITE A WHILE....WILL BACK TOWARD THE NORTH
ON THURSDAY AS A STRONG WARM FRONT (ORIENTED NORTHEAST TO
SOUTHWEST) MOVES INTO THE GULF AND APPROACHES SOUTHCENTRAL. THIS
SYSTEM CONTINUES TO LOOK MORE AND MORE IMPRESSIVE...WITH STRONG
LOW LEVEL CONVERGENCE AND A BROAD UPPER TROUGH WITH A LONG
SOUTHERLY FETCH OF WARM AIR AND MOISTURE. THUS...EXPECT MODERATE
TO HEAVY RAIN TO QUICKLY SPREAD ACROSS THE GULF ON THURSDAY. WITH
THE CHANGE IN LOW LEVEL FLOW EXPECT MOISTURE TO MAKE IT OVER THE
MOUNTAINS AND BRING LIGHT RAIN TO INLAND PORTIONS OF SOUTHCENTRAL
LATE THURSDAY THROUGH AT LEAST EARLY FRIDAY. HAVE STARTED TO
TREND HIGHER WITH POPS...THOUGH IF THERE IS GOOD CONSISTENCY IN
GUIDANCE TONIGHT MAY NEED TO GO QUITE A BIT HIGHER.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE COMBINATION OF THE THERMAL TROUGH AND THE ZERO TO MINUS ONE
LIFTED INDICES WILL INCREASE THE POSSIBILITIES FOR SOME ISOLATED
THUNDERSTORMS FOR THE LATE AFTERNOON AND EVENING TIME-FRAME
TODAY. OTHERWISE...WE WILL CONTINUE TO HAVE WIDESPREAD SHOWERS
DEVELOPING IN THE BRISTOL BAY AREA BEFORE SPREADING INTO THE
LOWER KUSKOKWIM VALLEY/DELTA WITH THE EAST/SOUTHEASTERLY FLOW.
THE OTHER CONCERN TODAY WILL BE WITH THE LOW STRATUS AND AREAS OF
FOG DEVELOPING ALONG THE SOUTHWEST COASTLINE THIS MORNING. THE
BIGGEST CHALLENGE WILL BE HOW FAR THE LOW STRATUS/FOG WILL ADVECT
INLAND BEFORE DISSIPATING BY THE LATE MORNING HOURS. BY THURSDAY A
NORTH PACIFIC LOW WILL TRACK JUST SOUTH OF THE ALASKA PENINSULA.
THIS WILL BRING GALE FORCE NORTHEASTERLY WINDS ON THE PACIFIC SIDE
OF THE EASTERN ALEUTIANS AND THE ALASKA PENINSULA REGION. THE
FRONTAL BOUNDARY ASSOCIATED WITH THIS SYSTEM WILL SWING THROUGH
THE BRISTOL BAY REGION BY THURSDAY AFTERNOON. THIS WILL RESULT IN
SOME PRECIPITATION SPILLING OVER THE ALEUTIAN RANGE INTO THE
BRISTOL BAY INLAND AREAS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE WESTERN ALEUTIANS WILL BE UNDER THE INFLUENCE OF A RIDGE OF
HIGH PRESSURE THIS MORNING. WHILE A LOW PRESSURE SYSTEM WILL DROP
DOWN OFF THE KAMCHATKA PENINSULA WITH AN ASSOCIATED WEATHER FRONT
MOVING INTO THE WESTERN ALEUTIANS BY THURSDAY MORNING. THIS WILL
RESULT IN GUSTY SOUTHWESTERLY WINDS ACCOMPANIED BY RAIN AND STRATUS.
WHILE THE EASTERN ALEUTIANS WILL BE AFFECTED BY A NORTH PACIFIC
LOW THAT WILL TRACK JUST SOUTH OF THE CHAIN BY THIS EVENING. AS
THIS SYSTEM TRACKS FARTHER TOWARDS THE NORTHEAST THE PRESSURE
GRADIENTS WILL STRENGTHEN. THEREFORE...LOOK FOR GALE FORCE EAST
TO NORTHEASTERLY WINDS ON THE PACIFIC SIDE ALONG THE EASTERN
ALEUTIANS EXTENDING TOWARD KODIAK ISLAND AREA. THIS WILL BRING A
SWATH OF MOISTURE WITH STRATUS/RAIN ALONG THE CHAIN BY THURSDAY
MORNING HEADING INTO FRIDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
BIG PICTURE MOVING FORWARD IS THAT THE PATTERN WILL BE MORE
DYNAMIC THAN WE HAVE SEEN IT OVER THE PAST SEVERAL WEEKS. A
STRONGER NORTH PACIFIC LOW TRACKING TOWARD THE WESTERN GULF
THURSDAY AFTERNOON WILL WEAKEN AND BECOME MORE COMPLEX BY FRIDAY
MORNING. THIS SYSTEM WILL PUSH A WARM FRONT INTO THE GULF OF AK ON
THU AND INTO SOUTH CENTRAL ON FRI...PULLING UP A HEALTHY AMOUNT OF
SUB- TROPICAL MOISTURE INTO THE GULF AND BRING MODERATE RAIN TO
THE COASTLINE. WINDS WILL ALSO INCREASE TO GALE-FORCE ACROSS
PORTIONS OF THE GULF...ESPECIALLY THE BARRIER JET REGION. IT DOES
NOT LOOK LIKE MUCH PRECIPITATION WILL MAKE IT INLAND...AS THIS
LOOKS LIKE A SOLID DOWN-SLOPING SCENARIO WHICH SHOULD KEEP MOST OF
THE RAIN CONFINED TO THE GULF COAST. THE LOW THEN QUICKLY EXITS
THE AREA OVER THE WEEKEND LEAVING SOME RIDGING IN PLACE. ANOTHER
LOW QUICKLY MOVES IN TO THE BERING SEA OVER THE WEEKEND WHILE SOME
RIDGING BUILDS FROM THE NORTH PACIFIC OVER THE MAINLAND.

MODELS ARE IN MUCH BETTER AGREEMENT IN HANDLING THE SERIES OF LOWS
PUSHING OFF THE KAMCHATKA PENINSULA AND INTO THE WESTERN BERING
LATER IN THE WEEK AND 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.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 130 131 132 136 137 138 150 155
         351

&&

$$

SYNOPSIS AND MODEL DISCUSSION...RLF
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...TP


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.