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
000
FXAK68 PAFC 010042
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
442 PM AKDT MON AUG 31 2015

.ANALYSIS AND UPPER LEVELS...
EVEN THOUGH THE UPPER LOW CENTER OVER THE STATE HAS MOVED OUT
OVER THE GULF THERE IS STILL ENOUGH OF A GRADIENT BETWEEN THIS LOW
AND RIDGING OVER THE EASTERN BERING TO CONTINUE TO BRING STRONG
NORTHWEST WINDS TO THE SOUTHERN MAINLAND. THE WIND GUSTS OVER
SOUTHCENTRAL WERE STRONGER IN THE MORNING DUE TO A POTENTIAL
VORTICITY ANOMALY PUSHING THROUGH THE AREA FROM THE MAIN LOW
CENTER HELPING TO MIX DOWN THE STRONGER WINDS FROM ALOFT. THIS
WAS ADDITIONALLY AIDED BY COLD AIR ADVECTION MOVING IN FROM THE
NORTH. WEST OF THE RIDGING ANOTHER LOW IS SLOWLY TRACKING NORTH
JUST TO THE WEST OF THE WESTERN ALEUTIANS. THIS LOW AND ITS
ASSOCIATED FRONT THAT STRETCHES THROUGH THE EASTERN ALEUTIANS HAVE
BEEN BRINGING RAIN TO THE ISLANDS.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD AGREEMENT OVERALL. THERE ARE SOME MINOR
DIFFERENCES OUT WEST WITH THE FRONT MOVING ACROSS THE BERING AND
THE NEXT LOW THAT MOVES IN SOUTH OF THE ALEUTIANS. ALL THE MODELS
HAVE THE FRONT MAKING LANDFALL ON THE SOUTHWEST COAST TUESDAY
NIGHT. THE BIGGEST DIFFERENCE BETWEEN THEM IS THE NAM IS A COUPLE
HOURS FASTER THAN THE OTHERS WHICH ALSO LEADS TO IT PUSHING
THROUGH FASTER. WITH THE LOW TRAVELING SOUTH OF THE ALEUTIANS
WEDNESDAY INTO THURSDAY THE NAM AND GFS HAVE THE LOW JUST SOUTH OF
THE ISLANDS WHILE THE EC AND GEM HAVE AN EVEN FURTHER SOUTH
SOLUTION. THIS LEADS TO THE NAM AND GFS BRINGING IN MORE RAIN FOR
THE ISLANDS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE PRIMARY FORECAST CHALLENGE OVER THE NEXT 24-48 HOURS WILL BE
REFINING THE DETAILS OF THE CONTINUED OUTFLOW WINDS AND HOW THEY
IMPACT OVERNIGHT LOW TEMPERATURES. A BRIEF LULL IN THE WINDS IS
EXPECTED THIS EVENING INTO TONIGHT AS THE MAIN LOW PULLS AWAY FROM
THE AREA. HOWEVER...THIS DIMINISHING TREND WILL BE SHORT LIVED AS
ANOTHER UPPER WAVE DROPS INTO THE GULF FROM THE NORTH LATE
TONIGHT/EARLY TUESDAY MORNING ACCOMPANIED BY A RE-ENFORCING SHOT
OF COLD AIR ADVECTION. THIS WILL KEEP GUSTY NORTH WINDS OVER THE
AREA AND PRODUCE A SECONDARY PEAK IN STRONG GAP WINDS THROUGH
FAVORED AREAS ALONG THE GULF COAST THROUGH TUESDAY MORNING. THIS
SHOULD HELP TO INHIBIT RADIATIONAL COOLING AND KEEP TEMPERATURES
ABOVE FREEZING FOR MOST OF THE AREA TONIGHT WITH THE EXCEPTION OF
TYPICALLY SHELTERED AREAS SUCH AS EAST ANCHORAGE. WINDS WILL THEN
GRADUALLY DIMINISH THROUGH WEDNESDAY AS HIGH PRESSURE BUILDS INTO
SOUTHCENTRAL AK FROM THE WEST...LEADING TO THE POTENTIAL FOR MORE
WIDESPREAD COLDER TEMPERATURES ON TUESDAY NIGHT.

FIRE WEATHER CONCERNS WILL ALSO HAVE TO BE MONITORED OVER THE NEXT
48 HOURS AS DRY NORTHERLY FLOW PERSISTS OVER THE AREA...RESULTING
IN GUSTY WINDS WITH AFTERNOON MINIMUM RH VALUES APPROACHING 30
PERCENT FROM THE MATANUSKA AND SUSITNA VALLEYS INTO THE ANCHORAGE
BOWL.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AN AMPLIFYING UPPER LEVEL RIDGE OVER THE EASTERN BERING WILL
CONTINUE TO SHIFT EASTWARD OVER THE SOUTHWEST MAINLAND
TONIGHT. AS A RESULT...GUSTY NORTHWESTERLY FLOW WILL SLOWLY
DIMINISH TUESDAY MORNING...AND TEMPERATURES WILL BECOME SLIGHTLY
WARMER AS THE RIDGE BUILDS EASTWARD THROUGH WEDNESDAY. DRIER
CONDITIONS WILL PERSIST THROUGH TUESDAY...AS WINDS BEGIN TO SHIFT
TO A SOUTHERLY DIRECTION AHEAD OF AN APPROACHING FRONTAL SYSTEM
FROM THE SOUTHWEST. THIS WILL USHER IN ANOTHER ROUND OF RAIN AND
WINDY CONDITIONS OVER PARTS OF THE SOUTHWEST MAINLAND FROM TUESDAY
EVENING THROUGH WEDNESDAY EVENING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
AS THE UPPER LEVEL RIDGE OVER THE BERING SHIFTS EAST A LARGE
VERTICALLY STACKED LOW OFF OF THE KAMCHATKA PENINSULA WILL TRACK
NORTHEAST INTO THE FAR WESTERN BERING. A NORTH PACIFIC SURFACE
LOW WILL CROSS THE CENTRAL AND EASTERN ALEUTIANS TUESDAY MORNING
WITH AN ASSOCIATED FRONTAL SYSTEM THEN LIFTING NORTH AND EAST
ACROSS THE BERING BY TUESDAY EVENING...BRINGING IN GUSTY SOUTHEAST
WINDS IN THE 30 TO 35 KT RANGE OVER THE EASTERN BERING TUESDAY
MORNING THROUGH WEDNESDAY MORNING. MEANWHILE AN UPPER LEVEL
TROUGH TO THE SOUTH OF THE MAIN WESTERN BERING UPPER LOW WILL
SWING EAST DRAGGING SHOWERS ACROSS THE ALEUTIANS FROM WEST TO EAST
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

THE FRONT MOVING INLAND ACROSS SOUTHWEST ALASKA WILL SLOW DOWN A
LITTLE BIT ON THURSDAY AS IT BEGINS TO PUSH UP AGAINST SFC HIGH
PRESSURE OVER MUCH OF THE ALASKA MAINLAND. THIS WILL KEEP MUCH OF
SOUTHWEST AND SOUTHCENTRAL ALASKA IN A FAVORABLE AREA TO SEE
PERIODS OF RAINFALL THROUGH THE MAJORITY OF THE WEEKEND. RAIN
CHANCES WILL DIMINISH FROM WEST TO EAST SUNDAY MORNING WITH THE
PASSAGE OF THE UPPER LEVEL TROUGH. SOME TIMING ISSUES ARE PRESENT
AS TWO UPPER LOWS (ONE OVER THE NORTHERN BERING AND THE OTHER IN
THE NORTH PACIFIC) MAY OR MAY NOT INTERACT WITH ONE ANOTHER
HEADING INTO THE WEEKEND. THE GFS HAS THE LOW IN THE BERING
DROPPING SOUTH AND INTERACTING WITH THE LOW MOVING TOWARD THE GULF
OF ALASKA WHICH WILL KEEP THE UPPER LEVEL FLOW IN A MORE ZONAL
PATTERN. THE ECMWF...HOWEVER...KEEPS THESE TWO LOWS SEPARATE WITH
THE NORTHERN BERING LOW CUT OFF FROM THE MEAN FLOW AND SLOWLY
MEANDERING EASTWARD. THIS WOULD ALLOW AN UPPER LOW COMING OFF THE
KAMCHATKA TO AMPLIFY THE LONGWAVE PATTERN LEADING TO A
STRENGTHENING RIDGE OVER MUCH OF THE MAINLAND. THE GFS FAILS TO
AMPLIFY THE PATTERN AS THE ZONAL FLOW AND STRONG JET WOULD SHUNT
THIS UPPER LOW INTO ALASKA BEFORE IT HAS TIME TO AMPLIFY THE
PATTERN. THE ECMWF SOLUTION STILL LOOKS TO BE THE MORE FAVORABLE
SOLUTION ALTHOUGH MAYBE NOT WITH THE EXTREME AMPLIFICATION THE
MODEL IS CURRENTLY DEPICTING. THERE IS STILL QUITE A BIT OF
UNCERTAINTY AT THIS TIME SO IT IS TOUGH TO REALLY BUY INTO ANY ONE
SOLUTION BUT IT APPEARS MORE LIKELY THAT THE PATTERN RE-AMPLIFIES
HEADING INTO NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 131 132.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...MC


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