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FXAK68 PAFC 211222
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
422 AM AKDT SUN SEP 21 2014
.ANALYSIS AND UPPER LEVELS...
THE MAJOR FEATURE EVIDENT ON WATER VAPOR IMAGERY THIS MORNING IS A
DEVELOPING SYSTEM IN THE NORTHEASTERN PACIFIC. THIS BAROCLINIC
LEAF IS ON THE DOWNSTREAM SIDE OF THE PERSISTENT LONG-WAVE OVER
SOUTHERN ALASKA WHICH IS BEING FORCED TO PROPAGATE EASTWARD BY THE
DEVELOPING SYSTEM AS WELL AS UPPER RIDGING IMPINGING FROM THE
WEST. WHAT IS LEFT OF THE UPPER TROUGH DOES NOT LOOK IMPRESSIVE
WITH NO AREAS OF SIGNIFICANT LIFT EVIDENT...ONLY DECAYING PLUMES
OF MOISTURE ASSOCIATED WITH DIURNAL CONVECTION WHICH ARE QUICKLY
FADING AWAY. A STRONGER WAVE IS SHOWING UP OVER CENTRAL/NORTHERN
ALASKA THAT WILL SKIRT OUR NORTHERN ZONES BUT IS BEING KEPT AT
BAY BY THE UPPER RIDGE NOSING IN FROM THE WEST. FURTHER OUT
WEST...THE KAMCHATKA LOW LOOKS SPENT AND ILL-DEFINED WITH A BROAD
ANTI- CYCLONIC CIRCULATION OVER MUCH OF THE BERING SEA. THE JET
STREAM IS WELL TO THE SOUTH IN THE MID-LATITUDES AND VERY ZONAL IN
NATURE.

&&
.MODEL DISCUSSION...
GUIDANCE REMAINS IN GOOD AGREEMENT WITH THE PATTERN ALOFT FOR THE
NEXT FEW DAYS WILL LITTLE DISCREPANCY FROM MODEL TO MODEL. THE
DEVELOPING SYSTEM IN THE NORTHEASTERN PACIFIC HAS INTRODUCED SOME
SLIGHT DIFFERENCES IN STRENGTH AND TIMING...ESPECIALLY WITH THE
GFS WHICH DOES NOT DEVELOP THE SYSTEM NEARLY AS MUCH AS THE OTHER
GUIDANCE. THE SYSTEM WILL MISS MOST OF THE SOUTHCENTRAL AS IT
MOVES INTO THE YUKON BUT EASTERN PORTIONS OF THE COPPER RIVER
BASIN COULD BE AFFECTED. THE BIGGEST EFFECT WILL BE ON THE LOW
LEVEL WIND FIELD AS TROUGHING SETTING UP ALONG THE COAST WILL
INDUCE SOME VERY WINTER-LIKE OUTFLOW WINDS ALONG THE GULF COAST.
BOTH DOMAINS PREFERRED THE ECMWF WITH THE CURRENT FORECAST
PACKAGE. 

&&
.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...WHILE THE TROUGH ALOFT HAS WEAKENED
SIGNIFICANTLY...A POOL OF COLD AIR ALOFT AND A DISTURBANCE
SKIRTING THE ALASKA RANGE WILL KEEP AT LEAST SOME SHOWERY ACTIVITY
ACROSS THE AREA. A FRONT ALOFT ASSOCIATED WITH A TROUGH OVER THE
BROOKS RANGE WILL BRING MORE STABLE AIR ALOFT WHICH WILL SUPRESSCONVECTION.
THE QUESTION IS HOW MUCH CLEARING WILL THERE BE AHEAD OF THE FRONT
TO ENCOURAGE SURFACE HEATING? THE BEST WINDOW WILL BE IN THE MID
TO LATE AFTERNOON DURING PEAK SURFACE HEATING JUST AS THE TAIL OF
THE UPPER TROUGH SWINGS THROUGH. THE 00Z SOUNDING OVER ANCHORAGE
YIELDED 600 J/KG OF INSTABILITY WITH A CONVECTIVE TEMPERATURE OF
62F. THE ENVIRONMENT TODAY SHOULD BE JUST AS CONDUCIVE AS WE WILL
NOT HAVE SOUTHEAST WINDS OFF THE SURFACE AND LESS CLOUD COVER.

EXPECT AFTERNOON SHOWERS FROM THE WESTERN KENAI THROUGH THE
SUSITNA VALLEY...ESPECIALLY EAST. WINDS WILL REMAIN LIGHT BEFORE
SWITCHING TO THE NORTHWEST WITH SOME GUSTS. THE NEXT COUPLE DAYS
WILL BE COOLER AND DRIER AS RIDGING ALOFT BUILDS OVER THE AREA. 

SOUTHWEST ALASKA...DRY CONDITIONS AND DECREASING CLOUDS CAN BE
EXPECTED TODAY. SOME GUSTY NORTHERLY WINDS WILL DEVELOP IN THE
AFTERNOON FOR INTERIOR BRISTOL BAY BEFORE DIMINISHING ON MONDAY. 

BERING SEA/ALEUTIANS...A FRONTAL BOUNDARY WILL WASH OUT OVER THE
CENTRAL ALEUTIANS TODAY BRINGING SOME SPOTTY SHOWERS. AN UPPER LOW
PRESSURE DRIFTS EASTWARD THROUGH THE WEEK KEEPING SCATTERED
SHOWERS IN THE FORECAST. 


&&
.LONG TERM FORECAST...
BEGINNING THE EXTENDED PERIOD ON WEDNESDAY...THE REGION WILL BE
UNDER THE INFLUENCE OF A SPLIT JET STREAM REGIME...WITH A DISTINCT
POLAR JET TO OUR NORTH...AND A MUCH STRONGER AND ACTIVE
SUBTROPICAL JET STREAM ACROSS THE NORTH PACIFIC. THIS WILL BE A
SOMEWHAT LARGE SHIFT FROM THE PREVIOUS TWO WEEKS WHERE THE
SUBTROPICAL JET STREAM WAS IN PHASE WITH THE POLAR JET...HELPING
TO PROMOTE A VERY ACTIVE PATTERN FOR ALASKA. THIS SPLIT JET STREAM
PATTERN WILL LINGER THROUGH FRIDAY...WITH UPPER LEVEL DISTURBANCES
TRACKING THROUGH NORTHERN AND CENTRAL ALASKA. THE NET EFFECT WILL
BE COOLER AND DRY AIR OCCASIONALLY DRIVING SOUTHWARD INTO THE GULF
OF ALASKA. OTHERWISE...THIS WILL LIKELY REPRESENT THE DRIEST AND
OVERALL MOST PLEASANT STRETCH OF WEATHER IN SEPTEMBER OVER THE
PAST THREE YEARS. OUTFLOW GAP WINDS INTO THE GULF OF ALASKA WILL
PEAK WEDNESDAY AND THEN POSSIBLY AGAIN ON SATURDAY. EXPECT THE
COLDEST TEMPERATURES OF THE YEAR ACROSS MANY LOCATIONS AS
OVERNIGHT TEMPERATURES PLUMMET WITH FAVORABLE RADIATIONAL COOLING.
BY FRIDAY...THE ECMWF IS HINTING AT A NORTH PACIFIC LOW TRACKING
INTO SOUTHWEST AND EVENTUALLY SOUTHCENTRAL...BUT CURRENTLY THAT IS
A LOW PROBABILITY SOLUTION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

MTL/JA SEP 14

Alaska Region Headquarters
222 West 7th Avenue #23
Anchorage, AK 99513-7575
Voice: 1-907-271-5088
Fax: 1-907-271-3711
Recorded Forecast: 1-800-472-0391
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Page Modified: 03 Feb 2008 18:00 UTC
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