Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 040021
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
421 PM AKDT THU SEP 3 2015

.ANALYSIS AND UPPER LEVELS...
THE RIDGE THAT HAS PRODUCED NICE WEATHER FOR THE LAST FEW DAYS
ACROSS SOUTHERN ALASKA HAS SHIFTED EAST WITH THE RIDGE AXIS NOW
LOCATED NEAR THE ALCAN BORDER. THIS HAS USHERED IN BROAD AND MOIST
SOUTHWESTERLY FLOW TO THE MAINLAND. THE MOST NOTICEABLE FEATURE ON
AFTERNOON SATELLITE IMAGERY IS A FAIRLY VIGOROUS SHORTWAVE TROUGH
MOVING ACROSS THE ALASKA PENINSULA AND KODIAK ISLAND INTO LOWER
COOK INLET. THIS FEATURE IS FOCUSING A STEADIER AND MORE INTENSE
BAND OF RAIN THAT IS BRINGING WIDESPREAD RAIN FROM BRISTOL BAY
THROUGH THE NORTH GULF COAST AND ALL POINTS BETWEEN.

BEHIND THIS SHORTWAVE TROUGH ARE WEAKER BUT CONTINUED WESTERLY
WINDS ACROSS THE BERING SEA WITH WIDESPREAD FOG/STRATUS IN PLACE
ACROSS THE BERING SEA. FURTHER EAST EVEN ONCE THE RAIN ENDS
ACROSS SOUTHWEST ALASKA THINGS WILL NOT CLEAR OUT MUCH AS THIS
ONSHORE FLOW IS CONTINUALLY REINFORCING THE LOW CLOUDS ALREADY
MOVING ONSHORE.

&&

.MODEL DISCUSSION...

THE MODELS HAVE COME INTO BETTER AGREEMENT WITH THE KEY DETAILS OF
THE FORECAST OVER THE NEXT FEW DAYS. ONE OF THE MAIN QUESTIONS HAS
BEEN WHEN AND HOW A SURFACE LOW DEVELOPS IN THE NORTHERN GULF TONIGHT
AND TOMORROW. THE NAM AND ECMWF ARE NOW DEPICTING AN INITIAL LOW
TO DEVELOP OVER THE NORTHWEST GULF AND QUICKLY THEREAFTER IS
REPLACED BY A SECONDARY DEVELOPMENT FURTHER EAST. THIS MAKES SENSE
GIVEN FAIRLY DIFFUSE UPPER LEVEL FORCING MECHANISMS TO KEEP ENERGY
LOCKED INTO ONE CONSOLIDATED LOW CENTER (WHICH IS WHAT THE GFS IS
TRYING TO DO). THEREFORE WE WILL SHY AWAY FROM THE GFS SOLUTION
TODAY IN FAVOR OF THE NAM/EC/GEM-REGIONAL SOLUTIONS.

&&

.FIRE WEATHER...

A COOL AND WET WEATHER PATTERN HAS MOVED INTO MAINLAND ALASKA AND
WILL GENERALLY STICK AROUND THROUGH NEXT WEEK. NO LOW RH ISSUES OR
STRONG WINDS IN INTERIOR AREAS ARE EXPECTED AS WEAK SOUTHWEST FLOW
KEEPS THE STATE UNDER SIGNIFICANT CLOUD-COVER.

&&

.HYDROLOGY...

THE SNOW GLACIER-DAMMED LAKE DEEP IN THE KENAI MOUNTAINS CONTINUES
TO RELEASE WATER INTO SNOW RIVER KENAI LAKE AND THE KENAI RIVER.
THE KENAI RIVER AT COOPER LANDING HAS ENTERED MINOR FLOOD
STAGE AND A FLOOD ADVISORY REMAINS IN EFFECT FOR THE KENAI RIVER
FROM KENAI LAKE TO SKILAK LAKE AS WELL AS FOR LOW LYING AREAS
AROUND KENAI LAKE. SEE ADVISORY STATEMENTS FOR THE MOST UP TO
DATE INFORMATION.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
RAINFALL WILL CONTINUE TO SPREAD EAST INTO THE COPPER RIVER BASIN
AND THE NORTHERN GULF COAST OVERNIGHT AS THE SHORTWAVE CONTINUES
ITS MARCH EAST THROUGH THE REGION. THE BACKSIDE OF THE WAVE IS
VERY EVIDENT ON SATELLITE AND RADAR IMAGERY THIS AFTERNOON WITH
THE HEAVIEST OF THE RAINFALL HAVING CLEARED KODIAK ISLAND AND
BEGINNING TO TAPER OFF OVER THE SOUTHERN KENAI PENINSULA. THIS
TREND IS EXPECTED TO CONTINUE OVERNIGHT WITH STRATIFORM RAIN
TURNING INTO A MORE SHOWERY PATTERN IN THE WAKE OF THE SHORTWAVE.
BY SATURDAY A WEAK SHORTWAVE RIDGE WILL QUICKLY TRANSIT THROUGH
THE AREA LIMITING SHOWERS TO MAINLY THE ALASKA RANGE AND THE
WRANGELLS. ALTHOUGH THE RIDGE WILL BE MOVING THROUGH THE PATTERN
WILL REMAIN FAIRLY MOIST AND ZONAL OVER THE REGION WITH ENOUGH LOW
LEVEL MOISTURE TO KEEP SKIES MOSTLY CLOUDY OVER THE AREA.

&&

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

A SERIES OF UPPER LEVEL DISTURBANCES ARE TRACKING FROM THE EASTERN
BERING INTO THE MAINLAND BRINGING A WIDESPREAD AREA OF MOISTURE
AND RAIN INTO SOUTHWEST ALASKA. THE HEAVIEST RAIN WILL BE THROUGH
TOMORROW MORNING BEFORE THE UPPER LOW MOVES EAST. IN THE
WAKE OF THESE LOWS EXTENSIVE LOW CLOUDS AND PATCHY FOG WILL MOVE
INLAND WITH THE ONSHORE FLOW REGIME. THERE WILL BE A BRIEF BREAK
IN RAIN BEFORE ANOTHER LOW OVER THE BERING SEA MOVES INTO
SOUTHWEST ALASKA SATURDAY BRINGING ANOTHER SHOT OF INTERMITTENT
RAIN TO THE AREA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

A BROAD UPPER TROUGH WITH A SERIES OF EMBEDDED WAVES WILL MAKE
SLOW EASTWARD PROGRESS THROUGH SATURDAY WITH INTERMITTENT LIGHT
RAIN AND SHOWERS TRACKING OVER THE BERING AND ALEUTIANS. AN
ELONGATED FRONTAL ZONE WILL MOVE INTO THE WESTERN ALEUTIANS
SATURDAY EVENING BRINGING SOUTHERLY WINDS AND RAIN WITH IT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
RAIN WILL GRADUALLY TAPER OFF ACROSS SOUTHERN ALASKA THIS WEEKEND
AS A POTENT SHORTWAVE AND A WEAK SURFACE REFLECTION SHIFT FURTHER
INTO THE EASTERN GULF OF ALASKA BEFORE FALLING APART OVER THE
PANHANDLE. WEAK RIDGING WILL DEVELOP BRIEFLY BEHIND THIS PARTING
SHORTWAVE AS A SERIES OF UPPER LEVEL LOWS IN THE BERING SEA DROP
SOUTH AND CREATE A ZONAL UPPER LEVEL PATTERN AS COMPARED TO THE AMPLIFIED
PATTERN SEEN AS OF LATE. THIS ZONAL FLOW WILL KEEP MUCH OF ALASKA
IN A FAVORABLE LOCATION FOR STORMS TO TRACK FROM THE BERING SEA
INTO INTERIOR LOCATIONS OF ALASKA. EARLY NEXT WEEK MODELS ARE
HINTING AT AN ARCTIC TROUGH DIGGING DOWN OVER THE MAINLAND AND
JOINING UP WITH THE NORTHERN STREAM. THIS CAN BRING IN AN
UNSEASONABLY COLD AIR MASS FROM THE ARCTIC OVER THE SOUTHERN
MAINLAND AS THE ARCTIC TROUGH DIVES FURTHER SOUTH BY MIDWEEK. AS A
RESULT NEAR NORMAL TEMPERATURES WILL PERSIST THROUGH THE
BEGINNING OF NEXT WEEK AND WOULD DROP BELOW NORMAL BY THE MIDDLE
OF NEXT WEEK SHOULD THIS ARCTIC TROUGH DIVE SOUTH OVER SOUTHWEST
AND SOUTHCENTRAL ALASKA. THE MOST NOTABLE CHANGE FROM PREVIOUS
MODEL RUNS IS THAT ALL GUIDANCE IS NOW HINTING AT THE ZONAL FLOW
KEEPING THE EXTRATROPICAL SYSTEM IGNACIO SOUTH OF THE GULF MONDAY
THROUGH TUESDAY MORNING BEFORE TRACKING IT INLAND OVER THE
SOUTHERN PANHANDLE. OVERALL THERE IS STILL A LOT OF UNCERTAINTY
WITH THE TIMING AND PLACEMENT OF THIS SYSTEM AS WELL AS OTHER
SYSTEMS OUT WEST LEAVING FORECAST CONFIDENCE LOW THROUGH THE LONG
TERM.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FLOOD ADVISORY ZONE 121 AND 125.
MARINE...GALE 119 131.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...RF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...TP



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