Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 031313
AFDAFC

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

.ANALYSIS AND UPPER LEVELS...
THERE IS A 120 KNOT SOUTHWESTERLY JET STREAK TRACKING INTO THE
ALASKA PENINSULA AND KODIAK ISLAND REGION THIS MORNING. THIS
SYNOPTIC FEATURE WILL MOVE THE UPPER LEVEL RIDGE POSITIONED OVER
THE CENTRAL GULF EXTENDING INTO COPPER RIVER BASIN EASTWARD.
UPSTREAM THERE ARE SEVERAL SHORTWAVES WITH THE FIRST SHORTWAVE
LOCATED OVER THE BRISTOL BAY INTERIOR. THE SECOND UPPER LEVEL
SHORTWAVE OVER THE CENTRAL ALEUTIANS IS ASSOCIATED WITH THE
CLOSED LOW AT 500 MB LOCATED JUST EAST OF THE KAMCHATKA PENINSULA.
AT THE SURFACE THERE IS A 1006 MB NORTH PACIFIC LOW PRESSURE
SYSTEM THAT HAS CROSSED OVER THE EASTERN ALEUTIANS INTO THE
BRISTOL BAY REGION THIS MORNING. THIS FEATURE IS BRINGING
WIDESPREAD RAIN AND FOG TO THE EASTERN BERING SEA AND THROUGH THE
SOUTHWEST ALASKA REGION BEFORE SPILLING OVER INTO THE SOUTHCENTRAL
REGION. THE SATELLITE IMAGERY REFLECTS A LARGE SWATH OF MOISTURE
OVER THE AFOREMENTIONED REGIONS WITH THE ASSOCIATED WEATHER FRONT
MOVING THROUGH THE SOUTHWESTERN GULF REGION. THIS IS REFLECTED ON
THE RADAR IMAGERY WITH NUMEROUS SHOWERS MOVING UP THROUGH THE COOK
INLET AND THE WESTERN GULF AREA.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD AGREEMENT WITH THE LOW PRESSURE SYSTEM MOVING
INTO THE BRISTOL BAY REGION AND THE WEATHER FRONT THROUGH THE
WESTERN GULF THIS MORNING. THIS LOW WILL MOVE INTO THE BRISTOL BAY
INTERIOR BY THE AFTERNOON BEFORE FALLING APART AS IT MOVES FARTHER
INLAND. THE MODELS ARE SHOWING A TRIPLE POINT LOW DEVELOPING IN THE
GULF BY FRIDAY AND TRACKING TO THE SOUTHEAST ALASKA REGION BY
SATURDAY AFTERNOON BEFORE DISSIPATING. THE GFS WAS MOVING THIS LOW
THROUGH THE GULF FASTER THEN THE OTHER MODELS. THE BIGGEST CHALLENGE
WILL BE WITH THE TIMING OF PRECIPITATION AS THE DIFFERENT SYNOPTIC
FEATURES MOVE THROUGH THE SOUTHWEST AND SOUTHCENTRAL REGION. THE
PREFERRED MODEL OF CHOICE WAS THE NAM. THE FORECAST CONFIDENCE IS
ABOVE AVERAGE AS WE HEAD INTO THE WEEKEND.

&&

.FIRE WEATHER...
THE SOUTHWESTERLY FLOW WILL CONTINUE TO BRING MOISTURE AND WIDESPREAD
WETTING RAINS TO THE SOUTHWEST/SOUTHCENTRAL ALASKA REGION BEFORE
TAPERING OFF BY LATE FRIDAY. IN THE WAKE OF THE RAIN THE AIRMASS
WILL REMAIN QUITE MOIST WITH GENERALLY WEAK AND DIFFUSE FLOW.
THEREFORE EXTENSIVE CLOUDINESS WILL PERSISTS INTO THE WEEKEND
MAINTAINING FAIRLY COOL TEMPERATURES AND RELATIVELY HIGH RHS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A SUBTROPICAL JET IS POINTED RIGHT TOWARD THE SOUTHERN MAINLAND
OF ALASKA TODAY HELPING TO TRANSPORT DEEP TROPICAL MOISTURE INTO
THE REGION. A SERIES OF UPPER LEVEL WAVES WILL FOCUS THE RAIN AS
IT OVERSPREADS SOUTHCENTRAL ALASKA DURING THE DAY. SINCE THE
ENERGY IS SPLIT AMONG MULTIPLE FEATURES RAINFALL INTENSITY WILL BE
VARIABLE...BUT MOSTLY ON THE LIGHT SIDE. THE GULF COAST WILL SEE
HEAVIER RAIN ASSOCIATED WITH A SURFACE FRONTAL SYSTEM AND A WEAK
SURFACE LOW WHICH DEVELOPS NEAR KODIAK ISLAND THIS AFTERNOON.

ANOTHER UPPER LEVEL SHORT-WAVE TROUGH TRACKING EASTWARD ACROSS
THE BERING WILL ARRIVE IN THE GULF FRIDAY AND KICK THE SURFACE LOW
AND MUCH OF THE RAIN EASTWARD AND OUT OF SOUTHCENTRAL. BROAD AND
WEAK CYCLONIC FLOW WILL PERSIST WITH VERY WEAK RIDGING UPSTREAM.
WITH NOTHING TO HELP DRY OUT THE AIRMASS MOSTLY CLOUDY SKIES WILL
PERSIST THROUGH SATURDAY...AND LIKELY BEYOND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...THU AND
FRI)...WET AND MILD WEATHER WILL CONTINUE FOR THE END OF THE WEEK.
A SURFACE LOW IS ACTIVELY DEVELOPING JUST NORTH OF THE ALASKA
PENINSULA. THIS SYSTEM COUPLED WITH DECENT UPPER LEVEL JET SUPPORT
AND PRECIPITABLE WATER VALUES NEAR 1.2 INCHES (COLD BAY) WILL
CONTINUE TO PUSH WIDESPREAD RAIN INTO BRISTOL BAY. WINDS ARE
RELATIVELY LIGHT WITH THIS SYSTEM AND THAT IS ALLOWING FOG TO
BECOME WIDESPREAD AND LOCALLY DENSE IN SPOTS. THE LOW WILL TRACK
INLAND TO THE NORTHEAST THROUGH THE DAY TODAY AND BRING RAIN ALL
THE WAY UP THROUGH LOWER KUSKOKWIM VALLEY AND THE Y-K DELTA. THE
LOW WILL FALL APART OVER THE ALASKA RANGE LATE TONIGHT INTO EARLY
FRIDAY. THIS WILL ALLOW PRECIPITATION TO BECOME MORE SHOWERY IN
NATURE...BUT THE SHOWERS WILL STILL BE WIDESPREAD ACROSS SOUTHWEST
AK. FLOW WILL SHIFT FROM SOUTHERLY TO WESTERLY FRIDAY. THIS WILL
BRING MORE FOG TO JUST ABOUT ALL AREAS...ESPECIALLY THE ALASKA
PENINSULA AND THE COAST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...THU AND
FRI)...THE UPPER LEVEL LOW OFF THE COAST OF KAMCHATKA CONTINUES TO
DRIVE THE SENSIBLE WEATHER FOR THIS REGION. AS IT PUSHES YET
ANOTHER WEAK UPPER LEVEL WAVE ACROSS THE BERING...WINDS WILL
REMAIN SOUTH TO WEST WITH WIDESPREAD FOG AND SHOWERS. SPEEDS
SHOULD SUB-SMALL CRAFT FOR THE ENTIRE AREA. THE LOW FINALLY
STARTS ITS SLOW TRACK ACROSS THE BERING SEA LATE FRIDAY. THIS WILL
BRING A SLIGHTLY MORE FOCUSED AREA OF SHOWERS MOVING FROM WEST TO
EAST AS WE START INTO THE WEEKEND.

&&

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

RAIN WILL CONTINUE TO TAPER OFF ACROSS SOUTHERN ALASKA FRIDAY
EVENING THROUGH THE START OF THE UPCOMING WEEKEND AS A POTENT
SHORTWAVE AND A WEAK SURFACE REFLECTION SHIFT INTO THE EASTERN
GULF OF ALASKA BEFORE FALLING APART OF THE PANHANDLE. SHORTWAVE
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 VS 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. THE MOST NOTABLE CHANGE FROM YESTERDAY IS
THAT ALL GUIDANCE IS NOW HINTING AT THE ZONAL FLOW AMPLIFYING
TOWARD THE MIDDLE OF NEXT WEEK WHICH WILL ALLOW THE PHASING OF THE
AMPLIFYING TROUGH OVER THE NORTH PACIFIC TO MERGE WITH THE
NORTHERN STREAM. THE PHASING OF THESE SYSTEMS LOOKS TO USHER IN
ANOTHER UNSEASONABLY COLD AIR MASS FROM THE ARCTIC AS AN ARCTIC
TROUGH DIVES SOUTH. THERE IS STILL A LOT OF UNCERTAINTY WITH THE
TIMING OF THIS HAPPENING BUT GUIDANCE HAS BEEN HINTING AT THIS FOR
MULTIPLE DAYS AND MODELS ARE GETTING CLOSER TO A SOLUTION EACH
DAY. IT LOOKS AS IF NEAR NORMAL TEMPERATURES WILL PERSIST THROUGH
THE BEGINNING OF NEXT WEEK AND WOULD DROP A GOOD BIT BELOW NORMAL
BY THE MIDDLE OF NEXT WEEK SHOULD THIS ARCTIC TROUGH DIVE SOUTH
OVER SOUTHWEST AND SOUTHCENTRAL ALASKA.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...MC



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