Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 290023
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
423 PM AKDT SAT MAR 28 2015

.ANALYSIS AND UPPER LEVELS...
A LONG-WAVE TROUGH IS CENTERED OVER THE NORTH PACIFIC WITH THE
SUBTROPICAL JET DIVING FROM THE NORTHWEST PACIFIC DOWN TO 35N AND
THEN BACK NORTHEAST TO BRITISH COLUMBIA. NESTLED IN THE CENTER OF
THE TROUGH IS A VERY LARGE CYCLONIC CIRCULATION CONTAINING TWO
PRIMARY LOWS...AN UPPER LOW SOUTH OF THE SOUTHERN TIP OF THE
ALASKA PENINSULA AND A MATURE VERTICALLY STACKED LOW SOUTH OF
KODIAK ISLAND. THE LATTER IS LIFTING NORTHWARD TOWARD KODIAK
ISLAND PUSHING A GALE FORCE OCCLUDED FRONT NORTHWARD ACROSS THE
GULF. THE MAIN UPPER TROUGH AXIS EXTENDING EASTWARD FROM THE LOW
CENTER IS BECOMING ORIENTED EAST-WEST THIS MORNING LEADING TO VERY
SLOW NORTHWARD PROGRESSION OF THE FRONT. MIDDLETON ISLAND RADAR
SHOWS SOME LIGHT PRECIP AFFECTING WESTERN PRINCE WILLIAM SOUND
WITH THE HEAVIER MORE SIGNIFICANT RAIN SUPPRESSED TO THE SOUTH
FOR THE TIME BEING. THE REST OF SOUTHCENTRAL IS DRY WITH MAINLY
MID TO HIGH LEVEL CLOUDINESS. ONE OF THE MOST IMPRESSIVE FEATURES
NOTED IN SATELLITE IMAGERY IS A SHORT-WAVE OVER THE EASTERN GULF.
THIS LOOKS MORE IMPRESSIVE THAN MODELS INDICATE...SO WILL HAVE TO
KEEP AN EYE ON IT AS IT TRACKS WEST-NORTHWEST ACROSS THE GULF.

A SERIES OF UPPER WAVES ARE ROTATING WESTWARD ACROSS SOUTHWEST
ALASKA AND THE EASTERN BERING SEA PRODUCING A FEW BANDS OF
RAIN...BUT NOTHING VERY SIGNIFICANT. THERE IS ONE STRONGER UPPER
WAVE BRINGING STEADIER PRECIP ALONG THE BACK SIDE OF THE TROUGH
PRIMARILY BETWEEN DUTCH HARBOR AND ATKA. LOOKING UPSTREAM A
STRONG SHORT-WAVE IS DIGGING ACROSS THE NORTHWEST PACIFIC DRIVING
A SURFACE FRONT EASTWARD TOWARD THE WESTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT WITH HANDLING OF THE LOW HEADED
TOWARD KODIAK ISLAND AND ASSOCIATED FRONTAL SYSTEM. SOLUTIONS
DIVERGE SUNDAY NIGHT AND MONDAY AS THE OTHER UPPER CENTER ROTATES
SOUTH OF THIS CENTER. THE GFS/ECMWF ARE BULLISH IN DEVELOPING A
NEW SURFACE LOW AND MOVING IT INTO THE SOUTHERN GULF WHILE THE
OTHER MODELS INDICATE MORE OF A WEAKNESS IN THE PRESSURE FIELD.
IF A SURFACE LOW DOES DEVELOP THERE DOES NOT SEEM TO BE ANY
FORCING MECHANISM TO CAUSE IT TO DEVELOP INTO ANYTHING
SIGNIFICANT. FOR NOW WILL STICK WITH A WEAKER SOLUTION WITHOUT ANY
REALLY WELL DEFINED LOW.

OUT WEST THE ECMWF IS NOTABLY FASTER WITH TRACK OF A DEVELOPING
LOW ALONG THE ALEUTIAN CHAIN ON MONDAY. THIS MAKES SOME SENSE WITH
STRENGTHENING UPPER JET IN THIS AREA. SINCE ECMWF IS THE OUTLIER
WILL HOLD OFF ON ANY CHANGES FOR NOW AND STICK WITH THE SLOWER
SOLUTION INDICATED BY THE REST OF THE MODELS.

&&

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

AS THE FRONT APPROACHES THE COAST AND WEAKENS IT WILL SPREAD RAIN
SHOWERS ALONG THE COAST WITH SOME OVERNIGHT SNOW INLAND TONIGHT.
GALE FORCE WINDS NEAR THE FRONT WILL GRADUALLY WEAKEN INTO SUN. THE
UPPER LOW NEAR KODIAK WILL THEN CONTINUE TO SEND WAVES AROUND THE
GULF THROUGH MON RESULTING IN PERIODIC COASTAL RAIN SHOWERS AND
MOUNTAIN SNOW SHOWERS...WITH SOME RAIN SHOWERS CROSSING THE KENAI
AND CHUGACH MOUNTAINS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...SUN AND
MON)...THE QUIET PATTERN SHOULD ONLY CONTINUE TO GET QUIETER FOR
THE NEXT COUPLE OF DAYS. EARLY SUN...A SURFACE LOW WILL DRIFT
SOUTHEAST OF KODIAK ISLAND. THIS WILL REINFORCE THE DRY
NORTHEASTERLY FLOW FOR MOST OF THE MAINLAND AND SHOULD BRING
ANOTHER DAY OF AT LEAST PARTLY SUNNY SKIES. LATER SUN INTO
MON...MODELS HAVE SOME DISCREPANCIES IN HANDLING THAT AREA OF LOW
PRESSURE. THEY STRUGGLE WITH HOW IT TRANSFERS SOME ENERGY FROM THE
PACIFIC SIDE OF THE ALASKA PENINSULA INTO BRISTOL BAY.
REGARDLESS...EVEN THE WORST CASE SCENARIO WOULD ONLY BRING SOME
LIGHT RAIN AND SNOW SHOWERS THROUGH AREAS EAST OF THE KUSKOKWIM
DELTA. THESE SHOWERS WOULD FAVOR THE EASTWARD UPSLOPE AREAS OF
THE AHKLUN AND KILBUCK RANGES. TEMPERATURES WILL REMAIN ON THE
MILD SIDE...SO ANY SNOW WILL BE CONFINED PRIMARILY TO THE COLDER
OVERNIGHT HOURS AND HIGHER ELEVATIONS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...SUN AND
MON)...THE BEST COLD AIR AND THERMAL BOUNDARY REMAINS CENTERED
OVER THE CENTRAL BERING INTO THE CENTRAL ALEUTIANS. THIS SAME AREA
THAT HAS BEEN IMPACTING THE PRIBILOFS AND ATKA THE PAST 24 HOURS
IS NOW ACTUALLY GETTING A REINFORCING SHOT OF MOISTURE FROM A
WEAKENING TROUGH FROM THE EAST. THIS TROUGH IS HELPING TO JUST
PUSH THE BOUNDARY JUST FAR ENOUGH WEST TO CLEAR THE PRIBILOFS...BUT
IT WILL BRING MORE PRECIPITATION TONIGHT FOR AREAS FROM DUTCH
HARBOR TO ATKA. WE FINALLY SEE THIS BOUNDARY YIELD SUNDAY TO A
SHORTWAVE RIDGE MOVING IN FROM THE WESTERN ALEUTIANS. THIS
SHORTWAVE RIDGE WILL HELP TO BRING A DRYING TREND THROUGH THE
CENTRAL ALEUTIANS WITH JUST SOME SHOWERS REMAINING...MAINLY ON THE
BERING SIDE OF THE ISLANDS.

MEANWHILE...A NEW WEAK AREA OF LOW PRESSURE WILL SLING A FRONT
THROUGH THE WESTERN ALEUTIANS EARLY SUN. THIS FRONT WILL LOOSE
JUST ABOUT ALL OF ITS UPPER LEVEL SUPPORT INTO MON AND JUST
STRETCH OUT FROM NORTHWEST TO SOUTHEAST AS IT FALLS APART. THE
UPPER LEVEL ENERGY THEN SHIFTS TO A DEVELOPING LOW THAT TAKES AIM
ON ADAK LATE MON. THIS WILL BRING ANOTHER ROUND OF SNOW AND RAIN
ALONG WITH SOME WARMER AIR TO THE CENTRAL ALEUTIANS THROUGH THE
EARLY PART OF THE WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH MONDAY. MONDAY NIGHT
IS WHERE WE START TO SEE SOME DIFFERENCES IN THE MODELS. THE ECMWF
BECOMES A LOT FASTER WITH A LOW OVER THE ALEUTIAN CHAIN MONDAY
NIGHT INTO TUESDAY VERSUS THE NORTH AMERICAN MODELS. ALL THE
MODELS SETTLE A LOW INTO THE GULF OF ALASKA THURSDAY. THE REASON
THE ECMWF RACES AHEAD OF THE REMAINDER OF THE MODELS IS DUE TO A
SHORT WAVE DISTURBANCE RACING OUT WITH A JET STREAK ON MONDAY
NIGHT. THE REMAINDER OF THE MODELS SWING THE CLOSED LOW AT A
SIMILAR PACE INTO THE GULF WEDNESDAY AFTERNOON AND OVER THE MIDDLE
OF THE GULF ON THURSDAY. THE CURRENT LOW IN THE GULF OF ALASKA
LOOKS TO REMAIN IN THE AREA THROUGH TUESDAY WITH RAIN AND WIND ON
THE DOWNTURN.

MEANWHILE...ANOTHER LOW MOVES TO THE WESTERN BERING SEA WEDNESDAY.
NOW THIS IS WHERE IT STARTS TO GET MORE COMPLICATED. THE BIG
QUESTION IS THE ENERGY ASSOCIATED WITH THIS LOW AND HOW IT
INTERACTS WITH ENERGY AN UPPER LEVEL LOW OVER THE CHUKCHI SEA.
MODEL RUN-TO-RUN CONSISTENCY WITH THIS TIME FRAME IS QUITE
POOR...SO UNCERTAINTY IS HIGH CONCERNING DETAILS OF THE FORECAST.
ONE THING THAT IS CERTAIN IS A STRONG RIDGE WILL DEVELOP OVER THE
BERING SEA FRIDAY AND SATURDAY.

AT THE SURFACE...THE ALEUTIAN LOW ON MONDAY NIGHT AND TUESDAY WILL
BRING MODERATE RAIN AND WIND TO THE ALEUTIAN CHAIN THROUGH
WEDNESDAY BEFORE IT ENTERS THE GULF. BEHIND THE SYSTEM...COLD AIR
ADVECTION WILL BRING AREAS OF GALE FORCE WINDS AND SNOW SHOWERS.
AS THE LOW MOVES INTO THE GULF ON WEDNESDAY...GALE FORCE WINDS AND
MODERATE RAIN TO RING THE GULF OF ALASKA. WINDS AND RAIN WILL
DIMINISH THURSDAY OVER THE GULF OF ALASKA REGION. NOT MUCH PRECIP
TO MAKE IT INLAND AT ALL. THIS LOW WILL BE SHOVED TO THE PACIFIC
NORTHWEST BY SATURDAY. OVER SOUTH CENTRAL...MID LEVEL INSTABILITY
MAY BRING A FEW SHOWERS. MEANWHILE A FRONT WILL REACH THE WESTERN
ALEUTIANS WEDNESDAY AND PUSH ACROSS THE BERING SEA THURSDAY AND
FRIDAY BUT WEAKEN BEFORE THE COAST AS IT FIGHTS THE RIDGE. THE
PATTERN BECOMES QUITE AMPLIFIED AT THIS TIME. NO MATTER THE ECMWF
OR GFS...THERE WILL BE RAIN AND WIND FOR THE WESTERN HALF OF THE
BERING WITH A RIDGE OVER THE EASTERN BERING AND SOUTHWEST ALASKA.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...119 120 130 131 138 150 174
 HVY FRZG SPRY...179 185
FIRE WEATHER...NONE.

&&

$$

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



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