Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 171311
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
411 AM AKST WED DEC 17 2014

.ANALYSIS AND UPPER LEVELS...
ALASKA REMAINS FIRMLY ENTRENCHED WITHIN A LONG-WAVE TROUGH. A
CLOSED LOW IS NEARLY STATIONARY OVER THE NORTH CENTRAL BERING SEA
WHILE A STRONG AMPLIFIED SUBTROPICAL JET IS PRODUCING AN ACTIVE
STORM TRACK ACROSS THE NORTH PACIFIC. THE STORM TRACK CURVES
NORTHWARD AS IT REACHES THE EAST PACIFIC THANKS TO A STRONG
BLOCKING RIDGE DOWNSTREAM OVER WESTERN CANADA. SATELLITE IMAGERY
SHOWS A LARGE INTENSE STORM SOUTH OF THE EASTERN ALEUTIANS AND
ALASKA PENINSULA JUST BEGINNING TO CURVE NORTHEASTWARD.
SCATTEROMETER DATA SHOWS A LARGE AREA OF STORM FORCE WINDS WITH
THIS LOW...BUT IT IS TOO FAR SOUTH TO HAVE MUCH IMPACT ON ALASKA.
MEANWHILE ANOTHER LARGE AND DEEP STORM SYSTEM IS MAKING ITS WAY
ACROSS THE FAR NORTHWEST PACIFIC.

WITH WEAK FEATURES NORTH OF THE SUBTROPICAL JET THE WEATHER
ACROSS ALASKA IS GENERALLY ON THE QUIET SIDE. A SERIES OF WEAK
UPPER LEVEL SHORT-WAVE TROUGHS ARE LIFTING NORTHWARD ACROSS THE
GULF AND SOUTHCENTRAL. PRECIPITATION IS GENERALLY ON THE LIGHT
SIDE...ALTHOUGH LOW TO MID-LEVEL INSTABILITY IS PRODUCING SOME
LOCALIZED HEAVY SHOWERS. A LOW LEVEL ABOVE FREEZING WARM NOSE
PERSISTS FROM THE WESTERN KENAI PENINSULA TO ANCHORAGE AND PARTS
OF THE MATANUSKA VALLEY...ALTHOUGH THE 00Z SOUNDING FROM ANCHORAGE
SHOWS THE WET BULB DOWN IS NOW DOWN AROUND ZERO. THEREFORE...IF
ENOUGH QPF FALLS INTO THE ABOVE FREEZING LAYER PRECIP WILL QUICKLY
CHANGE TO ALL SNOW AND THERE MAY BE SOME VERY LIGHT ACCUMULATION.
ON THE OTHER HAND...IF PRECIP REMAINS LIGHT THEN IT WILL TAKE
LONGER TO CHANGE TO ALL SNOW AND THERE LIKELY WILL NOT BE ANY
SNOW ACCUMULATION.

&&

.MODEL DISCUSSION...
MODELS CONTINUE TO STRUGGLE WITH SMALL SCALE FEATURES MOVING
THROUGH SOUTHCENTRAL CREATING A CHALLENGING PRECIPITATION FORECAST
FOR THE REMAINDER OF TONIGHT THROUGH WEDNESDAY MORNING. WILL MAKE
HEAVY USE OF RADAR AND SATELLITE TRENDS FOR THE EARLY PORTION OF
THE FORECAST.

THERE IS INITIALLY EXCELLENT AGREEMENT WITH STRONG PACIFIC LOW
TRACKING TOWARD GULF...BUT RAPIDLY DIVERGE LATE THURSDAY WITH
SHORT-WAVE ROUNDING THE LOW AND FORMING A SECONDARY LOW. ECMWF
SHOWS SOME RUN-TO-RUN CONSISTENCY AND IS A NICE MIDDLE GROUND
SOLUTION. WILL TREND FORECAST THAT DIRECTION RECOGNIZING THERE IS
A LARGE DROP OFF IN FORECAST CONFIDENCE BEGINNING THURSDAY NIGHT.

MEANWHILE...MODELS ARE REALLY STRUGGLING WITH SYSTEMS SOUTH OF
THE ALEUTIANS BEGINNING WEDNESDAY NIGHT. WITH A 200+ KNOT
SUBTROPICAL JET POISED TO CROSS THE NORTH PACIFIC THIS IS A
FAVORABLE ENVIRONMENT FOR RAPID CYCLOGENESIS...WITH LOWS FORMING
IN SUCCESSION AS THE JET HEADS EASTWARD. A DYNAMIC SITUATION SUCH
AS THIS IS HARD FOR THE NUMERICAL GUIDANCE TO CAPTURE. THERE IS A
TREND IN THE LATEST SOLUTIONS TOWARD BRINGING PRECIP AND GALE
FORCE WINDS FARTHER NORTH. WILL APPLY THIS TREND TO THE FORECAST.
DUE TO THE COMPLEXITY OF THE SITUATION FORECAST CONFIDENCE ALONG
THE ALEUTIANS IS BELOW AVERAGE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE LAST OF A SERIES OF WEAK UPPER LEVEL SHORT-WAVES WILL EXIT TO
THE NORTH TODAY WHILE A SHORT-WAVE RIDGE BUILDS IN AHEAD OF THE
STRONG PACIFIC STORM SYSTEM. THUS...EXPECT PRECIPITATION TO
TAPER OFF FOR ALL BUT THE GULF COAST WHERE CONTINUE LOW LEVEL
INSTABILITY WILL KEEP A FEW SHOWERS AROUND. LOW LEVEL FLOW WILL
SHIFT AROUND TO THE NORTH WEDNESDAY NIGHT AND THURSDAY AS THE
STORM MAKES ITS WAY TOWARD THE GULF....WHICH SHOULD PREVENT ANY
WIDESPREAD FOG PROBLEMS. WITH DECREASING CLOUDS TEMPERATURES WILL
SLOWLY RETURN TO SOMEWHERE CLOSER TO SEASONAL NORMALS. WITH THE
STORM REMAINING WELL TO THE SOUTH PRECIP AND WINDS WILL BE
CONFINED TO THE GULF COAST WHILE INLAND AREAS WILL STAY DRY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SOUTHWEST ALASKA WILL REMAIN ON THE OUTER PERIPHERY OF MAJOR
FEATURES. THUS WEATHER WILL REMAIN QUITE BENIGN OVER THE NEXT
COUPLE DAYS WITH JUTS A FEW PASSING SHOWERS. THERE ARE SOME AREAS
OF FOG OUT THERE RIGHT NOW...BUT DRY LOW LEVEL OFFSHORE FLOW WILL
DEVELOP THIS AFTERNOON AND EVENING WHICH SHOULD HELP ERODE MOST
IF NOT ALL OF THE FOG.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE ALEUTIANS WILL BE ON THE NORTH END OF STRONG STORMS TRACKING
ACROSS THE NORTH PACIFIC. THUS...EXPECT OCCASIONAL WINDY AND RAINY
CONDITIONS. OTHERWISE RELATIVELY BENIGN CONDITIONS WILL PERSIST
ACROSS THE BERING SEA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
ALTHOUGH THERE ARE SOME DIFFERENCES WITH HANDLING OF PARTICULAR
STORM SYSTEMS IN THE FRIDAY THROUGH TUESDAY TIME PERIOD NUMERICAL
GUIDANCE IS IN GOOD AGREEMENT ON THE EVOLUTION OF THE LARGE SCALE
PATTERN. THE UPPER FLOW WILL UNDERGO AMPLIFICATION LATE THIS WEEK
THROUGH THE WEEKEND AS A TROUGH DIGS OUT OF ASIA CAUSING A RIDGE
TO BUILD OVER THE WESTERN BERING. THIS WILL THEN CAUSE DOWNSTREAM
TROUGH TO AMPLIFY...WITH LOWS CONSOLIDATING INTO A SINGLE LOW
SOMEWHERE OVER THE WESTERN GULF OR BRISTOL BAY AREAS. THUS...THERE
WILL BE A SHIFT FROM SYSTEMS MOVING RAPIDLY FROM WEST TO EAST
ACROSS THE NORTH PACIFIC AND INTO THE GULF TO A MORE STAGNANT
PATTERN WITH ONE LARGE CYCLONIC CIRCULATION DOMINATING THE
WEATHER. PRIOR TO AND DURING THE CHANGE IN PATTERN ACTIVE WEATHER
WILL BE FOCUSED ALONG THE SOUTHERN TIER OF THE FORECAST
AREA...ALONG THE ALEUTIANS AND ALASKA PENINSULA AND INTO THE GULF
OF ALASKA. THE BERING SEA AND MUCH OF SOUTHWEST AND SOUTHCENTRAL
ALASKA WILL REMAIN ON THE DRY SIDE...WITH JUST AN OCCASIONAL
CHANCE OF PRECIP AS UPPER WAVES MOVE THROUGH. LOW LEVEL WARM AIR
WILL CONTINUE TO PENETRATE SOUTHCENTRAL ALASKA AND PORTIONS OF
SOUTHWEST ALASKA...SO TEMPERATURES WILL GENERALLY REMAIN ABOVE
NORMAL AND THERE WILL BE A THREAT OF FREEZING RAIN IF ANY PRECIP
DOES MAKE IT INLAND.

LOOKING OUT TO EARLY NEXT WEEK MORE SIGNIFICANT CHANGES ARE LIKELY
AS THE UPPER LEVEL WAVES PROGRESS EASTWARD...WITH THE HIGHLY
AMPLIFIED TROUGH WHICH MOVES OUT OF ASIA HEADING INTO THE BERING
SEA MONDAY AND TUESDAY. CONDITIONS WILL BE EXTREMELY FAVORABLE FOR
DEVELOPMENT OF DEEP SURFACE LOWS. THUS EXPECT MUCH MORE ACTIVE
WINTER-LIKE WEATHER TO RETURN TO THE BERING SEA AND
ALEUTIANS...AND MOST LIKELY SOUTHWEST AND SOUTHCENTRAL ALASKA BY
NEXT WEDNESDAY AND THURSDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...119 120 127 130 131 132 136 137 138 139
                        150 155 175 176 177 178 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB
LONG TERM...SEB


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