Freeze Warning 3, NWS Anchorage, AK

763 
WWAK71 PAFC 201706
NPWAER

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE ANCHORAGE AK
906 AM AKDT FRI SEP 20 2013

AKZ101-111-201815-
/X.EXP.PAFC.FZ.W.0003.000000T0000Z-130920T1700Z/
ANCHORAGE-MATANUSKA VALLEY-
INCLUDING THE CITIES OF...ANCHORAGE...EAGLE RIVER...INDIAN...
EKLUTNA...PALMER...WASILLA...SUTTON...CHICKALOON
906 AM AKDT FRI SEP 20 2013

...FREEZE WARNING HAS EXPIRED...

WHILE SOME PLACES REMAIN BELOW FREEZING THIS
MORNING...ABUNDANT SUNSHINE WILL CAUSE TEMPERATURES TO RISE
THROUGHOUT THE DAY.

$$

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT THU SEP 19 2013

.ANALYSIS AND UPPER LEVELS...
ALOFT...A DEEP UPPER TROUGH REMAINS OVER THE MAINLAND PORTION OF THE
STATE WITH AN ANCHOR LOW REMAINING IN PLACE OVER INTERIOR ALASKA. A
BROAD RIDGE REMAINS IN PLACE OVER THE NORTH PACIFIC AND SOUTHERN
BERING SEA WITH A STRONG 150+ KT JET STREAM FLOWING OVER THE TOP AND
TURNING SOUTHWARD INTO THE BASE OF THE LONGWAVE TROUGH. MEANWHILE AT
THE LOWER LEVELS...A LOW SOUTH OF THE PANHANDLE IS MOVING NORTHWARD
AND STRENGTHENING RAPIDLY WITH THE HELP OF A 120 KT JET STREAK COMING
UP OUT OF THE LONGWAVE TROUGH. SATELLITE IMAGERY SHOWS THE
CIRCULATION STARTING TO BECOME ELONGATED TO THE NORTH. OVER
SOUTHCENTRAL...A SHORTWAVE TROUGH OVERNIGHT CAUSED CLOUDS AND RAIN
SHOWERS TO LINGER AROUND COOK INLET THROUGH THE MORNING HOURS...BUT
HAS NOW MOVED TO THE EAST ALLOWING SUNSHINE TO BREAK OUT IN A MAJOR
WAY FROM THE WESTERN KENAI TO ANCHORAGE. LOW CLOUDS AND LIGHT RAIN
AND SNOW SHOWERS CONTINUE ACROSS THE COPPER RIVER BASIN. OUT
WEST...HIGH CLOUDS AND RELATIVELY BENIGN WEATHER PREVAIL ACROSS THE
BERING SEA REGION...THOUGH A NEW LOW IS BEGINNING TO FORM SOUTHWEST
OF THE WESTERN ALEUTIANS.

.MODEL DISCUSSION...
MODELS SEEM TO BE LOCKING INTO A SYNOPTIC SOLUTION FOR BOTH OF THE
STRONG STORMS THAT WILL AFFECT THE FORECAST AREA THROUGH THE WEEKEND.
THE LOW MOVING UP TOWARD THE PANHANDLE IS EXPECTED TO REACH PEAK
INTENSITY THIS EVENING AROUND 971 MB. WHILE ALL MODELS SHOW A SIMILAR
SOLUTION THE NAM WAS A BIT SOUTH AND EAST OF THE GFS/EC/GEM CONSENSUS
WITH THE TRACK OF THE SURFACE LOW AND WAS REMOVED FROM CONSIDERATION
IN THE AFTERNOON FORECAST. THE MORE IMPACTFUL STORM FOR OUR FORECAST
AREA WILL BE THE LOW DEVELOPING NEAR THE WESTERN ALEUTIANS THAT WILL
CROSS THE BERING AND REACH THE GULF BY SATURDAY MORNING. HERE AGAIN
THE 12Z NAM IS A NOTABLE OUTLIER...KEEPING A GOOD PORTION OF THE
STORM ALONG OR SOUTH OF THE ALEUTIAN CHAIN. THIS SCENARIO IS NOT
SUPPORTED BY THE OTHER MODELS AND LIKELY STEMS FROM A MUCH WEAKER
SUPPORTING UPPER LEVEL WAVE THAN THE OTHER MODELS HAVE ALL SHOWN FOR
SEVERAL DAYS. HERE AGAIN THE NAM WAS EXCLUDED.

.SHORT TERM FORECAST...
SOUTHCENTRAL...SKIES ARE FINALLY CLEARING AROUND COOK INLET...A TREND
THAT SHOULD CONTINUE TO SPREAD TO THE NORTH AND EAST THROUGHOUT THE
EVENING HOURS. THE SHORTWAVE TROUGH THAT MOVED THROUGH COOK INLET
EARLIER IS DISSIPATING AND IS HEADED OFF TO THE EAST...THOUGH THE NEW
MODEL RUNS ARE SUGGESTING ANOTHER TROUGH WILL MOVE THROUGH UPPER COOK
INLET LATE THIS EVENING BEFORE AMPLIFYING OVER THE COPPER RIVER BASIN
TOWARD MORNING. THINKING AT THIS TIME IS THAT THE ATMOSPHERE SHOULD
BE SUFFICIENTLY DRY FROM THE WESTERN KENAI TO ANCHORAGE AND THE
MAT-SU TO PREVENT A REPEAT OF THE SHOWERS THAT OCCURRED THIS
MORNING...BUT NORTHERN SECTIONS OF THE COPPER RIVER BASIN WILL LIKELY
STILL HAVE ENOUGH RESIDUAL LOW-LEVEL MOISTURE TO ALLOW SOME AREAS OF
RAIN/SNOW TO DEVELOP YET AGAIN...ESPECIALLY AT HIGHER ELEVATIONS.
OTHERWISE...THE COLDEST NIGHT OF THE SEASON SO FAR LOOKS INCREASINGLY
LIKELY TONIGHT AS MUCH OF ANCHORAGE AND THE WESTERN KENAI WILL DROP
TO NEAR OR BELOW FREEZING TONIGHT AND AGAIN ON FRIDAY NIGHT. WITH
RECENT RAINFALL THERE MAY ALSO BE SOME LOCALIZED FOG THAT DEVELOPS
AROUND KNIK ARM TOWARD BUTTE TONIGHT WHERE NORTHERLY WINDS ARE THE
LIGHTEST.

SOUTHWEST...BENIGN NORTHWESTERLY FLOW WILL BECOME MORE NORTHEASTERLY
AND OFFSHORE BY FRIDAY EVENING AS THE STRONG BERING LOW PASSES SOUTH
OF THE MAINLAND. COASTAL SECTIONS OF THE BRISTOL BAY ZONE AND ALASKA
PENINSULA WILL SEE MUCH MORE IN THE WAY OF RAINFALL...THOUGH PRECIP
MAY SPREAD FAR ENOUGH INLAND TO PRODUCE A BIT OF MIXED RAIN/SNOW OVER
INTERIOR PORTIONS OF BRISTOL BAY BEFORE THE LOW MOVES INTO THE GULF
ON SATURDAY.

BERING SEA AND ALEUTIANS...CONFIDENCE IS INCREASING REGARDING DETAILS
OF THE DEVELOPING LOW EXPECTED TO TRACK THROUGH THE SOUTHERN BERING
THROUGH THE END OF THE WEEK. THE STORM WILL BEGIN TO UNDERGO RAPID
INTENSIFICATION THIS EVENING...AND WILL CONTINUE TO GET STRONGER AS
IT TRACKS ALL THE WAY TO THE GULF BY SATURDAY. PRIMARY THREAT FROM
THIS STORM WILL BE STRONGER WINDS THAN HAVE BEEN EXPERIENCED IN A
WHILE...WITH THE VERY FAST STORM MOVEMENT EXAGGERATING WINDS THAT
WILL ALREADY BE STRONG ON THE BACKSIDE OF THE LOW. STRONGEST WINDS
WILL OCCUR FRIDAY AFTERNOON AND EVENING FROM ATKA TO DUTCH HARBOR.
WHILE THESE WINDS SHOULD NOT APPROACH WARNING LEVEL...GUSTS
APPROACHING 60 MPH LOOK INCREASINGLY LIKELY. VIRTUALLY ALL AREAS WILL
ALSO SEE A PERIOD OF HEAVY RAIN ASSOCIATED WITH THIS STORM...BUT DUE
TO THE RAPID STORM MOVEMENT THIS SHOULD BE RELATIVELY SHORT-LIVED AT
MOST LOCATIONS.

.LONG TERM FORECAST...
LONG RANGE MODELS CONTINUE TO SHOW THE LONGWAVE TROUGH OVER THE
MAINLAND RETROGRADING BY EARLY NEXT WEEK BEFORE BREAKING DOWN INTO A
MOVE PROGRESSIVE PATTERN BY MIDWEEK. CONFIDENCE IS LOW IN SPECIFIC
FEATURES...BUT A SLIGHT WARMUP BACK TO MORE SEASONABLE TEMPERATURES
LOOKS FAIRLY LIKELY FOR MUCH OF THE MAINLAND AS THE STORM TRACK
SHIFTS BACK TO THE BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 130 155 170 171  172 175
FIRE WEATHER...NONE

AMD SEP 13