Small Craft Advisory 61, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
524 AM AKST WED JAN 21 2015

.ANALYSIS AND UPPER LEVELS...
A VERTICALLY STACKED LOW CONTINUES TO SPIN WELL SOUTH OF THE
CENTRAL ALEUTIANS WHILE AN ASSOCIATED FRONT IS BRINGING RAIN AND
SNOW TO THE ALEUTIANS AND GALE FORCE WINDS AS FAR NORTH AS THE
PRIBILOF ISLANDS. THIS SYSTEM WILL REMAIN NEARLY STATIONARY
THROUGH TODAY BEFORE ANOTHER LOW DEVELOPS ON THE EASTERN EDGE OF
THE LOW LATE TONIGHT. ANOTHER UPPER LEVEL LOW CAN BE SEEN ENTERING
THE NORTHWEST COAST WITH A ASSOCIATED SHORTWAVE STRETCHING FROM
THE CENTRAL INTERIOR INTO THE COPPER RIVER BASIN. THIS SHORTWAVE
IS BRINGING SNOW SHOWERS TO THE CENTRAL AND EASTERN COPPER RIVER
BASIN...WHICH WILL DIMINISH BY LATE THIS MORNING AS THE SHORTWAVE
MOVES INTO THE YUKON TERRITORY. THIS UPPER LOW WILL CONTINUE
MOVING SOUTHEAST INTO THE INTERIOR...AND WILL SUPPLY THE COLD AIR
NEEDED FOR SNOW AROUND SOUTHCENTRAL LATER THIS WEEK. WEAK RIDGING
CONTINUES BETWEEN THESE LOWS...STRETCHING FROM THE NORTHERN BERING
SEA TO THE SOUTHERN MAINLAND. FOG AND STRATUS HAVE DEVELOPED UNDER
THIS RIDGE...ESPECIALLY OVER THE INTERIOR SOUTHWEST MAINLAND AND
BRISTOL BAY WHERE THE OFFSHORE FLOW IS MUCH WEAKER.

&&

.MODEL DISCUSSION...
WITH LITTLE SIGNIFICANT WEATHER THE MODEL DISCREPANCIES IN THE
EARLY TERM...THE FOCUS TODAY SHIFTS TO THE DEVELOPING LOW NEAR THE
GULF ON THURSDAY AND THE POSSIBILITY SNOW TO SOUTHCENTRAL. THE
MODELS HAVE NOW COME INTO MUCH BETTER AGREEMENT WILL DIMINISH AS
A SECONDARY LOW DEVELOPS TO THE SOUTH OF THE AKPENN LATE TONIGHT INTO
THURSDAY. THERE IS ALSO GOOD AGREEMENT ALOFT THAT THIS DEVELOPING
LOW WILL BECOME THE PRIMARY UPPER LOW BY THURSDAY MORNING...ALLOWING
FOR A FRONT TO STRETCH FROM THE NORTH GULF COAST INTO THE AKPENN
BY THURSDAY EVENING. AT THIS SAME TIME THERE ARE SUBTLE
DIFFERENCES WITH HOW FAR THE UPPER TROUGH DESCENDING INTO THE
INTERIOR WILL DIG...WITH THE EC TRENDING SLIGHTLY FURTHER
NORTH...THE GFS FURTHER SOUTH...AND THE NAM TO THE EAST.
DIFFERENCES ALSO EXIST AT THE SURFACE WITH THE TIMING AND
LONGEVITY OF AN INVERTED TROUGH THAT WILL DEVELOP UNDER THIS LOW
AND MOVE INTO SOUTHCENTRAL. THE GFS AND EC ARE IN GOOD AGREEMENT
GENERAL AGREEMENT THAT AN ELONGATED INVERTED TROUGH WILL DEVELOP
OVER THE KENAI PENINSULA ON THURSDAY AFTERNOON THROUGH
FRIDAY...WHILE THE NAM IS TRENDING SLIGHTLY FURTHER TO THE EAST
AND QUICKER. THESE DIFFERENCES...WHILE SUBTLE...WILL MAINLY IMPACT
NOT IF SNOW WILL FALL OVER SOUTHCENTRAL...BUT HOW MUCH AND FOR HOW
LONG. OTHER THEN THE DIFFERENCES AROUND SOUTHCENTRAL...THERE IS
VERY GOOD AGREEMENT INTO THIS WEEKEND THAT SOME OF THE COLDEST AIR
OF THE SEASON WILL MOVE OVER THE SOUTHERN MAINLAND WITH OFFSHORE
FLOW THROUGHOUT THE SOUTHWEST.

&&

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

GUSTY OUTFLOW WINDS WHICH DIMINISHED THIS MORNING WILL INCREASE
AGAIN THIS AFTERNOON ACROSS THE NORTH GULF AND EASTERN KENAI PEN
AS A LOW MOVING NORTHEAST ACROSS THE GULF TIGHTENS PRESSURE
GRADIENTS. WINDS WILL DIMINISH IN THESE AREAS TONIGHT AS THE LOW
WEAKENS AND GRADIENTS RELAX SOME. A FRONTAL SOUTH OF THE GULF
MOVES NORTH THU AND SPREADS PRECIPITATION TO MUCH OF THE NORTH
GULF COAST AND EASTERN KENAI THU AFTERNOON AND ACROSS THE
REMAINDER OF THE SOUTHCENTRAL MAINLAND THU NIGHT AND INTO FRI.
PRECIPITATION ALONG THE COASTS WILL PROBABLY START AS SNOW BUT
SHOULD TRANSITION TO A MIX OF SNOW AND RAIN. INLAND AREAS SHOULD
REMAIN ALL SNOW THROUGH FRI. MODELS DIFFER SOME IN THE DETAILS BUT
ALL POINT TO A BROAD DEFORMATION ZONE SETTING UP FROM THE COOK
INLET REGION TO OVER THE SUSITNA VALLEY THU NIGHT AND CONTINUING
IN SOME FORM INTO FRI. IF THIS WHERE TO OCCUR THEN THERE WOULD BE
POTENTIAL FOR A PROLONGED MEASURABLE SNOW FALL EVENT. WHILE
CONFIDENCE IS GROWING THAT SNOW WILL OCCUR...IT IS STILL NOT
CERTAIN WHERE...WHEN...AND HOW MUCH.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)... DRY
OFFSHORE NORTHEASTERLY FLOW WILL GRADUALLY STRENGTHEN AND BRING
COLDER TEMPERATURES INTO THE REGION THROUGH THE END OF THE WEEK.
SOME SHOWERS ARE EXPECTED TO DEVELOP ALONG THE ALASKA PENINSULA
AND ALASKA RANGE THURSDAY AFTERNOON AND PERSIST THROUGH FRIDAY
NIGHT...AS A FRONTAL SYSTEM FROM THE NORTH PACIFIC APPROACHES AND
STALLS OVER THE AREA. WINDS WILL BECOME RATHER GUSTY ACROSS
PORTIONS OF THE SOUTHWEST MAINLAND WEDNESDAY...PEAKING BY THURSDAY
AFTERNOON AND SLOWLY DIMINISHING INTO THE WEEKEND. WITH THE COLDER
AIR FILTERING DOWN AND GUSTY WINDS OVER THE AREA...THERE IS FAIRLY
GOOD CONFIDENCE THAT WIND CHILLS IN THE 15 BELOW TO 30 BELOW RANGE
WILL DEVELOP AND PERSIST THROUGH THE END OF THE WEEK.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
NORTHEAST WINDS WILL INCREASE TO GALE FORCE ACROSS MUCH OF THE
ALEUTIANS AND BERING SEA...AS A NORTH PACIFIC LOW MOVES TOWARD THE
ALASKA PENINSULA. THE APPROACH OF THE NORTH PACIFIC LOW WILL ALSO
ACT TO DEVELOP STRONG GAP WINDS ALONG THE THE EASTERN ALEUTIANS
AND ALASKA PENINSULA DURING THE DAY THURSDAY...AND PERSIST THROUGH
FRIDAY AFTERNOON AS THE LOW WEAKENS AND TRACKS TO THE SOUTHEAST.
RAIN AND SNOW SHOWERS WILL BE PREVALENT ALONG THE ALEUTIAN
CHAIN...WITH DRIER CONDITIONS FOR THE EASTERN AND CENTRAL BERING.
WEAK HIGH PRESSURE WILL BUILD OVER THE WESTERN ALEUTIANS AND
BERING THURSDAY...WITH A WEAK UPPER LEVEL DISTURBANCE MOVING
THROUGH THE AREA FRIDAY AND PRODUCING SHOWERS OVER THE AREA
THROUGH THE END OF THE WEEK. A FRONTAL SYSTEM ASSOCIATED WITH A
FAIRLY STRONG NORTH PACIFIC LOW WILL APPROACH THE WESTERN
ALEUTIANS EARLY SATURDAY MORNING...BRINGING THE NEXT ROUND OF
GUSTY WINDS AND PRECIP TO THE WESTERN ALEUTIANS FOR THE WEEKEND.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
IT IS STILL LOOKING LIKE A PATTERN CHANGE IS COMING FOR THIS TIME
FRAME WITH SOME OF THE COLDEST AIR OF THE SEASON TO REMAIN OVER
THE AREA INTO EARLY NEXT WEEK BEFORE TEMPERATURES LOOK TO MODERATE
SLIGHTLY. MOST OF THE AREA WILL SEE DRY CONDITIONS FOR THE WEEKEND
INTO EARLY NEXT WEEK...ALTHOUGH SOME LOCATIONS ACROSS
SOUTHCENTRAL AK COULD SEE LIGHT SNOW CONTINUING WITH THE UPPER
LEVEL TROUGH STILL OVERHEAD.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...MBS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1126 AM AKST WED JAN 21 2015

AKZ101-111-121-145-220100-
ANCHORAGE-MATANUSKA VALLEY-WESTERN KENAI PENINSULA-SUSITNA VALLEY-
INCLUDING THE CITIES OF...ANCHORAGE...EAGLE RIVER...INDIAN...
EKLUTNA...PALMER...WASILLA...SUTTON...CHICKALOON...KENAI...
SOLDOTNA...HOMER...COOPER LANDING...TALKEETNA...WILLOW...CANTWELL
1126 AM AKST WED JAN 21 2015

...SIGNIFICANT SNOWFALL EXPECTED IN SOUTHCENTRAL ALASKA...

A COLD UPPER LEVEL TROUGH WILL MOVE TOWARD SOUTHCENTRAL ALASKA
FROM THE NORTHWEST THURSDAY NIGHT AS AN ELONGATED SURFACE LOW
MOVES INTO THE NORTHWEST GULF OF ALASKA. SNOWFALL WILL MOVE INTO
THE AREA FROM THE SOUTHEAST THURSDAY NIGHT AND THEN STALL OVER
COOK INLET THROUGH THE SUSITNA VALLEY BEFORE BEING PUSHED EASTWARD
THROUGH FRIDAY NIGHT OR SATURDAY.

ANCHORAGE AND MATANUSKA VALLEY AREAS...SNOWFALL SHOULD BEGIN LATE
AFTERNOON OR EARLY EVENING ON THURSDAY BEFORE BECOMING LIGHT OR
POSSIBLY EVEN ENDING LATE THURSDAY NIGHT THROUGH FRIDAY MORNING.
THE SNOWFALL WILL THEN MOVE BACK INTO THE AREA FRIDAY AFTERNOON
AND CONTINUE INTO SATURDAY. THIS SECOND SHOT OF SNOW WILL LIKELY
PRODUCE MORE SNOWFALL THAN THE FIRST PART OF THE EVENT.

THE SUSITNA VALLEY...SNOW WILL MOVE IN FROM THE SOUTHEAST THURSDAY
EVENING AND THEN STALL OVER THE SUSITNA VALLEY BEFORE MOVING BACK
TO THE EAST FRIDAY NIGHT INTO SATURDAY.

THE KENAI PENINSULA...SNOWFALL SHOULD BEGIN THURSDAY AFTERNOON IN
THE KACHEMAK BAY AREA AND SPREAD NORTHWARD. THE MAIN SNOW AREA
WILL PUSH OVER THE INLET BUT SOME SNOW SHOULD REMAIN OVER MOST OF
THE PENINSULA THROUGH FRIDAY EVENING. SNOWFALL AMOUNTS WILL BE
QUITE VARIABLE OVER THE PENINSULA AND WILL BE DEPENDENT ON THE
LOCATION THE MAIN SNOW AREA STALLS OVER. IF THE MAIN SNOW BAND
DOES NOT PUSH QUITE AS FAR WESTWARD OVER COOK INLET SNOW AMOUNTS
MAY BE HIGHEST OVER THE AREA FROM STERLING TO KENAI.

THIS DEVELOPING STORM SYSTEM IS RATHER COMPLEX IN NATURE WHICH IS
STILL CAUSING SOME UNCERTAINTY AS TO WHERE THE SNOWFALL WILL BE
HEAVIEST. IT IS EXPECTED THAT THIS WILL BE THE HEAVIEST SNOWFALL
OF THE SEASON SO FAR FOR MOST OF THE AREA. DETAILS ON SNOW
AMOUNTS WILL BEGIN TO BECOME AVAILABLE WITH THE FORECASTS ISSUED
AT 4 PM THIS AFTERNOON.

FOR LATEST FORECAST INFORMATION PLEASE GO TO:
WEATHER.GOV/ANCHORAGE