Small Craft Advisory 168, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
545 AM AKST FRI FEB 19 2016

.ANALYSIS AND UPPER LEVELS...

VERY ACTIVE WEATHER IS AFFECTING MANY PORTIONS OF SOUTHERN ALASKA
THIS MORNING. COMPARATIVELY SPEAKING...THE EAST SIDE IS THE LEAST
SO. A VERTICALLY STACKED LOW OVER THE SOUTHWESTERN GULF HAS BEEN
DRIFTING SOUTHWARD...LARGELY ENDING MUCH OF THE PRECIPITATION
EXCEPT OVER PORTIONS OF SOUTHEASTERN KODIAK ISLAND. VERY LIGHT
NORTHERLY WINDS BEING DRAWN INTO THIS LOW PERSIST THROUGH THE COOK
INLET REGION...INCLUDING ANCHORAGE. THE LATEST ACARS SOUNDINGS
SHOW SOME COOLING OF THE LOWEST LEVELS...BUT THE WINDS ARE TOO
LIGHT TO LEAD TO MUCH DOWNSLOPING. WITH ONLY SOME REMNANT HIGH
CLOUDS...TEMPERATURES HAVE LARGELY FALLEN INTO THE TEENS ACROSS
MOST OF THE COOK INLET REGION. FOR ANCHORAGE...THIS IS THE THIRD
STRAIGHT NIGHT WITH TEENS FOR TEMPERATURES.

ACROSS SOUTHWEST ALASKA...SURFACE RIDGING IS MAKING LIGHT NORTH TO
NORTHEAST WINDS THE NORM. REMNANT CLOUD COVER FROM THE PRECIPITATION
EVENT OF THE PAST COUPLE DAYS HAS HELPED TO KEEP FOG FORMATION
FROM IMPACTING THE BRISTOL BAY REGION. HOWEVER DUE TO CLEAR
SKIES...THE SAME CANNOT BE SAID FOR THE KUSKOKWIM DELTA. THE DELTA
HAS BEEN SOCKED IN OCCASIONALLY DENSE FREEZING FOG FOR MOST OF THE
DAY YESTERDAY THROUGH THE OVERNIGHT LAST NIGHT. THE 00Z BETHEL
SOUNDING SHOWS WHY...A STRONG INVERSION FROM THE SURFACE THROUGH
MOST OF THE LOWEST 100 MB OF THE ATMOSPHERE HAS TRAPPED NEARLY
SATURATED AIR IN THE LOWEST FEW HUNDRED FEET OF THE ATMOSPHERE.
INCREASING WINDS IN THE LOWEST LEVELS OVER THE PAST SEVERAL HOURS
HAVE FINALLY ALLOWED SOME DRIER AIR TO WORK IN AS VISIBILITIES
BEGAN IMPROVING LAST NIGHT.

FOR THE BERING/ALEUTIANS: THE MOST ACTIVE WEATHER IS OCCURRING
ACROSS THE BERING AND ALEUTIANS THIS MORNING. AN ACERBIC TROUGH
LOCATED JUST WEST OF THE PRIBILOF ISLANDS HAS BEEN CAUSING SNOW
THROUGHOUT THE AFTERNOON AND EVENING YESTERDAY ON THE ISLANDS.
HOWEVER...WITH STRONG SOUTHEAST FLOW...TEMPERATURES HAVE REMAINED
ABOVE FREEZING IN BOTH THE ISLANDS. HOWEVER WITH THE SHARP TROUGH
BEING SO CLOSE...ANY EASTWARD DRIFT COULD BRING THE STRONG
NORTHERLY WINDS LURKING WEST OF THE TROUGH BACK TO THE
ISLANDS...WHICH IN TURN COULD MAKE FOR RAPIDLY DETERIORATING
CONDITIONS...A WINTER WEATHER ADVISORY REMAINS IN EFFECT.

FURTHER SOUTH...A LOW EMBEDDED WITHIN THE TROUGH IS MOVING ACROSS
THE EASTERN ALEUTIANS...ONCE IT PASSES SOUTH OF THE ISLANDS THIS
MORNING...BLIZZARD CONDITIONS ARE EXPECTED NEAR NIKOLSKI. A STRONG
LOW OVER THE NORTHWEST BERING IS DRIFTING BACK TOWARDS THE
NORTHERN KAMCHATKA PENINSULA...BUT STRONG WINDS AND ROUGH SEAS
ACROSS THE WESTERN BERING CONTINUE THIS MORNING.

LAST BUT NOT LEAST...BETWEEN THE LOW OVER THE NORTHWEST BERING AND
A HIGH OVER THE SUBTROPICS... UNSTABLE CUMULUS IS RACING EASTWARD
WITH THE LATEST ARCTIC INTRUSION OVER THE WESTERN ALEUTIANS. THE
SUBTROPICAL JET IS CAUSING THE RAPID MOVEMENT OF THE COLDER AIR
OVER THE ALEUTIANS AND NORTH PACIFIC. THE LEADING EDGE OF THE JET
NORTH OF 40N IS PUSHING A DISTURBANCE OVER THE NORTHEAST PACIFIC.

THIS DISTURBANCE WILL TURN SHARPLY NORTHWARD OVER THE NEXT 24
HOURS AND WILL BE THE CAUSE OF THIS WEEKENDS ACTIVE WEATHER IN
SOUTHCENTRAL.

&&

.MODEL DISCUSSION...

MODEL VARIABILITY AND INCONSISTENCY FOR SOUTHERN ALASKA HAS BEEN
PARTICULARLY NOTABLE WITH THIS LATEST ROUND OF FORECAST MODEL
RUNS. FOR CONSISTENCYS SAKE...NONE OF THE MODELS ALONE WERE
ESPECIALLY PREFERRED AND RELATIVELY FEW CHANGES WERE MADE BEYOND
36 HOURS. WHILE THERE IS GENERAL AGREEMENT BETWEEN THE MODELS ON
THE MOVEMENT AND INTENSITY OF THE LARGE-SCALE FEATURES SHORT-
TERM...THE CAUSES FOR THE ACTIVE WEATHER IN THE FORECAST WILL ALL
BE ON THE MESOSCALE...FOR WHICH THE MODELS ARE HIGHLY VARIABLE.

FOR THE ONGOING BLIZZARD WARNING...THE AREAS THAT EXPERIENCE THE
WORST OF THE BLIZZARD CONDITIONS WILL BE DETERMINED BY WHERE
EXACTLY A BAND THAT IS ONLY ABOUT 10-20 MILES WIDE SETS UP. DUE TO
A LACK OF OBSERVATIONS ANYWHERE NEAR NIKOLSKI...THE MODELS DO
THEIR BEST WITH THE INFORMATION THEY ARE GIVEN. AS SUCH...WHILE
CONFIDENCE IS HIGH FOR BLIZZARD CONDITIONS OCCURRING...WHERE THEY
ARE EXPECTED REMAINS VERY UNCERTAIN. THE ONGOING FORECAST FOR
NIKOLSKI WESTWARD REMAINS THE BEST FORECAST THIS MORNING. AS THE
STRONG LOW OVER THE NORTHWEST BERING DRIFTS NORTHWESTWARD AND THE
LOW OVER THE EASTERN ALEUTIANS MOVES SOUTHEASTWARD...A RESULTING DEFORMATION
BAND AND TRAILING TROUGH WILL BE THE FOCUS FOR THE BLIZZARD
CONDITIONS...AND THIS IS HIGHLY DEPENDENT ON HOW QUICKLY THOSE
FEATURES MOVE. A FEW MILES SEPARATION BETWEEN THE MODEL GUIDANCE
MAKES THE DIFFERENCE BETWEEN HOURS OF BLIZZARD CONDITIONS AND
SCATTERED SNOW SHOWERS.

FOR THIS WEEKENDS POTENTIAL WINTER EVENT IN SOUTHCENTRAL...THE EC
HAS BEEN THE MOST CONSISTENT RUN TO RUN...BUT THE NAM AND GFS ARE
IN BETTER AGREEMENT WITH BOTH EACH OTHER AND THE CURRENT FORECAST.
THE LARGE DISCREPANCIES BETWEEN THE MODELS REMAIN THIS
MORNING...AND THIS PART OF THE FORECAST REMAINS ESPECIALLY LOW
CONFIDENCE. THE NAM AND GFS ARE THE PESSIMISTIC MODELS...LARGELY
FORECASTING DOWNSLOPING AND WARM TEMPERATURES. THE EC IS VERY
OPTIMISTIC IN TERMS OF PRECIPITATION AMOUNTS...THOUGH PRECIPITATION
TYPE ISSUES WOULD REMAIN EVEN IF IT WERE TO VERIFY VERBATIM. ONE
OF THE THINGS THE MODELS LARGELY AGREE ON IS THAT SIMILAR TO MUCH
OF THE WINTER SO FAR...THE DISTURBANCE COMING FROM THE SOUTHEAST
WILL BRING WARM AIR ALONG WITH THE SUPERABUNDANT MOISTURE. STAY
TUNED FOR MORE UPDATES.

&&

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

THE PRIMARY LOW PRESSURE COMPLEX WILL REMAIN SOUTH OF KODIAK ISLAND
THROUGH SAT NIGHT. A SERIES OF OF FRONTAL TROUGHS ASSOCIATED WITH
THIS LOW COMPLEX WILL MOVE NORTH ACROSS THE GULF BRINGING PERIODS
OF GALES...ESPECIALLY WITH THE SECOND FRONT SAT/SAT NIGHT.
PRESSURE GRADIENTS ASSOCIATED WITH THESE FEATURES WILL ALSO
PRODUCE BRISK GAP WINDS THROUGH FAVORED LOCALS (TURNAGAIN
ARM/PORTAGE VALLEY/MAT VALLEY). PRECIPITATION WITH THESE FRONTAL
FEATURES WILL LARGELY IMPACT THE GULF COAST ESPECIALLY WITH THE
FIRST OF THE TWO FRONTS TO MOVE INTO THE NORTHERN GULF TONIGHT.
SOME SPILL OVER SNOW WILL BE LIKELY ACROSS THE CHUGACH SAT NIGHT
WITH THE SECOND FRONT. PRECIPITATION WILL REMAIN SNOW INLAND
AREAS OF WITH A MIXTURE ALONG THE COASTS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
LOW CLOUDS AND STRATUS OVER TO KUSKOKWIM DELTA WILL CONTINUE TO
DIMINISH THIS MORNING AS OFFSHORE FLOW CONTINUES TO INCREASE. WITH
THIS EXCEPTION OF THIS FOG/STRATUS...THE WEATHER THROUGHOUT THE
SOUTHWEST SHOULD REMAIN QUIET WITH OFFSHORE FLOW AND PARTLY CLOUDY
SKIES. CLOUD COVER WILL THEN RETURN TO THE AREA THIS EVENING A
LOW APPROACHING KODIAK ISLAND BRINGS A RAIN AND SNOW TO BRISTOL
BAY INTO SATURDAY. THIS LOW WILL ALSO BRING GUSTY WINDS ALONG THE
ALEUTIAN/ALASKA RANGES THROUGH SATURDAY...THOUGH THESE SHOULD NOT
REACH ADVISORY CRITERIA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE MAIN FOCUS OVER THE BERING SEA CONTINUES TO BE CENTERED AROUND
THE DEFORMATION BAND THAT STRETCHES FROM JUST WEST OF THE
PRIBILOFS INTO THE EASTERN ALEUTIANS. OVERNIGHT THIS BAND SETUP
SLIGHTLY FURTHER TO THE WEST OF THE PRIBILOF ISLANDS THAN
EXPECTED...PREVENTING THE HEAVIEST SNOWFALL FROM FALLING OVER THE
ISLANDS. AS A RESULT THE SNOW ADVISORY FOR THAT AREA WAS
CANCELLED OVERNIGHT AS ANY SNOWFALL THAT DOES FALL TODAY SHOULD BE
LIGHT. TO THE SOUTH...BLIZZARD CONDITIONS ARE STILL EXPECTED ALONG
THE SOUTHERN EDGE OF THE DEFORMATION BAND FOR THE NIKOLSKI AREA
THIS MORNING. WINDS AT NIKOLSKI HAVE BEGUN TO SHIFT TO THE
NORTHWEST AND ARE EXPECTED TO INCREASE DRAMATICALLY OVER THE
COURSE OF THIS MORNING AS HEAVY SNOWFALL AND BLIZZARD CONDITIONS
BEGIN. THERE IS NOW VERY GOOD CONFIDENCE THAT BLIZZARD CONDITIONS
WILL NOT REACH UNALASKA AS WINDS AND SNOWFALL WILL REMAIN MUCH
LIGHTER WITH TEMPERATURES ABOVE FREEZING. INSTEAD THESE AREAS
SHOULD EXPECT A FEW INCHES OF WET SNOW ACCUMULATION WITH GUSTY
EAST WINDS TODAY.

OVER THE WESTERN BERING...STRONG COLD AIR ADVECTION WILL BRINGING
WIDESPREAD SNOW SHOWERS AND HEAVY FREEZING SPRAY TO THE WESTERN
BERING/ALEUTIANS INTO THIS EVENING. THESE CONDITIONS SHOULD THEN
IMPROVE THIS EVENING AS WINDS AND COLD AIR ADVECTION DIMINISH.

&&

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

THE MAJOR WEATHER EVENT OF THE MID TO LONG TERM WILL BE ON DAY 3
WITH THE ARRIVAL OF A ROBUST FRONT INTO THE SOUTHCENTRAL ALASKA ON
SUNDAY WITH A WEAK LOW MOVING NORTHWESTWARD INTO THE KENAI
PENINSULA AND PRINCE WILLIAM SOUND SOMETIME SUNDAY AFTERNOON/EVENING.
MODELS ARE COMING INTO SOMEWHAT BETTER AGREEMENT WITH THE TIMING
AND LOCATION OF THIS EVENT...BUT WITH THAT BEING SAID THERE IS
STILL A GOOD BIT OF UNCERTAINTY WITH THE IMPACTS TO THE INTERIOR
SECTIONS OF SOUTH CENTRAL ALASKA. ALONG THE COAST...CONFIDENCE IS
HIGH FOR PERIODS OF HEAVY PRECIPITATION TO BEGIN EARLY SUNDAY
MORNING THROUGH SUNDAY NIGHT. AT SEA LEVEL...PRECIPITATION IS
EXPECTED TO REMAIN ALL RAIN WITH WET SNOW EXPECTED INLAND AND AT
HIGHER ELEVATIONS ALONG THE COASTAL MOUNTAINS. IN INTERIOR
REGIONS...THE FORECAST ON SUNDAY IS NOT AS CLEAR CUT. ALL GUIDANCE
IS INDICATING THAT WINDS AT 925 THROUGH 700 MB WILL BE STRONG
ENOUGH /AT LEAST 45-65KT/ TO PUSH MOISTURE OVER THE MOUNTAINS AND
INTO UPPER COOK INLET AND THE MATANUSKA AND LOWER SUSITNA VALLEYS.
MODEL QPF VALUES FOR THE 12Z AND 18Z RUNS WERE RANGING FROM
AROUND 1-2 INCHES LIQUID EQUIVALENT IN THE GREATER ANCHORAGE AREA
ON SUNDAY. HOWEVER...LATEST MODEL GUIDANCE IS SHOWING MUCH LESS
THAN A TENTH OF AN INCH OF LIQUID EQUIVALENT. THIS ABRUPT CHANGE
IN LIQUID IS LARGELY DUE TO THE MODELS PLACING THE UPPER LEVEL JET
FURTHER TO THE EAST WHICH KEEPS MUCH OF THE LARGE SCALE MOISTURE
CLOSER TO VALDEZ AND YAKUTAT. GUIDANCE IS STILL VARYING FROM RUN
TO RUN AND MODEL TO MODEL AND COULD CHANGE ABRUPTLY AGAIN TODAY
SHOULD THE MODELS PUSH THE JET FURTHER WEST BACK TOWARD ANCHORAGE.

WITH ALL THIS SAID...THE FORECAST HAS CHANGED A GOOD FIT FROM THAT
OF THE THURSDAY AFTERNOON PACKAGE. THERE STILL LOOKS TO BE A
LIKELY PERIOD OF PRECIPITATION ON SUNDAY MORNING BUT BY SUNDAY
AFTERNOON IT LOOKS LIKE A LACK OF DEEP MOISTURE AND DOWNSLOPING
WILL SEVERELY LIMIT PRECIPITATION ACROSS INLAND AREAS. THE
FORECAST FOR SUNDAY WILL BEAR WATCHING OVER THE NEXT 24-48 HOURS
AS THERE IS STILL (ALTHOUGH LESS LIKELY THAN YESTERDAY) THE
POTENTIAL FOR A DECENT/SIGNIFICANT WINTER EVENT ON SUNDAY.

DAYS 4 THROUGH 7...MODELS ARE IN GROSS AGREEMENT IN THE SYNOPTIC
PATTERN AT THE UPPER LEVELS WITH A STOUT RIDGE BUILDING ALONG THE
WEST COAST OF NORTH AMERICA FROM THE BROOKS RANGE SOUTHWARD ALONG
THE CASCADES INTO CENTRAL CALIFORNIA WITH A BROAD TROUGH OVER THE
NORTH PACIFIC/BERING SEA. THIS TROUGH IS EXPECTED TO HAVE TWO MAIN
CENTERS...ONE LOCATED ROUGHLY AROUND 45N 165W AND A SECOND CENTER
OVER THE SEA OF OHKOSK. AS WITH THE UPPER LEVELS...MODELS ARE IN
BROAD AGREEMENT WITH A SERIES OF LOWS MOVING THROUGH THE ALEUTIANS
AND THE BERING SEA THROUGH THE BROAD UPPER TROUGH WITH A SURFACE
HIGH ALONG THE SE ALASKA/BC COAST. DUE TO DIFFERENCES IN
TIMING...STRENGTH...AND POSITIONS WITH THESE SYSTEMS THE DAY 4
THROUGH 7 FORECAST LEANS HEAVY ON THE WPC FORECAST /WHICH IS
MOSTLY THE 00Z EC ENSEMBLE/. THIS SOLUTION MOVES A 970-975 MB LOW
ALONG THE SOUTH END OF THE ALEUTIANS MONDAY AND TUESDAY BEFORE
MERGING INTO A BROAD LOW SOUTH OF THE ALASKA PENINSULA BY
THURSDAY. THIS PATTERN WILL KEEP THE KODIAK AND THE GULF COAST IN
A WET PATTERN THROUGH THE EXTENDED PERIOD.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WARNING...185.
MARINE...HEAVY FREEZING SPRAY...160 178 180 181 185.
         STORM...119 120 127 130 131 138 139 176 185
         GALE...170 172 173 174

&&

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