Gale Warning 223, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
445 PM AKST WED MAR 9 2016

.ANALYSIS AND UPPER LEVELS...
A STRONG ZONAL UPPER LEVEL JET IS PROGRESSING EASTWARD JUST SOUTH
OF THE WESTERN ALEUTIANS. A DEEPENING ELONGATED LOW (WITH CENTRAL
PRESSURE DROPPING THROUGH THE 970S) IS TRACKING EASTWARD RIGHT
ALONG THE ALEUTIAN CHAIN WITH AN OCCLUDING FRONT BEGINNING TO
SPREAD NORTH AND WEST FROM THE LOW CENTER. EXPECT RAPIDLY
DETERIORATING CONDITIONS AS THIS FRONT CONTINUES EASTWARD. THE
AIR MASS OUT AHEAD OF THIS IS COLD ENOUGH TO SUPPORT SNOW (AS IS
BEING OBSERVED IN ADAK THIS MORNING). SINCE THE FRONT IS ALREADY
OCCLUDING DON'T EXPECT A WHOLE LOT OF WARM ADVECTION...BUT ENOUGH
TO CHANGE PRECIP TO RAIN (OR VERY WET SNOW) ALONG THE ALEUTIANS
TODAY.

LOOKING DOWNSTREAM A HIGH AMPLITUDE TROUGH REMAINS POSITIONED OVER
THE NORTHEAST PACIFIC AND GULF OF ALASKA WITH AN ELONGATED RIDGE
EXTENDING FROM SOUTHCENTRAL TO BRISTOL BAY. A MATURE VERTICALLY
STACKED LOW IS SLOWLY LIFTING NORTHWARD INTO THE GULF...WITH THE
VAST MAJORITY OF IMPACTS REMAINING OVER THE GULF. HOWEVER...A
WEAK FRONT WHICH CROSSED THE GULF YESTERDAY/LAST NIGHT HAS EVOLVED
INTO A DEFORMATION BAND OVER BRISTOL BAY...WITH AREAS OF VERY
LIGHT PRECIP. THIS HAS CONTRIBUTED TO EXTENSIVE CLOUD COVER FOR
MUCH OF SOUTHWEST/SOUTHCENTRAL ALASKA...WITH MOISTURE NOW STUCK
BENEATH THE UPPER RIDGE.

&&

.MODEL DISCUSSION...
MODELS ARE IN VERY GOOD AGREEMENT WITH HANDLING OF LARGE SCALE
FEATURES AND OVERALL FORECAST CONFIDENCE IS HIGH. THERE ARE STILL
A COUPLE FORECAST CHALLENGES. THE MAIN ONE IS DETERMINING DETAILS
OF PRECIP TYPE AND TRANSITIONS AS WARM OCCLUSION SPREADS NORTH AND
EAST ACROSS THE BERING SEA AND ALEUTIANS. IN PARTICULAR...IT
APPEARS THE WARM OCCLUSION WILL REMAIN SOUTH OF SAINT PAUL ISLAND
AND ONLY REACH SOMEWHERE NEAR SAINT GEORGE ISLAND. THUS A COLDER
AND SNOWIER SOLUTION IS BECOMING MORE LIKELY. ANOTHER FORECAST
CHALLENGE IS THE PRECIP FORECAST OVER SOUTHWEST ALASKA...AS MORE
SUBTLE FEATURES INTERACT WITH EACH OTHER TONIGHT INTO TOMORROW.
FORTUNATELY...ANY PRECIP THAT DOES FALL WILL BE LIGHT AND SHORT-
LIVED SO THE PRIMARY IMPACTS WILL BE TO AVIATION (LOW CEILINGS AND
BRIEFLY REDUCED VISIBILITIES).

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
LINGERING MIDDLE AND HIGH CLOUDS WILL HANG AROUND PORTIONS OF THE
COOK INLET REGION AND SUSITNA VALLEY THIS EVENING...OTHERWISE
EXPECT A PLEASANT EVENING WITH LITTLE CLOUD COVER AND ABOVE NORMAL
TEMPERATURES. EARLY TOMORROW MORNING A DECAYING FRONT ASSOCIATED
WITH A WEAKENING SYSTEM IN THE GULF WILL APPROACH THE KENAI
PENINSULA. THE FRONT WILL BRING SCATTERED SHOWERS TO MAINLY THE
SEWARD AREA. MOST OTHER AREAS...ESPECIALLY INLAND WILL SEE
ANOTHER BLUEBIRD DAY WITH CONTINUED ABOVE NORMAL TEMPERATURES AND
LIGHT WINDS. CONDITIONS CHANGE A BIT OVERNIGHT THURSDAY INTO
FRIDAY WHEN THE REMNANTS OF THE GULF SYSTEM PUSH UP INTO THE NORTH
GULF COAST. THE FRONT WILL BRING RAIN AND SNOW SHOWERS...MAINLY
ALONG THE COAST BUT SOME SPRINKLES COULD MAKE IT OVER THE
MOUNTAINS WITH THESE SHOWERS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
RELATIVELY BENIGN CLOUDY CONDITIONS WILL CONTINUE THROUGH THIS
EVENING IN A REGION OF WEAK SURFACE AND UPPER LEVEL FLOW BETWEEN
THE RESPECTIVE LOWS OVER THE GULF AND BERING. AN ELONGATED UPPER
LEVEL WAVE STRETCHED OVER THE KUSKOKWIM DELTA TODAY WILL PUSH
FURTHER INLAND TONIGHT...CAUSING WEAK LIFT OVER AN ALREADY MOIST
ENVIRONMENT. THIS WILL BRING INCREASED CHANCES OF LIGHT SNOW THIS
EVENING TO PORTIONS OF BRISTOL BAY AND THE KUSKOKWIM VALLEY
THROUGH THURSDAY AFTERNOON. WINDS WILL THEN BEGIN TO INCREASE OUT
OF THE NORTHEAST ON THURSDAY AS THE PRESSURE GRADIENT TIGHTENS IN
RESPONSE TO THE ADVANCING BERING LOW. THE FRONT IS EXPECTED TO
REMAIN OFFSHORE AS IT MOVES INTO THE SOUTHEAST BERING THURSDAY
AFTERNOON...KEEPING ANY PRECIPITATION CHANCES MAINLY LIMITED TO
AREAS ALONG THE IMMEDIATE COAST AND OVER THE ALEUTIAN RANGE
THROUGH FRIDAY MORNING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE STRONG LOW ENTERING THE WESTERN BERING WILL BE THE DOMINANT
FEATURE IMPACTING THE REGION THROUGH FRIDAY MORNING AS IT SKIRTS
THE ALEUTIAN CHAIN...WITH THE MAIN FORECAST CHALLENGES FOCUSING ON
PRECIPITATION (AMOUNTS AND TYPES) ALONG THE FRONT...AND THE STRONG
WINDS ON THE BACKSIDE OF THE LOW CENTER. THE FRONT WILL PUSH
QUICKLY EASTWARD THROUGH THE CENTRAL ALEUTIANS EARLY THIS EVENING
AND INTO THE EASTERN ALEUTIANS/BERING BY LATER TONIGHT...THEN INTO
THE AKPEN AND SOUTHWEST COAST DURING THE DAY THURSDAY.
PRECIPITATION WILL BEGIN AS SNOW BUT SHOULD QUICKLY BEGIN TO MIX
WITH OR CHANGE TO RAIN AS WARM NORTH PACIFIC AIR PUSHES IN BEHIND
THE FRONT...WHICH SHOULD HELP TO PRECLUDE ANY BLOWING SNOW
CONCERNS ALONG THE ALEUTIAN CHAIN. HOWEVER...SOME AREAS OF BLOWING
SNOW ARE EXPECTED OVER THE PRIBILOF ISLANDS...AS CURRENT MODEL
GUIDANCE KEEPS MOST OF THE WARMER AIR SOUTH OF SAINT PAUL ISLAND
AND STRONG FRONTAL WINDS OVER THE AREA TONIGHT. ATTENTION THEN
SHIFTS TO THE STRONG WINDS ON THE BACKSIDE OF THE LOW BY LATE
TONIGHT AS COLD ADVECTION AND FAVORABLE JET SUPPORT COME TOGETHER
OVER THE WEST CENTRAL ALEUTIANS. WARNING LEVEL WINDS WILL IMPACT
ADAK EARLY THURSDAY MORNING BEFORE SPREADING EAST TOWARDS ATKA BY
THURSDAY AFTERNOON. A WIDE SWATH OF STORM FORCE WINDS WILL ALSO
IMPACT THE COASTAL WATERS OVER THE WESTERN AND CENTRAL PARTS OF
THE CHAIN THROUGH THURSDAY NIGHT. WIDESPREAD SHOWERY CONDITIONS...
PERIODICALLY HEAVY AT TIMES...WILL ALSO FOLLOW IN THE WAKE OF
THIS SYSTEM OVER THE WESTERN AND CENTRAL ALEUTIANS/BERING WHERE
COLD AIR ADVECTION IS MORE PROMINENT. THESE CONDITIONS WILL
SLOWLY SHIFT EASTWARD OVER THE EASTERN ALEUTIANS BY FRIDAY
MORNING... BRINGING THE SHOWERY AND GUSTY CONDITIONS TO THE AREA.

&&

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

BEGINNING FRIDAY EVENING THERE WILL BE A BROAD GULF LOW AND A
LEFTOVER FRONT ALONG THE GULF COAST. THE NORTH PACIFIC JET WILL BE
DIVING TOWARD THE WESTERN UNITED STATES COASTLINE...WHICH WILL
ALLOW FOR WEAK HIGH PRESSURE TO DEVELOP OVER SOUTHERN ALASKA
SATURDAY AND SUNDAY. A WEAK LOW OVER THE EASTERN BERING WILL CLIP
THE SOUTHWEST COAST AND MAY BRING SOME RAIN AND SNOW BY
MONDAY...BUT SOUTHCENTRAL WILL REMAIN DRY THROUGH AT LEAST
MONDAY. THEREAFTER THERE IS MUCH UNCERTAINTY WITH THE
AFOREMENTIONED BERING LOW PHASING WITH A CUTOFF LOW ACROSS THE
NORTH PACIFIC...WHICH WILL BRING INCREASING CHANCES OF
PRECIPITATION BY MIDWEEK...ALTHOUGH THERE IS MUCH HIGHER
CONFIDENCE BY THIS POINT OF THE EXTENDED FORECAST. OTHERWISE...IN
THE MEAN TIME...TEMPERATURES WILL REMAIN ABOVE CLIMATE NORMS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 187.
MARINE...STORMS 173 174 175 175 177 178 412 413. GALES 130 155
160 165 170 171 172 179 180 411.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...JA