Storm Warning 33, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
125 PM AKST TUE MAR 9 2010

.SHORT TERM...SATELLITE IMAGERY THIS MORNING SHOWING FRONTAL
BAND MOVING ACROSS THE PANHANDLE. WITH THE FRONTAL PASSAGE WINDY
CONDITIONS HAVE BEEN DIMINISHING AS WINDS SHIFT FROM SE TO SW.
COLD AIR BEHIND THE FRONT WITH TEMPERATURES DROPPING THROUGH THE
DAY AND STRATIFORM PRECIP CHANGING TO SHOWERS AND TRANSITIONING
FROM RAIN TO SNOW. SHORT WAVE NEAR PAYA BROUGHT A QUICK SNOW FALL
OF ABOUT 5 INCHES SO EXTENDED THE WINTER ADVY TO NOON. WIND GUSTS
OVER ZONE 28 LINGERED ON A BIT LONGER SO EXTENDED WIND ADVY OUT
TO NOON. WINDS OVER HAINES AND SKAGWAY HAVE BEEN UP AND DOWN
THROUGH OUT THE DAY BUT OVER ALL SEEING ADVY LVL GUSTS CONTINUE.
SNOW SHOWERS HAVE EXTENDED A BIT FURTHER DOWN THE COAST SO SEEING
MINOR ACCUMULATIONS NEAR ZONE 27 AS WELL AS ZONE 22 AND 23. UPPER
END GALE TO NEAR STORM FORCE WINDS ALONG THE N INNER CHANNELS
HAVE DIMINISHED THROUGH THE AFTERNOON TO SCMR.

MOVING IN TO A BRIEF QUIET PERIOD AS A WEAK RIDGE MOVES OVER THE
PANHANDLE TUE NIGH INTO WED. EXPECTING WINDS TO DIMINISH WITH POST
FRONTAL SHOWER ACTIVITY TO CONTINUE. PRECIP TYPE WILL TRANSITION
TO ALL SNOW WITH SOME RAIN SNOW MIX OVER THE SOUTHERN AREAS. NOT
EXPECTING MORE THEN 1 TO 3 INCHES OF ACCUMULATION AT THIS TIME.
THE LULL IN THE WEATHER WILL BE SHORT LIVED AS LOW MOVING UP FORM
THE PAC INTO THE SE GULF DEEPENING TO AROUND 960 MB. WED AFTERNOON
INTO WED NIGHT. 850 WINDS REACHING 70 TO 80 KTS NEAR HAND OFF
PERIOD. HIGHEST GUSTS WILL OCCUR TOMORROW NIGHT AND AFTER
COORDINATION WITH THE LONG TERM ISSUING WIND ADVY FOR ZONE 22, 23,
26 AND 29 WITH HIGH WIND WATCH FOR 27 AND 28. SOME MODEL
DISAGREEMENT IN EXACT TRACK OF THE WED NIGHT LOW. GFS IS A BIT
QUICKER THAN NAM AND MORE TO THE N. 00Z EC WAS A GOOD COMPROMISE
AS THE 12Z EC WENT MORE IN LINE WITH THE GFS. USED A BLEND OF 00EC
AND 12GFS. FINAL TRACK OF THE LOW WILL HAVE THE BIGGEST IMPACT ON
PRECIP TYPE FOR NORTH CENTRAL ZONES. FURTHER TO THE SOUTH WILL
KEEP MORE SNOW IN THE FCST AS A MORE N TRACK WILL BRING MORE
MIXING OF RAIN. HIGH QPF VALUES FOR THE SOUTH AS THE LOW BRINGS A
LONG FETCH OF MOISTURE.

FORECAST CONFIDENCE IS ABOUT AVERAGE WITH SOME TIMING ISSUES ON
CURRENT WIND EVENTS DIMINISHING. SHOWER ACTIVITY ALSO CAUSING SOME
ISSUES WITH VIS AND CEILING HEIGHTS FOR THE AFTERNOON.

.LONG TERM...LONG WAVE PATTERN REMAINS CONSISTENT WITH YESTERDAYS
MODEL RUNS WITH THE COLD LONGWAVE TROUGH IN THE CENTRAL GULF
THURSDAY WEAKENING AND RETROGRADING TO OVER THE ALASKAN PENINSULA
BY THE WEEKEND. THIS WILL ALLOW THE COOLER TEMPERATURES AND
RAIN/SNOW LINE TO RETREAT NORTHWARD TO NEAR THE ICY STRAIT
CORRIDOR BY THE EARLY PART OF THE WEEKEND. BOTH THE 12Z ECMWF AND
GFS ENSEMBLES AS WELL AS OPERATIONAL MODELS WERE LESS PROGRESSIVE
WITH THE MID LEVEL PATTERN MONDAY ONWARD WITH A STRONGER MID LEVEL
RIDGE BUILDING INTO WESTERN CANADA OVER THE WEEKEND. STILL ONLY
MINOR CHANGES MADE PAST DAY 4 BLENDING TOWARD THE HPC SOLUTION
WHICH WAS SIMILAR TO YESTERDAYS PATTERN DUE TO THE RELATIVELY
CONSISTENT MODEL RUNS OVER THE PAST DAY OR SO. INTO THE MIDDLE OF
NEXT WEEK MODELS ARE HAVING A DIFFICULT TIME DETERMINING HOW LONG
A MID LEVEL TROUGH WILL REMAIN IN THE BERING AND SO FORECAST
CONFIDENCE DROPS BELOW AVERAGE AFTER MONDAY. MOST OF THE FOCUS IN
THE LONG TERM WAS NEAR HAND OFF WITH SHORT TERM AS A STORM FORCE
LOW MOVES INTO THE SOUTHEASTERN GULF AND OVER THE PANHANDLE
WEDNESDAY NIGHT THROUGH THURSDAY NIGHT AND ITS EXACT TRACK WILL
MAKE A MAJOR DIFFERENCE IN POSSIBLE SNOW AMOUNTS ACROSS THE
CENTRAL AND NORTHERN PANHANDLE THURSDAY.

USED A BLEND OF THE 12Z GFS AND 00Z ECMWF NEAR HAND OFF WITH SHORT
TERM THROUGH DAY 3 AS BOTH THESE MODELS PROVIDED A GOOD MIDDLE
GROUND WITH THE STORM FORCE LOW MOVING ONSHORE THE PANHANDLE NEAR
WESTERN BARANOF ISLAND EARLY THURSDAY MORNING. THE 12Z ECMWF WAS FURTHER
WEST WITH THE SURFACE LOW TRACK AND THE 12Z/18Z NAM WERE FURTHER
EAST AND EACH OF THESE MODEL RUNS WERE NOT CONSISTENT WITH THE
PREVIOUS OVERNIGHT MODELS. THE 00Z ECMWF HAD A VERY GOOD
REPRESENTATION OF THE DOUBLE LOW STRUCTURE MOVING INTO THE
SOUTHEAST GULF WEDNESDAY NIGHT AS IS SHOWN IN BOTH THE 12Z GFS AND
00Z ECMWF 850 MB AND 700 MB HEIGHT AND WIND FIELD. 850 MB
TEMPERATURES WILL REMAIN COLD ENOUGH TO SUPPORT SNOW FROM THE ICY
STRAIT CORRIDOR NORTHWARD UNTIL AROUND 9 PM WEDNESDAY NIGHT...BUT
THE STRONG NORTHERLY SURFACE PRESSURE GRADIENT AND LOCALLY WINDY
CONDITIONS ALONG LYNN CANAL WILL DRY OUT THE LOW LEVEL ENVIRONMENT
AND KEEP SNOWFALL AMOUNTS BELOW ADVY. WITH THE LESSER PRECIP
AMOUNTS ACROSS THE NORTHERN AND CENTRAL PANHANDLE DUE TO DOWNSLOPE
FLOW WEDNESDAY NIGHT AND THURSDAY...THE MAIN FORECAST PROBLEM WITH
THIS STORM FORCE WILL BE THE STRONG WINDS ACROSS THE SOUTHERN
PANHANDLE WEDNESDAY NIGHT THROUGH THURSDAY MORNING. WITH 850 MB
WINDS NEAR 80 KNOTS AND THE SURFACE LOW EAST OF 140 HAVE
COORDINATED WITH SHORT TERM TO EXTEND THE HIGH WIND WATCH INTO
WEDNESDAY NIGHT FOR AKZ027 AND AKZ028 WITH GALES IN ASSOCIATED
WATERS AND WIND ADVISORIES INTO THE CENTRAL PANHANDLE. WILL ALSO SEE A
STRONG SECOND WRAP ADVECT ACROSS THE PANHANDLE THURSDAY AFTERNOON
AND EVENING AND WILL SEE NEAR WIND ADVY GUSTS ALONG THE OUTER
COAST. CONCERNED THAT AS THE SURFACE LOW MOVES INTO THE YUKON LATE
THURSDAY AFTERNOON THAT COULD SEE HIGH WIND GUSTS NEAR
SKAGWAY...BUT WILL KEEP GUSTS LIMITED ATTM FOR FURTHER MODEL RUN
CONSENSUS. WILL SEE GALE FORCE NORTHERLY WINDS BECOME SOUTHERLY BY
THURSDAY NIGHT ACROSS THE NORTHERN PANHANDLE.

FRIDAY AND SATURDAY WILL CONTINUE TO SEE ONSHORE FLOW THROUGH 500
MB ACROSS THE PANHANDLE WITH SOUTHERLY SURFACE FLOW AND WITH 850
MB TEMPERATURES BELOW -10 C WILL SEE SCATTERED TO NUMEROUS SNOW
SHOWERS EACH DAY. ATTM...DON'T SEE A STRONG FORCING MECHANISM TO
ORGANIZE THE SNOW SHOWER ACTIVITY AND SO BELIEVE THE SNOW AMOUNTS
WILL REMAINING BELOW ADVY CRITERIA. THE NEXT STRONG OCCLUSION MOVES
INTO THE GULF ON SATURDAY AND WITH MID LEVEL THICKNESS VALUES
WARMING INTO THE WEEKEND WILL SEE THE RAIN/SNOW LINE RETREAT TO ALONG
AND NORTH OF ICY STRAIT. GALE FORCE WINDS WILL SPREAD ACROSS THE
GULF ON SATURDAY WITH WIND ADVY GUSTS ALONG THE OUTER COAST OVER
THE WEEKEND.

FORECAST CONFIDENCE REMAIN ABOVE AVERAGE THROUGH NEXT MONDAY WITH
THE LONG WAVE PATTERN...BUT STILL MODELS REMAIN INCONSISTENT WITH
THE SURFACE LOW TRACK WEDNESDAY NIGHT AND THURSDAY AND SO THIS
SITUATION BEARS WATCHING. TEMPERATURES AND PRECIP AMOUNTS WILL
REMAIN NEAR NORMAL INTO EARLY NEXT WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY FROM 3 PM WEDNESDAY TO MIDNIGHT AKST WEDNESDAY
     NIGHT FOR AKZ022-023-026-029.
         HIGH WIND WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY
     EVENING FOR AKZ027-028.
         WIND ADVISORY UNTIL 6 PM AKST THIS EVENING FOR AKZ018-019.
MARINE...GALE WARNING FOR PKZ012-013-022-033>036-041>043.
         SMALL CRAFT ADVISORY FOR PKZ011-021-031-032-051-052.

&&

PRB/PSS