Storm Warning 62, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
150 PM AKST SUN DEC 7 2008

.SHORT TERM...SOUTHEAST ALASKA IS STILL UNDER VERY STABLE AND
MOIST CONDITIONS WITH LIGHT RAIN...DRIZZLE AND AREAS OF FOG.
THESE CONDITIONS WILL CONTINUE TO PERSIST THROUGH THIS EVENING
UNTIL A UPPER LEVEL LOW OVER THE NORTHERN GULF DRIFTS OVER THE
AREA TONIGHT. THIS FEATURE WILL MIX UP THE BOUNDARY LAYER AND
INCREASE THE WINDS TO LIFT CEILING AND TO IMPROVE THE
VISIBILITIES.

 AS THE UPPER LEVEL LOW DRIFTS EAST INTO CANADA LATE TONIGHT A
UPPER RIDGE WILL BUILD OVER THE GULF IN ADVANCE OF THE MAJOR LOW
LIFTING OUT OF THE NORTH PACIFIC TONIGHT. THIS RIDGE WILL DRIFT
OVER THE PANHANDLE AS AN OCCLUDED FRONT...ASSOCIATED WITH THE
DEEP 958MB LOW IN THE SW GULF...MOVES INTO THE EAST CENTRAL GULF
MON AFTERNOON. THIS FRONT WILL INCREASE WINDS OVER THE GULF TO
MAX SMALL CRAFT BY THE AFTERNOON AND TO MAX GALES OVER THE
NORTHERN AND CENTRAL GULF. ALONG WITH THE STRONG WINDS PLACES
NEAR THE LAND WILL SEE INCREASE OUTFLOW WINDS TO 50-60 KT. WINDS
OVER THE INNER CHANNELS WILL ALSO INCREASE DUE TO THE INCREASE IN
THE PRESSURE GRADIENT BETWEEN THE INTERIOR 1040 MB HIGH AND THE
FRONT APPROACHING THE PANHANDLE. WINDS OVER E/W CHANNELS WILL
INCREASE TO SMALL CRAFT BY THE AFTERNOON. OVER THE N/S CHANNELS
WINDS WILL INCREASE IN THE LATE MORNING TO SMALL CRAFT MAINLY
OVER THE FAR NORTHERN INNER CHANNELS AND CONTINUE TO INCREASE TO
GALES OVER NORTH LYNN BY THE AFTERNOON. LOCALLY BREEZY TO WINDS
CONDITIONS WILL DEVELOP NEAR PAYA AND OVER THE NORTHERN INNER
CHANNELS AS THE PRESSURE GRADIENT BETWEEN THE YUKON AND THE
PANHANDLE WILL INCREASE TO NEAR 16 MB. WILL ISSUE A WIND ADVY FOR
PAGY ZONE DUE TO THE LARGE PRESSURE GRADIENT.

 THE ARCTIC FRONT WILL GET PULLED SOUTHWARD AS THE FRONT
APPROACHES THE PANHANDLE SO TEMPS WILL BEGIN TO FALL LATE TONIGHT
AND NOT STOP THROUGH THE DAY. TEMPS WILL FALL INTO THE UPPER 20S
OVER THE FAR NORTHERN AREAS TO THE LOWER 30S OVER THE NORTHER
CENTRAL AREAS. PRECIP WILL START SLOWLY OVER THE AREA IN THE
MORNING AS THERE IS STRONG DIFLUENCE AT THE MID-LEVELS. SO FOR
THE MOST PART THERE WILL BE A CHANCE OF LIQUID TO MIX PRECIP OVER
SE AK IN THE MORNING BUT THROUGH THE DAY AS TEMPS FALL THE
NORTHERN AREAS WILL TURN TO ALL SNOW WITH ACCUMULATION LESS THAN
3 INCHES. THE SOUTHERN HALF OF THE FORECAST AREA WILL REMAIN TO
SEE ALL RAIN AS THE COLD AIR WILL NOT MAKE IT DOWN THERE AS OF
MON AFTERNOON. THE HAINES AREA MAY SEE THE SNOW BE MORE STEADY IN
THE MORNING AS THE INTERACTION BETWEEN THE NORTH STREAM AND
SOUTHERN STREAM WILL INCREASE CONVERGENCE AND LIFT.

.LONG TERM...SIGNIFICANT SNOW EVENT POTENTIAL FOR NORTHERN ZONES
IN SE PANHANDLE. 12Z GFS UKMET AND EC ARE COMING INTO BETTER
AGREEMENT ON TRACK AND STRENGTH OF GALE FORCE LOW MOVING NNE INTO
THE NORTHERN GULF OF ALASKA MONDAY AND TUESDAY. 12Z NAM WAS THE
OUTLIER SOLUTION AS IT HAD SIGNIFICANT DIFFERENCES IN BOTH THE
TRACK AND STRENGTH OF THE LOW. BLENDED TWO THIRDS 12Z GFS WITH ONE
THIRD INHERITED GRIDS THROUGH DAY 4. MINIMAL CHANGES WERE MADE TO
THE GRIDS DAYS 5 THROUGH 8. LONG TERM SHOWS A DRYING TREND BY LATE
WEEK. MODELS ARE IN GOOD AGREEMENT THROUGH FRIDAY MORNING. AFTER
FRIDAY THE MODELS ARE DISPLAYING CONSIDERABLE SPREAD WITH LONGWAVE
PATTERN SHIFT. FORECAST CONFIDENCE IS ABOVE AVERAGE THROUGH DAY 4
AND LOWER THAN AVERAGE DAY 4 THROUGH DAY 8.

BOTH THE EC AND UKMET SOLUTIONS DEMONSTRATE A SHIFT TOWARDS THE
MORE AGGRESSIVE GFS SOLUTION WHICH BRINGS THE ARCTIC FRONT SOUTH
OF JUNEAU AND IN GENERAL THE FURTHEST SOUTH COMPARED TO THE EC AND
UKMET. DIFFERENCES ON THE POSITION ON THE ARCTIC FRONT ARE LESS
WITH TODAYS MODEL RUNS THAN THEY WERE YESTERDAY. THE 12Z EC
SOLUTION HAS THE ARCTIC FRONT RETREAT BACK TO THE NORTH QUICKER
THAN THE GFS OR UKMET. THE EC HAS A WEAKER GRADIENT BETWEEN THE
LOW IN THE GULF AND THE HIGH IN THE YUKON AS THE YUKON HIGH IN THE
EC IS 4 TO 6 MB LOWER AND IS POSITIONED FURTHER EAST. BELIEVE THE
OFF SHORE GRADIENTS IN THE GFS AND UKMET ARE MORE REALISTIC AND
WILL PREVENT THE MORE RAPID RETREAT OF THE ARCTIC FRONT AS SHOWN
IN THE EC. IMPACTS FOR SENSIBLE WEATHER IN THE NORTHERN
ZONES...LOW LEVEL COLD AIR STAYS LONGER AND GREATER PORTION OF
MOISTURE FALLS AS SNOW. THE GFS EC AND UKMET ALL INDICATE A TRIPLE
POINT LOW MOVING NE OUT OF THE GULF COMING INTO THE PANHANDLE NEAR
SOUTHERN BARANOF ISLAND AND THEN MOVING UP FREDERICK SOUND. THIS
TRACK WOULD PUT JUNEAU UNDER THE NORTHWEST DIVERGENCE ZONE WHICH
HAS THE POTENTIAL TO ENHANCE SNOWFALL. AT THIS POINT THE 12Z GFS
RUN DOES NOT DEVELOP A STRONG DIVERGENCE FIELD. EXACT TRACK OF THE
LOW ALONG WITH THE POSITION AND RETREAT OF THE ARCTIC FRONT AND
POTENTIAL DEVELOPMENT OF A STRONG NORTHWEST DIVERGENCE ZONE WILL
BE KEY TO SNOWFALL AMOUNTS ACROSS THE NORTHERN PANHANDLE. AT THIS
POINT 6 TO 12 INCHES OF TOTAL SNOWFALL ARE POSSIBLE FOR HAINES AND
WATCH AREAS. WINTER STORM WARNING WILL BE ISSUED FOR HAINES ZONE
THIS AFTERNOON. IN ADDITION TO SNOWFALL POTENTIAL AS THE 1040MB
HIGH MOVES THROUGH THE YUKON STRONG WINDS ARE EXPECTED OUT OF
INTERIOR BAYS AND PASSES. WIND ADVISORY WILL BE POSTED FOR
SKAGWAY. WINDS ARE ALSO EXPECTED TO INCREASE TO ADVISORY LEVELS IN
ZONE 27 WITH THE APPROACH OF THE LOW OUT OF THE GULF OF ALASKA.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY FROM 9 PM MONDAY TO 6 AM AKST TUESDAY FOR AKZ027.
         WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY AFTERNOON
     FOR AKZ018-020-021-025.
         WINTER STORM WARNING FROM 6 PM MONDAY TO 6 PM AKST TUESDAY FOR
     AKZ019.
         WIND ADVISORY FROM 1 PM MONDAY TO 6 AM AKST TUESDAY FOR AKZ018.
MARINE...GALE WARNING FOR PKZ011>013-021-022-031>035-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ036.

&&

ABJ/CCC