Small Craft Advisory 283, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
1245 PM AKDT MON APR 11 2011

.SHORT TERM...A BROAD LOW PRESSURE AREA WILL REMAIN OVER THE
GULF THROUGH TUE. A LOW PRESSURE TROF IS JUST ENTERING THE SE
GULF AND WILL CONTINUE NNE INTO THE ERN GULF AND SE AK TONIGHT
BUT WILL LIKELY DISSIPATE AS IT GETS TO THE NRN AREA LATE TONIGHT
OR EARLY TUE. AN OCCLUDED FRONT WILL FORM JUST S OF THE ERN GULF
LATE TONIGHT AND BEGIN TO LIFT NWD INTO THE SE GULF TUE...SLOWLY
STRENGTHENING AS IT DOES. A LOW PRESSURE WAVE WILL BEGIN TO
DEVELOP JUST SW OF THE HAIDA GWAII (FORMERLY QUEEN CHARLOTTE
ISLANDS) AREA TUE AFTERNOON.

 MAIN FORECAST ISSUE WILL BE PRECIP POTENTIAL. THE DEEP LAYER
MEAN FLOW WILL GO FROM SSW TO SSE OVER THE AREA DURING THE NIGHT
TONIGHT...AND BECOME MORE SELY TUE. THIS NORMALLY LEADS TO A
DIMINISHING PRECIP THREAT ESPECIALLY NRN AREAS. HOWEVER...THE
TROF MOVING IN TONIGHT AND FRONT TUE WILL KEEP GOOD DEEP LAYER
LIFT GOING MUCH OF THIS TIME SO POPS WILL BE HIGHER THAN THEY
NORMALLY WOULD BE IN THIS DEVELOPING FLOW SCENARIO. THAT BEING
SAID...STILL LOOKS LIKE THE SRN AND COASTAL AREAS WILL HAVE MOST
PRECIP OVER THE NEXT 24 HRS...AND WILL GENERALLY KEEP CAT POPS IN
THOSE AREAS THROUGH TUE. POPS WILL DROP SLOWLY AS YOU GO N AND
E...WITH LOWEST POPS AROUND THE PAGY AREA THROUGH THE PERIOD. THE
PRECIP THREAT WILL ALSO DROP OFF SOMEWHAT AROUND PAYA AS LOWER
LEVEL FLOW TURNS MORE ELY LATER TONIGHT AND TUE.

 OTHERWISE...AIRMASS IS STILL COOL ENOUGH TO SUPPORT SNOW SHOWERS
OVER MUCH OF THE NRN AREA SO WILL KEEP MENTION OF SOME SNOW GOING
INTO TUE MORNING THERE. WARMER AIR SHOULD WORK ITS WAY NWD INTO
THE SRN AREA LATER TONIGHT AND TUE AHEAD OF DEVELOPING OCCLUDED
FRONT SO EXPECT PRECIP OVER THE S TO REMAIN RAIN EXCEPT FOR SOME
MIXED PRECIP AROUND HYDER DURING THE MORNING HOURS TUE.

 WINDS WILL GENERALLY NOT BE A PROBLEM ALTHOUGH WILL HAVE SCA
LEVEL SE WINDS IN CLARENCE STRAIT TONIGHT INTO TUE...WITH SCA
LEVEL E WINDS DEVELOPING OUT OF CROSS SOUND LATER TONIGHT. MAY BE
A SMALL AREA OF SCA WINDS IN THE FAR SERN GULF TUE AFTERNOON AS
OCCLUDED FRONT STRENGTHENS JUST SW OF THERE. SEAS WILL REMAIN ON
THE HIGH SIDE ESPECIALLY SERN GULF AREA...SO SCA FOR SEAS WILL BE
KEPT GOING SE OF THE CAPE FAIRWEATHER AREA.

&&

.LONG TERM...MODELS ARE IN GENERAL AGREEMENT WITH THE UPPER LEVEL
SHORTWAVE TROUGH WEAKENING ACROSS THE GULF AND SOUTHEAST ALASKA
WITH A CUT-OFF UPPER LOW SLOWLY FADING OUT TOWARDS THE WEEKEND.
THE VERTICALLY STACKED LOW...AS A BIG SURFACE GYRO...OVER THE GULF
WILL CONSEQUENTLY DISORGANIZE AND A HIGH PRESSURE OVER THE
NORTHERN CANADA CONTINUING TO ENHANCE THROUGH THE LONG TERM
PERIODS. A SERIES OF WEAK TROUGHS ASSOCIATED WITH THE PERSISTING
LOW WILL CONTINUE TO DRIFT NORTH ACROSS THE FORECAST DOMAIN
THROUGH WEDNESDAY NIGHT. MODELS CONTINUE HINTING A DEVELOPING LOW
NEAR BRITISH COLUMBIA COAST LATE THURSDAY INTO FRIDAY. A GOOD
MODEL CONSENSUS WAS DRAWN FROM THE GFS AND NAM THROUGH THURSDAY
MORNING. MODEL SPREADS BECAME LARGER THURSDAY EVENING ONWARD AND
THE ENSEMBLE BASED HPC OUTPUTS WERE USED FOR THE REST OF THE LONG
TERM PERIODS.

 A WEAK FRONTAL BOUNDARY DEVELOPING IN THE SOUTHEAST GULF LATE
TUESDAY WILL DRIFT NORTH ACROSS THE PANHANDLE WITH LIKELY TO
CATEGORICAL POPS OVER THE FORECAST DOMAIN TUESDAY NIGHT INTO
WEDNESDAY MORNING. OTHER THAN THAT...NO MAJOR STORM SYSTEM
DEVELOPS WITHIN THE AREA OF THE BIG GYRO BUT A SERIES OF WEAK
TROUGHS CONTINUE DRIFTING NORTH ACROSS THE FORECAST DOMAIN WITH
GENERALLY LIGHT PRECIPITATION. EMBEDDED SMALLER FEATURES ARE
HANDLES A LITTLE DIFFERENTLY WITH VARIOUS MODELS FOR TIMING AND
POSITION...BUT IN GENERAL INCREASING OFFSHORE LOW LEVEL FLOW WILL
SUBPRESS PRECIPITATION ACROSS THE NORTHERN PANHANDLE TOWARDS THE
WEEKEND AND THROUGH THE EARLY NEXT WEEK. RELATIVELY WARM AIR MASS
WILL ENTRAIN THE AREA FROM THE SOUTH BY THE MID WEEK AND THE
PRECIPITATION WILL MOSTLY LIKELY LIGHT RAIN SHOWERS...EXCEPT THE
NORTHERN MOST ZONES WITH MIXED PRECIPITATION WILL CONTINUE AT
NIGHT TIMES THROUGH MID WEEK. INCREASING NORTHERLY PRESSURE
GRADIENT AND OFFSHORE LOW LEVEL FLOW WILL GENERATE SMALL CRAFT
WINDS ACROSS MUCH OF THE OUTSIDE WATERS AND INNER CHANNELS THROUGH
MID WEEK.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-036-041.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ042-043.

&&

RWT/AHN