FXAK67 PAJK 312127

AFDAJK



SOUTHEAST ALASKA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE JUNEAU AK

127 PM AKDT SAT JUL 31 2010



.SHORT TERM...WEAKENING WAVES ON THE POLAR FRONT ZONE HAVE BEEN

CONTINUING TO TRACK ENE ACROSS THE GULF OF ALASKA, WITH THE LAST

EXAMPLE MOVING ONSHORE THE PANHANDLE N OF PASI AT THIS TIME. THE

FOLLOWING WAVES WILL DISSIPATE  UPSTREAM OF OUR FORECAST DOMAIN,

DUE TO THE RIDGE ALOFT  OVER THE EASTERN GULF REDEVELOPING

UPSTREAM OVER THE  CENTRAL GULF OF ALASKA. CHANGES TO THE SHORT

RANGE FORECAST PACKAGE ARE SMALL, WITH THE LARGEST CHANGE BEING

SMALLER RAINFALL AMOUNTS SMALLER THAN PREVIOUSLY FORECAST. 



 THE LONG-WAVE RIDGE ALOFT THAT EXTENDS N OVER THE ERN GLFALSK

HAS BEEN DISSIPATING MOST OF THE THE WEAK SHORT WAVES MOVING E

THROUGH IT. THE PRIMARY EXCEPTION IS THE ONE SUCH POLAR FRONT 

WAVE THAT IS PROVIDING PRECIPITATION THAT HAS SPREAD SE TO A

PAJN- PASI LN AT THIS TIME. THE RIDGE ALOFT WILL REDEVELOP AFTER

THIS WAVE, AND THE FOLLOWING WAVES WILL BE WEAKER AND DISSIPATE 

EARLIER IN THE TRACK ACROSS THE GLFALSK. 



 THE GOES IR IS CONSISTENT WITH A DIFFUSE OCFNT MOVING ONSHORE

THE PNHDL AT THIS TIME. RAINFALL AMOUNTS AT PACV AND PAYA HAVE

NOT REACHED THE MDT CATEGORY, I.E. WHAT THE PUBLIC FORECASTS 

REFER TO AS "HEAVY". 



 THE 12Z GFS HAS BEEN USED AS THE PRIMARY GUIDANCE, HOWEVER THE

NAM PRESSURE GRADIENTS WERE USED TO GENERATE WIND VALUES IN THE

INNER CHANNELS. SEVERAL MODEL SOURCES WERE USED FOR THE POPS. 



 PATCHY RADIATIVE FOG IS FORECAST FOR THE CENTRAL PNHDL FOR LATE

TONIGHT. 



 && 



 .LONG TERM...RATHER QUIET WEATHER PATTERN IN STORE FOR THE

PANHANDLE THIS WEEK AS A HIGH PRESSURE RIDGE BUILDS IN THE

EASTERN GULF. A RIDGE OF HIGH PRESSURE WILL BUILD IN THE EASTERN

GULF BOTH AT THE SURFACE AND ALOFT BY SUNDAY NIGHT. THE PRESENTS

OF WHICH WILL CAUSE NW FLOW OVER MOST OF THE PANHANDLE DRYING US

OUT AND CLEARING UP THE CLOUDS IN THE AREA. THE MARINE LAYER MAY

STILL BE A PROBLEM ALONG THE OUTER COAST AND THE INNER CHANNELS

NEAR THE COAST BUT PARTLY CLOUDY SKIES SHOULD BE THE RULE

ELSEWHERE. WITH THE CLEARER SKIES TEMPS ACROSS THE AREA WILL RISE

INTO THE 60S AND 70S FOR DAYTIME HIGHS IN MOST PLACES THIS WEEK. 



 THE ONLY MAJOR FORECASTING CONCERN OTHER THEN THE MARINE LAYER

IS HOW LONG WILL THIS RIDGE LAST. THE MODELS ARE CURRENTLY AT

ODDS ON THIS WITH THE GFS BEING THE MOST AGGRESSIVE AT EVICTING

THE RIDGE. THE GFS STARTS PUSHING THE 500 MB RIDGE TO THE EAST

AND STARTS FLATTENING THE SURFACE RIDGE AS SOON AS LATE WED DUE

TO AN ADVANCING UPPER SHORT WAVE FROM THE ALASKA PENINSULA. THE

EC ON THE OTHER HAND HANGS ON TO THE RIDGE, BOTH SURFACE AND

500 MB, THROUGH LATE THURS BEFORE AN UPPER LOW STARTS PUSHING

BOTH EAST. ENSEMBLE SUPPORT SEEMS TO FAVOR THE EC IN THIS CASE.

EITHER WAY, PRECIP ONCE AGAIN ENTERS THE FORECAST BY FRIDAY. 



 MID RANGE FORECAST WAS UPDATED WITH A BLEND OF THE GFS AND SOME

NAM AS THE GFS INITIALIZED A GOOD PRECIP FOOTPRINT COMPARED TO

THE ACTUAL OBS AND THE NAM DID A GOOD JOB ON THE PRESSURES OVER

THE PANHANDLE. FARTHER OUT SWITCHED TO THE EC WITH A BIT OF THE

HPC GRIDS AS THE EC HAD BETTER RUN TO RUN CONSISTENCY THAN THE

GFS AND HAD THE SUPPORT OF THE ENSEMBLES IN HOW LONG THE RIDGE

LASTED. FORECAST CONFIDENCE IS HIGH. 





.AJK WATCHES/WARNINGS/ADVISORIES...

PUBLIC...NONE.

MARINE...SMALL CRAFT ADVISORY FOR PKZ041-042. 



&&



$$



JBT/EAL