Small Craft Advisory 592, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM ADT TUE JUL 17 2007

.ANALYSIS AND UPPER LEVELS...

THE UPPER CENTER IS OVER THE CENTRAL ALEUTIANS WITH A TROUGH
EXTENDING INTO INTERIOR ALASKA. THIS SUPPORTS TO SURFACE LOW OVER THE
CENTRAL ALEUTIANS THAT HAS A FRONT EXTENDING EAST SOUTHEAST TO A
TRIPLE POINT LOW SOUTH OF COLD BAY. AN UPPER LEVEL RIDGE IS OVER THE
WESTERN GULF OF ALASKA WITH A SURFACE HIGH ALSO IN PLACE OVER THE
WESTERN GULF. AN UPPER LOW IS OVER THE ALCAN BORDER OF THE COPPER
RIVER BASIN WHICH IS SUPPORTING THE SURFACE BASED EASTERLY WAVE.

.MODEL DISCUSSION...

MODELS HAVE A MINOR ISSUE WITH THE POSITION OF THE LOW MOVING FROM
SOUTH OF COLD BAY TO SITKINAK THROUGH WED MORNING. THE GFS HOLDS A
MORE NORTHERLY TRACK THAN THE NAM. THIS APPEARS TO BE A MORE
REASONABLE SOLUTION IN LIGHT OF THE SURFACE AND UPPER LEVEL RIDGE
OVER THE WESTERN GULF THAT SHOULD FORCE THE MORE NORTHERLY TRACK. THE
GFS AND NAM ARE IN AGREEMENT THROUGH 60 HOURS IN THE GULF. OUT WEST
THE MODELS STILL DO NOT HANDLE THE INCOMING ALEUTIAN LOW LATER IN THE
WEEK VERY WELL. THE RUN TO RUN DIFFERENCE BY 60 HOURS IS NEARLY 300
NM. THIS LEAVES A LARGE DEGREE OF UNCERTAINTY IN THE LONGER RANGE
FORECAST.

BACK TO THE SHORT TERM THE MODELS APPEAR TO BE HANDLING THE UNSTABLE
CONDITIONS WELL WITH GOOD CAPE VALUES FROM THE COPPER RIVER BASIN
WEST TO THE KUSKOKWIM VALLEY TODAY. TO THE WEST THE MODELS HAVE NOT
DONE AS WELL AS THE FORECASTED GALE FORCE WIND ALONG THE SOUTH SIDE
OF THE ALASKA PENINSULA HAS NOT YET MATERIALIZED. ALTHOUGH SHIP
REPORTS OF 30 KT WINDS HAVE BEEN RECEIVED SOUTH OF THE AREA.

.SHORT TERM FORECAST...

SOUTH AND EAST OF THE AK RANGE...THE EASTERLY WAVE WILL HAS NOT MADE
MUCH IF ANY PROGRESS WEST AND THEREFORE EXPECT THE CLOUDS TO REMAIN
EAST OF GLENNALLEN. THE DIFLUENT REGION IN THE HIGHER LEVELS WILL
ENHANCE THE VERTICAL LIFT AND SUPPORT MORE UNSTABLE CONDITIONS OVER
THE EASTERN BASIN THROUGH THIS EVENING. INCREASED MOIST SOUTHERLY
FLOW WED WILL CONTINUE TO PROVIDE MOISTURE FOR SCATTERED SHOWER
ACTIVITY OVER THE BASIN WED WITH ISOLATED THUNDERSTORMS.

THE FRONT ASSOCIATED WITH THE ALASKA PENINSULA LOW WILL BRING RAIN TO
KODIAK ISLAND THROUGH THIS EVENING THAT WILL SPREAD TO THE OUTER
COASTAL REGIONS OF THE KENAI PENINSULA WED. ON WED AND THU THE
THERMAL TROUGH WILL SET UP FROM THE COPPER RIVER BASIN WEST ACROSS
THE SUSITNA VALLEY TO ALONG THE ALASKA RANGE IN THE KUSKOKWIM VALLEY
WHICH WILL BE THE FOCUS FOR THE THREAT OF THUNDERSTORMS.

IN THE WEST...AS ONE LOW EXITS THE ALEUTIANS WED ANOTHER LOW IS ON
DECK TO MOVE IN AND AFFECT THE WESTERN ALEUTIANS THU. HIGH PRESSURE
BUILDS FROM THE EXTREME WESTERN ALEUTIANS TO THE PRIBILOFS THROUGH
THU.

OVER SW AK...AFTERNOON AND EVENING SHOWERS OVER THE MOUNTAINS WITH
ISOLATED THUNDERSTORMS.

.LONG TERM FORECAST...
THE HIGH DEGREE OF MODEL UNCERTAINTY WITH REGARD TO THE NEXT ALEUTIAN
LOW MEANS LOW CONFIDENCE ON THE FORECASTS OVER WESTERN ALASKA LATE
THIS WEEK INTO THE WEEKEND. THE EASTERN HALF OF THE FORECAST AREA
SHOULD SEE ANOTHER EASTERLY WAVE BRINGING RAIN TO THE COPPER RIVER
AREA SAT THAT COULD SPREAD WEST TO SOUTH CENTRAL ALASKA SUN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

SAM JUL 07