Small Craft Advisory 640, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM ADT MON AUG 6 2007

.MODEL DISCUSSION...
THE GFS AND NAM IN GOOD AGREEMENT THROUGH TUESDAY NIGHT AND THEN THE
DEPTH AND TIMING OF DIGGING TROUGH NEAR 170E DIFFER. EURO AND GFS
MODELS IN GOOD AGREEMENT TODAY THROUGH WEDNESDAY NIGHT. THAT IS WHERE
THE DIFFERENCES BEGIN TO SHOW UP. ALL THE DIFFERENCES SHOW UP IN THE
WESTERN AND CENTRAL BERING SEA. THE GFS WANTS A MORE CONSOLIDATED LOW
SYSTEM MOVING NORTH ACROSS SHEMYA LATE IN THE WEEK WHEREAS THE EC
PUSHES A WEAKER BROAD LOW NORTH. THE UKMET ON THE OTHER HAND HAS A
STRONGER LOW DEVELOPING A BIT LATER (SATURDAY). TAKING A LOOK AT THE
CANADIAN GLOBAL MODEL...IT AGREES MORE WITH THE GFS AND UKMET OF A
MORE CONSOLIDATED LOW DEVELOPING. HOWEVER...A LOOK AT THE CANADIAN
ENSEMBLES SHOWS THE OPERATIONAL RUN A BIT OF AN OUTLIER WITH THE
DEPTH OF THE UPPER TROUGH OVER THE WESTERN NORTH PACIFIC. THE GFS
ENSEMBLES HAVE GOOD AGREEMENT AT THE SURFACE AND UPPER LEVELS THROUGH
ABOUT FRIDAY NIGHT THEN THE UNCERTAINTY RISES CONSIDERABLY.

.ANALYSIS AND UPPER LEVELS...
THE SYNOPTIC PATTERN IS GOING TO AMPLIFY OVER THE NEXT FEW DAYS. A
DEFINITE LONG WAVE CLOSED LOW FORMS NEAR KAMCHATKA WITH A RIDGE OVER
THE EASTERN BERING AND TROUGH OVER THE PANHANDLE BY THE END OF THE
WEEK. HOWEVER...THIS PATTERN IS DEFINITELY WITHIN THE UNCERTAINTY
RANGE.

A LARGE STACKED LOW OVER THE WESTERN BERING NEAR KAMCHATKA WITH HIGH
PRESSURE OVER THE CENTRAL AND EASTERN BERING. IN ADDITION...A LOW
PRESSURE SYSTEM MOVING ACROSS THE MAINLAND TODAY. A COUPLE OF UPPER
LEVEL WAVES EMBEDDED IN THIS TROUGH WHICH WILL EXIT THE AREA LATE
TONIGHT. SHOWERS HAVE DIMINISHED SOMEWHAT OVER SOUTH CENTRAL AND
SOUTHWEST ALASKA. THIS PATTERN WILL CONTINUE INTO TOMORROW AS
EVERYTHING SHIFTS A BIT FARTHER EAST WITH THE LOW MOVING TOWARD THE
CENTRAL BERING AND THE RIDGE MOVING TO THE WEST COAST OF ALASKA.

.SHORT TERM FORECAST...
MAINLAND...
UPPER LEVEL TROUGH WITH A COUPLE SHORT WAVE TROUGHS MOVING THROUGH
THE MAINLAND TODAY. THE WEST TO NORTHWEST FLOW ALOFT BEHIND THIS
SYSTEM IS DRYING THE AIR MASS OUT OVER THE MAINLAND AS WELL THROUGH
TONIGHT. THIS DRYING WILL SPREAD EAST FROM THE WEST COAST THIS
AFTERNOON THROUGH SOUTH CENTRAL TOMORROW. ISOLATED TO SCATTERED
SHOWERS EXPECTED THROUGH TONIGHT ESPECIALLY ON WINDWARD SLOPES. THE
ACTIVITY WILL LAST A BIT LONGER OVER SOUTH CENTRAL. A TROUGH OF LOW
PRESSURE IN THE GULF COMBINED WITH WEST TO NORTHWEST WIND CREATING
IDEAL CONDITIONS FOR MODERATE TO STRONG WINDS THROUGH GAPS OVER SOUTH
CENTRAL AND ALONG THE ALEUTIAN MOUNTAIN CHAIN. THAT GRADIENT TO
LESSEN WEDNESDAY. ANOTHER SHORT WAVE TROUGH WITH A SUPPORTIVE JET TO
DIG SOUTH THROUGH SOUTH CENTRAL WEDNESDAY PROVIDING LIFT FOR SHOWERS.
HOWEVER...LITTLE MOISTURE TO DEAL WITH BY THIS TIME. THE BIG STORY
WOULD BE A PUSH IN NORTHERLY WIND STILL CONTINUING MODERATE NORTH TO
WEST WINDS THROUGH GAPS OVER SOUTH CENTRAL ALBEIT LIGHTER. THE LIGHT
TO MODERATE NORTHERLY DRIER FLOW TO REMAIN THROUGH THURSDAY. IN THE
MEANTIME...HIGH PRESSURE SETTLES OVER WESTERN ALASKA.

ALEUTIAN CHAIN AND BERING...
HIGH PRESSURE WITH LOW CLOUDS OVER THE CENTRAL AND EASTERN BERING
WITH A STRONG FRONT OVER THE WESTERN BERING. THE PARENT LOW TO THE
FRONT IS JUST EAST OF THE KAMCHATKA PENINSULA. THE LOW WILL NOT MOVE
MUCH INTO WEDNESDAY BUT WILL SLOWLY WEAKEN. THE ASSOCIATED FRONT TO
WEAKEN AS WELL WHILE IT MOVES TO THE EAST TONIGHT AND TOMORROW. GALE
FORCE WINDS WILL BE GONE BY TOMORROW. A STRONG JET AND ASSOCIATED
SHORT WAVE TROUGH TO ROUND THE LOW THURSDAY DRAGGING THE UPPER LOW
SOUTH AND CONTINUE TO WEAKEN THE SURFACE LOW NEAR KAMCHATKA. A SECOND
LOW TO FORM IN THE BASE OF THE LOW SOUTH OF SHEMYA LATE THURSDAY.
THIS LOW TO TAKE OVER AND BECOME STACKED AS WELL FRIDAY WITH HIGH
PRESSURE REMAINING OVER THE EASTERN BERING.

.LONG TERM FORECAST...
THE UNCERTAINTY IS AROUND FOR THE LATE WEEK INTO THE WEEKEND PERIOD
OVER THE BERING. HOWEVER...THE OUTLIER FOR LATE IN THE WEEK FOR THE
OVERALL PATTERN IS THE ECMWF. SO...GENERALLY FOR LATE IN THE WEEK
THROUGH THE WEEKEND THE FORECAST IS FOR A LOW NEAR SHEMYA WITH
MODERATE TO STRONG WINDS AND PRECIPITATION FOR THE CENTRAL AND
WESTERN ALEUTIANS/BERING. THE EASTERN BERING WILL SEE A FRONT REACH
ACROSS THE AREA FROM THE LOW SATURDAY AND PUSH TO THE WEST COAST
SUNDAY. THE LOW WILL MOVE TO JUST EAST OF THE KAMCHATKA AT THIS TIME
AS WELL. OVER SOUTH CENTRAL...LIGHT WINDS AND INCREASING CLOUDINESS
THROUGH THE WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 130 175
FIRE WEATHER...NONE

JN AUG 07