Small Craft Advisory 423, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKDT FRI MAY 22 2009

.MODEL DISCUSSION...MODEL INITIALIZATIONS SIMILAR AND SYNOPTIC
PATTERN IS IN GOOD AGREEMENT AND REASONABLE THROUGH MON.
500MB/SURFACE PATTERNS OVER THE MAINLAND AND GULF ARE SIMILAR THROUGH
TUE. MODELS HOWEVER DIFFER SOME ON THE HANDLING OF THE BERING SEA
RIDGE.

.UPPER LEVELS...
BLOCKING PATTERN STILL IN THE PROCESS OF SETTING UP. THE RIDGE STILL
BUILDS WEST FROM THE CANADIAN YUKON TERRITORY TO OVER THE NORTHERN
MAINLAND AS A CUT-OFF LOW FORMS IN THE GULF OF ALASKA. THE PORTION OF
THE RIDGE OVER CANADA IS PINCHED OFF AS A TROUGH DIGS SOUTH FROM THE
CANADIAN ARCTIC. THE PORTION OF THE RIDGE OVER THE MAINLAND LINKS UP
WITH THE BUILDING RIDGE OVER THE BERING SEA ON SAT NIGHT. THE CUT-OFF
LOW CENTER OVER THE GULF WILL INTENSIFY SOME OVER THE NEXT 24 HOURS
THEN SLOWLY WEAKEN AS IT LINGERS JUST SOUTH OF THE GULF TUE.

.SHORT TERM FORECAST...
.EAST...EXPECT CURRENT PATTERN WITH A THERMAL TROUGH OVER THE
INTERIOR...HIGH PRESSURE RIDGE ALONG THE NORTHERN GULF...AND LOW OVER
THE GULF TO PERSIST INTO EARLY NEXT WEEK. LOW CENTER SOUTHEAST OF
KODIAK ISLAND WILL MOVE A LITTLE NORTH TONIGHT AND INTENSIFY SOME.
PRESSURE GRADIENTS BETWEEN THE NORTHERN GULF HIGH WILL PRODUCE GALES
IN THE NORTH GULF AND WESTERN GULF COASTAL MARINE AREAS. EXPECT WINDS
WILL DIMINISH SAT NIGHT AND SUN AS LOW CENTER DRIFTS SOUTH AND
WEAKENS. GUSTY AFTERNOON AND EVENING WINDS DRIVEN BY DIURNAL PRESSURE
DIFFERENCES BETWEEN THE INTERIOR THERMAL TROUGH AND COASTAL RIDGE
SHOULD CONTINUE THROUGH SAT OVER SOUTHCENTRAL ALASKA AND THE COPPER
RIVER BASIN. DIURNAL WINDS SHOULD BE SOMEWHAT LIGHTER ON SUN AS THE
COASTAL RIDGE IF FORECAST TO THE WEAKER. CONDITIONS SHOULD BECOME
INCREASING MORE UNSTABLE SAT AND SUN AS THE THERMAL TROUGH
INTENSIFIES. SO SHOULD SEE AFTERNOON AND EVENING SHOWERS OVER
SOUTHCENTRAL AND THE COPPER RIVER BASIN. STABILITY INDICES AT THIS
TIME SUGGEST THUNDERSTORM ACTIVITY WILL BE PREDOMINATELY CONFINED TO
THE NORTHERN COPPER RIVER BASIN AND SUSITNA VALLEY ALONG THE ALASKA
RANGE...HOWEVER EARLY 700 MB STEERING FLOW LIKELY TO CARRY
THUNDERSTORMS INTO VALLEY SECTIONS.

.SOUTHWEST MAINLAND...THERMAL TROUGH WILL PERSIST OVER THE SOUTHWEST
MAINLAND THROUGH THE WEEKEND. CONVECTION LOOKS LIKE IT WILL START
EARLIER TODAY AS SHORT WAVE TRIGGER MOVES ACROSS THE REGION.
STABILITY INDICES INDICATE AFTERNOON AND EVENING THUNDERSTORMS OVER
THE KUSKOKWIM VALLEY...EASTERN DELTA...AND INTERIOR BRISTOL BAY ZONE.
COOLER TEMPS WITH NORTHERLY FLOW SHOULD HELP TO STABILIZE THE WESTERN
DELTA.

.BERING SEA/ALEUTIANS/AK PEN...WEAKENING FRONTAL TROUGH AND
ASSOCIATED WAVES OVER THE BERING SEA AND EASTERN ALEUTIANS WEAKEN AND
DRIFT SOUTH OF THE ALEUTIANS SAT NIGHT AS HIGH PRESSURE BUILDS OVER
THE BERING SEA. HIGH PRESSURE WILL HOLD THROUGH EARLY NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 120 130 132 138 AND 150.
FIRE WEATHER...RED FLAG WARNING ZONE 111

RMC MAY 09