Small Craft Advisory 532, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
155 PM AKDT SAT JUL 4 2009

.MODEL DISCUSSION...
MODELS ARE IN EXTREMELY GOOD AGREEMENT THROUGH THE SHORT TERM
FORECAST. BY THE END OF THE HOLIDAY WEEKEND SOME DIFFERENCES ARISE IN
THE PLACEMENT AND STRENGTH OF A LOW IN THE BERING AND A TROUGH IN
THE PANHANDLE...BUT THE DIFFERENCES ARE FAIRLY MINOR.

.ANALYSIS AND UPPER LEVELS...
EXTREMELY AMPLIFIED PATTERN CONTINUES ACROSS SOUTHERN ALASKA. A UPPER
LEVEL RIDGE EXTENDS FROM THE PACIFIC NORTH ACROSS THE ENTIRE STATE
INTO THE ARCTIC OCEAN. TWO TROUGHS ARE LOCATED ON THE EITHER SIDE OF
THIS RIDGE. TO THE WEST OF THE RIDGE...ACROSS THE BERING...AN UPPER
LEVEL TROUGH IS EVIDENT WITH A CUT OFF SURFACE LOW PRESSURE SYSTEM IS
IN THE FAR WEST BERING. THIS LOW WILL CONTINUE TO MOVE SLOWLY OUT OF
THE BERING AND INTO EASTERN RUSSIA. ANOTHER LOW IS STRENGTHENING ON
THE SOUTHERN PART OF THIS UPPER LEVEL TROUGH WITH THE SURFACE FEATURE
LOCATED JUST SOUTHWEST OF THE ALEUTIANS. TO THE EAST OF THE RIDGE
ANOTHER UPPER LEVEL TROUGH IS LOCATED ACROSS EXTREME EAST CENTRAL
ALASKA AND THE PANHANDLE. A THERMAL TROUGH EXTENDS OFF OF THIS UPPER
LEVEL TROUGH AND WILL ENHANCE INSTABILITY ACROSS THE COPPER RIVER
BASIN.

.SHORT TERM FORECAST...
IT APPEARS THE ANCHORAGE AREA WILL SEE A WARM AND QUIET FOURTH OF
JULY HOLIDAY WITH THUNDERSTORMS POSSIBLE IN THE COPPER RIVER BASIN.
THE UPPER LEVEL RIDGE CONTINUES TO BUILD...INCREASING TEMPERATURES AT
850 MB...WHILE UPPER LEVEL TEMPERATURES CONTINUE TO BE RELATIVELY
COOL. THIS WILL CREATE RELATIVELY FAVORABLE LAPSE RATES FOR
CONVECTION. CURRENT THINKING IS THAT CAP AND SUBSIDENCE WILL SUPPRESS
CONVECTION IN THE ANCHORAGE AREA...BUT CONVECTION IS STILL LIKELY
ACROSS THE COPPER RIVER BASIN SPECIFICALLY AROUND THE CHUGACH
MOUNTAINS. YESTERDAY HAD A VORTICITY MAX MOVE INTO THE AREA...
HELPING A CELL PRODUCE HALF INCH HAIL...BUT TODAY IT APPEARS THERE
WILL BE LITTLE ADDITIONAL MESOSCALE FORCING SO JUST EXPECTING GARDEN
VARIETY THUNDERSTORMS. ALSO ARE SLIGHTLY CONCERNED WITH LOW RELATIVE
HUMIDITY ACROSS THE COPPER RIVER BASIN BUT NOT CONFIDENT FOR REACHING
RED FLAG CRITERIA. PATCHY HAZE WILL ALSO BE POSSIBLE...ESPECIALLY
AROUND THE ANCHORAGE AREA...WITH SUBSIDENCE ALOFT AND LIGHT WINDS.

FURTHER TO THE WEST LOCALLY DENSE FOG CAN BE EXPECTED...ESPECIALLY
ACROSS THE KUSKOKWIM DELTA. HAVE ADDED A HEADLINE FOR FOG FOR THE
KUSKOKWIM DELTA AND IT LOOKS LIKE WITH DRY AIR ALOFT...LIGHT
WINDS...AND SURFACE BASED INVERSION...FOG AND LOW STRATUS WILL ONCE
AGAIN BE POSSIBLE TONIGHT. ACROSS THE ALEUTIANS A LOW WILL MOVE INTO
THE REGION BY THE END OF THE WEEKEND. WINDS WITH THIS LOW WILL BE
GUSTY..SO HAVE POSTED A GALE WARNING FOR THE CENTRAL AND EASTERN
ALEUTIANS.

.LONG TERM FORECAST...
LOOKS LIKE THE RIDGE ACROSS CENTRAL ALASKA WILL HOLD THROUGH THE END
OF NEXT WEEK. THIS RIDGE WILL SLOWLY WARM UP THE UPPER
LEVELS...BRINGING WARMER TEMPERATURES TO THE SURFACE AND ALSO
INCREASING STABILITY ALOFT...DECREASING CHANCES FOR THUNDERSTORMS.
LOW IN THE BERING WILL SKIRT THE PERIPHERY OF THIS RIDGE AND REMAIN
JUST OFFSHORE OF WESTERN ALASKA IN THE BERING. GUSTY WINDS WILL
REMAIN POSSIBLE WITH THIS SYSTEM DUE TO THE STRONG PRESSURE GRADIENT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE WARNING 170 172 175
FIRE WEATHER...NONE

TARALDSEN JUL 09