Small Craft Advisory 481, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT SUN JUN 16 2013

.MODEL DISCUSSION...MODEL FORECASTS ARE REASONABLE AND IN GOOD
AGREEMENT ON SYNOPTIC SCALE FEATURES THROUGH THE SHORT TERM.
AFTERNOON PACKAGES WILL BE BASED IN PART ON THE NAM IN THE EAST AND A
BLEND OF THE NAM AND ECMWF IN THE WEST.

.ANALYSIS
.500 MB...THE LARGE BLOCKING HIGH OVER THE MAINLAND HELD IN PLACE FOR
YET ANOTHER DAY. MORNING SATELLITE IMAGERY SHOWS CIRRUS CLOUDS
ROTATING CLOCKWISE AROUND THE CENTER ANCHORED OVER THE CENTRAL
MAINLAND. SATELLITE IMAGERY ALSO SHOWED MID AND HIGH LEVEL
MOISTURE..ASSOCIATED WITH A BROAD TROUGH OVER THE CENTRAL BERING
SEA...STREAMING NORTH ACROSS THE AK PEN AND EASTERN BERING. THE
BLOCKING PATTERN OVER THE MAINLAND WILL PERSIST THROUGH MID WEEK
THOUGH IT CHANGES ORIENTATION SOME. THE MAINLAND RIDGE RETREATS TO
THE NORTHERN TIER OF ALASKA WED AS A LOW MOVING SOUTH ACROSS THE
YUKON TERRITORY MOVES TO THE GULF OF ALASKA WED AFTERNOON. THIS SETS
UP A STRONG EAST FLOW ACROSS THE SOUTHERN THIRD OF THE STATE AND WILL
LIKELY BE REFLECTED WITH STRONGER SURFACE PRESSURE GRADIENTS AND
LOCALLY GUSTY PRESSURE DRIVEN FLOWS ACROSS SOUTHCENTRAL MON AND TUE.
THE LONG WAVE OUT WEST SLOWLY WEAKENS AND LIFTS NORTH WED.

.SURFACE...

A WEAK LOW PRESSURE TROUGH EXTENDED FROM SE ALASKA TO OVER THE NORTH
GULF THIS MORNING. HIGH PRESSURE WAS OBSERVED INLAND. GUSTY GAP WINDS
WERE EVIDENT ACROSS THE EASTERN KENAI NEAR WHITTIER AND ACROSS VALDEZ
NARROWS. FAIR SKIES WITH THE EXCEPTION OF A LITTLE CIRRUS WAS EVIDENT
ACROSS MUCH OF THE SOUTHERN MAINLAND. THE STRATUS DESK OVER THE GULF
RETREATED TO THE SOUTH AND EAST SOME OVERNIGHT AND ONLY A WEAK MARINE
LAYER WAS ABLE TO GET INTO THE NORTHERN INLET. CLOUDY CONDITIONS WERE
ALSO OBSERVED OVER THE BERING SEA AND ALEUTIANS WITH RAIN ALONG A
WEAKENING STATIONARY FRONTAL BOUNDARY EXTENDING NORTH ACROSS THE AK
PEN AND EASTERN BERING SEA. THE THERMAL TROUGH IS EXPECTED TO
CONTINUE TO STRENGTHEN ACROSS THE SOUTHERN MAINLAND OVER THE NEXT DAY
OR SO WITH ANOMALOUSLY WARM 850 MB TEMPS.

.SHORT TERM FORECAST...

THE MAIN SURFACE FEATURE WILL BE THE STRENGTHENING SURFACE TROUGH
STRETCHING EAST TO WEST ACROSS THE MAINLAND. 850 MB TEMPS WILL REMAIN
WARM OVER THE NEXT COUPLE OF DAYS AND PRODUCE WIDESPREAD 70S TO 80S
WITH SOME 90S IN INTERIOR AREAS. THE UPPER CAP ACROSS ACROSS THE
MAINLAND FORECAST AREAS WILL SUPPRESS CONVECTION TODAY. MON AND TUE
COULD BECOME MORE ACTIVE AS THE CAP WEAKENS WITH THE RETREAT OF THE
UPPER HIGH TO THE NORTH. THINKING NOW MAYBE ISOLATED THUNDERSTORM
POTENTIAL(SOME DRY) ALONG MAINLY HIGHER ELEVATIONS...BEST TUE. WET
CONDITIONS WILL PERSIST OVER THE BERING SEA/ALEUTIANS AS A SERIES OF
SURFACE LOWS ASSOCIATED WITH THE BROAD UPPER TROUGH CONTIUES ITS
INFLUENCE ACROSS THE REGION.

FIRE WEATHER HAZARDS WILL BE THE MAIN CONCERN OVER THE NEXT COUPLE OF
DAYS AS WARM AND RELATIVELY DRY CONDITIONS PERSIST ACROSS INLAND
AREAS FROM THE COPPER RIVER BASIN TO INTERIOR SW ALASKA. RED FLAG
CONDITIONS FOR LOW RH VALUES SHOULD PERSIST THROUGH MON/TUE EVE FOR
THE KUSKOKWIM VALLY...INTERIOR BRISTOL BAY...SUSITNA VALLEY AND THE
COPPER RIVER BASIN. INCREASING PRESSURE GRADIENTS ACROSS SOUTHCENTRAL
WILL ALSO PRODUCE GUSTY NORTH WINDS ACROSS THE COPPER RIVER BASIN AND
NE WINDS ACROSS THE MAT VALLEY MON AFTERNOON AND TUE. THESE TWO ZONES
ARE FLAGGED FOR WATCHES MON AFTERNOON AND TUE AND MOST LIKELY WILL BE
UPGRADED. THE MAT VALLEY IS THE MOST CHALLENGING OF THE TWO IN
COORDINATING CRITICAL RH VALUES WITH WINDS. WINDS COULD DIE IN THE
AFTERNOON BEFORE CRITICAL RH VALUES ARE REACHED. THERE IS ALSO THE
POSSIBILITY THAT THE MAT WINDS AT NIGHT WILL DRY THINGS OUT ENOUGH TO
PRODUCE RED FLAG CONDITIONS DURING THE OVERNIGHT HOURS.

.LONG TERM FORECAST...
A PATTERN SHIFT FOR WEDNESDAY INTO THE END OF THE WEEK LOOKS POSSIBLE
WITH THE RIDGE CENTER MOVING NORTH. MODELS DIFFER WITH THE ALIGNMENT
ON THE UPPER LEVEL FEATURES...BUT WITH THE PATTERN CHANGE
TEMPERATURES MAY MODERATE AT THE END OF THE WEEK WITH A POSSIBILITY
FOR SHOWERS MOVING IN FROM THE GULF.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...RED FLAGS ZONE 111 141 145 152 161(INLAND).

RMC JUN 13