Small Craft Advisory 442, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM ADT TUE MAY 15 2007

.ANALYSIS AND UPPER LEVELS...A STABLE PATTERN ALOFT WITH A LARGE
ELONGATED CUT-OFF LOW CENTERED NEAR 50N 153W WITH TROUGH EXTENDING
WESTWARD ACROSS THE BERING SEA TO A SMALL CONCENTRIC CLOSED LOW OVER
THE SEA OF OKHOTSK. THERE IS STRONG RIDGING TO THE EAST OVER THE
WESTERN U.S./CANADA AND A WEAK CLOSED RIDGE OVER FAR EAST RUSSIA
AND THE CHUKCHI SEA. WATER VAPOR IMAGERY SHOWS SEVERAL SHORT-WAVES
EMBEDDED IN THE LARGE CYCLONIC CIRCULATION FROM THE EASTERN BERING
TO THE NORTH PACIFIC TO THE GULF AND BACK UP OVER MAINLAND ALASKA.
THE MOST SIGNIFICANT WAVES NOW AFFECTING THE FORECAST AREA ARE
ROTATING SOUTHWESTWARD ALONG THE SOUTHWEST ALASKA COAST AND
SOUTHWARD TOWARD THE EASTERN ALEUTIANS AND AKPENN. A BAND OF SHOWERS
IS NOTED ON THE BETHEL RADAR HEADING OFFSHORE. THERE IS ALSO A
DECENT SHORTWAVE MOVING SOUTHEASTWARD ALONG THE WESTERN ALEUTIANS.
THE FEW SURFACE OBS OUT WEST ARE NOT REPORTING PRECIP...BUT THERE
IS A NARROW BAND OUT. FINALLY...THE STRONGEST SHORT-WAVE IS ROUNDING
THE BOTTOM OF THE LOW CENTERED AT 50N 153W.

AT THE SURFACE THERE IS A DISSIPATING LOW SPINNING ABOUT 130 NM
SOUTHEAST OF CHIGNIK WITH A TROUGH SOUTHEASTWARD TO A DEVELOPING
LOW NEAR 51N 140W. THIS LOW IS DEEPENING IN RESPONSE TO STRONG
SHORT-WAVE ROUNDING THE TROUGH ALONG WITH UPPER DIVERGENCE IN LEFT
EXIT REGION OF A JET STREAK. EVERYTHING IS ROTATING NORTHWARD TOWARD
THE GULF. A DYING SURFACE FRONT EXTENDS FROM THE KUSKOKWIM DELTA TO
THE INTERIOR (IN LINE WITH UPPER SHORT-WAVE). VISIBLE SATELLITE
IMAGERY SHOWS QUITE A BIT OF SUN ACROSS THE SOUTHERN
MAINLAND...ESPECIALLY INLAND. THERE ARE AREAS OF WEAK SUBSIDENCE
ALOFT...BUT THERE WILL BE ENOUGH SURFACE HEATING TO DESTABILIZE THE
ATMOSPHERE AND PRODUCE ISOLATED TO SCATTERED SHOWERS. LIFTED INDEX
VALUES ARE FORECAST TO REMAIN ABOVE ZERO SO DO NOT EXPECT ANY
THUNDERSTORMS. BASED ON SATELLITE TRENDS AND PROXIMITY TO DYING
FRONT...BEST CHANCE OF CONVECTION LOOKS TO BE FROM BETHEL EASTWARD
TO THE KILBUCK MOUNTAINS AND NORTHEASTWARD INTO THE KUSKOKWIM VALLEY.

OUT WEST THERE IS A STATIONARY FRONT FROM KAMCHATKA TO THE CENTRAL
ALEUTIANS. MAIN IMPACT IS SOME SMALL CRAFT WINDS ALONG THE FRONT.
A DECENT MOISTURE GRADIENT IS NOTED WITH DEW POINTS IN THE 30S SOUTH
OF THE FRONT AND IN THE 20S NORTH OF THE FRONT. WITH HIGH PRESSURE
TO THE NORTH AND EAST THE FRONT HAS BEEN SHEARING APART THE LAST
COUPLE DAYS AND WILL CONTINUE TO DO SO.

.MODEL DISCUSSION...CONTINUE TO PREFER THE GFS MODEL WHICH
INITIALIZED WELL AND SHOWS VERY GOOD RUN-TO-RUN CONSISTENCY. 18Z
VERIFICATION SHOWED ALL MODELS WERE A FEW MILLIBARS WEAK WITH THE
NORTHEAST PACIFIC DEVELOPING LOW. THEREFORE...WILL GO WITH A SLIGHTLY
DEEPER SOLUTION AND INCREASE THE WINDS ABOVE MODEL GUIDANCE AS THIS
LOW MOVES INTO THE GULF. ALSO OF NOTE IS A SHORT-WAVE PROGGED TO DROP
DOWN FROM THE BEAUFORT SEA AND YUKON TONIGHT AND WEDNESDAY AND
BACK-DOOR ITS WAY INTO THE COPPER RIVER BASIN ON THURSDAY. THIS
SHORT-WAVE LOOKS MORE IMPRESSIVE THAN PAST RUNS AND COMBINE WITH
TROUGH APPROACHING FROM THE SOUTH COULD LEAD TO DECENT RAINFALL FOR
PORTIONS OF THE COPPER RIVER BASIN THE NEXT COUPLE DAYS. WITH THIS
IN MIND WILL TREND WETTER FOR THIS REGION.

.SHORT TERM FORECAST...AS DEVELOPING LOW HEADS INTO THE GULF TONIGHT
RAIN WILL OVERSPREAD COASTAL REGIONS AND WINDS WILL
INCREASE...REACHING SMALL CRAFT TO GALE FORCE ON WEDNESDAY.
COMBINATION OF WEAK WAVES ALOFT AND SURFACE HEATING WILL PRODUCE
ISOLATED TO SCATTERED AFTERNOON/EVENING SHOWERS...ESPECIALLY OVER
SOUTHWEST ALASKA. THESE WILL QUICKLY TAPER OFF AS TEMPS BEGIN TO
COOL. AS THE LOW MOVES TOWARD THE WESTERN GULF ON WEDNESDAY RIDGE
WILL BUILD ALONG THE NORTH GULF COAST AND WITH SUNSHINE INLAND
THERMAL TROUGH WILL SET UP. THE COMBINATION OF PRESSURE GRADIENTS
AND AIR DENSITY GRADIENTS FROM DIFFERENTIAL HEATING WILL RESULT IN
WIDESPREAD GUSTY WINDS WEDNESDAY AFTERNOON/EVENING ACROSS MUCH OF
THE SOUTHERN MAINLAND. EXPECT WINDSPEEDS ON THE ORDER OF 15 TO 25 MPH
WITH STRONGER WINDS IN THE USUAL PLACES SUCH AS TURNAGAIN ARM/KNIK
RIVER VALLEY/COPPER RIVER. IT LOOKS LIKE MOST OF SOUTHCENTRAL WILL
SEE QUITE A BIT MID TO HIGH CLOUDS BY AFTERNOON WHICH SHOULD HELP
LEVEL OFF RELATIVE HUMIDITY IN THE AFTERNOON. HOWEVER...OVER
SOUTHWEST ALASKA (ESPECIALLY THE KUSKOKWIM VALLEY) RELATIVE
HUMIDITIES WILL DROP INTO THE 20S WITH LOTS OF SUNSHINE. RIGHT NOW
DO NOT THINK WINDS WILL BE STRONG ENOUGH TO REACH RED FLAG WARNING
BUT WILL KEEP A CLOSE EYE ON THIS AND RE-EVALUATE WITH THE NEXT
MODEL RUN. BY WEDNESDAY EVENING COPPER RIVER BASIN WILL BE RECEIVING
SYNOPTIC LIFT FROM THE NORTH AND THE SOUTH...SO RAIN IS LIKELY
WEDNESDAY EVENING THROUGH THURSDAY. THE UPPER TROUGH AXIS MOVING
ACROSS THE GULF ON WEDNESDAY WILL SWING OVER SOUTHCENTRAL LATE
THURSDAY AND TOWARD SOUTHWEST ON FRIDAY WHILE A STRONG SHORT-WAVE
DROPPING INTO THE BACK SIDE OF THE TROUGH REPOSITIONS THE UPPER LOW
CENTER FARTHER SOUTH OVER THE PACIFIC. ALTHOUGH THERE IS A CHANCE
OF CONVECTION INLAND EVERY DAY THIS WEEK...CHANCES WILL INCREASE
SIGNIFICANTLY TOWARD THE END OF THE WEEK AS UPPER TROUGH MOVES
IN...MOISTURE INCREASES...AND UPPER LEVELS COOL A BIT RESULTING
IN A MORE UNSTABLE ATMOSPHERE.

OUT WEST...THE SURFACE HIGH WILL REMAIN FIRMLY ENTRENCHED OVER THE
WESTERN BERING AND WILL BUILD OVER THE ALEUTIANS AS THE STATIONARY
FRONT DISSIPATES. SYSTEMS APPROACHING FROM THE WEST WILL BE HELD
SOUTH OF THE ALEUTIANS...BUT SOME WIND AND PRECIP MAY APPROACH THE
ALEUTIANS WEDNESDAY NIGHT THROUGH THURSDAY NIGHT. BACK OVER THE
EASTERN ALEUTIANS AND AKPENN WEAK WAVES ALOFT WILL CONTINUE TO
PROVIDE OCCASIONAL LIGHT PRECIP. THE WARMING TREND ALOFT WILL
CONTINUE THROUGH THE WEEK SO THAT THE PREDOMINANT PRECIP-TYPE
WILL BE RAIN.

.LONG TERM FORECAST...MEDIUM RANGE MODELS INDICATE LARGE CYCLONIC
CIRCULATION OVER THE NORTHEAST PACIFIC AT WEEKS END WILL PROGRESS
EASTWARD INTO CANADA OVER THE WEEKEND. HOWEVER ANOTHER CLOSED
CIRCULATION WILL SET UP SOUTH OF THE AKPENN. OUT WEST IT LOOKS LIKE
WEAK RIDGING ALOFT AND HIGH PRESSURE AT THE SURFACE WILL KEEP THE
CENTRAL TO WESTERN BERING DRY AND CALM. THEREFORE...DONT EXPECT
MUCH CHANGE IN THE OVERALL WEATHER FOR DAYS 4 THROUGH 7.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...120 130 132.
FIRE WEATHER...NONE.

SEB MAY 07