Small Craft Advisory 718, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
645 AM ADT TUE SEP 4 2007

.ANALYSIS AND UPPER LEVELS...12Z IR IMAGERY SHOWS THE PRIMARY FEATURE
CONTINUES TO BE THE LARGE LOW CENTERED OVER THE AKPEN WITH AN
ELONGATED OCCLUDED FRONT ASSOCIATED MOVING ONSHORE ALONG THE NORTH
GULF COAST BRINGING RAIN TO THE WESTERN KENAI WITH RADAR SHOWING A
BROAD FRONTAL BAND OF PRECIP PREPARING TO MOVE NORTH INTO PRINCE
WILLIAM SOUND OVER THE NEXT FEW HOURS. THE STRONG UPWARD VERTICAL
MOTION (UVM) ALONG THE FRONT HAS BEEN ENHANCED BY A POWERFUL
SHORTWAVE ROTATING INTO THE NORTHERN GULF AROUND THE BASE OF THE MAIN
UPPER LOW IN IN CONJUNCTION WITH THE ARRIVAL OF THE LEFT EXIT REGION
OF A 300MB JET STREAK MOVING INTO THE NORTHEASTERN GULF. SURFACE
CYCLOGENESIS ALONG THE FRONT IN ASSOCIATION WITH THESE FEATURES IS
VISIBLE IN THE SATELLITE IMAGERY AND SURFACE OBS THIS MORNING EAST OF
KODIAK CITY...THE MODELS HAVE HAD DIFFICULTY PICKING UP THIS FEATURE
THIS MORNING. THE STRONG UVM HAS EVEN GENERATED A FEW LIGHTNING
STRIKES OVER THE WATERS SOUTH OF CAPE SUCKLING AND ICY BAY OVER THE
LAST HOUR. WINDS ALONG THE FRONT ARE CURRENTLY NEARING GALE FORCE
ACROSS THE NORTHERN GULF.

BACK TOWARDS THE ORIGINAL LOW CENTER...SHOWERS ARE ROTATING ACROSS
BRISTOL BAY AND THE AKPEN WITH ISOLATED SHOWERS ACROSS THE KUSKOKWIM
DELTA WHILE STRONG WINDS ON THE BACKSIDE OF THE LOW ARE IMPACTING THE
WESTERN AKPEN AND EASTERN ALEUTIANS. A STRONG SHORTWAVE ACCOMPANIED
BY A WEAK SURFACE LOW IS DROPPING ACROSS THE CENTRAL BERING SEA WHILE
HIGH CLOUDS ARE BEGINNING TO OVERSPREAD THE WESTERN ALEUTIANS IN
CONJUNCTION WITH THE ARRIVAL OF A POWERFUL UPPER LEVEL JET THAT
EXTENDS BACK INTO EASTERN ASIA.

.MODEL DISCUSSION...MODELS ARE IN VERY GOOD AGREEMENT OVERALL FOR
MUCH OF THE FORECAST PERIOD. THAT SAID...THERE IS CONCERN IN THE
SHORT TERM OVER THEIR HANDLING OF THE LOW IN THE GULF. NEITHER THE
NAM OR THE GFS SEEM TO BE PICKING UP THE SECONDARY CIRCULATION THAT
HAS DEVELOPED OVERNIGHT JUST SOUTHEAST OF KODIAK. GIVEN THE OVERALL
SCALE OF THE SYSTEM...THIS INITIALIZATION ISSUE SHOULD NOT HAVE MAJOR
CONSEQUENCES FOR THE FORECAST WITH THE EXCEPTION OF HAVING TO BUMP UP
THE WINDS ALONG THE NORTH GULF COAST SLIGHTLY TO ACCOUNT FOR THE
CYCLOGENESIS.

THE OTHER MODEL ISSUE TO NOTE IS THE UNCERTAINTY REGARDING THE LOW
PRESSURE SYSTEM THAT HAD BEEN PROGGED TO MOVE INTO THE WESTERN GULF
FROM THE SOUTH ON THU. THE 12Z RUN FROM YESTERDAY CONTINUED TO
ADVERTISE THIS FEATURE...HOWEVER THE 00Z OPERATIONAL RUN HAD
DISPENSED WITH THE SYSTEM...PREFERRING TO KEEP IT IN THE MID
LATITUDES. THIS WAS ALSO THE UNANIMOUS CONCLUSION OF THE GFS ENSEMBLE
MEMBERS AS WELL AS THE OTHER MAJOR OPERATIONAL MODELS. GIVEN THIS
AGREEMENT...MAJOR ADJUSTMENTS WERE MADE TO THE GRIDS TO FALL INTO
LINE WITH THE 00Z GFS RUN FOR THU AND BEYOND. THE CHANGES TO THE
GRIDS BECOME LESS PRONOUNCED BY FRI NIGHT ONCE THE OLF LOW IS OUT OF
THE PICTURE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE FRONT WILL CONTINUE TO MOVE ONSHORE ALONG
THE GULF COAST TODAY BRINGING PLENTY OF RAIN. EASTERLY WINDS SHOULD
DROP THIS AFTERNOON AS THE FRONT MOVES INLAND. RAIN WILL BE MAINLY
ALONG THE EASTERN KENAI AND PRINCE WILLIAM SOUND AREAS WITH THE
WESTERN KENAI ANCHORAGE BOWL AND MATSU BEING IN THE RAIN SHADOW. AS
THE LOW WEAKENS SOUTH OF PRINCE WILLIAM SOUND TONIGHT AND THE WINDS
DIMINISH SHOWERS SHOULD INCREASE IN COVERAGE IN THE AREAS PREVIOUSLY
IN THE RAIN SHADOW. SCATTERED SHOWERS WILL LINGER ACROSS MUCH OF
SOUTHCENTRAL ON WED AS THE REMNANTS OF THE LOW MOVE INLAND AND A
BROAD WEAK AREA OF LOW PRESSURE COVERS THE REGION. A CHANCE OF
SHOWERS WILL CONTINUE THROUGH THU AS MOISTURE FROM THE OLD LOW
LINGERS OVER THE REGION AND FLOW REMAINS LIGHT.

SOUTHWEST ALASKA AND THE BERING SEA...WINDS ALONG THE AKPEN WILL
DIMINISH BY THIS AFTERNOON AS THE LOW MOVES INTO THE GULF OF ALASKA
THOUGH SHOWERS WILL LINGER ACROSS BRISTOL BAY WITH ISOLATED SHOWERS
POSSIBLE IN THE KUSKOKWIM VALLEY AND DELTA. THE SHORTWAVE TROUGH
DROPPING SOUTHEAST ACROSS THE BERING WILL BRING RAIN...THOUGH NOT
MUCH IN THE WAY OF WIND GIVEN THE WEAK PRESSURE GRADIENT...TO THE
PRIBILOFS AND INTO THE EASTERN ALEUTIANS. THIS SHORTWAVE MOVES ACROSS
THE AKPEN TONIGHT GIVING THEM ANOTHER SHOT OF RAIN WHILE SHORTWAVE
RIDGING BEHIND THIS SYSTEM KEEPS THE CENTRAL AND WESTERN ALEUTIANS
DRY...BUT CLOUDY. ANOTHER LOW FORMS JUST EAST OF KAMCHATKA TONIGHT
AND A FRONT MOVES INTO THE WESTERN ALEUTIANS WED BRINGING RAIN AND
GALES. THIS LOW QUICKLY PROGRESSES EAST ON THU...SHUNTED FORTH BY A
POWERFUL UPPER LEVEL JET CENTERED ALONG 45N WITH THE FRONT BRINGING
RAIN TO THE EASTERN ALEUTIANS AND AKPEN.

.LONG TERM FORECAST...THE LARGE LOW IN THE BERING BECOMES THE
DOMINANT SYSTEM IN ALASKA BY THE LATTER HALF OF THE WEEK COURTESY OF
A SERIES OF POWERFUL JET STREAKS THAT CREATE NEW LOWS THAT ROTATE
AROUND EACH OTHER AND MERGE IN THE BERING SEA...ESTABLISHING THE
LONGWAVE TROUGH THERE BY THE WEEKEND WITH WET AND WINDY WEATHER THE
RULE ACROSS THE ALEUTIANS AS A RESULT OF THE SERIES OF LOWS MOVING
INTO THE BERING. A SERIES OF SHORTWAVES ROTATING ACROSS MAINLAND SW
AK WILL KEEP SHOWERS IN THE FORECAST THROUGH THE EXTENDED PERIODS.
THE DIGGING OF THE LONGWAVE TROUGH OVER THE BERING SEA SETS UP BROAD
LONG FETCH SOUTHWEST FLOW ACROSS SOUTHCENTRAL ALASKA BY THE
WEEKEND...SIGNALING THE POSSIBLE START OF AN EXTENDED PERIOD OF WET
BUT MILD WEATHER THAT LASTS INTO NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 120 130 150 155 175 176
FIRE WEATHER...NONE.

WOOD SEP 07