Small Craft Advisory 457, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM ADT WED MAY 23 2007

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVEL PATTERN ACROSS ALASKA
CONSISTS OF A RIDGE CENTERED BETWEEN 130W AND 140W FROM THE NORTHEAST
PACIFIC TO SOUTHEAST ALASKA TO THE YUKON...AND A LONG-WAVE TROUGH TO
THE WEST ACROSS THE NORTH PACIFIC AND BERING SEA REGION. THE UPPER
JET IS NEARLY ZONAL ACROSS THE NORTH PACIFIC BETWEEN 30N AND 45N
AND THEN MAKES A SHARP NORTHWARD TURN AROUND 150W...HELPING TO DRIVE
STORMS NORTHWARD TOWARD THE AKPENN. SEVERAL CLOSED ARE EMBEDDED
WITHIN THE UPPER TROUGH...TWO OF WHICH ARE THE FOCUS OF TODAYS
SHORT-TERM FORECAST.

FIRST THERE IS A LOW THAT PASSED JUST SOUTH OF THE KENAI PENINSULA
THIS MORNING AND IS NOW TRACKING ACROSS THE ALASKA RANGE INTO THE
KUSKOKWIM VALLEY. BASED ON INTERPRETATION OF SATELLITE IMAGERY IT WAS
ORIGINALLY THOUGHT THAT THERE WAS A SURFACE ROTATION. HOWEVER AS THE
LOW MOVED THROUGH THE BARREN ISLANDS REGION OBSERVATIONS DID NOT
SUPPORT THIS CONCLUSION. QUIKSCAT WINDS ALSO SHOWED NO SURFACE LOW.
SO IT APPEARS THIS IS A VERY STRONG MID-TO-UPPER LEVEL LOW WHILE AT
THE SURFACE THERE IS A FRONT FROM THE NORTH GULF COAST TO AN OLD LOW
DOWN NEAR SAND POINT. THE KENAI AND MIDDLETON ISLAND RADAR FILLED IN
QUICKLY THIS MORNING AS THE LOW APPROACHED...BUT STRONG EASTERLY FLOW
ACROSS THE KENAI AND CHUGACH HAS RESULTED IN A JUST A FEW SPRINKLES
FROM THE WESTERN KENAI TO ANCHORAGE TO THE MAT VALLEY. EASTERLY FLOW
IS TRENDING DOWNWARD AS THE LOW MOVES INLAND AND UPPER FLOW IS
VEERING TOWARD THE SOUTH SO SOME LIGHT RAIN IS LIKELY THIS AFTERNOON.
AREAS OF RAIN ALSO EXTEND ACROSS SOUTHWEST ALASKA AND THE EASTERN
BERING SEA. CONDITIONS REMAIN DRY FURTHER EAST OVER THE COPPER RIVER
BASIN. RHS ONLY ROSE INTO THE UPPER 30S TO UPPER 40S OVERNIGHT AND
ARE FALLING BACK THROUGH THE 30S THIS MORNING. ALTHOUGH THERE IS
SIGNIFICANT CLOUD COVER OVER THE COOPER BASIN RHS SHOULD STILL MAKE
IT DOWN INTO THE 20S THIS AFTERNOON. WITH SURFACE RIDGING ALONG THE
NORTH GULF WINDS WINDS WILL INCREASE AND PRODUCE A HIGH FIRE DANGER
ACROSS THE COPPER BASIN...A RED FLAG WARNING IS IN EFFECT THROUGH
THIS EVENING.

THE SECOND LOW OF CONCERN TODAY IS AROUND 400NM SOUTH OF THE AKPENN.
BOTH THE SURFACE AND UPPER LOW ARE ELONGATED N-S. WATER VAPOR IMAGERY
SHOWS A STRONG SHORT-WAVE ROTATING NORTHWARD ALONG THE EAST SIDE OF
THE UPPER LOW. THIS WILL LIKELY FORM A SECOND LOW CENTER TO THE
NORTH OF THE CURRENT ONE. THIS SYSTEM IS TRACKING NORTHWARD TOWARD
THE AKPENN SO THERE WILL NOT BE MUCH OF A BREAK BETWEEN SYSTEMS.

THE WESTERN BERING AND ALEUTIANS ARE UNDER A BLANKET OF STRATUS/FOG
WITH HIGH PRESSURE AT THE SURFACE AND WEAK FLOW ALOFT.

.MODEL DISCUSSION...MODELS INITIALIZED POORLY WITH THE LOW CURRENTLY
MOVING INTO THE KUSKOKWIM VALLEY. THERE WAS NO INDICATION OF A
CLOSED CIRCULATION UNTIL 300 MB. BASED ON SATELLITE IMAGERY THERE
WAS CLEARLY ROTATION BELOW THAT LEVEL. ALSO THE MODELS TRACK THIS
FEATURE A BIT TOO FAR TO THE WEST. SO FOR THE NEXT 6 TO 12 HOURS
WILL MAKE SMALL ADJUSTMENTS TO FORECASTS TO ACCOUNT FOR STRONGER
DYNAMICS AND SLIGHTLY ALTERED TRACK.

THE MODELS INITIALIZED WELL WITH OTHER SYNOPTIC FEATURES INCLUDING
THE SYSTEM SOUTH OF THE AKPENN AND ARE IN DECENT AGREEMENT THROUGH
THE SHORT-TERM. THERE IS ALSO GOOD RUN-TO-RUN CONSISTENCY WITH
TUESDAYS 00Z RUN.

.SHORT TERM FORECAST...AS THE UPPER LOW CONTINUES TO TRACK INLAND
THIS AFTERNOON/EVENING SURFACE FRONT WILL MOVE ONSHORE AND QUICKLY
DISSIPATE...ALLOWING SURFACE RIDGE TO BUILD BACK ALONG THE NORTH GULF
COAST. AS ALL OF THIS OCCURS SURFACE WINDS WILL SHIFT TO THE SOUTH
TO SOUTHEAST AND INCREASE TO 15 TO 30 MPH ACROSS MUCH OF
SOUTHCENTRAL. WITH UPPER FLOW ALSO SHIFTING TO THE SOUTH THERE WILL
BE SHOT FOR A BRIEF PERIOD OF LIGHT RAIN FROM THE WESTERN KENAI TO
ANCHORAGE TO THE MAT VALLEY. BRIEF GUSTY WINDS WILL ALSO EXTEND INTO
SOUTHWEST ALASKA. THIS CHANGE WILL BE BRIEF THOUGH...WITH THE NEXT
SYSTEM NOT FAR BEHIND THE FLOW ACROSS THE SOUTHERN MAINLAND WILL
SHIFT BACK TO SOUTHEAST TO EAST LATE TONIGHT INTO THURSDAY MORNING.
SO INLAND AREAS WILL QUICKLY DRY OUT WHILE RAIN WILL MOVE TO COASTAL
AREAS...THE AKPENN...EASTERN ALEUTIANS...AND THE PRIBILOFS. THE
SURFACE RIDGE WILL PERSIST ALONG THE GULF COAST THE NEXT FEW DAYS AS
FRONT MOVE INTO THE GULF...MAINTAINING OCCASIONALLY GUSTY WINDS IN
THE USUAL PLACES. COMBINATION OF EASTERLY LOW TO MID LEVEL FLOW AND
UPPER RIDGE BUILDING OVER INLAND ALASKA MEANS MOST INLAND PORTIONS
OF SOUTHERN ALASKA WILL REMAIN MOSTLY DRY FOR THE REST OF THE WEEK.

AS MEDIUM RANGE MODELS HAVE BEEN PREDICTING...THE UPPER LOW CURRENTLY
SOUTH OF THE AKPENN WILL MOVE TO THE EASTERN BERING SEA FRIDAY SO
MOST OF PRECIP WILL BE CENTERED OVER THE EASTERN BERING...SOUTHWEST
ALASKA...AND THE GULF OF ALASKA. NO CHANGE OUT OVER THE CENTRAL TO
WESTERN BERING WHERE WEAK SURFACE HIGH AND DIFFUSE FLOW ALOFT WILL
MAINTAIN CALM CONDITIONS.

.LONG TERM FORECAST...UPPER LOW WILL REMAIN OVER THE EASTERN BERING
WITH TROUGH AXIS EXTENDING EASTWARD TO THE GULF OF ALASKA. THIS WILL
LIFT NORTHWARD EVER SO SLIGHTLY...IMPROVING CHANCE OF SHOWERS OVER
INLAND AREAS. ZONAL JET TO THE SOUTH WILL KEEP STORM TRACK DOWN OVER
THE NORTH PACIFIC THROUGH EARLY NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 130 138.
FIRE WEATHER...RED FLAG WARNING 141.

SEB MAY 07