Small Craft Advisory 483, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM ADT THU MAY 31 2007

.ANALYSIS AND UPPER LEVELS...CYCLONIC FLOW CONTINUES OVER MUCH OF THE
STATE AS A LARGE UPPER LOW WITH SURFACE REFLECTION REMAINS ANCHORED
IN PLACE SOUTH OF THE ALASKA PENINSULA. THE RESULTING ONSHORE FLOW
COMBINED WITH THE REMNANTS OF AN OLD FRONTAL BOUNDARY HAS BROUGHT
CONTINUED RAIN OVERNIGHT TO USUAL WINDWARD SLOPES OF THE COASTAL
MOUNTAINS ALONG THE NORTHERN GULF COAST AND KODIAK ISLAND WITH DRIER
CONDITIONS ON THE LEEWARD SIDE OF THE MOUNTAINS. RADAR IS SHOWING
WEAK ECHOES MOVING ACROSS THE BRISTOL BAY REGION THIS
MORNING...HOWEVER WHATEVER LIGHT PRECIP THERE IS DOES NOT APPEAR TO
BE REACHING THE GROUND. NORTHERLY RETURN FLOW ACROSS THE BERING SEA
AROUND THE MAIN LOW IS BRINGING PRECIP INTO PACD AND PADU THIS
MORNING WHILE PASN REMAINS MIRED IN STRATUS. A COMPACT MID TO UPPER
LEVEL LOW IS SEEN ON IR IMAGERY DROPPING INTO THE CENTRAL BERING
WHILE TO THE WEST SURFACE RIDGING IS TRAPPING THE MARINE LAYER AND
KEEPING LOW CLOUDS OVER THE WESTERN BERING AND WESTERN ALEUTIANS.

.MODEL DISCUSSION...
GOOD AGREEMENT AMONG THE MODELS IN THE SHORT TERM HOWEVER AGREEMENT
BREAKS DOWN BY 12Z SUNDAY. THE 12Z RUNS OF THE GFS AND THE UKMET ARE
MORE AGRESSIVE IN DEVELOPING AND ROTATING A SURFACE LOW INTO THE GULF
SUNDAY NIGHT WHILE THE NAM AND THE ECMWF FAVOR A MUCH SLOWER AND
WEAKER LOW. GIVEN THE STRENGTH OF THE JET CURRENTLY MOVING INTO AND
AROUND THE BASE OF THE UPPER LOW...THE DEVELOPMENT OF A STRONGER LOW
SEEMS MORE REASONABLE. AFTER 84 HOURS THE GENERAL PICTURE AMONG THE
MODELS REMAINS SIMILAR WITH THE LONGWAVE TROUGH GRADUALLY
RETROGRADING WEST ACROSS THE BERING SEA AND A STRONGER LOW DROPPING
INTO THE WESTERN BERING MONDAY EVENING. THERE IS PRETTY STRONG
DISAGREEMENT BETWEEN THE GFS AND THE ECMWF ON THIS FEATURE...HOWEVER
GIVEN THE SURPRINGLY GOOD AGREEMENT AMONG THE GFS ENSEMBLE MEMBERS
AND THE RESEMBLANCE OF THE GFS SOLUTION TO THE PREVIOUS ECMWF
RUN...MORE CONFIDENCE IS PLACED IN THE GFS SOLUTION.

.SHORT TERM FORECAST...MUCH OF THE SAME TODAY AS THE UPPER LOW
REMAINS ENTRENCHED AND THE ONSHORE FLOW CONTINUES ACROSS THE NORTHERN
GULF AND KODIAK ISLAND. SHOWER ACTIVITY ACROSS INLAND PORTIONS OF
SOUTHCENTRAL WILL BE LIMITED THIS AFTERNOON AS A WEAK SURFACE HIGH
MOVES ALONG THE COAST AND OVER SOUTHCENTRAL. THE EASTERN ALEUTIANS
AND AKPEN SHOULD CONTINUE TO SEE SHOWERY WEATHER IN NORTHERLY FLOW.
THE ARRIVAL OF THE UPPER LOW DROPPING SOUTH ACROSS THE BERING SEA
SHOULD PROVIDE SOME ENHANCEMENT TO PRECIPITATION LATE TONIGHT AND
INTO TOMORROW FOR THOSE AREAS. CYCLONIC FLOW ALONG WITH RELATIVELY
WEAK SOUTHEASTERLY LOW LEVEL FLOW SHOULD ALLOW FOR SHOWERS TO DEVELOP
ACROSS THE KUSKOKWIM VALLEY THIS AFTERNOON. ISOLATED THUNDERSTORMS
MAY BE POSSIBLE ACROSS THE MIDDLE KUSKOKWIM VALLEY AND ALONG THE
KUSKOKWIM MOUNTAINS IN AN AREA OF ENHANCED SURFACE CONVERGENCE
BETWEEN THE THERMAL LOW IN THE INTERIOR AND SURFACE RIDGING SOUTH OF
THE ALASKA RANGE. CLODUY BUT DRY SKIES ARE EXPECTED ACROSS THE
WESTERN ALEUTIANS UNDER THE SURFACE RIDGE.

LOOK FOR MORE RAIN ALONG THE NORTHERN GULF COAST SATURDAY AS A
SHORTWAVE ROTATES ONSHORE. AFTERNOON AND EVENING SHOWER ACTIVITY
INLAND SHOULD BE MORE WIDESPREAD...PARTICULARLY ACROSS THE COPPER AND
SUSITNA RIVER VALLEYS AS THE THERMAL LOW BECOMES BETTER ESTABLISHED
AND THE AFOREMENTIONED SHORTWAVE MOVES ONSHORE. PRECIPITATION ACROSS
THE AKPEN AND EASTERN ALEUTIANS SHOULD TAPER OFF BY SATURDAY NIGHT AS
THE UPPER LOW OUT THERE CONTINUES SOUTHEAST AND OUT OF THE PICTURE
AND WEAK SOUTHERLY FLOW TAKES OVER.

THE GULF COAST SHOULD SEE A BRIEF RESPITE FROM THE RAINY WEATHER ON
SUNDAY IN THE WAKE OF THE SHORTWAVE AND THE SURFACE FLOW TURNS
NORTHERLY. RIDGING ALOFT SHOULD KEEP A CAP ON CONVECTION ACROSS THE
REST OF SOUTHCENTRAL. CONVECTION WILL CONTINUE TO BE A POSSIBILITY
SUNDAY AFTERNOON ACROSS THE KUSKOKWIM VALLEY CLOSER TO THE THERMAL
LOW. A POWERFUL SHORTWAVE PROGGED TO DROP INTO THE WESTERN BERING SEA
SHOULD BRING RAIN TO THE WESTERN ALEUTIANS BY SUNDAY EVENING WHILE
ANOTHER WEAKER LOW SHOULD SKIRT SOUTH OF THE ALEUTIANS ON THE NORTH
SIDE OF THE NORTH PACIFIC JET...WITH SOME PRECIP OCCURRING ALONG THE
PERIPHERY OF THIS SYSTEM IN THE CENTRAL ALEUTIANS.

.LONG TERM FORECAST...AS DISCUSSED EARLIER...THE LONG TERM FORECAST
CALLS FOR THE GRADUAL RETROGRADING OF THE LONGWAVE TROUGH TO THE WEST
AND THE REESTABLISHMENT OF THE MAIN UPPER LOW COMPLEX TO THE BERING
SEA WITH A SECONDARY UPPER LOW SOUTH OF THE GULF OF ALASKA BY
MIDWEEK. THIS SIGNIFIES A STORMIER PATTERN FOR THE ALEUTIANS THAT
WILL BRING WETTER WEATHER PARTICULARLY INTO THE WESTERN AND CENTRAL
ALEUTIANS. MEANWHILE...SOUTHCENTRAL SHOULD SEE THE BEGINNINGS OF A
DRIER PATTERN AS THE LONGWAVE RIDGE BEGINS TO ENCROACH ON THE AREA BY
WEDNESDAY.

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

WOOD JUN 07