Small Craft Advisory 748, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTH CENTRAL AND SOUTHWEST ALASKA
300 PM AKDT MON SEP 29 2008

.ANALYSIS AND UPPER LEVELS...
A NEGATIVELY TILTED TROUGH WITH AXIS EXTENDING FROM SOUTHWEST
MAINLAND ALASKA TO AN UPPER LOW LOCATED NEAR 37N 140W. A BROAD AREA
OF LOW PRESSURE PERSISTS OVER THE BERING SEA WITH THE ANCHOR LOW
LOCATED NEAR THE KAMCHATKA PENINSULA. THE MOST SIGNIFICANT SURFACE
FEATURE IS A DEVELOPING LOW IN THE SOUTHERN GULF UNDER THE SHARP
UPPER LEVEL TROF...ASSISTED BY A S TO N FLOWING 110 KT JET.

.MODEL DISCUSSION...
SIMILAR TO THE PREVIOUS FORECAST DISCUSSION...THERE IS MUCH DEBATE
AND UNCERTAINTY ABOUT THE DEVELOPING LOW IN THE SOUTHERN GULF. WHAT
IS CERTAIN IS THAT THE MODELS DO NOT HAVE A GOOD HANDLE ON THIS
STORM. WHILE THE GFS AND NAM HAVE TRENDED STRONGER AND FURTHER
WEST...THE ECMWF AND UKMET CONTINUE WITH A MORE WESTERN TRACK TOWARD
PRINCE WILLIAM SOUND. THERE IS A LACK OF SURFACE OBSERVATIONS
AVAILABLE WHERE THE LOW IS DEVELOPING SO WE ARE HAVING TO TRY AND
DECIPHER THE SATELLITE IMAGERY TO DETERMINE WHICH MODELS ARE
INITIALIZING BEST. WE ARE NOT THRILLED WITH ANY OF OUR CHOICES BUT IT
STILL SEEMS THAT THE EC AND UKMET ARE PICKING UP ON THE SLIGHTLY MORE
AMPLIFIED RIDGE ALONG THE NORTHEASTERN GULF. THIS LENDS TO A DEEPER
SURFACE LOW WHICH WOULD RETROGRADE WESTWARD AS IT REACHES MAXIMUM
INTENSITY...ANOTHER SIGN THAT THE EC/UKMET SOLUTION IS THE CORRECT
CHOICE. STILL NOT COMPLETELY CONVINCED IN THIS SCENARIO...WILL GO
WITH THE 12Z UKMET WHICH IS A WATERED DOWN VERSION OF THE EC. THIS
WILL BRING AT LEAST SMALL CRAFT WINDS TO THE COASTAL WATERS AND RAIN
AND SNOW TO THE PRINCE WILLIAM SOUND AND TO MOST OF THE COPPER RIVER
BASIN. WE MADE VERY LITTLE CHANGES TO THE FORECAST BEYOND THE FIRST
48 HOURS. AT THE POINT...MODELS ARE TOO INCONSISTENT TO TRY AND ADD
ANY VALUE BEYOND THOSE FIRST COUPLE OF DAYS.

.SHORT TERM FORECAST...
...SOUTHCENTRAL...
THE CHALLENGE WITH THIS FORECAST BECOMES HOW FAR WEST THE
PRECIPITATION SPREADS AND IN WHAT FORM IT FALLS OVER THE COPPER RIVER
BASIN WHERE TEMPERATURES ARE THE COLDEST. WARM AIR ADVECTING
NORTHWARD ON THE EASTERN SIDE OF THE LOW WILL HELP KEEP THE
PRECIPITATION LIQUID. THE EXCEPTION WILL BE ON THE NORTH AND WESTERN
SIDE OF THE COPPER RIVER BASIN WHERE A MIXTURE OF RAIN AND SNOW IS
MORE LIKELY. IF THE POSITION AND STRENGTH OF THE LOW PANS OUT...THE
OTHER CHALLENGE WILL BE THE POSSIBILITY FOR RAIN IN ANCHORAGE. AT
THIS POINT...WILL ONLY MENTION A CHANCE OF RAIN FOR TUESDAY AND LET
THE EVENING SHIFT TAKE A LOOK AT THE 00Z MODELS TO SEE IF WE NEED TO
INCREASE TO A LIKELY WORDING.

...SOUTHWEST ALASKA...
A WEAK UPPER LOW WILL REMAIN CENTERED NEAR THE LOWER KUSKOKWIM RIVER
THROUGH MID WEEK. THE UPPER LEVEL CYCLONIC CIRCULATION COUPLED WITH A
MOIST BOUNDARY LAYER WILL CONTINUE THE MOSTLY CLOUDY CONDITIONS WITH
SCATTERED SHOWERS. ONSHORE FLOW WILL ALSO HELP AREAS OF FOG DEVELOP
IN THE LATE NIGHT AND EARLY MORNING HOURS ALONG THE COAST. THE
POTENTIAL FOR SNOW WILL BE LIMITED TO THE UPPER KUSKOKWIM BUT NOT
EXPECTING ANY SIGNIFICANT ACCUMULATIONS THROUGH MID WEEK. GRANTED
CONFIDENCE BEYOND THE FIRST 48 HOURS IS LOW...THE GFS HAS HINTED AT
SOME MORE COLD AIR SPILLING SOUTHWARD OVER SOUTHWEST MAINLAND AND THE
BERING SEA. IF THIS SCENARIO PROVES CORRECT...THIS WOULD BRING SNOW
SHOWERS TO MOST OF OUR WESTERN DOMAIN BY THE END OF THE WEEK.

...BERING SEA/ALEUTIANS...
RELATIVELY BENIGN WEATHER PATTERN CONTINUES WITH A THE BROAD AREA OF
LOW PRESSURE. WIDESPREAD STRATUS AND FOG ARE THE NORM FOR THIS TIME
OF YEAR ACROSS THE BERING SEA.

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

AB SEP 08