Small Craft Advisory 739, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
300 PM AKDT THU SEP 25 2008

.ANALYSIS AND UPPER LEVELS...
A VERTICALLY STACKED LOW IS CENTERED 250 MILES SOUTHEAST OF KODIAK
ISLAND WHILE A SIGNIFICANT SHORTWAVE NEAR THE KUSKOKWIM DELTA IS
BEING DRAGGED SOUTHWARD BY THE POLAR JET. AN UPPER TROUGH EXTENDS
FROM SOUTHWEST ALASKA TOWARD THE NORTHERN YUKON VALLEY. A LARGE
AMPLITUDE RIDGE OF HIGH PRESSURE ANCHORED OVER NORTHEASTERN SIBERIA
PERSISTS OVER THE CENTRAL BERING SEA. FURTHER WEST...ANOTHER
VERTICALLY STACKED LOW REMAINS NEARLY STATIONARY NEAR THE SOUTHERN
TIP OF THE KAMCHATKA PENINSULA.

.MODEL DISCUSSION...
RUN TO RUN CONSISTENCY BEYOND 48 HOURS IS VERY POOR WITH ALL MODELS.
NAM AND GFS HANDLE THE LOW IN THE SOUTHERN GULF DIFFERENTLY. PREFER
THE 12Z GFS SOLUTION BUT WILL ONLY BE MAKING CHANGES TO THE FORECAST
IN THE FIRST 48 HOURS GIVEN THE UNCERTAINTY. THE PREVIOUS FORECAST
WAS BASED OFF OF YESTERDAYS 12Z GFS WHICH IS STILL IN RELATIVE
AGREEMENT WITH THE GFS ENSEMBLE MEAN...ALTHOUGH HIGH STANDARD
DEVIATION AMONG THE MANY MEMBERS OF THE GFS ENSEMBLE IS HINTING AT
THE HIGH DEGREE OF UNCERTAINTY IN THE FORECAST EARLY NEXT WEEK.

.SHORT TERM FORECAST...

SOUTHCENTRAL...
A SIMILAR WEATHER PICTURE AS YESTERDAY AS SHOWERS HAVE TAPERED OFF
OVER THE MUCH OF THE INTERIOR ALTHOUGH WIDESPREAD SHOWER ACTIVITY
PERSISTS OVER THE NORTHERN GULF AND WESTERN KENAI PENINSULA. CLEARING
OVER THE INTERIOR LEAD TO SOME AREAS OF DENSE FOG THIS MORNING. EARLY
THIS AFTERNOON...LOW STRATUS STILL HANGING TOUGH ALONG KNIK ARM AND
THE LOWER SUSITNA VALLEY. SHOWERS ARE AGAIN DEVELOPING NEAR TURNAGAIN
ARM AND DRIFTING NORTHWEST TOWARD THE ANCHORAGE BOWL. ANTICIPATE A
REPEAT OF YESTERDAYS WEATHER WITH NUMEROUS SHOWERS DEVELOPING THIS
EVENING...TAPERING OFF OVERNIGHT WITH AREAS OF FOG DEVELOPING TOWARD
SUNRISE. SOME SUNNY BREAKS ARE POSSIBLE FRIDAY ALTHOUGH NOT
ANTICIPATING ANY SIGNIFICANT CLEARING UNTIL SATURDAY.

DURING THE WEEKEND THE FORECAST BECOMES A LITTLE MORE
CHALLENGING...COMPLICATED BY THE LACK OF CONSISTENCY IN THE MODELS.
WHAT IS EVIDENT AT THIS TIME IS A COLD CORE LOW WILL DROP SOUTH OUT
OF THE ARCTIC AIDED BY A N-S ORIENTED 90 KT POLAR JET. THE FIRST
SHORTWAVE THAT WILL BRING THE CLEARING TO THE AREA WILL ARRIVE LATE
FRIDAY NIGHT AND SATURDAY MORNING. THE SECOND FRONTAL PASSAGE WILL BE
LATER IN THE WEEKEND AND WILL HAVE COOLER AIR ASSOCIATED WITH IT.
WHAT IS UNCLEAR IS HOW MUCH COOL AIR WILL SPILL OVER THE ALASKA RANGE
AND REACH SOUTHCENTRAL ALASKA. THE LATEST GFS IS TAKING THE BULK OF
THE UPPER LEVEL SUPPORT AND QUICKLY EJECTING IT EASTWARD INTO
NORTHWEST CANADA. THIS IS FAIRLY DIFFERENT FROM PREVIOUS MODEL RUNS
THAT WERE PLACING THE COLD CORE UPPER LOW OVER SOUTHCENTRAL ALASKA
THROUGH EARLY NEXT WEEK. WHATEVER COOL AIR DOES MANAGE TO SPILL OVER
THE ALASKA RANGE WILL BE SHORT LIVED WITH THE LACK OF UPPER SUPPORT
IF THE 12Z GFS PANS OUT. THE MOST LIKELY SCENARIO IS A FEW COOLER
THAN AVERAGE NIGHTS WITH SEASONAL AND PLEASANT DAYS. AT THIS POINT
WITH THE DRY AIR MOVING OUT IN ADVANCE OF THE COLD AIR...DO NOT
ANTICIPATE ANY SNOW FOR SOUTHCENTRAL ALASKA.

SOUTHWEST ALASKA...
WEATHER IS IMPROVING OVER THE SOUTHWEST INTERIOR TODAY. VISIBLE
SATELLITE SHOWING WIDESPREAD CLEARING OVER MUCH OF THE UPPER
KUSKOKWIM VALLEY. SOME RESIDUAL MOISTURE TRAPPED IN LOW LYING AREAS
IS RESULTING IN STRATUS AND PATCHY FOG THROUGH THE EARLY AFTERNOON
HOURS. THE INITIAL PUSH OF DRY AIR WILL REACH THE SOUTHWEST INTERIOR
FRIDAY BRINGING A MUCH NEEDED BREAK FROM THE GLOOMY WEATHER.
NORTHERLY WINDS AND COOL TEMPERATURES WILL PREVAIL THROUGH THE
WEEKEND.

BERING SEA/ALEUTIANS...A WEATHER FRONT IS WEAKENING THIS EVENING AS
IT CROSSES THE CENTRAL ALEUTIANS. AHEAD OF THE FRONT...SOUTHEASTERLY
SMALL CRAFT WINDS AND WIDESPREAD RAIN WILL BE TAPERING OFF THROUGH
TOMORROW AS THE FRONT ENCOUNTERS A LARGE AREA OF HIGH PRESSURE OVER
THE CENTRAL AND EASTERN BERING SEA. ANOTHER MUCH STRONGER FRONT WILL
MOVE ACROSS THE WESTERN ALEUTIANS LATE FRIDAY. MAX GALE FORCE WINDS
ARE LIKELY ALONG AND AHEAD OF THE FRONT. THE EC AND GFS ARE HINTING
AT STORM FORCE WINDS WITH THE SUPPORT OF A STRONG 180 KT SUBTROPICAL
JET FEEDING THE SYSTEM.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 176.
FIRE WEATHER...NONE.

AB SEP 08