Small Craft Advisory 798, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
150 PM ADT THU SEP 27 2007

.ANALYSIS AND UPPER LEVELS...THE WEATHER MAKER TODAY IS A VERTICALLY
STACKED LOW OVER THE WESTERN BERING SEA (NEAR 55N 178E). THE FRONTAL
SYSTEM HAS PROGRESSED QUICKLY OFF TO THE EAST THIS MORNING THANKS
TO A 160 KT UPPER JET ON THE FRONT SIDE OF THE TROUGH. THE JET CORE
EXTENDS OVER THE CENTRAL AND EASTERN ALEUTIANS INTO THE EASTERN
BERING SEA. THE OCCLUDED FRONT IS WRAPPED NEARLY ALL THE WAY AROUND
THE LOW CENTER...EXTENDING WEST ALONG THE WESTERN ALEUTIANS THEN
NORTH AROUND THE BACK SIDE OF THE LOW...EASTWARD ACROSS THE NORTHERN
BERING TO A TRIPLE POINT EAST OF THE PRIBILOF ISLANDS. THE COLD FRONT
THEN EXTENDS BACK SOUTH AND WEST WITH CURRENT POSITION AT 20Z AROUND
DUTCH HARBOR. SURFACE OBS AND QUIKSCAT WINDS SHOW SOLID GALES ALONG
THE FRONT (GUSTS TO 46KT AT COLD BAY). THE STRONGEST WINDS ARE BEING
OBSERVED SOUTH OF THE LOW CENTER ALONG THE OCCLUSION. THERE IS A
TIGHT PRESSURE GRADIENT BETWEEN LOW AND A SUB-TROPICAL HIGH OVER THE
NORTH PACIFIC AND THERE IS DECENT COLD ADVECTION ALOFT. SO FAR THE
PEAK OBSERVED WIND IS 52KT AT ADAK. KING SALMON RADAR IS SHOWING
RAIN AHEAD OF THE FRONT JUST STARTING TO MOVE INTO THE PICTURE...SO
CONDITIONS WILL HEAD DOWN HILL QUICKLY ALONG THE SOUTHWEST COAST
THIS AFTERNOON. A RIDGE OF HIGH PRESSURE IS BUILDING AHEAD OF THE
SYSTEM FROM SOUTHWEST ALASKA INTO SOUTHCENTRAL AND THE WESTERN GULF.
THERE IS ONE LAST SHORT-WAVE ALOFT ALONG THE TOP OF THE RIDGE THAT
HAS BEEN MOVING THROUGH THE KUSKOKWIM VALLEY AND WESTERN SUSITNA
THIS MORNING. THE KUSKOKWIM IS SOCKED IN WITH LOTS OF LOW CLOUDS
AND SHOWERS. THERE ARE SOME LOW LEVEL CLOUS LEFT OVER FROM THE
SUSITNA VALLEY SOUTH TO NORTHERN COOK INLET. OTHERWISE...THE REST
OF SOUTHCENTRAL HAS CLEARED OUT.

.MODEL DISCUSSION...EXCELLENT MODEL PERFORMANCE CONTINUES WITH GOOD
CONSISTENCY AMONG THE DIFFERENT MODEL SOLUTIONS AND IN RUN-TO-RUN
COMPARISON.

.SHORT TERM FORECAST...

SOUTHCENTRAL...RAIN WILL SPREAD TO KODIAK ISLAND THIS EVENING AND
THE REST OF SOUTHCENTRAL LATE TONIGHT AND FRIDAY MORNING. STRONG
EASTERLY FLOW ALONG THE FRONT WILL PRODUCE DOWNSLOPE DRYING ON
THE LEE SIDE OF THE KENAI AND CHUGACH MOUNTAINS. MODELS INDICATE SOME
FAIRLY STRONG SHORT-WAVES ROTATING OVERHEAD OF THESE AREAS...SO
THINK THERE WILL AT LEAST BE A PERIOD OF VERY LIGHT RAIN OR
SPRINKLES. AS THE FRONT BECOMES PARALLEL TO THE NORTH GULF COAST
EXPECT A BARRIER JET TO FORM. AT THIS POINT IT LOOKS LIKE MAX GALES
WILL SUFFICE ALONG THE COAST WITH GALES INTO PRINCE WILLIAM SOUND.
STRONG WINDS WILL ALSO MAKE INTO CORDOVA...PASSAGE CANAL...AND WEST
THROUGH PORTAGE VALLEY. PREFER THE GFS AND UKMET MODEL SOLUTION WHICH
DEVELOPS A WEAK TRIPLE POINT LOW JUST OFF THE SOUTHERN TIP OF THE
KENAI PENINSULA FRIDAY MORNING. THIS WILL BEND ISOBARS ENOUGH TO
SHIFT FLOW TO THE NORTH FROM THE SUSITNA VALLEY DOWN TO COOK INLET.
WITH GUSTY WINDS OUT OF THE MATANUSKA VALLEY. THIS MAY ALSO HAVE THE
EFFECT OF DIMINISHING WESTERN TURNAGAIN ARM WINDS WHILE WINDS IN THE
EASTERN SIDE OF THE ARM AND PORTAGE VALLEY REMAIN STRONG DUE TO THE
INFLUENCE OF THE FRONT ALONG THE NORTH GULF COAST. THE BERING LOW
WILL QUICKLY TRACK INTO THE GULF FRIDAY EVENING...SO THIS WILL NOT
BE A LONG DURATION WIND EVENT. FLOW WILL QUICKLY BACK TO THE NORTH
ACROSS SOUTHCENTRAL FRIDAY NIGHT RESULTING IN A DRYING TREND
INLAND...WHICH WILL THEN SPREAD TO THE COAST SATURDAY. AS VERY
PROGRESSIVE FLOW CONTINUES THE NEXT SYSTEM WILL BE ON THE DOORSTEP
WITH MORE CLOUDS AND SHOWERS ON TAP FOR SUNDAY.

SOUTHWEST ALASKA...RAIN WILL OVERSPREAD MOST OF SOUTHWEST ALASKA
TONIGHT ALONG WITH GUSTY WINDS ALONG THE ALEUTIAN AND ALASKA RANGES.
A DRYING TREND WILL BEGIN FRIDAY NIGHT AS THE LOW MOVES INTO THE
GULF AND THEN THE NEXT FRONTAL SYSTEM WILL MOVE ONSHORE BY
SUNDAY...BRINGING ANOTHER ROUND OF RAIN FOR SOUTHWEST ALASKA.

BERING SEA/ALEUTIANS/AKPEN...MAX GALE WESTERLIES WILL PERSIST SOUTH
OF THE LOW CENTER ALONG THE ALEUTIANS AND AKPEN TONIGHT AND FRIDAY.
MODELS HAVE ALSO TRENDED TOWARD STRONGER COLD ADVECTION ON THE BACK
SIDE OF THE LOW AS SHORT-WAVES DROP DOWN THE WEST SIDE OF THE TROUGH.
THERE WILL ALSO BE A 170 KT JET ALOFT. COMBINATION OF STRONG WINDS
ALOFT...COLD ADVECTION...AND SUBSIDENCE BEHIND SHORT-WAVES WILL
PRODUCE SOME VERY GUSTY WINDS OF AT LEAST 40 TO 45 KT FROM THE
PRIBILOFS FRIDAY MORNING TO EASTERN ALEUTIANS AND AKPEN FRIDAY NIGHT.
WILL LIKELY SEE STORM FORCE GUSTS THROUGH CHANNELED AREAS OF THE
EASTERN ALEUTIANS AND AKPEN. A SHORT-WAVE RIDGE OF HIGHER AMPLITUDE
THAN THE PAST COUPLE WILL BUILD OVER THE CENTRAL BERING FRIDAY AND
FORCE THE NEXT SYSTEM TO TRACK FARTHER NORTH. THE FRONTAL SYSTEM WILL
TRACK ACROSS THE BERING SEA AND ALEUTIANS FRIDAY NIGHT AND SATURDAY
AND A STRONG JET WILL FLATTEN PUT THE RIDGE BY SATURDAY NIGHT
ALLOWING THE LOW TO TRACK EASTWARD ACROSS THE NORTHERN BERING SEA
THROUGH SUNDAY. ONCE AGAIN THE STRONGEST WINDS WILL SET UP SOUTH OF
THE LOW CENTER WITH 4O TO 45 KT WESTERLIES LIKELY.

.LONG TERM FORECAST...THE MODELS ARE TRENDING TOWARD A COLDER
SOLUTION FOR MAINLAND ALASKA IN THE EXTENDED. THE BERING SYSTEM WILL
TRANSLATE EASTWARD THE BEGINNING OF NEXT WEEK WHILE THE NEXT SYSTEM
DROPS OUT OF RUSSIA AND BUILDS A HIGH AMPLITUDE RIDGE OVER THE
WESTERN BERING. A SHORT-WAVE ALSO DROPS DOWN FROM TH POLE INTO
NORTHERN ALASKA MID WEEK AND INTO SOUTHERN ALASKA FOR LATE IN THE
WEEK. THIS WILL ALLOW FOR THE TRANSPORT OF ARCTIC AIR SOUTHWARD
ACROSS THE EASTERN BERING AND ALASKA AS WE HEAD THROUGH THE WEEK.
IF THIS SOLUTION VERIFIES THIS WILL BE THE STRONGEST PUSH OF COLD
AIR SO FAR THIS SEASON AND LEAD TO THE POTENTIAL FIRST SNOWFALL
ACROSS THE REGION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 120 125 130 132 150 155 160 165 170 171 172 175 176
               179 185
FIRE WEATHER...NONE.

SEB SEP 07