FXAK69 PAFG 081402
AFDAFG
NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
502 AM AKST TUE DEC 8 2009
.DISCUSSION...
THE NAM AND GFS MODEL FORECASTS ARE VERY SIMILAR THROUGH THURSDAY
MORNING. THE STRONG HIGH PRESSURE ALOFT OVER THE MAINLAND WILL
HOLD STEADY. THE OLD NORTH PACIFIC LOW IS NOW HEADED WEST TOWARD
KAMCHATKA AND WEAKENING AS IT GOES.
THE NEXT DEVELOPMENT IS A 984 MB LOW WHICH AT 9 PM AKST MONDAY WAS
CENTERED NEAR 43 DEGREES NORTH 153 DEGREES WEST. ON THE
GEOSTATIONARY SATELLITE IMAGERY THIS SYSTEM HAS GAINED STRENGTH
AND HAS A SOLID CLOUD SHIELD AHEAD OF IT. THE GFS MODEL FORECASTS
THIS LOW TO MOVE NORTHWEST AND TO CROSS THE ALEUTIANS NEAR ADAK
WEDNESDAY EVENING. AS THIS OCCURS...EASTERLY WINDS ON THE BERING
SEA COAST WILL INCREASE SOME FOR 12 TO 18 HOURS BEFORE AGAIN
DIMINISHING. THIS IS REFLECTED IN THIS MORNINGS MARINE FORECASTS.
ANOTHER WEAKER LOW MAY FOLLOW...CROSSING THE ALEUTIANS NEAR
AMCHITKA ON FRIDAY BEFORE TURNING LEFT AND HEADING TOWARD
KAMCHATKA. THE MAKINGS OF THIS LOW LOOK GOOD. A LONG CYCLONIC
OUTFLOW OF COLD OVER THE SEA OF OKHOTSK HAS BEEN
ESTABLISHED...WITH A BROAD 1500 MILE FETCH DOWN TO ABOUT 40
DEGREES NORTH 165 DEGREES EAST. WHILE THE LOW AND FRONT OUT AHEAD
OF THIS FLOW ARE NOT YET WELL ORGANIZED THEY LOOK LIKE THEY SOON
WILL BE. THIS MEANS THAT ANOTHER INCREASE IN WIND OVER THE WATERS
WEST OF SAINT LAWRENCE ISLAND CAN BE EXPECTED AT THE END OF THIS
WEEK. SINCE THE TRACK OF THIS END OF THE WEEK LOW WILL BE SO FAR
WEST THE INCREASE IN WINDS OVER THE SAINT LAWRENCE ISLAND WATERS
WILL NOT BE MUCH...30 KNOTS WOULD BE A REASONABLE GUESS.
HIGH PRESSURE AT THE SURFACE WILL REMAIN OVER THE ALASKA MAINLAND
THIS WEEK...ASSURING CLEAR SKIES /EXCEPT WHERE SOME AREAS OF THIN
FOG FORM IN VALLEYS/ AND NO PRECIPITATION UNTIL SOMETIME IN THE
DISTANT FUTURE. ON THE NORTHERN EDGE OF THIS AREA OF HIGH
PRESSURE...WEAK AND COLD GRAVITY DRIVEN FLOW DOWN TO THE COAST
WILL HELP MAINTAIN THE WEAK SURFACE TROUGH OF LOW PRESSURE WHICH
HAS BEEN JUST OFFSHORE FROM BARROW TO MACKENZIE BAY FOR OVER A DAY
NOW.
POLAR ORBITING SATELLITE IMAGERY SHOWS LINGERING DECKS OF LOW
STRATUS CLOUDS AND SOME FOG OVER THE NORTH SLOPE...ESPECIALLY NEAR
THE COAST. THE OFFSHORE WINDS UP THERE ARE NOT AT ALL STRONG
ENOUGH TO SHOO THE GLOOM AWAY FROM THE LAND. THIS LOOKS LIKE IT
WILL BE THE CASE FOR THE REST OF THE WEEK AND PERHAPS
BEYOND...EVEN WHEN THE SURFACE WINDS BECOME LIGHT WESTERLY.
THERE IS ALSO SOME LOW CLOUD OVER THE YUKON DELTA AND THE LOWER
YUKON VALLEY. KALTAG WENT FROM CLEAR AT 2 AM AKST TO 400 FEET
OVERCAST AT 4 AM. THE SCENE AT FORT YUKON WAS SIMILAR.
HOWEVER...SKIES OVER THE VAST MAJORITY OF THE REALM ARE CLEAR.
THE VERY WARM AIR ALOFT...ALONG WITH CLEARING SKIES HAS LEFT VERY
STRONG TEMPERATURE INVERSIONS OVER MOST INTERIOR VALLEYS. THIS IS
REFLECTED IN THE GREAT RANGES OF TEMPERATURES IN THIS MORNINGS
ZONE FORECASTS...FOR AT LEAST THE SECOND RUNNING.
AS HAD BEEN EXPECTED...THE LONG LIVED SOUTHEAST GALES OVER THE
BERING SEA PUSHED BACK THE EDGE OF THE PACK ICE...BUT NOT ENOUGH
TO CREATE MUCH OPEN WATER IN PKZ210. ONE DETAIL ON THE NORTH
BERING SEA WIND FORECASTS THIS MORNING IS WORTH MENTION. SAVOONGA
WINDS ARE SOUTH SOUTHEAST GUSTING TO 49 KNOTS. THIS IS NOT
REPRESENTATIVE FOR THE AREA. WITH WINDS FROM SOUTH SOUTHEAST TO
SOUTH SOUTHWEST SAVOONGA HAS SUPER GRADIENT DOWN SLOPE FLOW THAT
EXCEEDS THE STRENGTH OF WIND AT GAMBELL.
IN THE MEDIUM RANGE...UNCERTAINTY REMAINS TO THE SAME LARGE EXTENT
AS FOR MUCH OR ALL OF THE PAST WEEK. THE TWO MODELS DIVERGE
STARTING ON SATURDAY OF THIS WEEK. THIS TIME...THE GFS FORECASTS AN
ARCTIC OUTBREAK OVER THE EASTERN MAINLAND OF ALASKA THAN DOES THE
EUROPEAN MODEL. HOWEVER...STARTING NEXT TUESDAY...THE EUROPEAN
MODEL SURPASSES THE GFS MODELS FORECAST STRENGTH OF ARCTIC
OUTBREAK. GIVEN THE VERY WANDERING PATTERN OF FORECASTS BEYOND
DAY FIVE THERE IS LITTLE CONFIDENCE IN THE FORECAST FARTHER OUT IN
TIME.
COASTAL HAZARD POTENTIAL DAYS 3 AND 4...NONE
&&
.AFG WATCHES/WARNINGS/ADVISORIES...
GALE WARNING FOR PKZ210.
BRISK WIND ADVISORY FOR PKZ220-PKZ225.
&&
$$
TF DEC 09
