AFDAFG
NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS
AK
600 AM AKST SUN NOV 6 2011
.DISCUSSION...
THERE ARE TWO LOW PRESSURE SYSTEMS
IN THE FORECASTS THIS MORNING.
LOW NUMBER 1...
THIS SYSTEM MOVED EASTWARD FROM THE
PRIBILOF ISLANDS ON SATURDAY
MORNING...AND REACHED KUSKOKWIM BAY
SUNDAY EVENING. THE GFS AND
EUROPEAN COMPUTER WEATHER FORECAST
MODELS PRODUCED AN EXCELLENT
FORECAST FOR THIS SYSTEM...AND DID
SO CONSISTENTLY FROM ONE MODEL
RUN TO THE
NEXT OVER THE PAST 3 DAYS.
LOW NUMBER 1 BROUGHT WINTER STORM
CONDITIONS TO THE YUKON DELTA
ON SATURDAY...AND CONSIDERABLE SNOW
SHOWERS TO THE LOWER YUKON
VALLEY. THE REMAINING WEATHER WITH THIS LOW
CONSISTS OF SCATTERED
SNOW SHOWERS...SOME OF WHICH ARE
PRODUCING BRIEFLY NEAR BLIZZARD
CONDITIONS...OVER THE YUKON DELTA
AND PARTS OF THE LOWER YUKON
VALLEY. THE WINTER STORM WARNING FOR THE
YUKON DELTA AND THE
WINTER WEATHER ADVISORY FOR THE
LOWER YUKON VALLEY REMAIN IN
EFFECT THIS MORNING.
THE GFS MODEL FORECASTS THE PARENT
PORTION OF THIS LOW...NOW JUST
EAST OF KUSKOKWIM BAY...TO WEAKEN AS
IT CONTINUES TO MOVE INLAND
TODAY.
THE ACTIVE PORTION OF THIS SYSTEM IS
A BREAKOFF LOW WHICH IS NOW
OVER
PRINCE WILLIAM SOUND.
THE WEATHER FRONT AHEAD OF THE BREAKOFF
LOW IS GOING TO ELONGATE INTO THE
CENTRAL YUKON TERRITORY TONIGHT
AND
MONDAY.
THIS IS A GOOD PATTERN FOR SNOW IN THE FORTYMILE
COUNTRY
AND EASTERN ALASKA RANGE.
IT IS THE BASIS OF THE SNOWFALL
FORECAST
FOR THESE AREAS ON MONDAY.
IN ADDITION...THE LEADING END
OF THIS WEATHER FRONT IS EXPECTED TO
REACH THE EASTERN BROOKS
RANGE THIS EVENING. PART OF IT WILL
FORM A SMALL LOW PRESSURE
CENTER OFF DEMARCATION POINT...AND
THIS WILL BRING THE WINDS
ON THE COAST FROM DEMARCATION POINT
TO CAPE HALKETT AROUND TO
LIGHT WESTERLY TONIGHT.
THERE WAS BRISK SOUTH FLOW OVER THE
ALASKA RANGE FROM ISABELL
PASS OUT TO ILIAMNA LAST NIGHT. THE
WEATHER STATION AT ANTLER
CREEK...ON THE PARKS HIGHWAY NEAR
DENALI PARK...RECORDED SOUTH
WINDS TO 54 MPH LATE SATURDAY
EVENING. THE WINDS ARE NOW
DIMINISHING.
THE WIND FLOW ALOFT OVER THE
NORTHERN ALASKA MAINLAND IS ALSO
WEAKENING...AND WILL BE LIGHT BY
MONDAY MORNING. THE AIR MASS NOW
OVER THE INTERIOR CAME IN FROM THE
BERING SEA ON SATURDAY. COOLING
ALOFT ALONG WITH THESE LIGHTER WINDS
WILL PRODUCE SCATTERED SNOW
SHOWERS
OVER THE INTERIOR OVER THE NEXT TWO DAYS.
.........LOW
NUMBER 2............
THIS
WILL BE THE LAST AND STRONGEST IN A SERIES OF ACTIVE WEATHER
SYSTEMS WHICH FORMED IN THE NORTH PACIFIC.
THE GFS AND EUROPEAN
MODEL
FORECASTS HAVE BEEN COMING INTO STILL CLOSER AGREEMENT WITH
SUCCESSIVE
MODEL RUNS OVER THE PAST TWO DAYS.
LOW
NUMBER 2 IS A DEVELOPING STORM WHICH CAME INTO VIEW AS IT
MOVED OFF THE COAST OF JAPAN LATE SATURDAY
EVENING. IT IS
FORECAST
TO BE A 960 MILLIBAR LOW NEAR ATTU /AT THE WEST END OF
THE
ALEUTIAN ISLANDS/ ON TUESDAY MORNING...AND A 945 MILLIBAR LOW
NEAR BERING STRAIT ON WEDNESDAY MORNING.
THE
NORTHWEST PACIFIC SATELLITE IMAGERY OVERNIGHT HAS SHOWN THIS
SYSTEM
GATHERING STRENGTH AS WELL AS MOVING RAPIDLY EASTWARD...AT
A
SPEED AROUND 50 MPH. THIS IMAGERY...SURFACE WEATHER
ANALYSES...AND
THE GREAT CONSISTENCY OF THE COMPUTER WEATHER
FORECAST
MODELS...ARE THE CRUCIAL INGREDIENTS THAT SUPPORT THE
FORECAST
OF STORM FORCE WINDS AND THE POSSIBILITY OF MAJOR COASTAL
FLOODING ON THE NORTHWEST COAST TUESDAY AND
WEDNESDAY.
LOW
NUMBER 2 IS REMARKABLY SIMILAR TO THE STORM THAT CAUSED MAJOR
COASTAL
FLOODING ON THE NORTHWEST ALASKA COAST ON NOVEMBER 11 AND
12
IN 1974. THE ONLY DIFFERENCE OF ANY NOTE IS THAT THE 1974 STORM
CENTER
CROSSED THE ALEUTIANS NEAR THE INTERNATIONAL DATE LINE.
THIS
NOVEMBERS STORM IS DUE TO CROSS THE ALEUTIAN CHAIN AT ITS
WEST
END ON TUESDAY MORNING. THIS NOVEMBERS STORM IS FORECAST TO
REACH
BERING STRAIT WEDNESDAY MORNING. THE 1974 STORM ALSO ENDED
UP AT BERING STRAIT.
IN A FEW WORDS...THE ORIGINS AND PATHS OF
THESE
STORMS ARE SLIGHTLY DIFFERENT...BUT THEIR DESTINATIONS ARE
THE SAME.
THE
OCEAN TIDES ALONG THE NORTHWEST ALASKA COAST THIS WEEK ARE AT
AVERAGE LEVELS.
THE OCEAN TIDES AT THE TIME OF THE 1974 STORM WERE
AT
MOST A FOOT OR TWO ABOVE THIS YEARS. HENCE...THIS IS A
MINOR
FACTOR. IN THE 1974 STORM...THE
WIND DRIVEN RISE IN SEA LEVEL WAS
CLOSE TO 10 FEET.
IN
THE 1974 STORM THERE WAS CONSIDERABLE SEA ICE IN NORTON
SOUND. THE SOUTHEAST CHUKCHI
SEA...FROM BERING STRAIT UP TO
BARROW
INCLUDING KOTZEBUE SOUND...HAD EXTENSIVE ICE COVER DURING
THE 1974 STORM.
THIS YEAR THERE IS ONLY A SMALL AREA OF SHORE ICE
IN EASTERN NORTON SOUND.
ON THE CHUKCHI SEA COAST THERE IS ONLY A
NARROW
STRETCH OF ICE...LESS THAN 10 MILES WIDE...FROM BERING
STRAIT TO POINT HOPE.
KOTZEBUE SOUND IS 50 TO 70 PERCENT ICE
COVERED. ALL OF THIS MEANS IS
THAT THERE WILL BE VERY LITTLE SHORE
ICE TO PROVIDE SOME PROTECTION TO THE COAST.
THE
COASTAL FLOODING IN THE 1974 STORM BEGAN AT MID DAY IN NORTON
SOUND...AND
TOWARD EVENING IN KOTZEBUE SOUND. IF LOW NUMBER 2
FOLLOWS
THE SCRIPT OF THE FORECAST MODELS...THE COASTAL FLOODING
WITH
THIS YEARS STORM WOULD BEGIN IN NORTON SOUND ON TUESDAY
EVENING...AND
ALONG THE CHUKCHI SEA COAST FROM BERING STRAIT TO
POINT
HOPE ON TUESDAY NIGHT.
THE
LATEST GFS MODEL FORECASTS INDICATE A SHARP CHANGE IN THE
WIND
OVER NORTON SOUND ON WEDNESDAY MORNING...SHIFTING FROM
SOUTHEAST
TUESDAY NIGHT TO SOUTHWEST WEDNESDAY MORNING. IF THE
OUTCOME
ON WEDNESDAY FOLLOWS THIS FORECAST...THERE WOULD BE
ADDITIONAL
COASTAL FLOODING ON THE YUKON DELTA AND IN EASTERN
NORTON SOUND.
LOW
NUMBER 2 IS GOING TO BE A DANGEROUS STORM.
THE POLAR ORBITING SATELLITE IMAGERY
FROM 4 AM AKST THIS MORNING
SHOWS EXTENSIVE CLOUD COVER OVER THE INTERIOR. THIS IS ASSOCIATED
WITH THE
BREAKOFF LOW IN PRINCE WILLIAM SOUND. THERE ARE SPIRAL
CLUSTERS OF SNOW SHOWERS AROUND THE
WEAKENING PARENT LOW PRESSURE
SYSTEM
JUST EAST OF KUSKOKWIM BAY.
THE EASTERN BROOKS RANGE IS
MOSTLY CLEAR...AND SCATTERED CUMULUS
CLOUDS ARE SET IN BANDS IN
NORTHERLY
FLOW FROM POINT HOPE DOWN PAST DALL POINT.
COASTAL HAZARD POTENTIAL DAYS 3 AND
4 /TUESDAY NOVEMBER 8 AND
WEDNESDAY
NOVEMBER 9/...
STORM AND MAJOR COASTAL FLOODING
POSSIBLE FROM DALL POINT TO
POINT HOPE STARTING TUESDAY EVENING
ON THE YUKON DELTA UP TO
BERING STRAIT...AND FROM BERING
STRAIT UP TO POINT HOPE STARTING
TUESDAY
NIGHT...AND CONTINUING THROUGH WEDNESDAY.
&&
.AFG WATCHES/WARNINGS/ADVISORIES...
WINTER
STORM WARNING FOR AKZ214.
WINTER WEATHER ADVISORY FOR AKZ215.
HEAVY
FREEZING SPRAY WARNING FOR PKZ200-PKZ210-PKZ220-PKZ225.
SMALL CRAFT ADVISORY FOR PKZ200-PKZ210-PKZ220-PKZ225.
BRISK WIND ADVISORY FOR PKZ245.
&&
$$
TF
NOV 11