Heavy Rain in Alaska, June 13 to 14, 2012

NORTHERN ALASKA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FAIRBANKS AK
253 PM AKDT TUE JUN 12 2012

...UPDATED TO ADD PARAGRAPHS ON WEST COAST TEMPERATURES AND THE
MEDIUM RANGE FORECASTS...

.DISCUSSION...
A FAIRLY STRONG LOW ALOFT HAS MOVED SLOWLY OUT OF THE NORTHERN
YUKON TERRITORY AND IS EXPECTED TO BE CENTERED JUST WEST OF FORT
YUKON LATE THIS AFTERNOON. THE GFS COMPUTER WEATHER FORECAST MODEL
HAS THIS LOW OVER MCKINLEY PARK WEDNESDAY AFTERNOON AND WEAKENING
OVER THE KENAI PENINSULA THURSDAY MORNING. THE NAM MODEL FORECASTS
THE LOW TO REACH PRINCE WILLIAM SOUND THURSDAY EVENING.
OVERALL..THE GFS MODEL FORECASTS A PATH OF THE LOW CENTER FARTHER
WEST AND SLOWER THAN THE NAM. THUSFAR...THE LOW ALOFT HAS INDEED
BEEN SLOW MOVING...SO THE GFS IS THE PREFERRED MODEL TODAY.

REGARDING THE MOVEMENT OF THE LOW ALOFT...TODAYS GEOSTATIONARY
VISIBLE SATELLITE IMAGERY HAS CLEARLY SHOWN THE LOW AND ITS SLOW
MOVEMENT TO THE SOUTHWEST. THIS SYSTEM HAS HELD CLOUDS OVER THE
EASTERN BROOKS RANGE AND SOME OF THE YUKON FLATS.

THE LOW ALOFT IS BRINGING PRETTY COLD AIR OVER THE INTERIOR. ON
WEDNESDAY AFTERNOON...THE TEMPERATURE DIFFERENCE BETWEEN 850
MILLIBARS AND 500 MILLIBARS / ROUGHLY FROM 5000 FEET TO 18000 FEET
/ IS FORECAST TO BE AS MUCH AS 32 CELSIUS DEGREES. THIS WILL
PRODUCE A TRULY UNSTABLE AIR MASS AND THUNDERSTORMS APPEAR TO BE A
SURE BET FOR THE EASTERN INTERIOR...PARTICULARLY THE PORTION
WITHIN 150 MILES OF THE ALASKA RANGE.

THE LOW ALOFT BROUGHT A COLD FRONT DOWN OVER THE NORTHERN INTERIOR
THIS MORNING. THE FRONT IS NOW MOVING OVER THE SOUTHERN INTERIOR
AND THE ALASKA RANGE. CLEARING HAS BEEN TAKING PLACE OVER THE
INTERIOR.

LOW CLOUDS AND FOG REMAIN OVER THE ARCTIC SLOPE EAST OF
WAINWRIGHT. A WELL DEFINED SURFACE TROUGH OF LOW PRESSURE
EXTENDING FROM HUSLIA TO POINT HOPE HAS REINFORCED RAPID MOVEMENT
OF A BAND OF LOW CLOUDS FROM NEAR BARROW AROUND THE EAST CHUKCHI
SEA AND ON DOWN OVER THE WESTERN SEWARD PENINSULA.

CIRCULATION AROUND THIS TROUGH IS STRONG FOR THIS TIME OF YEAR.
THE UPPER NOATAK WEATHER STATION...AT AN ELEVATION CLOSE TO 1000
FEET...IS REPORTING NORTHEAST WINDS GUSTING TO 38 MILES PER HOUR.
ON THE OTHER SIDE OF THE TROUGH...NOME IS REPORTING WEST WINDS
GUSTING TO 28 KNOTS / 32 MILES PER HOUR /. UNSURPRISINGLY...THE
NOME WEB CAMERA SHOWS FINE WHITECAPS OUT IN NORTON SOUND.

TEMPERATURES ON THE CHUKCHI AND BERING SEA COASTS OF NORTHERN
ALASKA REMAIN MOSTLY IN THE 30S...COOLER THAN NORMAL FOR JUNE.
GRADUAL MODERATION IS EXPECTED STARTING TOMORROW AS THE STRENGTH
OF ONSHORE FLOW DIMINISHES.

VISIBLE SATELLITE IMAGERY SLOWS LARGE AREAS OF OPEN WATER OFFSHORE
IN THE SOUTHEAST BEAUFORT SEA AND IN THE CHUKCHI SEA FROM JUST
WEST OF BARROW ALMOST AS FAR AS POINT HOPE. THE WESTWARD MOVEMENT
OF THE ICE OFFSHORE FROM KIVALINA TO POINT HOPE IS READILY
DISCERNIBLE ON THE VISIBLE IMAGERY. IN JUST OVER 6 HOURS IT HAS
MOVED ABOUT 5 MILES.

THE MEDIUM RANGE FORECAST MODELS PROJECT HIGH PRESSURE ALOFT AND
CONSIDERABLY WEAKER CIRCULATION TO SPREAD OVER NORTHWEST ALASKA ON
WEDNESDAY AND OVER THE REMAINDER OF THE REALM ON THURSDAY...WHERE
IT IS EXPECTED TO REMAIN FOR THE REST OF THIS WEEK. STARTING ON
SATURDAY...INCREASING WESTERLIES ARE EXPECTED TO DEVELOP...AND TO
CONTINUE SUNDAY AND MONDAY. THIS FLOW PATTERN WILL GRADUALLY
WEAKEN OVER THE REST OF THE WEEK.

TODAYS MODEL RUNS FORECAST STRONGER WESTERLIES OVER THE ARCTIC
NEXT WEEK THAN YESTERDAYS MODEL RUNS. IF TODAYS RUNS HOLD
REASONABLY TRUE...CHANGEABLE WEATHER CAN BE EXPECTED IN ALASKAS
ARCTIC NEXT WEEK.

HIGH PRESSURE AND WEAK CIRCULATION ALOFT ARE EXPECTED SOUTH OF THE
BROOKS RANGE NEXT WEEK. THIS CAN BE EXPECTED TO BRING WARMER
WEATHER AND TYPICAL AFTERNOON AND EVENING SHOWERS AND
THUNDERSHOWERS.

COASTAL HAZARD POTENTIAL DAYS 3 AND 4...NONE

&&

.FIRE WEATHER...
ASIDE FROM SOME WET THUNDERSTORMS IN THE SOUTHERN INTERIOR THERE
IS LITTLE OF SIGNIFICANCE. MINIMUM RELATIVE HUMIDITY THIS
AFTERNOON ON THE YUKON FLATS AND IN THE NOATAK VALLEY WILL BE
CLOSE TO 30 PERCENT. BRISK NORTHEAST WINDS...TO AROUND 20 MILES
PER HOUR...ARE BLOWING IN EXPOSED AREAS OF THE NORTHERN INTERIOR.

&&

.HYDROLOGY...
SOME RISES ARE UNDERWAY ON THE UPPER YUKON RIVER...THE RESULT OF
THE HEAVY RAINS IN THE SOUTHERN YUKON TERRITORY OVER THE PAST
WEEKEND. THE TANANA RIVER NEAR FAIRBANKS IS EXPECTED TO CREST
ABOUT 2 FEET BELOW BANK FULL LATE THURSDAY. OTHERWISE...NEARLY ALL
NORTHERN ALASKA RIVERS ARE AT SLOWLY FALLING STAGES...AND WELL
BELOW BANK FULL STAGES.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY FOR PKZ200.
&&

JUN 12