Heavy Rain in Alaska, August 26 to 27, 2015

NORTHERN ALASKA FORECAST DISCUSSION...CORRECTED...RESENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
346 PM AKDT TUE AUG 25 2015

ALOFT...
THERE IS A DEEP LONGWAVE TROUGH STRETCHING FROM WRANGEL ISLAND
ACROSS THE WESTER BERING SEA TO THE NW PACIFIC AND A RIDGE OVER
THE WESTERN GULF OF ALASKA OVER MAINLAND AK. THE RESULT OF THIS
TROUGH IS A VERY WET SW FLOW PATTERN FEEDING HIGH MOISTURE AIR
NORTHEAST ACROSS THE BERING SEA AND INTO A SERIES OF STRONG SHORT
WAVES AND THEIR ASSOCIATED SURFACE LOWS MOVING EAST ACROSS AK THE
NEXT SEVERAL DAYS. BY THU SEVERAL OF THE SHORT WAVES WILL MERGE TO
FORM A LONG WAVE TROUGH OVER MAINLAND AK WHICH WILL PERSIST INTO
THE WEEKEND. NORTHERN ALASKA WILL SEE SIGNIFICANT RAIN THROUGH
WED AND THEN MUCH COOLER TEMPERATURES THU INTO THE WEEKEND.

WE WILL SEE STRONG COLD AIR ADVECTION THAT WILL DROP THE 850
TEMPERATURES BELOW 0C IN NW ALASKA TOMORROW AND ACROSS THE BROOKS
RANGE AND ARCTIC AND WEST COASTS TOMORROW NIGHT. 850 TEMPERATURES
WILL BE BELOW 0C ACROSS THE ENTIRE FORECAST AREA BY THURSDAY
AFTERNOON.

SURFACE... A 990 MB LOW 300 NM WEST OF BARROW WILL MOVE TO 300 NM
NORTHWEST OF BARROW AS A 986 MB LOW BY 4PM WED...AND TO 400 NM
NORTH OF BARROW AS A 990 MB LOW BY 4PM THU. GALE FORCE EAST WINDS
NE OF THIS LOW. WILL SEE SW 20-30KT WINDS SOUTH OF THE LOW. WILL
SEE NW GALES SW OF THE LOW WED THROUGH THU.

A STATIONARY FRONT WILL EXTEND FROM BARROW TO NEAR KOTZEBUE TO
THE YUKON DELTA WITH THE WARM FRONT FROM DEADHORSE TO FAIRBANKS.
BY 4 AM WEDNESDAY THE STATIONARY FRONT BECOMES A COLD FRONT
STRETCHING FROM DEADHORSE TO TO YUKON DELTA. BY 4AM THURSDAY THE
COLD FRONT WILL STRETCH FROM OLD CROW TO FAIRBANKS TO DENALI WITH
THE ARCTIC FRONT FROM BARTER ISLAND TO AMBLER TO GAMBELL. BY 4PM
THU THE COLD FRONT WILL LIE FROM DAWSON TO TOK WITH THE ARCTIC
FRONT FROM OLD CROW TO FAIRBANKS TO DENALI. EXPECT HEAVY RAIN
BETWEEN THE WARM FRONT AND COLD/STATIONARY FRONT WITH 1-3 INCHES
OVER THE WEST COAST AND WESTERN INTERIOR THROUGH WED. THE HEAVIEST
RAIN WILL BE IN SW FACING SLOPES OF ZONES 208 218 AND 212. WILL
SEE 1-2 INCHES OF RAIN IN THE CENTRAL AND EASTERN INTERIOR TONIGHT
THROUGH THU. THERE WILL BE SW WINDS 25-35KT ALONG THE
STATIONARY/COLD FRONT.

WILL SEE RAIN CHANGE TO SNOW ALONG THE ARCTIC COLD FRONT FROM THE
BROOKS RANGE NORTH. COULD SEE 3-6 INCHES OF SNOW FROM THE BROOKS
RANGE NORTH WED NIGHT AND THU. COLD AIR WILL PUSH INTO THE
INTERIOR THURSDAY NIGHT INTO FRIDAY...CAUSING SNOW LEVELS TO
GRADUALLY DECREASE. SNOW LEVELS WILL DROP TO PASS LEVEL IN DENALI
NATIONAL PARK...AS WELL AS ELSEWHERE IN THE EASTERN ALASKA RANGE.
ACCUMULATING SNOWFALL IS POSSIBLE THURSDAY NIGHT INTO FRIDAY
MORNING IN THE ALASKA RANGE. IT IS ALSO POSSIBLE THAT THERE MAY BE
A MIX OF RAIN AND SNOW THURSDAY NIGHT INTO FRIDAY ACROSS THE
FOURTYMILE COUNTRY AS WELL AS IN THE HILLS NORTH OF
FAIRBANKS...ALTHOUGH SNOW ACCUMULATIONS ARE NOT EXPECTED IN THESE
AREAS.

DISCUSSION...
THE 12Z MODELS INITIALIZE WELL AND SHOW SIMILAR SOLUTIONS IN THE
HEIGHT AND PRESSURE FIELDS THROUGH FRIDAY AFTERNOON. THE 12Z GFS
AND ECMWF SEEM TO BE IN GOOD AGREEMENT IN TERMS OF THE AMOUNT AND
PLACEMENT OF PRECIPITATION THROUGH THURSDAY. THE NAM AGREES WITH
THE GFS AND ECMWF IN TERMS OF PLACEMENT OF PRECIPITATION THROUGH
THURSDAY...HOWEVER IT SHOWS LOWER QPF VALUES. WE HAVE OPTED TO
MORE HEAVILY WEIGHT THE GFS FOR THE POP AND QPF FIELDS.

COASTAL HAZARD POTENTIAL...
HIGH SURF CONTINUES FOR ZONES 211...212...213 AND 214. ALTHOUGH
THERE MAY BE BRIEF BREAK IN HIGH SURF CONDITIONS ON WEDNESDAY
MORNING IN ZONES 211...212 AND 214 IT APPEARS THAT THE SURF WILL
RAMP UP AGAIN WEDNESDAY EVENING...THUS I HAVE OPTED TO EXTEND
HIGH SURF ADVISORIES FOR THROUGH THURSDAY AFTERNOON FOR THESE
ZONES. WE ALSO OPTED TO EXTEND THE HIGH SURF ADVISORY FOR ZONE 207
AS HIGH SURF WAS EVIDENT ON THE KIVALINA WEBCAM AS OF 2 THIS
AFTERNOON. I ALSO ISSUED NEW HIGH SURF ADVISORIES FOR ZONES 201
AND 202 WITH THIS PACKAGE. WIND ON THE NORTH SLOPE WEST OF POINT
BARROW WILL BE FROM A FAVORABLE DIRECTION OVER A LONG FETCH
THROUGH FRIDAY. CURRENTLY...THE ADVISORIES EXTEND UNTIL THURSDAY
AFTERNOON...HOWEVER FUTURE SHIFTS WILL NEED TO EVALUATE WHETHER OR
NOT THE ADVISORIES ON THE WESTERN ARCTIC COAST WILL NEED TO BE
EXTENDED.

FIRE WEATHER...
NO ISSUES AT THIS TIME DUE TO VERY MOIST CONDITIONS.

HYDROLOGY...
A WIDESPREAD HEAVY PRECIPITATION EVENT ONGOING THIS AFTERNOON.
RAINFALL WILL CONTINUE TO SPREAD TO THE EAST ACROSS THE FORECAST
AREA. CURRENTLY HAVE FLOOD WATCHES OUT FOR ZONES
210...211...212...THESE FLOOD WATCHES HAVE EXTENDED UNTIL
WEDNESDAY NIGHT. FLOOD WATCHES WERE CANCELLED FOR ZONES 208 AND
217...FLOOD ADVISORIES WERE ISSUED FOR THESE ZONES.

SIGNIFICANT WATER LEVEL RISES ARE EXPECTED ON STREAMS AND RIVERS
ACROSS THE INTERIOR THIS WEEK. RAPID RISES ARE POSSIBLE BEGINNING
WEDNESDAY ON SMALLER STREAMS IN THE HIGHER TERRAIN...AND SOME
RIVERS MAY REACH BANKFULL LEVELS ON THURSDAY AND FRIDAY. THIS
INCLUDES THE CHENA...CHATANIKA...BEAVER CREEK...AND SALCHA RIVER
BASINS. THERE IS STILL SOME UNCERTAINTY IN THE LOCATION OF THE
HEAVIER RAINFALL AND WATER MAY GO OVERBANK IN SOME LOW LYING
LOCATIONS. GRAVEL BARS WILL BE INUNDATED AND INCREASED DEBRIS
WILL BE MOVING DOWN SOME RIVERS. LARGER RIVERS SUCH AS THE TANANA
AND YUKON WILL RISE THROUGH THE WEEKEND BUT WILL REMAIN BELOW
BANKFULL.
&&

.AFG WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FOR AKZ201-AKZ202-AKZ207-AKZ211-AKZ212-AKZ213-
AKZ214.

FLOOD WATCH FOR AKZ210-AKZ211-AKZ212.

SMALL CRAFT ADVISORY FOR PKZ200-PKZ215-PKZ220-PKZ225-PKZ230-
PKZ235-PKZ240.

GALE WARNING FOR PKZ200-PKZ210.
&&

AUG 15