Small Craft Advisory 45, NWS Fairbanks, AK

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
242 PM AKDT MON JUN 22 2015

.DISCUSSION...

MAIN FORECAST HIGHLIGHTS INCLUDE THE POTENTIAL FOR
THUNDERSTORMS AND CONTINUED WARMTH OVER THE INTERIOR...

22/12Z DETERMINISTIC MODEL SUITE CONTINUES GOOD MODEL CONTINUITY
DURING THE SHORT TERM WITH GOOD AGREEMENT REGARDING THE OVERALL
PATTERN THROUGH 00Z THURSDAY. BEYOND 00Z THURSDAY...SOME DISPARITY
BETWEEN THE ECWMF AND GFS REGARDING FEATURES...MORE NOTABLY WITH
THE HANDLING OF THE HIGH ARCTIC LOW THAT IS PROGGED TO DROP SOUTH
OVER THE NORTHWEST THURSDAY. HOWEVER...ALL MODELS ARE ADVERTISING
A PATTERN CHANGE LATE THIS WEEK...WHICH WILL USHER IN A COOLER
AIRMASS OVER THE WEST COAST AND NORTH SLOPE...BUT NOT QUIET
REACHING THE INTERIOR AS THE GFS AND ECWMF HAVE BACKED OFF ON THE
AMOUNT OF COOLING.

EASTERN AND CENTRAL INTERIOR...A VERY WARM...SMOKEY...STAGNANT
AIRMASS CURRENTLY OVER MUCH OF THE INTERIOR TODAY WILL PERSIST
THROUGH WEDNESDAY AS AN UPPER LEVEL RIDGE REMAINS OVERHEAD.
ISOLATED TO SCATTERED THUNDERSTORMS ARE ONCE AGAIN IN THE FORECAST
FOR MOST OF THE SOUTHERN INTERIOR. THE 22/12Z GFS AND NAME ARE PAINTING
LI VALUES OF -1C TO -3C WITH CAPE VALUES UPWARDS OF 700 J/KG OVER
THE SOUTH AND EAST OF FAIRBANKS....THOUGH MODEL PERFORMANCE
REGARDING THUNDERSTORMS HAS NOT BEEN THE BEST OF LATE. VISIBLE
SATELLITE IMAGERY COUPLED WITH LIGHTNING DATA OVER THE LAST FEW
HOURS HAVE SHOWN AN INCREASE IN CONVECTIVE ACTIVITY OVER THE
FORTYMILE COUNTRY WITH AROUND 20 TO 30 LIGHTNING STRIKES ALREADY
BEING REPORTED AS OF 1 PM AKDT. EXPECTING THAT CONVECTIVE ACTIVITY
WILL PICKUP SIGNIFICANTLY OVER THE NEXT FEW HOURS AND CONTINUE
THROUGH THE EVENING. ANOTHER ROUND OF THUNDERSTORMS AGAIN TOMORROW
AND WILL BE CONFINED TO ALONG THE ALASKA RANGE AND UPPER AND
MIDDLE TANANA VALLEY.

AREAS OF SMOKE REDUCING VISIBILITY TO AS LOW AS 1 MILE AT TIMES
HAS BEEN AN ISSUE FOR AREAS SOUTH OF THE YUKON RIVER TODAY AND
WILL LIKELY CONTINUE THROUGH MIDWEEK. VISIBILITY WILL LIKELY
BECOME WORSE AS MIXING HEIGHTS LOWER OVERNIGHT. SMOKE HAS ALSO
KEPT TEMPERATURES COOLER THAN WHAT GUIDANCE SUGGESTS YESTERDAY AS
WELL AS TODAY...AND HAVE MADE AN ADJUSTMENT TO INTERIOR
TEMPERATURES...KEEPING THEM COOLER BY A FEW DEGREES COMPARED TO
MODEL GUIDANCE.

A COOLING TREND IS EXPECTED TO START MID TO LATE THIS WEEK...AS
MODELS ARE ADVERTISING H850 TEMPERATURES TO COOL BY AT LEAST 5C
TO 10C BY THE WEEKEND...WITH SURFACE TEMPERATURES COOLING INTO THE
60S AND 70S.

NORTH SLOPE...A BROAD AREA OF FOG AND STRATUS OVER THE INTACT ICE
PACK...ACCORDING TO SUCCESSIVE VIIRS IMAGES...HAS BEEN MARCHING
SOUTH TOWARDS THE ARCTIC COAST THIS AFTERNOON. BARROW HAS RECENTLY
REPORTED DENSE FOG AND LOW CEILINGS IN STRATUS OVER THE LAST HOUR.
EXPECTING THAT THIS AREA WILL SPREAD SOUTH AND OVER ZONES 203 AND
204 LATER THIS EVENING AND OVERNIGHT AS A RIDGE OF HIGH PRESSURE
SHIFTS EAST ALONG THE ARCTIC COAST.

ONE MORE VERY WARM DAY IS EXPECTED BEFORE TEMPERATURES TAKE A
DOWNWARD TURN. TEMPERATURES ARE EXPECTED TO CLIMB BACK INTO THE
70S AND LOWER 80S OVER THE INLAND PORTION OF THE NORTH SLOPE WITH
UPPER 50S AND LOWER 60S ALONG THE COAST FOR TUESDAY. A
SURFACE/UPPER LEVEL LOW ORIGINATING OVER THE RUSSIAN ARCTIC WILL
MOVE EAST TOWARDS WRANGELL ISLAND AND THEN DROP SOUTHEAST TOWARDS
THE ARCTIC COAST BY THURSDAY. AN ASSOCIATED COLD FRONT WILL MOVE
IN TANDEM WITH THE LOW AND WILL USHER IN A MUCH COOLER AIRMASS TO
THE NORTH SLOPE...WEST COAST AND THE NORTHERN INTERIOR.
PRECIPITATION ASSOCIATED WITH THIS LOW WILL BE MAINLY RAIN AT
FIRST...BUT THE RAIN/SNOW LINE WILL SLOWLY CREEP
SOUTH...APPROACHING ZONE 201 BY THURSDAY AFTERNOON.

WEST COAST/WESTERN INTERIOR...DENSE FOG HAS MOVED IN OVER WESTERN
SAINT LAWRENCE ISLAND...THUS HAVE PUT OUT A DENSE FOG HEADLINE FOR
ZONE 213. THIS AREA OF FOG WILL MOVE NORTH OVER THE BERING STRAIT
AND TOWARDS THE CHUKCHI SEA COAST AFTER MIDNIGHT.

THE MODELS HAVE BACKED OFF CONSIDERABLY REGARDING THE COOLING THAT
WAS PREVIOUSLY ADVERTISED FOR MOST OF THE WEST COAST. PREVIOUS
RUNS HAVE HAD THE 0C ISOTHERM MOVING SOUTH ALONG THE
COAST...REACHING THE YUKON DELTA BY THE WEEKEND. THOUGH THE RECENT
GFS/ECWMF ARE CONFINING THE SOUTHWARD EXTENT OF THE 0C ISOTHERM TO
NORTH OF THE SEWARD PENINSULA. HOWEVER...THERE WILL BE A COOLING
NONETHELESS ACROSS WESTERN ALASKA OF AROUND 5C AT H850 BUT NOT AS
DRAMATIC AS PREVIOUSLY ADVERTISED. BY FRIDAY...TEMPERATURES WILL
BE IN THE 50S AND 60S.

COASTAL HAZARD POTENTIAL DAYS 3 AND 4...NONE

&&

.FIRE WEATHER...

SLIGHTLY DRIER TO THE NORTH OF THE SURFACE TROUGH TUESDAY...BUT
SHOULD NOT TRIGGER ANY RED FLAGS. THUNDERSTORMS WILL BE A MUCH
BIGGER ISSUE WITH ALL THE CURRENT FIRES AND A LOT OF FIRE FIGHTERS
IN THE FIELD. COOLER TEMPERATURES ON THE HORIZON FOR THE
WEEKEND...BUT WE HAVE TO GET THROUGH THE NEXT COUPLE WARM DAYS
FIRST.

&&

.HYDROLOGY...

FREEZING LEVELS NEAR 10000 FT SHOULD KEEP GLACIAL RIVERS RISING TO
CLOSER TO NORMAL WHILE MOST CLEAR RIVERS REMAIN VERY LOW.
BRIEF HEAVY DOWNPOURS WILL OCCUR IN THUNDERSTORMS BUT AREAL
EXTENT OF EACH SHOWER IS SMALL ENOUGH THAT NO PROBLEMS ARE EXPECTED.
COULD SEE RISE OF SMALL STREAMS IN THE ALASKA RANGE MON AND TUE IN
THESE THUNDERSTORMS.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY FOR PKZ225-PKZ230.
&&

LTH JUN 15