Heavy Snow in Alaska, May 27, 2009

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
424 AM AKDT WED MAY 27 2009

.DISCUSSION...
ALOFT...A STRONG UPPER TROUGH WILL REMAIN ALONG THE WEST COAST
THROUGH FRIDAY. THE UPPER ENERGY HAS NOW SPLIT WITH THE OTHER PIECE
OF THE TROUGH RACING OFF TOWARD THE WESTERN CANADIAN ARCHIPELAGO.
THIS HAS SQUASHED THE RIDGE THAT HELD FIRM ACROSS NORTHEAST AK AND
THE EASTERN BEAUFORT SEA. THE RIDGE WILL REMAIN TENACIOUS
THOU...AND ALTHOUGH IT GETS BEAT DOWN IT DOES ITS BEST TO HOLD ON
ALONG THE ALCAN BORDER MOST OF THE WEEK.

SURFACE...A RIDGE OF HIGH PRESSURE NEAR VICTORIA ISLAND WILL REMAIN
IN PLACE TROUGH FRIDAY. A SURFACE RIDGE WILL GRADUALLY BUILD BACK
INTO THE WESTERN CHUKCHI SEA IN THE WAKE OF THE STRONG LOW AND ITS
ASSOCIATED SURFACE TROUGH THAT HAS BROUGHT A STRONG FRONT ACROSS THE
ARCTIC COAST THAT SNAKES BACK DOWN INTO THE Y-K DELTA. THE LOW THAT
HAS BEEN SITTING AND SPINNING IN THE GULF OF AK WILL CONTINUE TO
MEANDER AROUND.

INTERIOR...TODAY SHOULD BE THE LAST DAY IN AN ACTIVE WEEK OF
CONVECTION ACROSS THE INTERIOR. THE THERMAL TROUGH LIFTS NORTH TODAY
AHEAD OF A STRONG COLD FRONT THAT PUSHES INTO THE CENTRAL INTERIOR
TODAY.  THE THERMAL TROUGH SHOULD BE ORIENTED FROM THE FORTYMILE
COUNTRY TO THE YUKON FLATS EAST OF FORT YUKON BY THIS AFTERNOON...AND
THIS AREA WILL HAVE THE BEST CHANCE OF THUNDERSTORMS LATER TODAY
INTO THIS EVENING. MUCH COOLER ACROSS THE WESTERN INTERIOR TODAY
WITH SHOWERS AND EVEN SOME AREAS OF STATIFORM RAIN. THE FRONT
CONTINUE TO PUSH EAST TONIGHT WITH SHOWERS DEVELOPING ACROSS THE
CENTRAL INTERIOR. THURSDAY WILL BE A MUCH COOLER DAY ACROSS THE
CENTRAL AND EASTERN INTERIOR WITH ISOLATED TO SCATTERED SHOWERS.
SOUTHERLY FLOW INCREASES TONIGHT AND THURSDAY WITH SOME GUSTY
SOUTH WIND IN THE PASSES OF THE AK RANGE THAT AT SOME POINT COULD
COME CLOSE TO ADVISORY LEVELS.

NORTH SLOPE...MUCH COLDER WEATHER FOR THE NEXT FEW DAYS. OVERRUNNING
SNOW EXPECTED IN THE PARTS OF THE BROOKS RANGE TO THE ARCTIC COAST...
AND THE AREA AROUND ATIGUN PASS WILL LIKELY PICK UP SIGNIFICANT
SNOWFALL TODAY AND TONIGHT. SOME ACCUMULATING SNOW ALSO LIKELY ALONG
PARTS OF THE CENTRAL BEAUFORT SEA COAST TONIGHT. THE WINTER STORM
WARNING FOR THE AREA AROUND THE PIPELINE LOOKS GOOD. THE DEEPER
MOISTURE LIFTS NORTH OF THE AREA ON THURSDAY WITH THE SNOW TAPERING
OFF TO SHOWERS.

WEST COAST...THE DEEP UPPER TROUGH WILL REMAIN ALONG THE WEST
COAST THROUGH THE END OF THE WEEK. ISOLATED RAIN AND SNOW SHOWERS
ARE EXPECTED THE NEXT FEW DAYS WITH BELOW AVERAGE
TEMPERATURES...BUT PRECIPITATION LOOKS SPOTTY AND AMOUNTS
LIGHT.

MID RANGE GUIDANCE COMING INTO AGREEMENT. LOW ALOFT CENTERED NEAR
KOTZEBUE SAT AFTERNOON WITH TROF ALOFT ROTATING THRU THE INTERIOR.
THIS MARKS THE LEADING EDGE OF SGFNT RIDGE BUILDING INTO THE GULF OF
ALASKA. BY MON AFTERNOON MOST GUIDANCE HAS 575+ HIGH NEAR OR A BIT
SOUTH OF CORDOVA...WITH MODERATE BUT LARGELY ANTI-CYCLONIC FLOW OVER
THE CWA. SOME DIFFERENCES THEREAFTER BUT SOME CONSENSUS ON BUILDING
THE HIGH INTO MAINLAND ALASKA FOR EARLY NEXT WEEK. THE MAIN ISSUES
HERE FOR SENSIBLE WEATHER WILL BE HOW MUCH PRECIP MAKES IT UP THE
WEST COAST. EAST OF 155W LOOKS QUITE LIKELY TO BE DRY AND WARM. HPC
GUIDANCE FOLLOWS THIS TREND AND SO WE PRETTY MUCH WENT WITH HPC FOR
THE MID RANGE.

&&

.FIRE WEATHER...
THERE WERE 757 CLOUD TO GROUND LIGHTNING STRIKES ACROSS THE STATE
YESTERDAY...WITH THE MAJORITY OF THEM TO THE SOUTH OF THE AK
RANGE. BEST CHANCE OF CLOUD TO GROUND LIGHTNING STRIKES TODAY WILL
BE ACROSS ZONE 224 AND ZONE 220 FROM FORT YUKON EAST. THE LOWEST
RHS TODAY WILL BE IN THIS AREA...WITH RHS MUCH HIGHER THAN
RECENT DAYS ACROSS THE REMAINDER OF THE INTERIOR. NO FIRE WEATHER
CONCERNS EXPECTED THURSDAY AND FRIDAY WITH COOLER TEMPS...A FEW
SHOWERS...AND HIGHER RHS.

&&

.HYDROLOGY...
THE LAST OF THE FLOOD WARNINGS FOR THE LOWER YUKON WERE PUT TO
REST YESTERDAY AS THE BREAKUP FLOOD THREAT HAS ENDED...AND THE
YUKON IS WITHIN BANKFULL AT ALL OF THE LOWER YUKON VILLAGES.
HOWEVER...HIGH WATER LEVELS WILL LIKELY CONTINUE FOR MANY DAYS DUE
TO THE EXTENSIVE OVERBANK FLOODING.

A FLOOD ADVISORY REMAINS IN EFFECT FOR THE COLVILLE RIVER AT
COLVILLE UNTIL 6 PM AKDT TODAY. THE WATER LEVELS HAVE DROPPED ABOUT
1/2 FOOT IN THE LAST DAY...BUT ICE JAMMING IS STILL POSSIBLE. COLDER
TEMPS THE NEXT FEW DAYS WILL SLOW/STOP THE SNOW MELT.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FOR AKZ206.
&&

CB/RT MAY 09