Hail in Alaska, May 23, 2010

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
356 PM AKDT SUN MAY 23 2010

.DISCUSSION...
THE NAM AND GFS MODELS OFFER SIMILAR FORECASTS THROUGH TUESDAY.
THE TROUGH ALOFT FROM THE CHUKCHI SEA TO SOUTHWEST ALASKA IS
FORECAST TO REMAIN IN PLACE THROUGH MONDAY...AND THEN TO DIVIDE
INTO TWO SECTIONS...ONE WITHDRAWING INTO THE CHUKCHI SEA AND THE
OTHER MOVING DOWN TO THE WESTERN GULF OF ALASKA.

A LARGE HIGH ALOFT NOW OVER THE ALASKA YUKON BORDER IS FORECAST TO
BUILD WESTWARD AND TO STRENGTHEN AS IT COVERS THE ENTIRE ALASKA
MAINLAND BY EARLY TUESDAY. THIS SYSTEM IS EXPECTED TO SHIFT
EASTWARD STARTING IN MID WEEK. THIS WILL LEAVE THE WAY OPEN FOR
MODERATE SOUTHERLY FLOW ALOFT LATE TUESDAY THROUGH WEDNESDAY. THIS
IS A LONG AWAITED CHANGE ON THE ALASKAN BERING SEA COAST...WHICH
HAS BEEN UNDER A REMARKABLY LONG LIVED NORTHERLY FLOW OF COLD AIR.

THIS INCOMING SOUTHERLY FLOW SHOULD BRING THE FIRST REAL INFLUX TO
THE NORTHERN ALASKA BERING SEA COAST IN SOME TIME. THE MODEL
OUTPUT STATISTICS FORECASTS DO NOT REFLECT THIS IMPORTANT CHANGE.

THIS READJUSTMENT IS NOT EXPECTED TO LAST VERY LONG...AS THE
NORTHWEST CANADA HIGH ALOFT RETURNS TO THE ALASKA MAINLAND ON
THURSDAY...WHERE IT CAN REASONABLY BE EXPECTED TO PERSIST INTO THE
UPCOMING WEEKEND OR LONGER.

THE AIRMASS OVER THE ALASKAN INTERIOR IS UNSTABLE. THIS HAS BEEN
EVIDENCED BY WELL NEARLY 200 STRIKES RECORDED BY THE ALASKA
LIGHTNING DETECTION SYSTEM OVER THE NORTHEASTERN INTERIOR SO FAR
TODAY. THE FORECAST CIRCULATION OVER THE INTERIOR IS FORECAST TO
CHANGE VERY MUCH ALL WEEK...SO ACTIVE CONVECTION AND SOME LATE
AFTERNOON AND EVENING THUNDERSTORMS ARE EXPECTED OVER THE INTERIOR
FOR THE DURATION OF THIS WEEK. THIS IS AN EARLY START TO THE
INTERIOR THUNDERSTORM SEASON...THOUGH IT HAS PRECEDENT IN SOME
RECENT YEARS. WEATHER BALLOONS HAVE MEASURED ABOUT ONE HALF OF AN
INCH OF PRECIPITABLE WATER OVER THE INTERIOR DURING THE PAST
COUPLE OF DAYS. THIS IS AMPLE FUEL FOR CONTINUED THUNDERSTORMS.
DURING THE PAST TWO HOURS...THE MOST ACTIVE THUNDERSTORM AREA HAS
BEEN OVER THE UPLANDS BETWEEN BIG DELTA AND CENTRAL.

RETURNING TO THE WEST COAST...THE SOUTHERLY INFLUX OF WARMER AIR
AT MID WEEK WILL NOT BE STRONG ENOUGH...OR OF ENOUGH DURATION TO
CAUSE A MAJOR RETREAT OF THE ICE PACK IN THE BERING SEA...BUT IT
WILL START THE PROCESS. AS OF FRIDAY...THE EDGE OF THE ICE PACK
IN THE ALASKAN SECTOR OF THE BERING SEA EXTENDED CLEAR DOWN TO THE
PRIBILOF ISLAND WATERS. THIS IS EXTRAORDINARY. THERE WILL AT LAST
BE SOME MODERATION TO THE EXTENDED PERIOD OF BELOW NORMAL
TEMPERATURES IN THE WEST. MOST OF THIS CHANGE WILL OCCUR SOUTH OF
BERING STRAIT. UP IN THE CHUKCHI SEA THERE WILL HARDLY BE A TOUCH
OF IT.

&&

.FIRE WEATHER...
TODAY IS THE MOST ACTIVE LIGHTNING DAY OF THE 2010 SEASON SO FAR.
MINIMUM RELATIVE HUMIDITY IN MUCH OF THE EASTERN AND NORTHERN
INTERIOR CONTINUES TO DROP BELOW 30 PERCENT...AND AFTERNOON WINDS
ARE LOCALLY GUSTY.

&&

.HYDROLOGY...
ICE IS MOVING DOWNSTREAM IN NORTHERN ALASKA RIVERS SOUTH OF THE
BROOKS RANGE UNEVENTFULLY FOLLOWING LAST WEEKS ICE JAMS. RUNOFF
HAS CONTINUED TO BE LOW FOR THE SEASON SO FAR...ESPECIALLY IN THE
EAST. RAINFALL HAS BEEN SCANT...SO THE MAJOR PORTION OF RIVER
FLOW CONTINUES TO BE SNOW AND GLACIER MELT IN THE MOUNTAINS.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FOR AKZ218-AKZ220.

RED FLAG WARNING FOR AKZ220.

BRISK WIND ADVISORY FOR PKZ240-PKZ245.
&&

TF MAY 10