Flood in Alaska, April 28 to 29, 2003

NORTH ALASKA FORECAST DISCUSSION
600 AM ADT MON APR 28 2003

THE ETA AND AVIATION MODELS DIFFER IN 2 RESPECTS. FIRST...THE SHORT
WAVE ALOFT NOW OVER THE WEST COAST IS FORECAST MOVE MORE SLOWLY BY
THE ETA MODEL. DUE TO THE PERSISTENCE OF THE HIGH ALOFT OVER THE
YUKON AND WESTERN N.W.T. THE ETA LOOKS BETTER IN THIS REGARD.

SECOND...A SHORT WAVE ALOFT COMING IN FROM CHUKOTKA. THIS SYSTEM IS
A NEW ONE ON OUR FIGURATIVE RADAR SCREEN. THE AVIATION MODEL
FORECASTS IT TO MOVE FASTER TO THE EAST THAN THE ETA MODEL. DUE TO
THE SLOW PROGRESS OF SYSTEMS OVER THE CHUKCHI SEA IN RECENT DAYS,
THE AVIATION MODELS FORECAST AGAIN SEEMS TOO FAST, AND THE ETA
LOOKS BETTER FOR NOW. THIS WILL BE CAREFULLY WATCHED ON FUTURE MODEL
RUNS...BECAUSE IF THE AVIATION MODEL IS CLOSE TO REALITY, THEN SOME
COLD AIR IS COMING IN FROM THE NORTHWEST SOONER THAN HAS BEEN
EXPECTED.

ALOFT...THE SHORT WAVE NOW OVER THE WEST COAST WILL BE OVER THE
CENTRAL INTERIOR TONIGHT...AND INTO THE YUKON TUESDAY. THE INCOMING
SHORT WAVE FROM CHUKOTKA WILL EXTEND FROM OSTROV VRANGELYA TO THE
ANADYR GULF TONIGHT...AND WILL BE IN THE WESTERN BROOKS RANGE TUESDAY
NIGHT.

AT THE SURFACE...COLDER AIR COMING IN FROM THE WEST TODAY WILL FORM
A COLD FRONT OVER THE EAST INTERIOR THIS AFTERNOON. THE FRONT WILL
MOVE INTO THE YUKON TONIGHT AND TUESDAY. HIGH PRESSURE WILL BUILD
FRON BRISTOL BAY UP OVER THE NORTH HALF OF THE BERING SEA BY TUESDAY
AFTERNOON. WINDS IN THE MARINE AREAS WILL BE QUITE LIGHT.

IN THE ARCTIC...VERY LIGHT WEST WINDS HAVE NOT HAD THE STRENGTH TO
PUSH LOW CLOUDS AND FOG OFFSHORE FROM ZONES 202, 203 AND 204 (EAST
OF WAINWRIGHT.) THE MODEL OUTPUT STATISTICS INDICATE IMPROVEMENT IN
VISIBILITY AND CEILING LATER TODAY, BUT THE PHYSICS OF THIS LOOK
UNCERTAIN. THE PRESENT TAFS INDICATE MVFR WEATHER THIS AFTERNOON AND
EVENING...BUT THE CONFIDENCE FACTOR ON THESE IS WEAK.

TEMPERATURES WILL GET STEADILY COLDER OVER THE NEXT 2 DAYS. THE
INCOMING SHORT WAVE ALOFT FROM CHUKOTKA LOOKS LIKE IT WILL BE A
GOOD MECHANISM FOR SNOW IN THE WEST HALF OF THE AREA TUESDAY
AFTERNOON AND TUESDAY NIGHT.

IN THE WEST...ON SHORE FLOW OVER THE UPCOMING 2 DAYS WILL RESULT IN
CONSIDERABLE LOW CLOUDS, IFR TO MVFR, OVER THE COASTS. THE SHORT
WAVE ALOFT NOW OVER THE WEST COAST IS NOT FORECAST BY THE MODELS TO
PRODUCE MUCH PRECIPITATION AT ALL IN THE COASTAL OR WEST INTERIOR
ZONES. THE PRECIPITATION FORECAST STILL SEEMS UNDERSTATED, SO SOME
MENTION OF SNOW IS BEING RETAINED. TEMPERATURES WILL GRADUALLY
GET COOLER. THE CHUKOTKAN SHORT WAVE ALOFT SHOULD BRING IN SOME
SNOW TO THE KOBUK VALLEY REGION TUESDAY AFTERNOON AND NIGHT.

IN THE INTERIOR...SAME IDEA ABOUT THE TROUGH ALOFT NOW OVER THE
WEST COAST...THIS SHOULD BE GOOD FOR AT LEAST SOME RAIN OR RAIN/SNOW
IN THE INTERIOR STARTING MID DAY TODAY THROUGH TUESDAY. AMOUNTS AND
DURATION WILL BE SCANT...BUT NOT ZERO EVERYWHERE. PRECIPITATION
TODAY WILL BE RAIN...AND SNOW TONIGHT AND TUESDAY. TEMPERATURES
COOLING FROM RECORD HIGHS THE PAST 3 DAYS TO BELOW NORMAL BY TUESDAY.

IN THE MEDIUM RANGE...BOTH THE MRF/AVIATION AND ECMF MODELS MOVE THE
CHUKOTKAN SHORT WAVE ALOFT INTO THE CENTRAL BROOKS RANGE TUESDAY
NIGHT. FOLLOWING THIS...THE SHORT WAVE IS FORECAST TO DROP INTO THE
YUKON WEDNESDAY NIGHT, WHILST HIGH PRESSURE ALOFT BUILDS UP OVER
WESTERN ALASKA. THIS PATTERN SUGGESTS AN OUTBREAK OF COOLER THAN
NORMAL AND RATHER DRY WEATHER OVER THE EASTERN MAINLAND THURSDAY AND
FRIDAY...WITH SOME RECOVERY IN TEMPERATURES OVER THE WEST FRIDAY.
AFTER THIS THE MODELS DIVERGE CONSIDERABLY. THE BEST GUESS APPEARS TO
BE TO ASSUME THAT THE RIDGE ALOFT FORECAST BY THE ECMF OVER WESTERN
ALASKA FRIDAY AND SATURDAY WILL BE RATHER A BLOCKING SYSTEM AND HOLD
THROUGH THE UPCOMING WEEKEND.

.AFG...WATCH/WARNING SUMMARY
PUBLIC...DENSE FOG ADVISORY ARCTIC COAST ZONES 202-203-204.
MARINE...NONE
FIRE WEATHER...NONE.

TF APR 03