Flood in Alaska, August 14 to 15, 2002

SOUTHEAST ALASKA FORECAST DISCUSSION
1045 AM ADT WED AUG 14 2002

.SHORT RANGE...UPPER LEVEL LOW IN NW CANADA CONTINUING EAST WHILE
STRONG UPPER LEVEL HIGH BUILDS NW INTO WESTERN GULF. A 110 KT
WEST-NORTHWEST JET WILL MOVE ACROSS THE FAR NORTHERN PANHANDLE
TODAY WITH SUBSIDENCE OF RIGHT ENTRANCE REGION OVER CENTRAL
PANHANDLE. NOT MUCH FLOW IN BOUNDARY LAYER THAT IS NEARLY
SATURATED. A WEAKENING COLD FRONT AND SURFACE TROUGH WILL DROP
SOUTHWARD ACROSS SOUTHEAST ALASKA TONIGHT.

STABLE BOUNDARY LAYER OVER WET GROUND TODAY WILL PERSIST WITH NO
REAL MECHANISM TO DRY OUT LOW LEVELS BUT GRADUAL DIURNAL HEATING.
LOW CLOUDS ALONG COAST AT THIS TIME FROM PAYA TO SITKA WILL
SLOWLY LIFT THROUGH DAY WITH A FEW SUN BREAKS THROUGH THE
AFTERNOON AND EARLY EVENING. LARGEST BREAKS ACROSS SOUTH CENTRAL
AND SOUTHERN PANHANDLE MAY FILL IN WITH SC THIS AFTERNOON THROUGH
SHALLOW CONVECTIVE PROCESS AND COULD EVEN SEE ISOLATED LIGHT
SHOWER. AS TROUGH DROPS SOUTH AND ATMOSPHERE COOLS THIS EVENING
...SHOULD SEE SKIES CLEAR BRIEFLY WHICH IS EXPECTED TO HELP
RADIATIVE FOG PROCESS OVERNIGHT AND WILL INCLUDE AREAS OF DENSE
FOG OVERNIGHT.

WINDS GENERALLY LIGHT AND VARIABLE THROUGH INNER CHANNELS TODAY.
OFFSHORE AND INTO SOUTHERN PANHANDLE NORTHWEST WINDS GENERALLY 10
TO 15 KT BUT COULD REACH 20 KT AROUND COASTAL HEADLANDS AND
CHANNELED AREAS.

A RIVER FLOOD WARNING FOR THE ALSEK REMAIN IN EFFECT THIS MORNING
WITH LAST OBSERVATION AROUND MIDNIGHT INDICATING CREST HAS
OCCURRED WITH LEVELS FALLING VERY SLOWLY. DRY CONDITIONS AND
COOLER TEMPERATURES ALOFT WILL HELP SPEED FALLS ON THIS RIVER
TODAY AND TONIGHT. LAST STAGE AT 89.7 (175,000 CUBIC FEET PER
SECOND) WITH FLOOD STAGE AT 88.0.

RUSSELL LAKE GAUGE SHOWED LAKE LEVEL LOWERING ABOUT 4 INCHES
BETWEEN MIDNIGHT TO 4 AM. FIRST GUESS IS THAT THE IS TRYING TO
REACH EQUILIBRIUM AFTER PAST DAYS HEAVY RAINS BUT COULD BE SIGN
THAT THE LAKE IS RELEASING. ANXIOUSLY AWAITING NEXT ROUND OF DATA
DUE AT 9 AM.

.LONG RANGE...
THURSDAY LOOKS LIKE IT IS SHAPING UP TO BE A BEAUTIFUL DAY. ONCE
THE MORNING FOG CLEARS UP WE SHOULD BE SEEING MOSTLY SUNNY SKIES
FOR MUCH OF THE PANHANDLE. ON THURSDAY A HIGH PRESSURE RIDGE
ALOFT STRETCHES FROM OFF OF THE CALIFORNIA COAST NORTHWEST
THROUGH THE GULF OF ALASKA AND ACROSS THE SOUTHWESTERN END OF THE
ALASKA PENINSULA. A BROAD UPPER LOW IS CENTERED OVER THE BEAUFORT
SEA AND AN UPPER TROUGH STRETCHES INTO WESTERN INTERIOR CANADA.
THE NORTHWESTERLY FLOW BETWEEN THE UPPER RIDGE AND TROUGH WILL
PUT THE PANHANDLE IN A REGION OF NORTHWESTERLY FLOW WHICH WILL
CLEAR THE AREA UP NICELY.

AT THE SURFACE A HIGH WILL BE CENTERED IN THE GULF OF ALASKA AND
A SLIGHT RIDGE WILL POKE ON TO THE NORTHEASTERN GULF COAST BY
THURSDAY MORNING. THIS WILL AID THE NORTHERLY TO NORTHWESTERLY
FLOW IN THE PANHANDLE. MEANWHILE AN INVERTED TROUGH WILL MOVE UP
THE COAST FROM THE SOUTH ADDING AN OFFSHORE COMPONENT TO THE
SURFACE FLOW IN SOUTHERN HALF OF THE PANHANDLE.

THROUGH THE DAY ON THURSDAY A SHORTWAVE TROUGH WILL SLIDE
SOUTHEASTWARD DOWN THE WESTERN NORTHWEST TERRITORY BORDER TO
NORTHWESTERN ALBERTA BY FRIDAY MORNING. THIS SHORTWAVE IS FAR
ENOUGH EAST THAT IT SHOULD NOT HAVE MUCH AFFECT ON THE PANHANDLE
OTHER THAN TO INTENSIFY THE NORTHWESTERLY FLOW ALOFT A BIT.
HOWEVER IT IS CLOSE ENOUGH THE AREA TO JUSTIFY KEEPING AN EYE ON
ITS POSITION AS IT MOVES SOUTHEAST.

THE NEXT FEATURE OF SIGNIFICANT INTEREST TO SOUTHEAST ALASKA IS A
SHORTWAVE TROUGH MOVING INTO THE NORTHERN GULF OF ALASKA ON
FRIDAY. THE ETA AND AVN 12Z RUNS ARE HANDLING THIS FEATURE
SIGNIFICANTLY DIFFERENTLY WITH THE AVN MOVING IT TOWARD THE
PANHANDLE MUCH FASTER. THE MAIN VORTICITY STAYS OFFSHORE IN THE
GULF BUT THE TROUGH SWITCHES THE FLOW ALOFT TO WESTERLY AND THAT
WITH THE LIFTING MECHANISM OF THE SHORTWAVE SHOULD BRING AT LEAST
SCATTERED IF NOT MORE NUMEROUS SHOWERS TO THE PANHANDLE. WITH THE
MODEL DISCREPANCIES IN TIMING I AM UNSURE AS TO HOW EARLY TO
BRING THE SHOWERS INTO THE FORECAST. USING THE FASTER AVN,
YAKUTAT WOULD BE LOOKING AT SHOWERS MIDDAY FRIDAY AND THE
NORTHERN PANHANDLE FRIDAY AFTERNOON/EVENING.

THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK THE FLOW PATTERN
STAYS GENERALLY THE SAME WITH THE MAJOR FEATURES ALOFT STAYING
FAIRLY STATIONARY. THE PREVAILING FLOW ALOFT OVER THE PANHANDLE
REMAINS NORTHWESTERLY WITH SHORTWAVES MOVING THROUGH. DO NOT SEE
MUCH REASON TO CHANGE THE MOSTLY CLOUDY WITH CHANCE OF RAIN OF
THE CURRENT PACKAGE. AT TIMES IT WILL BE BOTH AT BIT NICER AND A
BIT WETTER THAN THAT BUT NOT AT ALL SURE OF THE TIMING OF
INDIVIDUAL FEATURES YET SO THE GENERALIZATION IS A GOOD BET.

BY TUESDAY THE UPPER RIDGE IN THE GULF STARTS TO SHIFT EAST. THE
RIDGE AXIS NEARS THE PANHANDLE ON WEDNESDAY AND MOVES ONSHORE BY
THURSDAY. WILL TREND THE END OF THE EXTENDED TOWARD WETTER
WEATHER.

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...FLOOD WARNING ALSEK RIVER
MARINE...NONE
FIRE WEATHER...NONE

MM/JER