FXUS66 KOTX 272139
AFDGEG

EASTERN WASHINGTON AND NORTH IDAHO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WASHINGTON
230 PM PDT TUE MAY 27 2003

.SYNOPSIS...A STRONG UPPER LEVEL RIDGE WILL PROVIDE UNSEASONABLY WARM
TEMPERATURES THROUGH WEDNESDAY. LATE WEDNESDAY A COLD FRONT WILL MOVE
THROUGH FOR A THREAT OF THUNDERSTORMS WITH COOLER CONDITIONS ON
THURSDAY. BY FRIDAY A NEW UPPER RIDGE WILL BUILD INTO THE REGION FOR
ANOTHER WARMING TREND AND DRY WEATHER CONDITIONS.


.DISCUSSION...
.TONIGHT...SATELLITE INDICATES UPPER LEVEL RIDGE BECOMING HIGHLY
MERIDIONAL NEAR 140W THIS AFTERNOON. DOWNSTREAM OVER THE WEST COAST
A STRONG UPPER LEVEL RIDGE IS HOLDING WITH THE AXIS APPARENTLY OVER
WASHINGTON AND OREGON. RIDGE AXIS WILL PASS OVER THE FORECAST AREA
TONIGHT. MAIN SURFACE THERMAL TROUGH OVER THE COAST THIS AFTERNOON
BUT WILL GRADUALLY MIGRATE INTO THE FORECAST AREA OVERNIGHT. EXPECT
MOSTLY CLEAR SKIES REGION WIDE EXCEPT FOR SOME AC/CI PUSHING UP
FROM THE SOUTH WITH MILD LOW TEMPERATURES.

WEDNESDAY...ON WEDNESDAY NEW ETA AND AVN/GFS BOTH FAIRLY CONSISTENT
OVER PREVIOUS RUNS. CONSISTENT BUT STILL NOT IN GOOD AGREEMENT WITH
EACH OTHER IN HANDLING RIDGE BREAK DOWN. BOTH MODELS TRYING TO
PUSH AN UPPER LEVEL SHORT WAVE INTO THE TOP OF THE RIDGE WITH A
SURFACE FRONT PUSHING OVER THE CASCADES. GFS IS MORE PROGRESSIVE
AND LEAVES THE BASIN IN A FAIRLY STABLE POST FRONT AIR MASS BY THE
TIME OF MAXIMUM DIURNAL HEATING LATE IN THE DAY. THE ETA FEATURES
A SLOWER SYSTEM WHICH MAY ALLOW FRONT TO HOLD OFF UNTIL LATE IN THE
DAY OVER THE IDAHO PANHANDLE AND THE EASTERN BASIN ALLOWING THESE
REGIONS TO DESTABILIZE. GIVEN MERIDIONAL NATURE OF THE
RIDGE/TROUGH COUPLET SUGGESTING A SLOWER EASTWARD MOVEMENT OF THE
RIDGE AND THERMAL TROUGH AND BETTER ETA TERRAIN RESOLUTION FOR
SQUEEZING MARINE AIR MASS THROUGH THE CASCADES WILL GUARDEDLY TRACK
WITH THE ETA SOLUTION FOR WEDNESDAY. WARM START ALLOWS MID 80S HIGH
TEMPERATURES TO BE REACHED. WITH DEW POINTS AROUND 50 DEGREES AS LOW
LEVEL MARINE AIR FILTERS INTO THE BASIN EXPECT 500 TO 800 JOULES OF
CAPE DURING THE AFTERNOON OVER MUCH OF THE EASTERN FORECAST
AREA. MODEL SOUNDINGS SUGGEST A LAYER OF CONVECTIVE INHIBITION
BETWEEN 700 AND 800MB BUT THIS WAS ALSO PRESENT LAST SATURDAY AND
COULD BE OVERCOME BY OVER-ACHIEVING SURFACE TEMPERATURES AND/OR
SLIGHTLY HIGHER THAN FORECAST DEW POINT OR A WILD CARD LIKE A
GUST FRONT FROM DISTANT MOUNTAIN CONVECTION. POTENTIAL EXISTS FOR
A FEW AFTERNOON AND EVENING THUNDERSTORMS OVER THE PANHANDLE AND
EASTERN BASIN ZONES. WILL CARRY ON WITH CURRENTLY EXISTING SLIGHT
CHANCE POPS OVER THESE ZONES FOR WEDNESDAY AFTERNOON AND EVENING. FAR
WESTERN ZONES PROBABLY IN MORE STABLE POST FRONT MASS FOR SHOWERS BUT
NO THUNDER.

THURSDAY AND FRIDAY...MAIN FRONT PASSES THROUGH WEDNESDAY NIGHT WITH
DECENT MID LEVEL COOL ADVECTION AND FLOW BECOMING ZONAL. THIS FLOW
WILL QUICKLY END SHOWERS OVER THE BASIN BY THURSDAY MORNING BUT ALSO
LINGER SHOWERS IN THE MOUNTAINS OF THE IDAHO PANHANDLE INTO
THURSDAY AFTERNOON. THURSDAY PROBABLY ABOUT 10 DEGREES COOLER
THAN WEDNESDAY. NO SIGNIFICANT WEATHER AND TEMPERATURES RECOVERING A
FEW DEGREES ON FRIDAY AS THE NEXT UPPER LEVEL RIDGE PUMPS UP OVER THE
FORECAST AREA. /FUGAZZI


.SATURDAY THROUGH TUESDAY...EXTENDED FORECAST FROM THIS MORNING LOOKS
GOOD. THE 12Z RUN OF THE AVN MODEL INDICATES A NEW A FEATURE. A SMALL
EMBEDDED SHORTWAVE IN THE SOUTHWESTERLY FLOW ON SATURDAY. THE MODEL
INDICATES A GOOD DEAL OF PRECIPITATION OVER EASTERN WASHINGTON AND
NORTHERN IDAHO WITH THE FEATURE. THE CANADIAN MODEL DOES NOT PICK UP
ON THIS FEATURE. HOWEVER THE CANADIAN ENSEMBLE SPAGHETTI PLOTS FOR
500MB INDICATE THAT A LARGE NUMBER OF THE ENSEMBLE MEMBERS INDICATE A
WAVE SIMILAR TO THE AVN...ABEIT FURTHER SOUTH. AS PER COORDINATION
WITH ADJACENT OFFICES A CONSERVATIVE APPROACH WILL WORK BEST.
PRECIPITATION ON SATURDAY AFTERNOON WITH BE SLIGHT CHANCE VARIETY IN
THE EASTERN MOUNTAINS. OTHERWISE EXTENDED STAYS DRY FOR THE REMAINDER
OF THE PERIOD. /LERICOS


...THE INFORMATION IN THIS PRODUCT CONCERNING WARNINGS AND FORECASTS
IS VALID ONLY AT THE TIME OF ISSUANCE. THE LATEST WARNING AND
FORECAST INFORMATION WILL BE FOUND IN THE APPROPRIATE PRODUCTS...

GEG 055/086/051/074/048/076 022210
COE 053/087/049/074/047/076 022210
PUW 055/086/050/072/047/075 0221--
LWS 058/090/055/078/049/082 0221--
CQV 051/089/049/076/044/079 022210
SPT 049/084/049/072/045/078 022210
WWP 048/081/048/069/042/074 023210
MWH 055/088/052/076/048/079 011---
EAT 058/087/053/076/050/078 01111-
OMK 053/085/051/074/046/081 -22110


.OTX...NONE.

$$