Flash Flood in Washington, August 18, 2004

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WASHINGTON
230 PM PDT WED AUG 18 2004

.SYNOPSIS...A WEAK RIDGE WILL LIE OVER THE INLAND NORTHWEST THROUGH
THE REMAINDER OF THE WEEK. THIS WILL KEEP TEMPERATURES WARM...BUT
WITH SHOWERS AND THUNDERSTORMS DEVELOPING OVER THE MOUNTAINS EACH
AFTERNOON AND EVENING THROUGH FRIDAY. A COOLER AND WETTER PATTERN
WILL DEVELOP OVER THE WEEKEND.

&&

.DISCUSSION...
TODAY THROUGH SATURDAY...THE INLAND NORTHWEST REMAINS IN A WEAK
RIDGE PATTERN CAUGHT BETWEEN TWO STRONG LOW PRESSURE SYSTEMS. THE
ATMOSPHERE OVER THE AREA REMAINS MOIST AND UNSTABLE AND SCATTERED
SHOWERS AND THUNDERSTORMS HAVE DEVELOPED OVER THE MOUNTAINS THIS
AFTERNOON. IN THE ABSENCE OF ANY STRONG WAVES THESE ARE DRIVEN BY THE
DAYTIME HEATING AND SHOULD DISSIPATE SHORTLY AFTER SUNSET. THESE
STORMS ARE MOVING SLOWLY SOUTH SOUTHEASTWARD AND MAY PRODUCE MODERATE
TO HEAVY RAIN...SMALL HAIL AND OCCASIONAL LIGHTNING THROUGH THE
EVENING. THERE WILL BE LITTLE CHANGE IN THE OVERALL WEATHER PATTERN
SO EXPECT ABOVE NORMAL TEMPERATURES...MOSTLY CLEAR SKIES LATE
NIGHTS/MORNINGS AND PARTLY CLOUDY SKIES WITH MOUNTAIN SHOWERS AND
THUNDERSTORMS AFTERNOONS/EVENINGS THROUGH FRIDAY NIGHT. BY SATURDAY
WE BEGIN A CHANGE IN THE WEATHER PATTERN AS AN UPPER LEVEL TROUGH
APPROACHES THE WASHINGTON COAST . CC

SATURDAY NIGHT THROUGH WEDNESDAY...THE EXTENDED MODELS ARE NOW IN
FAIR AGREEMENT THAT WE WILL EXPERIENCE A MAJOR PATTERN CHANGE
OVER THE WEEKEND AS OUR PERSISTENT HOT RIDGE IS BROKEN DOWN AND
REPLACED BY A TROF OVER THE WESTERN US. TIMING COULD PROVE A LITTLE
PROBLEMATIC AS THE EXTENDED MODELS TEND TO BREAK DOWN STRONG RIDGES
A LITTLE TOO FAST. NONETHELESS...ITS HARD TO IGNORE WHAT THE
ENSEMBLE MEANS OFF THE CANADIAN AND GFS ARE SHOWING. THIS TRANSLATES
TO A GRADUAL COOLING OVER THE INLAND NW WITH A CHANCE OF
PRECIPITATION EACH DAY. BEST CHANCES WILL BE RESERVED FOR THE
CASCADES AND IDAHO PANHANDLE AS THE 850-700 MB FLOW REMAINS
PRIMARILY WESTERLY...HOWEVER WE CANNOT RULE OUT PRECIPITATION FROM
OCCURRING ANYWHERE WITHIN THE CWA. TEMPERATURES WILL SLIDE
BELOW NORMAL VALUES AND REMAIN THERE THROUGH MID-WEEK. THIS SHOULD
BE OUR FIRST PROLONGED STRETCH OF COOLER THAN NORMAL WEATHER SINCE
THE BEGINNING OF JULY. THE AIRMASS IN THIS REGIME WILL EXPERIENCE A
GRADUAL STABILIZATION SO THUNDERSTORMS WILL BECOME LESS LIKELY BY
MIDWEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...

SPOKANE        061 089 059 087 057 085/ 20 20 20 10 10 10
COEUR DALENE  059 089 057 087 055 085/ 20 20 20 05 10 10
PULLMAN        058 089 056 087 049 085/ 20 20 20 05 10 10
LEWISTON       066 092 064 090 057 088/ 20 20 20 05 10 10
COLVILLE       058 097 056 095 049 093/ 20 20 20 10 10 20
SANDPOINT      060 088 058 084 050 082/ 20 20 20 10 10 20
WALLACE        058 086 056 082 058 080/ 30 20 20 10 10 20
MOSES LAKE     063 095 061 093 056 091/ 00 00 00 00 00 10
WENATCHEE      067 092 065 090 062 087/ 00 10 10 00 10 10
OMAK           065 095 063 093 057 090/ 10 10 10 05 10 10
&&

.OTX...
ID...NONE.
WA...NONE.