Flash Flooding in Washington, September 27, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
245 PM PDT TUE SEP 27 2011

.SYNOPSIS...
HIGH PRESSURE WILL BUILD BACK INTO THE REGION TONIGHT THROUGH
FRIDAY...WHICH WILL RESULT IN MOSTLY SUNNY SKIES AND SEASONABLY
WARM TEMPERATURES. MOUNTAIN SHOWERS WILL BE ON THE INCREASE THIS
WEEKEND AND EARLY NEXT WEEK AS ANOTHER STORM SYSTEM TAKES UP
POSITION OVER THE PACIFIC NORTHWEST.

&&

.DISCUSSION...
TONIGHT...PERSISTENT FETCH OF MOISTURE STREWN ACROSS THE INLAND NW
FOR THE PAST 18HRS OR SO WILL GRADUALLY SHIFT SOUTH AND EAST OF
OUR AREA AS DRIER AIR BEGINS TO MOVE IN FROM THE WEST. LOOKS LIKE
ANY THREAT OF PRECIPITATION WILL OCCUR EARLY THIS EVENING AND
MAINLY IMPACT PORTIONS OF THE IDAHO PANHANDLE. LIGHT STRATIFORM
PRECIPITATION ASSOCIATED WITH THE FRONTAL BOUNDARY WILL GENERALLY
IMPACT THE CENTRAL PANHANDLE ZONES WHILE SHALLOW INSTABILITY AND
OROGRAPHIC ASCENT WILL PRODUCE ISOLATED LIGHT SHOWERS OVER THE
NORTHERN PANHANDLE. THE ONLY OTHER AREA OF PRECIPITATION WILL
OCCUR NEAR THE CASCADE CREST BUT MOST OF THAT WILL REMAIN AT OR
JUST SLIGHTLY EAST OF THE CREST. OTHERWISE SKIES WILL EXHIBIT A
CLEARING TREND FROM WEST TO EAST OVERNIGHT WHICH SUGGESTS THE
POSSIBILITY OF SHALLOW RADIATION FOG. 24HR RAINFALL TOTALS AS OF
2PM SHOWED WIDESPREAD RAINFALL AMOUNTS BETWEEN .15-.40 INCHES
ACROSS PORTIONS OF NORTHEAST WASHINGTON AND INTO THE NORTHERN
IDAHO PANHANDLE AND THESE ARE THE LOCATIONS MOST PRIMED FOR FOG.
FARTHER SOUTH AND WEST MUCH LESS PRECIPITATION FELL. OVERNIGHT
LOWS COULD ALSO GET QUITE CHILLY WITH SOME PATCHY FROST EXPECTED
FOR LOCATIONS SUCH AS DEER PARK...REPUBLIC...CHEWELAH...AND PRIEST
LAKE. THIS IS PAST THE CLIMATOLOGICAL FREEZE DATE FOR THESE
LOCATIONS NOT TO MENTION A FEW GOT DOWN TO FREEZING LAST WEEK SO
HIGHLIGHTS WILL NOT BE ISSUED. FX

WEDNESDAY THROUGH FRIDAY...RIDGING IN PLACE AMPLIFIES ALLOWING FOR
A WARMING AND DRYING TREND WEDNESDAY INTO FRIDAY. THE RIDGE AXIS
MIGRATES EASTWARD WITH TIME AND BY FRIDAY THE STORM TRACK ALONG
THE FAR WESTERN EDGE OF THE RIDGE IN CLOSE PROXIMITY TO THE
CASCADES...PERHAPS NOT CLOSE ENOUGH TO INCREASE POPS BY ANY
SIGNIFICANT AMOUNT HOWEVER THE SKY GRID WILL HINT AT ITS PRESENCE
BY MID AND HIGH LEVEL CLOUDS INCREASING AND SPREADING FROM WEST TO
EAST. /PELATTI

FRIDAY NIGHT THROUGH MONDAY NIGHT...MODELS ARE INDICATING A MAJOR
SHIFT IN THE WEATHER PATTERN AS HIGH PRESSURE BREAKS DOWN AND
ALLOWS WAVES OF MOISTURE TO MOVE INTO THE REGION OFF OF THE
PACIFIC OCEAN. EACH WEATHER DISTURBANCE WILL ROTATE AROUND A DEEP
UPPER LEVEL LOW PRESSURE SYSTEM SITUATED IN THE GULF OF ALASKA.
MODELS ARE INDICTING THE POSSIBILITY OF THREE SEPARATE WEATHER
DISTURBANCES TO MOVE THROUGH BY TUESDAY WITH EACH ABOUT 24 TO 36
HOURS APART. THERE ARE DISAGREEMENTS BETWEEN MODELS AS FAR AS THE
TIMING OF EACH WAVE...BUT MODELS ARE IN GENERAL AGREEMENT THAT
EACH WILL LIKELY BE A BIT WETTER THAN THE LAST.

THE FIRST FRONT LOOKS TO MOVE THROUGH SATURDAY NIGHT OR SUNDAY
MORNING. THIS FIRST SYSTEM LOOKS TO BE THE DRIEST OF THE THREE AND
WILL LIKELY USE UP MUCH OF ITS ENERGY TO BREAK DOWN THE RIDGE.
BEST CHANCES OF PRECIPITATION WILL BE ACROSS THE MOUNTAINS...BUT
SOME LIGHT SHOWER ACTIVITY IN THE VALLEYS WILL BE POSSIBLE AS
WELL. THE NEXT FRONTAL PASSAGE LOOKS TO BE SLIGHTLY WETTER THAN
THE FIRST WITH A BETTER CHANCE OF WIDESPREAD PRECIPITATION. THE
THIRD SYSTEM...WHICH IS BEING ADVERTISED AS THE WETTEST OF THE BUNCH
COULD BE OUR FIRST COLD AND WET FALL STORM SYSTEM OF THE SEASON.
TIMING FOR THIS SYSTEM WILL LIKELY BE EARLY TO MID WEEK. THE
CHANGE IN THE WEATHER PATTERN WILL BRING A SIGNIFICANT COOLING
TREND TO THE REGION. HIGH TEMPERATURES BY TUESDAY MAY ONLY GET
INTO THE LOW 50S FOR SOME VALLEY LOCATIONS. AS TEMPERATURES COOL
WITH EACH WEATHER SYSTEM...WE COULD SEE SNOWFALL FOR THE
MOUNTAINS...ESPECIALLY WITH THIS THIRD WAVE EARLY TO MID WEEK.
BEST CHANCES FOR MOUNTAIN SNOWFALL WILL BE IN THE CASCADES. SNOW
LEVELS ARE SET AS LOW AS ABOUT 5000 FEET...BUT WOULD NOT BE
SURPRISED IF THESE SNOW LEVELS ARE LOWERED WITH FUTURE
FORECAST UPDATES. WITH MODEL DISCREPANCIES STILL APPARENT AMONGST
THE LONG RANGE MODEL FORECASTS...TIMING OF EACH WAVE WILL NEED TO
BE REFINED. AT THIS POINT POPS WERE KEPT AT CLIMATOLOGY OR ABOVE
FRIDAY NIGHT INTO EARLY NEXT WEEK AND THEN INCREASED WELL ABOVE
CLIMATOLOGY WITH THE WETTEST SYSTEM SET TO MOVE THROUGH SOME TIME
EARLY TO MID WEEK. /SVH

&&

.AVIATION...

18Z TAFS...FRONTAL BOUNDARY SLOWLY EXITING EASTERN WASHINGTON AND
NORTHERN IDAHO TODAY. THE STABLE RAINFALL ALONG AND AHEAD OF THE
FRONT PRODUCING SOME MVFR CEILINGS COMBINED WITH IFR VISIBILITIES
WITH THE MORE INTENSE RAINFALL. ONCE FRONT EXITS AREA SOME SCATTERED
SHOWERS BEHIND IT COULD PRODUCE BRIEF AND LIMITED MVFR CEILINGS AND
VISIBILITIES TIL ABOUT 3Z THIS EVENING. THE ABUNDANT MOISTURE FAVORS
PATCHY FOG FORMATION FROM 10-18Z WEDNESDAY. ADDITIONALLY STRONG
SOUTHWEST FLOW ALOFT WILL ALLOW FOR ROBUST SOUTHWEST WINDS 10-20 MPH
WITH GUST UP TO 30 MPH IN THE AFTERNOON...AND FOR SPOTTY LOW LEVEL
WIND SHEAR FOR PLACES WHERE THE WIND DOESN'T MIX DOWN AS EFFECTIVELY
TO THE SURFACE. /PELATTI

&&

.PRELIMINARY POINT TEMPS/POPS...
SPOKANE        42  65  44  75  49  77 /  10   0   0   0   0   0
COEUR D'ALENE  42  66  43  75  47  75 /  10   0   0   0   0   0
PULLMAN        39  67  42  78  49  78 /  20   0   0   0   0   0
LEWISTON       48  73  48  83  54  83 /  10   0   0   0   0   0
COLVILLE       38  69  38  77  43  78 /  10   0   0   0   0  10
SANDPOINT      37  65  37  71  42  75 /  30   0   0   0   0   0
KELLOGG        42  63  43  74  48  76 /  30   0   0   0   0   0
MOSES LAKE     44  70  44  75  48  79 /   0   0   0   0   0   0
WENATCHEE      47  69  48  74  52  76 /  10   0   0   0   0   0
OMAK           40  70  42  74  45  76 /   0   0   0   0   0  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SPOKANE WA
546 AM PDT TUE SEP 27 2011

IDZ001>004-026-027-WAZ031>038-041>044-281300-
NORTHERN PANHANDLE-COEUR D'ALENE AREA-IDAHO PALOUSE-
CENTRAL PANHANDLE MOUNTAINS-LEWISTON AREA-
LEWIS AND SOUTHERN NEZ PERCE COUNTIES-NORTHEAST BLUE MOUNTAINS-
LOWER GARFIELD AND ASOTIN COUNTIES-WASHINGTON PALOUSE-
MOSES LAKE AREA-UPPER COLUMBIA BASIN-SPOKANE AREA-
NORTHEAST MOUNTAINS-OKANOGAN HIGHLANDS-WENATCHEE AREA-
EAST SLOPES NORTHERN CASCADES-OKANOGAN VALLEY-WATERVILLE PLATEAU-
546 AM PDT TUE SEP 27 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH IDAHO...
NORTH CENTRAL IDAHO...CENTRAL WASHINGTON...EAST CENTRAL
WASHINGTON...NORTH CENTRAL WASHINGTON...NORTHEAST WASHINGTON AND
SOUTHEAST WASHINGTON.

.DAY ONE...TODAY AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.