Damaging Winds in Washington, May 8, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
408 PM PDT TUE MAY 8 2007

.SYNOPSIS...TEMPERATURES WELL ABOVE AVERAGE TODAY AHEAD
OF A COLD FRONT ALONG THE COAST WILL COOL TO CLOSER TO NORMAL
VALUES FOR WEDNESDAY FOLLOWING FRONTAL PASSAGE TONIGHT. WIDELY
SCATTERED THUNDERSTORMS AND BREEZY WINDS ARE EXPECTED TO ACCOMPANY
THE PASSAGE OF THIS EVENINGS COLD FRONT. TEMPERATURES FOR TOMORROW
WILL BE NOTICEABLY COOLER.

&&

.DISCUSSION...
TONIGHT THROUGH THURS...ENTIRE FOCUS WILL BE ON THE CHANCE OF
SHOWERS AND THUNDERSTORMS LATE THIS AFTERNOON AND THIS EVENING. FCST
SOUNDINGS MODIFIED TO REFLECT A MORE ACCURATE SFC DEW PT TEMP CLEARLY
SHOWED A RATHER SIGNIFICANT SFC-BASED CAP UNTIL AROUND 21Z TODAY
ON GFS POINT SOUNDINGS. NAM HAS BEEN REJECTED GIVEN ITS DEW
PTS OF UP TO 10F TOO WARM. THAT SAID...THOUGH LG-SCALE FORCING FOR
ASCENT WILL INCREASE ACROSS THE CASCADES AND MY NRN ZONES NEAR THE
BC BORDER THIS AFTERNOON...ITS BEEN TOUGH TO GET MUCH MORE THAN A FEW
CLOUDS SO FAR TODAY GIVEN A 200MB DEEP DRY LYR BELOW 700MB OF 40
PERCENT. LATEST SATELLITE LOOPERS NOW SHOW EXPANDING CU FIELD OVER
THE ELEVATED HEAT AT MOISTURE SOURCES OF THE CASCADES AND OKANOGAN
HIGHLANDS OF WA...AS WELL AS ACROSS CENTRAL OREGON. THIS SUPPORTS OUR
THINKING FROM EARLIER TODAY THAT THERE WILL INITIALLY BE TWO HOT
SPOTS OF BEST SHOWER AND THUNDER POTENTIAL. THE FIRST AREA NEAR THE
CASCADES...AS THE SFC BECOMES UNCAPPED AND MOISTURE CONVERGENCE
INCREASES IN THE PRESENCE OF DEEPENING WLY FLOW ALONG THE CASCADE
CREST AND IN THE VCNTY OF THE WEAK COLD-FRONT. THE SECOND AREA OF
CONCERN...WHICH WILL BE SLOWER TO DEVELOP...WILL BE ACROSS SERN WA
AROUND THE N BLUE MTNS. WITH THIS BLUE MTNS AREA FARTHER FROM THE
VORT MAX OVER SW BC AND BEST LG-SCALE FORCING FOR ASCENT...WELL
LIKELY HAVE TO WAIT FOR THE SHOWERS NOW OVER C OREGON TO EXPAND
NE INTO NE OREGON AND TWD THE LEWISTON AREA. GIVEN THE RELATIVELY DRY
AIR MASS AND CAPE VALUES OF 350-550 J/KG-1 PER GFS...WELL ONLY LEAVE
IN THE MENTION OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS THIS
EVENING. WITH THE PROGRESSION OF THE COLD-FRONT INTO N ID BY
LATE TONIGHT...THE SHOWER THREAT WILL LAST MUCH OF THE NIGHT AND
EARLY WED MORNING FOR THE C ID PANHANDLE MTNS. STRENGTHENING COLD
ADVECTION ALONG THE CASCADES AND WRN BASIN ZONES WILL HELP TO
PRODUCE BREEZY WEST WINDS THIS EVENING. NO MAJOR CHANGES TO THE REST
OF THE FCST THROUGH THURS. BZ

THURSDAY NIGHT THROUGH TUESDAY...MODELS ROUGHLY IN AGREEMENT
THROUGH THE ENTIRE EXTENDED RANGE OF THE FORECAST WITH REGARD TO
THE OVERALL SYNOPTIC PATTERN AS WELL AS THE LOW LEVEL THERMAL
FIELD EVOLUTION. WITH A LARGE SCALE COLD FRONT SET TO MOVE TO THE
SOUTHEAST OF OUR CWA BY THE BEGINNING OF THE PERIOD...THE BULK OF
THE INSTABILITY AND SHOWER ACTIVITY LOOKS TO BE SHUNTED SOUTHEAST
OF US THROUGH MOST OF THE NEXT WEEK OR SO. HOWEVER WITH A RATHER
COMPLICATED PATTERN FEATURED OVER THE PACIFIC AT THE MOMENT...THE
MOVEMENT OF MESOSCALE FEATURES AND MEANDERING OF SYNOPTIC FEATURES
AND BOUNDARIES AS PERTURBATIONS IN THE FLOW OFF THE PACIFIC COME
TOWARD THE COAST IS FAR FROM CERTAIN EVEN THOUGH GOOD CONFIDENCE
IN A DECENT LARGE SCALE PATTERN AMPLIFICATION STILL EXISTS. WITH
THE FOCUS ON ALL MODELS FOR INSTABILITY NEAR TO AND JUST SOUTHEAST
OF THE CWA...AS WELL AS LARGE SCALE SOUTHWESTERLY FLOW PERSISTING
THROUGH THE ENTIRE PERIOD...BELIEVE IT MOST LIKELY THE
SOUTHEASTERN CWA WILL SEE THE BEST CHANCE AT SHOWERS AND
AFTERNOON THUNDERSTORMS AS LI VALUES APPROACH ZERO. WITH THIS
SAID...THE GFS SEEMS TO TARGET SLIGHTLY BETTER INSTABILITY FOR THE
SATURDAY/SUNDAY TIME FRAME OVER THE IDAHO PANHANDLE...WHILE THE
ECMWF MORE THAN LIKELY FAVORS FRIDAY. ALL THE WHILE...THE CANADIAN
MODEL SEEMS TO FOCUS SYNOPTIC LIFT OVER US FRIDAY NIGHT WITH A
NEGATIVELY TILTED SHORT WAVE EMBEDDED IN THE SOUTHWESTERLY UPPER
LEVEL FLOW. THE CURIOUS PART IS THAT NONE OF THE MODELS INDICATE
ANY QPF THROUGH THE DURATION OF THE EXTENDED FORECAST. AS A
RESULT...HAVE GREATLY SUBDUED QPF GRIDS...LIMITING THEM TO 0.01
INCH DURING ANY PERIOD AND KEPT ALL POPS IN THE MOUNTAINS AND AT
SLIGHT CHANCE. WITH TEMPERATURES AND INSTABILITY NOTED WITH
MUCAPES AND LI VALUES...HAVE ADDED THUNDERSTORMS EACH AND EVERY
AFTERNOON AND EVENING IN THE EASTERN MOUNTAINS DUE TO BETTER
INSTABILITY POOL AND WEAK UPSLOPE FLOW.

AFTER THE WEEKEND...THE MODELS SEEM TO HINT AT SOME MORE
SIGNIFICANT DISTURBANCE TOPPING THE RIDGE ON MONDAY. THIS IS
NOTICEABLE AT 500 MB ON THE CANADIAN...12Z GFS...AND 00Z
ECMWF...HOWEVER WITH THIS BEING FAR FROM SUPPORTED ON THE GEFS AND
12Z ECMWF...HAVE DECIDED NOT TO JUMP ON IT. HOWEVER...ONE THING
SEEMS TO HOLD TRUE...THE GFS...CANADIAN...AND ECMWF ALL SHOW
ANOTHER HIGH AMPLITUDE TROUGH DIGGING WELL OFF SHORE BY
MONDAY...AS A RESULT WE SHOULD EXPECT MORE PROLONGED RIDGE
AMPLIFICATION OVER THE WEST BY THE BEGINNING OF THE WEEK EVEN IF
THAT SYSTEM DOES MANAGE TO SLIP OVERHEAD ON MONDAY.

WITH 850 MB TEMPERATURES OF +13 TO +16C AND VERY EFFICIENT MIXING
FROM 850 MB DURING EVERY AFTERNOON OF THE PERIOD...TEMPERATURES
SHOULD REMAIN LARGELY IN THE 70S THROUGH NEXT TUESDAY. THIS IS
RIGHT IN LINE WITH MEX GUIDANCE...SO FELT NO COMPELLING REASON TO
STRAY TOO FAR FROM GUIDANCE TODAY. /FRIES

&&

.AVIATION...
THUNDERSTORMS HAVE GENERALLY REMAINED OVER OREGON TO THIS POINT...A
FEW CELLS MAY SNEAK INTO THE AREAS BETWEEN KMWH AND KPUW THIS
EVENING BEFORE QUICKLY DYING AS THE SUN SETS. OTHERWISE...VFR
CONDITIONS EXPECTED THROUGH 00Z THURSDAY. /FRIES

&&

.PRELIMINARY POINT TEMPS/POPS...
SPOKANE        51  69  42  71  47  74 /  20   0   0  10  10  10
COEUR DALENE  49  69  38  72  43  75 /  20   0  10  10  10  20
PULLMAN        49  68  40  70  44  73 /  20  10  10  10  10  10
LEWISTON       57  75  47  76  50  79 /  20  10  10  10  10  10
COLVILLE       46  72  39  75  40  77 /  20   0  10  10  10  20
SANDPOINT      50  68  38  69  42  72 /  20  10  10  20  10  20
KELLOGG        49  69  40  72  41  75 /  20  10  10  20  10  20
MOSES LAKE     52  75  42  75  44  79 /  10   0   0  10  10  10
WENATCHEE      53  74  47  74  50  78 /  10   0   0  10  10  10
OMAK           49  74  43  74  43  79 /  10   0   0  10  10  10

&&

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