FXUS66 KOTX 251143 CCA
AFDOTX
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE SPOKANE WA
341 AM PST WED NOV 25 2009
.SYNOPSIS...
WEAK HIGH PRESSURE OVER THE REGION WILL KEEP THE INLAND NORTHWEST
MAINLY DRY BUT CLOUDY TODAY AND THROUGH THE THANKSGIVING HOLIDAY.
THE EXCEPTION WILL BE THE CASCADES AND OKANOGAN VALLEY WHERE THERE
WILL BE A CHANCE OF VERY LIGHT RAIN AND HIGH MOUNTAIN SNOW. THURSDAY
NIGHT AND FRIDAY THE NEXT STORM SYSTEM WILL BRING MOUNTAIN SNOW
AND VALLEY RAIN. EXCEPT FOR MAINLY MOUNTAIN SNOW SHOWERS...THE
WEATHER WILL BE LARGELY QUIET BUT CLOUDY AND COOL WELL INTO NEXT
WEEK.
&&
.DISCUSSION...
TODAY THROUGH THURSDAY...PACIFIC SATELLITE LOOP IS DOMINATED BY A
DEEP GULF OF ALASKA TROUGH WHICH IS FORCING A BUILDING RIDGE ALOFT
OVER THE FORECAST AREA TODAY. A DEEP FETCH OF MOISTURE IS CLEARLY
APPARENT FEEDING INTO VANCOUVER ISLE. BOTH THE NAM AND GFS MODELS
INITIALIZE WELL WITH THIS FIELD OF MOTION...AND REFLECT SIMILAR
SOLUTIONS WHICH ARE PLAUSIBLE AGAINST SATELLITE EXTRAPOLATION. WITH
MINOR PERTURBATIONS MAINLY IMPACTING THE CASCADES AND FAR NORTH
ZONES...THIS OVERALL PATTERN WILL NOT CHANGE MUCH OVER THE NEXT 24
TO 36 HOURS. THE DEEP FETCH WILL CONTINUE TO TRAIN INTO BRITISH
COLUMBIA WITH SOME DEEP MOISTURE ON THE EASTERN FRINGE OF THIS
FETCH IMPINGING ON THE CASCADES AND RIDING OVER COOLER AIR TRAPPED
IN THE OKANOGAN VALLEY. SLOP OVER FROM THIS THIS OROGRAPHIC LIFT
INTO THE WESTERN CASCADES AND WEAK ISENTROPIC ASCENT OVER THE FAR
NORTHERN ZONES WILL WARRANT CHANCE POPS FOR MAINLY RAIN THROUGH
THE NEXT 26 HOURS. OTHERWISE...MODEL SOUNDINGS INDICATE AN
INVERSION LAYER OVER THE VALLEYS AND BASIN UNDER THE RIDGE
BEGINNING AT AROUND 4000 FEET MSL AND PERSISTING THROUGH TURKEY
DAY. WITH A MOIST LOW LEVEL AIR MASS AT LEAST PATCHY FOG EVERY
MORNING AND SOME AREAS OF STUBBORN LOW STRATUS DECKS PERSISTING
INTO THE AFTERNOON ARE A GOOD BET OVER MUCH OF THE BASIN AND
VALLEYS SURROUNDING THE BASIN. TEMPERATURES WILL LIKELY BE
SLIGHTLY MILDER THAN NORMAL IN THIS SOUTHWESTERLY MID LEVEL FLOW
REGIME WITH OVERNIGHT CLOUDS PREVENTING SIGNIFICANT
RADIATIONAL COOLING. /FUGAZZI
THURSDAY NIGHT THROUGH TUESDAY...WV/IR IMAGERY SHOWS A LONG- WAVE
TROUGH OVER THE NE PACIFIC...AND ROTATING INTO AND AROUND IT ARE
SEVERAL MID-LEVEL DISTURBANCES...SOME OF WHICH ARE EXPECTED TO
IMPACT THE INLAND NW.
THE FIRST DISTURBANCE WAS COMING TOWARD 150W EARLY WEDNESDAY. A
SFC LOW PROJECTED TO DEVELOP IN ADVANCE OF IT APPROACHES THE COAST
BY THURSDAY NIGHT. IT OCCLUDES AND DRAGS A FRONT OVER THE REGION
AS IT MOVES TO SOUTHEAST B.C. FRIDAY MORNING. AT PRESENT A PLUME
MOISTURE IS DIRECTED AT THE B.C. COAST WITH PWAT VALUES OVER AN
INCH. THE FRONT SHOULD TAKE ADVANTAGE OF THIS MOISTURE AND BRING A
HIGH PRECIPITATION RISK TO THE REGION. THERE ARE LINGERING MODEL
DISAGREEMENTS OVER HOW QUICKLY PRECIPITATION ADVANCES EAST.
HOWEVER THE CASCADES AND NORTHERN WASHINGTON ZONES WILL LIKELY SEE
PRECIPITATION ON OR DEVELOPING THROUGH THURSDAY NIGHT. OVERNIGHT
INTO FRIDAY MORNING CHANCES INCREASE TO LIKELY OVER ERN WA AND NRN
ID...WHILE THEY BEGIN TO DECREASE FROM THE LEE OF THE CASCADES AS
THE FLOW TURNS WESTERLY. P-TYPE IS EXPECTED TO BE MAINLY RAIN FOR
THE VALLEYS THROUGH FRIDAY...WITH THE SOUTHERLY FLOW AHEAD OF THE
FRONT KEEPING 850MB TEMPS ABOVE ZERO. HOWEVER SNOW LEVELS ARE
EXPECTED TO LOWER TO NEAR 3-4KFT BY FRIDAY AFTERNOON AS COLDER AIR
FILTER IN BEHIND THE FRONT...BRING THE POTENTIAL FOR SNOW IN THE
PASSES.
FRIDAY NIGHT INTO EARLY SATURDAY...A SECOND MID-LEVEL DISTURBANCE
(THAT WAS COMING ONTO THE ALEUTIANS WEDNESDAY MORNING) DIVES
SOMEWHERE ACROSS SW CANADA/NW US... WHILE SNOW LEVELS DROP TO NEAR
VALLEY FLOORS. THIS WILL KEEP THE RISK FOR PRECIPITATION ALIVE.
SOME MODEL RUNS HAVE DEPICTED 500 MB TEMPS AROUND -30 DEG
C...INDICATIVE OF DECENT INSTABILITY. THUS SOME CONVECTIVE BANDING
WITH LOCALIZED SIGNIFICANT SNOWFALL RATES ARE POSSIBLE ALONG AND
NEAR THE TRACK OF THIS DISTURBANCE. YET ITS PRECISE TRACK AND
EVOLUTION STILL NEEDS TO BE PINNED DOWN. GUIDANCE CONTINUES TO
WAVER IN THIS REGARD. SOME MODELS WEAKEN IT SIGNIFICANTLY AND
OTHERS SUGGEST IT MISSES THE REGION TO THE SOUTH OR NORTH. EITHER
WAY THE SYSTEM BEARS WATCHING.
A SHORT-WAVE RIDGE BUILDS IN SATURDAY AFTERNOON AND SUNDAY...WHICH
LINGERS INTO MONDAY. A WARM FRONT LIFTING IN SATURDAY NIGHT INTO
SUNDAY CARRIES SOME ISENTROPIC LIFT...BUT IT APPEARS TO BE WEAK
AND WILL PROVIDE MAINLY MOUNTAIN SNOW CHANCES. OTHERWISE LOOK FOR
SOME VALLEY STRATUS AND A RISK FOR PATCHY FOG. THE THIRD MID-LEVEL
DISTURBANCE APPROACHES TOWARD THE END OF THE PERIOD. THOUGH THERE
ARE STILL DISAGREEMENTS REGARDING ITS PRECISE EVOLUTION (INCLUDING
STRENGTH AND TIMING) IT SUPPORTS SOME CHANCE OF PRECIPITATION.
TEMPERATURES WILL REMAIN NEAR SEASONAL NORMS...SAVE FOR SLIGHT
WARMING MONDAY AHEAD OF THE THIRD DISTURBANCE...BEFORE COOLING
AGAIN. /JCOTE
&&
.AVIATION...
HIGH PRESSURE BUILDING INTO THE REGION HAS RESULTED IN WEAK WINDS
UNDER A STRONG SURFACE INVERSION. A LOW STRATUS DECK BTWN 2-3 KFT
AGL WILL CONTINUE AT LEAST THROUGH THE MORNING HOURS AT
KEAT...KGEG... KSFF...AND KCOE. DRIER AIR FROM THE NE SHOULD KEEP
WIDESPREAD FOG FROM DEVELOPING THIS MORNING...HOWEVER PATCHY AREAS
OF FOG WITH REDUCED VIS WILL BE POSSIBLE IN NORTHERN VALLEYS.
CEILINGS SHOULD LIFT TO VFR CONDITIONS AFTER 18Z...BUT LOWERING BACK
TO MVFR TONIGHT AS THE PERSISTENT SFC INVERSION STRENGTHENS UNDER
THE RIDGE. /SVH
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 42 33 42 36 40 30 / 0 0 0 50 70 30
COEUR D'ALENE 44 34 43 35 40 31 / 0 0 0 50 80 40
PULLMAN 42 34 45 36 39 30 / 0 0 0 20 70 50
LEWISTON 49 37 49 39 47 34 / 0 0 0 20 50 40
COLVILLE 44 35 41 34 41 31 / 10 20 20 50 60 20
SANDPOINT 41 30 36 35 37 31 / 10 10 10 50 80 40
KELLOGG 44 33 41 35 36 29 / 0 0 0 20 90 50
MOSES LAKE 48 31 45 34 46 29 / 0 10 10 40 20 10
WENATCHEE 45 37 44 34 45 33 / 0 20 20 40 10 10
OMAK 45 36 44 33 43 28 / 10 50 50 50 30 20
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
