000
FXUS66 KOTX 182340
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
435 PM PDT THU MAR 18 2010
.SYNOPSIS...
AFTER A VERY WEAK DISTURBANCE CLIPS NORTHERN IDAHO TONIGHT...HIGH
PRESSURE WILL BUILD INTO THE REGION FRIDAY AND SATURDAY FOR DRY
CONDITIONS. TEMPERATURES WILL WARM SEVERAL DEGREES ON SATURDAY AS
THE RIDGE MOVES OVERHEAD. THE NEXT SYSTEM WILL ARRIVE ON SUNDAY
AND MONDAY BRINGING A CHANCE FOR MOSTLY RAIN IN THE VALLEYS AND SNOW
IN THE MOUNTAINS.
&&
.DISCUSSION...
TONIGHT AND FRIDAY...WATER VAPOR SATELLITE SHOWS A VORT MAX WILL
MOVE SOUTHEAST ALONG THE BRITISH COLUMBIA AND ALBERTA BORDER INTO
NW MONTANA LATE THIS AFTERNOON AND EARLY EVENING. WITH THIS
FEATURE MOVING EAST OF N IDAHO...THE BEST INSTABILITY ASSOCIATED
WITH A COLD POOL OF -34C ALOFT WILL ALSO SLIDE TO THE EAST KEEPING
THE BEST THREAT FOR SHOWERS EAST OF THE AREA. STILL CAN NOT RULE
OUT AN ISOLATED SHOWER CLIPPING THE IDAHO/MONTANA BORDER...OTHERWISE
CUMULUS ASSOCIATED WITH AFTERNOON HEATING OVER THE NORTHERN AND
EASTERN MTNS WILL DISSIPATE AFTER SUNSET. WITH DEW POINTS IN THE
LOWER TO MID 20S AND MOSTLY CLEAR SKIES OVERNIGHT RADIATIONAL
COOLING WILL AGAIN BE EFFICIENT FOR ANOTHER COOL NIGHT SIMILAR TO
LAST NIGHT. ON FRIDAY UPPER LEVEL HIGH PRESSURE WILL BEGIN TO
BUILD IN RESULTING IN DRY CONDITIONS. HOWEVER RIDGE AXIS REMAINS
OFF THE COAST WITH 850MB TEMPS SIMILAR TO TODAY SO NO BIG
TEMPERATURE CHANGES ARE EXPECTED FRIDAY. JW
FRIDAY NIGHT TO SUNDAY...THE INLAND NW REMAINS UNDER HIGH PRESSURE
AND A DRY NLY FLOW UNTIL THE SYSTEM DEVELOPING NEAR 35N/145W COMES
IN. FRIDAY NIGHT TO SATURDAY A SFC HIGH SLOWLY SHIFTS ESE...THE
MID-LEVEL RIDGE AXIS NR THE COAST MIGRATES TOWARD ID AND THE NNW
FLOW TURNS W. THROUGH MUCH OF THIS PERIOD THERE IS AT LEAST WEAK
SUBSIDENCE AND THE ATMOSPHERE REMAINS RELATIVELY STABLE AND DRY.
IT IS NOT UNTIL SATURDAY AFTERNOON THAT SOME LOW-GRADE INSTABILITY
APPROACHES THE WESTERN CWA...WITH NEUTRAL OR WEAK LIFT WITH THE
APPROACH OF THE DEVELOPING LOW. EXPECT OCCASIONAL PERIODS OF
HIGHER CLOUDS AND SOME AFTERNOON CLOUD BUILD UP NEAR THE
CASCADES...BUT OTHERWISE QUIET WEATHER. TEMPERATURES ARE EXPECTED TO
BE ABOVE NORMAL... SUPPORTED BY 850 TEMPS PUSHING INTO THE
MID-SINGLE DIGITS SATURDAY AFTERNOON. SATURDAY NIGHT INTO SUNDAY THE
LOW SLIDES NNE TOWARD BC. IN CONJUNCTION...A WARM FRONT LIFTS ACROSS
THE CASCADES SATURDAY NIGHT QUICKLY FOLLOWED BY A COLD FRONT THAT
TRACKS ACROSS THE INLAND NW SUNDAY. MOST DEEPER MOISTURE AND LIFT IS
TIED TO THE COLD FRONT. EXPECT INCREASING CLOUDS THROUGH THE INLAND
NW SATURDAY NIGHT...WITH INCREASING RAIN AND HIGH MOUNTAIN SNOW
CHANCES OVER THE CASCADES. RAIN CHANCES WILL EXPAND EAST THROUGH
SUNDAY. A GFS/ECMWF BLEND IS FAVORED...PLACING THE HIGHEST
PRECIPITATION AMOUNTS OVER THE CASCADES. EXPECT BREEZY CONDITIONS
WITH THE PASSING FRONT...ALONG WITH COOLER TEMPERATURES SUNDAY
AFTERNOON RELATIVE TO SATURDAY. /JCOTE
SUNDAY NIGHT THROUGH TUESDAY...SHORTWAVE TROUGH WILL TRACK
ACROSS THE REGION BRINGING ELEVATED PRECIPITATION CHANCES AND
COOLER TEMPERATURES. THERE IS FAIR AGREEMENT AMONGST THE FORECAST
MODELS BUT STILL SOME UNCERTAINTY IN REGARDS TO WHAT DEGREE THE
LOW WILL RETROGRADE INTO THE BASE OF THE OFFSHORE RIDGE LEADING TO
SLIGHT TIMING DIFFERENCES WHEN THE SHORTWAVE CLEARS THE REGION
LATE TUESDAY. OTHERWISE...EVEN THE SLIGHT DIFFERENCES WITHIN THE
GUIDANCE YIELDS VERY LITTLE DIFFERENCE FOR THE UPCOMING WEATHER
ACROSS INLAND NW.
AS THE COLD POOL MOVES ACROSS THE REGION...JUST ABOUT EVERYWHERE
WILL HAVE A FAIR CHANCE FOR SHOWERS AS THE ATMOSPHERE BECOMES
INCREASINGLY UNSTABLE UNDER A -30 CELSIUS COLD POOL. THE HEAVIEST
AND MOST ORGANIZED PCPN WILL SET UP ALONG A WEAK AREA OF Q-VECTOR
CONVERGENCE AND ASSOCIATED HIGHER THETA-E AXIS WRAPPING UP THE
EASTERN FLANK OF THE SHORTWAVE WHICH WILL BE STRETCHED ACROSS THE
IDAHO PANHANDLE DOWN INTO NE OREGON. NOT ONLY WILL THE MOISTURE
CONTENT BE EXCEPTIONALLY HIGHER...BUT THE RELATIVELY
WARMER...MOIST LOW-LEVEL AIR WILL RESULT IN STEEPER 700-500H LAPSE
RATES AND FEED OFF LOW-LEVEL FORCING ASSOCIATED WITH W/NW
OROGRAPHIC FLOW INTO THE AFOREMENTIONED AREA. FOR THIS
REASONING...QPF AMOUNTS COULD BE ON THE ORDER OF 0.20" - 0.60".
THE MAIN CHALLENGE WILL BE HOW FAST SNOW LEVELS FALL. IT IS A
GIVEN THAT AS THE TROUGH MOVES ACROSS THE AREA...THE COLUMN
COOLS...AND SNOW LEVELS WILL BE FALLING. INITIALLY NEAR 3000-3500'
SUNDAY NIGHT STAYING SLIGHTLY ELEVATED ALONG THE THETA-E AXIS THEN
DOWN TO 2000' BY MONDAY NIGHT SO DEPENDING IN THE TRANSITION
THROUGH THE DAY MONDAY...THERE IS A MODERATE POTENTIAL FOR SNOW
ACCUMULATIONS AND WINTER HIGHLIGHTS ACROSS THE CAMAS
PRAIRIE...PALOUSE...INTO THE CENTRAL PANHANDLE MTNS.
ADDITIONALLY...THIS WILL ALSO BRING POTENTIAL FOR MODERATE
SNOWFALL ALONG THE CASCADE CREST AS 850-700H FLOW REMAINS W/NW
UNDER THE DOME OF INSTABILITY. WITH SOME SPILLOVER POSSIBLE INTO
THE UPPER EAST SLOPE VALLEYS. FOR THE REMAINDER OF THE
REGION...ISO-SCT SHWRS WILL BE MOST PROMINENT IN THE AFTERNOON HOURS
WITH SOME SURFACE HEATING...BUT WILL ALSO FOCUS ALONG MESOSCALE
VORTICITY MAXIMUMS WHICH TYPICALLY SPIN-UP IN THE CORE OF THESE
TROUGHS...BUT ARE POORLY MODELED DAYS IN ADVANCE.
ALTHOUGH VERY MARGINAL...THERE IS A SLIGHT POTENTIAL FOR AN
ISOLATED THUNDERSTORM MONDAY AFTN AS LI'S FALL -1 TO 0...LAPSE
RATES INCR NEAR 7.5C/KM...AND MARGINAL THERMODYNAMIC PROFILES
SETUP WITH SKINNY CAPE PROFILE ROUGHLY FROM 800-500MB OR WITHIN
THE -5 TO -25 CELSIUS LAYER. AS IN MOST SPRING- CASES...THE
COLUMN MAY BE TOO COOL TO GET SUFFICIENT CHARGE SEPARATION BUT ITS
WORTH KEEPING AN EYE ON...SPECIFICALLY ACROSS THE IDAHO
PANHANDLE.
TUESDAY NIGHT THROUGH THURSDAY NIGHT...HIGH PRESSURE WILL RETURN
TUESDAY NIGHT AND WEDNESDAY WITH A DRYING TREND AND SLOW WARMING
OF TEMPERATURES. ANOTHER WAVE WILL RIDE ALONG THE TOP OF THE RIDGE
WEDNESDAY NT AND THURSDAY HOWEVER THERE IS QUITE A BIT OF MODEL
SPREAD TO WHAT DEGREE THIS WAVE WILL IMPACT THE PAC NW. IN
COLLABORATION WITH NEIGHBORING OFFICES... HAVE DECIDED TO MAKE
LITTLE CHANGES TO THE FORECAST WHICH CONTINUES TO CALL FOR CLIMO
POPS AND NEAR SEASONAL TEMPERATURES. /SB
&&
.AVIATION...
SHORTWAVE RIDGING WILL CONTINUE TO BUILD INTO THE INLAND NW
THIS EVENING THROUGH TOMORROW RESULTING IN CONTINUED VFR
CONDITIONS AT ALL TAF SITES THROUGH 00Z SATURDAY. LINGERING
INSTABILITY OVER THE ID PANHANDLE WILL KEEP THE THREAT FOR
ISO SHWRS THROUGH 02Z MAINLY VCNTY KCOE THEN SKC SKIES WILL
RETURN REGION-WIDE. LIGHT NORTHERLY GRADIENTS THIS AFTN WILL
GRADUALLY BECOME NE AND LIGHT OVERNIGHT...ANTICIPATE A FEW GUSTS
TO 20KTS ACROSS KMWH-KGEG-KCOE BEFORE THE DECOUPLING OF THE BL
AFT 03Z. SB
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 27 49 29 57 34 53 / 0 0 0 0 0 20
COEUR D'ALENE 25 50 27 58 32 53 / 0 0 0 0 0 20
PULLMAN 22 50 29 60 35 55 / 0 0 0 0 0 20
LEWISTON 31 54 32 65 40 60 / 0 0 0 0 0 20
COLVILLE 23 53 26 58 31 57 / 0 0 0 0 0 30
SANDPOINT 28 48 26 53 29 50 / 10 0 0 0 0 20
KELLOGG 26 48 28 57 33 52 / 10 0 0 0 0 30
MOSES LAKE 28 57 30 61 36 59 / 0 0 0 0 0 10
WENATCHEE 33 54 32 60 38 55 / 0 0 0 0 10 20
OMAK 25 57 30 60 33 57 / 0 0 0 0 10 20
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
