FXUS66 KOTX 231200
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
359 AM PST WED DEC 23 2009
.SYNOPSIS...
THE UPPER LEVEL TROUGH OF LOW PRESSURE WHICH IMPACTED THE
INLAND NORTHWEST YESTERDAY WILL SHIFT INTO EASTERN MONTANA THIS
AFTERNOON. MEANWHILE...STRONG HIGH PRESSURE WILL GRADUALLY BUILD OVER
THE PACIFIC NORTHWEST. THIS RIDGE IS EXPECTED TO PERSIST THROUGH
NEXT WEEK...RESULTING IN LITTLE IF ANY CHANCE OF MEASURABLE
PRECIPITATION. IT WILL ALSO BRING INCREASING CHANCES FOR FOG AND
LOW CLOUDS IN THE VALLEYS.
&&
.DISCUSSION...
TODAY AND TONIGHT...EXTENDED BENIGN WEATHER PATTERN IS EXPECTED TO
START IN THIS PERIOD. THE DEEP TROUGH OF LOW PRESSURE WHICH
BROUGHT SHOWERS MAINLY TO THE IDAHO PANHANDLE WILL SHIFT INTO
EASTERN MONTANA BY LATE THIS AFTERNOON. DEEP NORTHWEST FLOW ON THE
BACK SIDE OF THE RIDGE WILL ALLOW A MUCH DRIER AIRMASS TO
INFILTRATE THE INLAND NW...ELIMINATING THE CHANCES FOR MEASURABLE
PRECIPITATION OVER MOST OF THE CWA. WE WILL HOLD ONTO SMALL
CHANCES OF PRECIPITATION FOR THE CENTRAL IDAHO PANHANDLE THROUGH
EARLY AFTERNOON...AS THE MEAN 850 MB FLOW TURNS NORTHWESTERLY WITH
TIME. THIS FAVORABLE OROGRAPHIC UPSLOPE FLOW REGIME WILL INTERACT
WITH A MOIST LAYER TRAPPED BENEATH 700 MBS. NORTHWEST FLOW TENDS
TO FAVOR THE CAMAS PRAIRIE AND SOUTHERN SHOSHONE COUNTY FOR
PRECIPITATION PROVIDED THERE IS MOISTURE AND DECENT POTENTIAL
INSTABILITY. NEITHER IS TOO IMPRESSIVE WITH THIS REGIME...BUT MORE
CRITICAL IS THE LACK OF A SATURATED DENDRITIC LAYER. GIVEN THE
TIME-HEIGHT SECTIONS AND MODEL SOUNDINGS OVER THE CAMAS PRAIRIE
AND SOUTHERN SHOSHONE COUNTY...WE SUSPECT THE MOISTURE
DISTRIBUTION AND LIFTING WILL ONLY SUPPORT FLURRIES.
ASIDE FROM THE PRECIPITATION...THE MAIN FOCUS WILL REVOLVE AROUND
TEMPERATURES. TYPICALLY WITH THE PASSAGE OF A DEEP UPPER LEVEL
TROUGH AND THE INTRUSION OF NORTH-NORTHWEST FLOW IN THE LOWER
ATMOSPHERE...WE SHOULD SEE A GOOD DROP IN
TEMPERATURES...ESPECIALLY GIVEN THE PRESENCE OF A 1040MB HIGH OVER
CENTRAL BC. HOWEVER IN THIS CASE...WE WILL PROBABLY JUST SEE A
GLANCING BLOW AS THE UPPER LEVEL JET ONLY TOUCHES THE NORTHERN ID
PANHANDLE THIS MORNING AND THEN RAPIDLY SHIFTS EAST. IF THE JET
REMAINED OVER THE INLAND NW AND CONTINUED TO DIG THROUGH THE
DAY...IT WOULD BE ANOTHER STORY. THE RAW MODEL
GUIDANCE...PARTICULARLY THE GFS...IS HAVING A DIFFICULT TIME WITH
THE TEMPERATURE FORECAST. IT PLUNGES TEMPS THROUGH THE DAY OVER
NORTH-CENTRAL WASHINGTON AS IT TAKES THE ARCTIC
AIRMASS INTO THE NORTHERN COLUMBIA BASIN BY AFTERNOON.
MEANWHILE...THE WARMER NAM SOLUTION...GIVEN THE TRACK OF THE UPPER
LEVEL JET...SEEMS MUCH MORE REASONABLE. WHILE THE TEMPS WILL NOT
LIKELY FALL AS MUCH AS THE GFS SHOWS...THE DEWPOINTS WILL PLUNGE
TODAY. THE LOW DEWPOINTS WILL MINIMIZE THE THREAT OF FOG TONIGHT
AND WILL ALSO ALLOW SOME OF THE PROTECTED VALLEYS TO SEE MIN
TEMPS DROP WELL INTO THE SINGLE DIGITS GIVEN CLEAR SKIES AND LIGHT
WINDS. FX
THURSDAY THROUGH SUNDAY...THERE IS GOOD MODEL AGREEMENT DURING
THIS PERIOD OF UPPER LEVEL HIGH PRESSURE MOVING OVER THE AREA. AS
IT DOES SO...850MB TEMPS SHOW A WARMING TREND. ON THURSDAY THEY
BEGIN AT -5C NEAR THE CASCADES AND -10C OVER N IDAHO
PANHANDLE...BEFORE MODERATING TO NEAR 0C OVER THE WEEKEND.
HOWEVER...IN THE VALLEYS WARMING WILL BE VERY TOUGH TO REALIZE DUE
TO STRENGTHENING TEMPERATURE INVERSIONS AND POOR MIXING POTENTIAL
WITH THE SHORT LATE DECEMBER DAYS. IN ADDITION BOUNDARY LAYER
MOISTURE WILL BE GRADUALLY INCREASING BENEATH THE INVERSION
ESPECIALLY AFTER RECENT RAINFALL. THIS WILL PROMOTE AN INCREASE IN
STRATUS AND FREEZING FOG IN THE VALLEYS ESPECIALLY OVER THE
WEEKEND WITH THE RIDGE MOVES ON TOP OF THE INLAND NW. THIS PATTERN
WILL LEAD TO AIR STAGNATION CONCERNS.
MONDAY THROUGH TUESDAY...THE STAGNANT PATTERN WILL LIKELY CONTINUE
INTO NEXT WEEK AS THERE ARE NO SIGNIFICANT FRONT PASSAGES SHOWING UP
IN THE MODELS TO SCOUR OUT THE COLD AIR IN THE VALLEYS. STRONG SPLIT
FLOW OFF THE COAST WILL GREATLY WEAKEN ANY SYSTEMS THAT ATTEMPT TO
MOVE OVER THE AREA MONDAY AND TUESDAY. JW
&&
.AVIATION...
MAIN AVIATION CONCERN FROM 12Z WED-12Z THU WILL BE AREA OF MVFR CIGS
OVER THE SE QUARTER OF WA AND MOST OF CENTRAL ID. THESE CLDS WILL
IMPACT ALL TAFS XCFP KMWH AND KEAT THROUGH AT LEAST EARLY
AFTN...HWVR DRIER AIR MOVING IN FROM THE NW WILL ERODE THE CLOUDS
FROM NW-SE THROUGH THE DAY. KGEG KSFF AND KCOE WILL SEE THE CLDS
ERODE FIRST...WITH PERIODIC MVFR CIGS PSBL THRU 15Z. KPUW WILL SEE A
MUCH SLOWER BREAKUP GIVEN AMOUNT OF CLDS UPSTREAM. WE WILL SHOOT FOR
A 18-19Z BREAKUP...BUT CONFIDENCE IS NOT TOO HIGH. KLWS WILL ALSO
SEE PERIODIC CIGS BTWN 035-050 THROUGH EARLY AFTERNOON. VFR
CONDITIONS EXPECTED AT ALL TAF SITES AFT 20Z AND CONTINUING THROUGH
12Z THU. FX
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 29 12 23 14 26 17 / 0 0 0 0 0 0
COEUR D'ALENE 30 13 24 15 27 16 / 0 0 0 0 0 0
PULLMAN 30 16 25 17 30 19 / 10 0 0 0 0 0
LEWISTON 35 20 30 19 29 19 / 10 0 0 0 0 0
COLVILLE 28 9 25 12 27 15 / 0 0 0 0 0 0
SANDPOINT 32 11 22 13 25 13 / 10 0 0 0 0 0
KELLOGG 28 12 22 13 25 12 / 20 0 0 0 0 0
MOSES LAKE 32 14 27 13 27 13 / 0 0 0 0 0 0
WENATCHEE 34 19 27 19 26 18 / 0 0 0 0 0 0
OMAK 28 10 24 10 25 15 / 0 0 0 0 0 0
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
