EASTERN WASHINGTON AND NORTH IDAHO AREA FORECAST DISCUSSION
NWS SPOKANE WASHINGTON
AFDGEG 230 AM PST SAT JAN 18 2003
.SYNOPSIS...A STRONG RIDGE OF HIGH PRESSURE WILL RESIDE OVER THE
PACIFIC NORTHWEST THROUGH THE WEEKEND. THIS WILL KEEP STRONG
TEMPERATURE INVERSIONS IN PLACE RESULTING IN PERSISTENT CLOUDINESS
FOR THE VALLEYS AND COLUMBIA BASIN. A WEAK STORM SYSTEM WILL MOVE UP
THE COAST ON MONDAY...POSSIBLY BRINGING SOME LIGHT PRECIPITATION TO
THE AREA.
.DISCUSSION...
.TODAY THROUGH SUNDAY...UPPER LEVEL LONGWAVE RIDGE PATTERN OVER THE
PAC NW SHOWS ALMOST NO DEVIATION THROUGH THE WEEKEND. THIS WILL
RESULT IN PERSISTENT INVERSIONS AND WIDESPREAD CLOUDINESS OVER MOST
OF EAST WASHINGTON. THE MIXING POTENTIAL BENEATH THE INVERSION LOOKS
VERY WEAK WITH MEAN WIND SPEEDS WELL BELOW 10 KTS IN MOST INSTANCES.
DESPITE THE CLOUDINESS...THE PRESENCE OF FOG WAS ALMOST NON-EXISTENT.
10Z NEPHANALYSIS SHOWS A NEARLY UNIFORM DECK OF STRATUS WITH BASES
RANGING FROM 2500 TO 3500 FT MSL AND TOPS PER EARLIER PIREPS AND
ACARS SOUNDINGS AROUND 4500 FT MSL. WE DO NOT EXPECT MANY CHANGES TO
TRANSPIRE WITH THIS DECK THROUGH SUNDAY. CONSEQUENTLY ALL LOCATIONS
BELOW 4500 FEET SHOULD REMAIN CLOUDY WHILE THE MOUNTAINS WILL
CONTINUE TO BASK IN SUN. TEMPS BENEATH THE STRATUS WILL DEVIATE
LITTLE DURING THIS TIME. YESTERDAY WAS A PRIME EXAMPLE OF WHAT CAN
HAPPEN WITH WIDESPREAD CLOUDS AND LIGHT WINDS AS MOST LOCATIONS
STRUGGLED TO ESCAPE THE LOWER TO MIDDLE 30S. THE VARIOUS MOS GUIDANCE
SUITES DO NOT REALLY HELP IN THIS SITUATION AND TEND TO FORECAST MUCH
WIDER TEMPERATURE SWINGS THAN WHAT WILL REALLY OCCUR. CONSEQUENTLY WE
WILL FORECAST COOLER HIGHS AND MILDER LOWS.
.SUNDAY NIGHT THROUGH MONDAY...THE LATEST GFS AND ETA SOLUTIONS TAKE
THE SHORTWAVE TROF...CURRENTLY NEAR THE DATELINE...TOWARD THE
LONGWAVE RIDGE AND ATTEMPT TO UNDERCUT IT BY LATE MONDAY. NOT TOO
CONFIDENT IT WILL BE THAT EASY TO DO...ESPECIALLY SINCE MUCH MORE
ENERGY WILL REMAIN FARTHER UPSTREAM TO THE WEST. WHILE THE AVN/GFS IS
FORECASTING LIGHT PRECIPITATION OVER OUR FAR NORTHERN ZONES AND NEAR
THE CASCADES LATE MONDAY AND MONDAY EVENING...THE ETA KEEPS OUR ZONES
DRY. THIS IS A SAFER BET ESPECIALLY SINCE THE SURFACE/850 MB LOW WILL
REMAIN FAR OFFSHORE WITH ONLY WEAK ASCENT EXPECTED NEAR THE CASCADES.
ISENTROPIC ASCENT WILL LIKELY BE TOO MEAGER TO HELP THE SITUATION
ELSEWHERE.
.TUESDAY THROUGH FRIDAY...MODELS SEEM TO BE SETTLING DOWN AFTER A
PERIOD OF TRYING TO BRING CONSIDERABLE COLD AIR INTO THE CWFA ON
EARLIER RUNS. SCENARIO NOW APPEARS TO AGREE ON A SERIES OF SHORT
WAVES MOVING INTO THE LONG WAVE RIDGE POSITION OVER THE NORTHWEST AND
WEAKENING IT AND PUSHING IT EAST...FORMING A NEAR ZONAL FLOW BY
FRIDAY. SEVERAL SHORT WAVES MOVING THROUGH THE NORTHWEST OVER THIS
FOUR DAY PERIOD WITH RAIN IN THE VALLEYS AND SNOW OVER THE MOUNTAINS.
SNOW LEVEL AND TEMPERATURES TO BE ON THE RISE TUESDAY THROUGH FRIDAY.
...THE INFORMATION IN THIS PRODUCT CONCERNING WARNINGS AND FORECASTS
IS VALID ONLY AT THE TIME OF ISSUANCE. THE LATEST WARNING AND
FORECAST INFORMATION WILL BE FOUND IN THE APPROPRIATE PRODUCTS...
GEG 034/029/035/029/036 00001
COE 035/029/036/029/036 00001
PUW 033/029/036/027/039 00001
LWS 035/032/039/034/042 00001
CQV 033/028/035/031/036 00001
SPT 035/028/036/028/033 00002
WWP 035/027/036/028/036 00002
EAT 035/031/037/032/036 00001
MWH 037/029/039/031/038 00001
OMK 035/029/036/027/033 00002
.OTX...NONE.