Funnel Cloud in Idaho, May 30, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
449 PM PDT FRI MAY 30 2008

.SYNOPSIS...
AN UNSTABLE UPPER LEVEL LOW CURRENTLY JUST OFF THE WASHINGTON
COAST WILL APPROACH THE INLAND NORTHWEST THROUGH THE WEEKEND.
UNSTABLE CONDITIONS ASSOCIATED WITH THIS LOW WILL CONTINUE TO
RESULT IN CHANCES OF THUNDERSTORMS....ESPECIALLY DURING THE
AFTERNOON AND EVENING HOURS.

&&

.DISCUSSION...
TONIGHT AND SATURDAY...WHILE THE OVERALL FLOW PATTERN OVER THE
REGION HAS CHANGED LITTLE OVER THE LAST 24 HOURS...WITH WEAK
SOUTH/SOUTHWESTERLY FLOW AHEAD OF AN OFFSHORE TROUGH...THE AIR
MASS HAS DRIED CONSIDERABLY OVER THE NORTHERN AND CENTRAL REACHES
OF THE FORECAST AREA. THUS THIS EVENINGS SHOWER AND POSSIBLE
THUNDERSTORM ACTIVITY WILL BE HEAVILY RETARDED AND CONFINED MAINLY
TO THE MOUNTAIN RANGES NORTH AND EAST OF THE BASIN. OVER THE FAR
SOUTHEASTERN ZONES A STUBBORN DEFORMATION REGION IS CREATING
LINGERING SHOWERS AND ISOLATED THUNDERSTORMS OVER SHOSHONE COUNTY
AND THE HIGHER TERRAIN SOUTH OF LEWISTON. THIS AREA WILL BE THE
MAIN FOCUS OF EVENING ACTIVITY...MINORING OUT AFTER SUNSET. FOR
THE LIONS SHARE OF THE FORECAST AREA TONIGHT WILL FEATURE BENIGN
CONDITIONS WITH LIGHT WINDS AND SEASONABLY COOL MORNING
TEMPERATURES BY DAWN.

FOR SATURDAY MODELS ARE IN REASONABLE AGREEMENT REFLECTING THE
APPROACH OF THE OFFSHORE TROUGH WHICH WILL BEGIN PUMPING INCREASED
MOISTURE AND WARMER AIR INTO THE FORECAST AREA. THIS WILL RESULT
IN A MILD DESTABILIZATION OF THE AFTERNOON AND EVENING AIR MASS
WITH A THREAT OF SHOWERS AND THUNDERSTORMS MAINLY OVER THE WESTERN
BASIN ZONES AND CASCADES CLOSEST TO THE INCOMING TROUGH BAROCLINIC
BAND. THERE WILL ALSO BE AN INCREASE IN THUNDERSTORM POTENTIAL
OVER THE MOUNTAINS NORTH AND EAST OF THE BASIN BY LATE AFTERNOON
AS WELL...WITH OROGRAPHY GIVING THE ADDED LIFT NECESSARY TO ALLOW
CONVECTIVE DEVELOPMENT IN THE SLIGHTLY DRIER AIR MASS TO THE EAST.
HIGH TEMPERATURES SATURDAY WILL LIKELY CREST A BIT ABOVE
CLIMATOLOGICAL NORMALS WITH SOME PRE-TROUGH WARM ADVECTION WORKING
INTO THE REGION. /FUGAZZI

SATURDAY NIGHT THROUGH MONDAY...SMALL SYNOPTIC SCALE LOW THAT IS
POSITIONED OFF THE COAST THAT IS NESTED IN A LARGER SPLIT FLOW IN
THE WESTERLIES OFF THE COAST ALLOWS FOR PROLONGED PERIOD OF
SOUTHERLY FLOW TO INFLUENCE EASTERN WASHINGTON AND NORTHERN IDAHO.
SHORTWAVES MIGRATING IN A SOUTH TO NORTH TRAJECTORY OVER NORTHERN
CALIFORNIA AND OREGON HAVE BEEN HINTED AT IN PAST AND PRESENT
MODEL RUNS FOR SOME TIME NOW SO SOME POPS TO ACCOMMODATE LEFTOVER
WEATHER FOR SATURDAY INTO THE EVENING HOURS AS WELL AS THAT WHICH
MAY WELL OCCUR OVERNIGHT WITH THE FORCING REMAIN JUSTIFIED. THE
LOW LATER ACTS AS A PIVOT POINT TO SWEEP A SOUTHWEST TO NORTHEAST
TRAVELING FRONT CAPABLE OF PRODUCING MEASURABLE PRECIPITATION
THROUGH EASTERN WASHINGTON AND NORTHERN IDAHO SUNDAY. THE ACTUAL
LOW ITSELF IS EJECTED FROM ITS OFF COAST POSITIONING AND PASSES
OVER EASTERN WASHINGTON AND NORTHERN IDAHO SUNDAY NIGHT AND
MONDAY. POINTS TO PONDER THAT ARE WORKING AGAINST HIGH POPS ARE
THE FACT THAT THE MOISTURE SOURCE FOR ALL THE ACTIVITY IS NOT WELL
MAINTAINED AND IS QUITE HARD TO PICK OUT IN MODEL MOISTURE FIELDS.
ADDITIONALLY THE SENSIBLE WEATHER WILL BE FOR THE MOST PART
CONVECTIVE IN NATURE WHICH FURTHER COMPLICATES WHERE TO ASSIGN
HIGHER POPS. AS FAR AS ASSIGNING THUNDER THREAT WILL CONTINUE TO
LIMIT IT TO AFTERNOON/EVENING PERIODS AND PRIMARILY TO THE
NORTHEAST MOUNTAINS OF WASHINGTON AND NORTHERN IDAHO
PANHANDLE. FIRST GUESS OF GENERALIZED STORM MOTION SATURDAY
EVENING TO THE NORTH AT ABOUT 15 MPH...SUNDAY AFTERNOON/EVENING
TO THE NORTH AT ABOUT 10 MPH...AND MONDAY TO THE SOUTHEAST AT 10
MPH. /PELATTI

MONDAY NIGHT THROUGH FRIDAY...A TRANSITION TO A PROGRESSIVE WEST
TO NORTHWEST FLOW WILL OCCUR MONDAY NIGHT AND PERSIST ALL THE WAY
THROUGH THE WEEK. THIS WILL YIELD TEMPERATURES COOLING TO SLIGHTLY
BELOW NORMAL VALUES. THERE WILL ALSO BE EMBEDDED SHORT WAVES
DROPPING DOWN IN THE FLOW WITH LOW AND MID LEVEL W-NW FLOW
RESULTING IN THE BEST PRECIPITATION CHANCES NEAR THE CASCADE CREST
AND THE MOUNTAINS OF NE WA/N IDAHO. OVERALL CONFIDENCE IN THE
DETAILS OF THESE WAVES IS LOW DUE TO MODEL TO MODEL DIFFERENCES.
ONE SUCH SHORT WAVE LOOKS TO TRACK THROUGH TUE/TUE NGT...FOLLOWED
BY ANOTHER WAVE LATE IN THE WORK WEEK. WITH THE COOL ONSHORE FLOW
PATTERN THE LOW LEVELS WILL BE MORE STABLE COMPARED TO THE
UPCOMING WEEKEND WITH VERY LITTLE TO NO THUNDERSTORM ACTIVITY
EXPECTED. THIS PATTERN WILL ALSO SUPPORT A HIGH CHANCE OF BREEZY
CONDITIONS AT TIMES ESPECIALLY IN THE WENATCHEE RIVER
VALLEY AND ON THE WATERVILLE PLATEAU. JW

&&

.AVIATION...
VISIBLE SATELLITE AND LIGHTNING DETECTION INDICATES A FEW
THUNDERSTORMS DOWN OVER THE CAMAS PRAIRIE AREA.  GIVEN LIGHT
STEERING FLOW THESE STORMS ARE NOT EXPECTED TO IMPACT KLWS THIS
EVENING.  OTHERWISE CUMULUS WILL DECREASE IN COVERAGE WITH THE LOSS
OF DAY TIME HEATING AFTER SUNSET OVER EASTERN WA/N IDAHO.  CUMULUS
WILL AGAIN BUILD TOMORROW AFTERNOON AS THE ATMOSPHERE DESTABILIZES
WITH ISOLD -TSRA EXPECTED.  GIVEN ISOLATED COVERAGE LEFT MENTION OUT
OF TAFS.  JW

&&

.PRELIMINARY POINT TEMPS/POPS...
SPOKANE        48  77  54  70  51  71 /  10  10  20  40  30  20
COEUR DALENE  46  77  53  67  52  69 /  10  10  20  40  30  20
PULLMAN        47  74  52  70  50  69 /  20  10  20  40  30  20
LEWISTON       53  82  56  75  55  75 /  30  10  20  30  20  20
COLVILLE       45  80  50  68  47  72 /  20  20  20  40  30  30
SANDPOINT      45  76  51  67  49  67 /  20  20  20  40  30  30
KELLOGG        46  74  50  66  47  67 /  20  20  20  50  40  30
MOSES LAKE     50  81  56  80  54  79 /  10  10  20  10  10  10
WENATCHEE      54  77  58  76  56  78 /  10  20  20  10  10  10
OMAK           50  83  54  72  51  73 /  10  20  20  20  10  10

&&

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