Flash Flooding in Idaho, May 6, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
201 PM PDT FRI MAY 6 2005

.SYNOPSIS...A WET STORM SYSTEM OVER NEVADA WILL SLOWLY EXIT THE
AREA FOR A SHORT DRYING TREND. ANOTHER PACIFIC SYSTEM WILL MOVE
INTO WESTERN OREGON BY SUNDAY FOR AN INCREASING THREAT OF
PRECIPITATION...ESPECIALLY ON MONDAY.

&&

.DISCUSSION...
TONIGHT...SQUEEZE PLAY CONTINUES THIS EVENING AS WESTERLY FLOW
FROM BC SYSTEM MEETS SOUTHERLY FLOW FROM NEVADA SYSTEM. CONFLUENCE
IS CURRENTLY ORIENTED FROM WALLA WALLA TO SANDPOINT...SO HAVE
HIGHEST POPS THERE AND EASTWARD. EXPECT THAT CONVECTIVE ACTIVITY
WEST OF THIS LINE WILL SLOWLY DIE OFF WITH SUNSET AS BC SYSTEM IS
ACTUALLY BRINGING IN SUBSIDENCE. LARGE SCALE LIFT FROM THE
CONVERGENT BAND WILL SLOWLY MOVE NORTH AND EAST TONIGHT...WITH
PRECIP LINGERING IN THE EASTERN PANHANDLE THROUGH THE NIGHT. WITH
SUCH WEAK SHEAR I AM NOT EXPECTING ANY SEVERE BUT WITH OBSERVED
CAPE VALUES NEARING 1000 J/KG ITS NOT IMPOSSIBLE THAT ONE OR TWO
CELLS MIGHT PRODUCE SEVERE HAIL.

SATURDAY...THIS LOOKS TO BE A FAIRLY BENIGN DAY...BETWEEN WEATHER
SYSTEMS. THE NEVADA LOW BEGINS TO KICK EAST AS OUR FLOW TURNS FROM
SOUTHERLY TO WEAK SOUTHWESTERLY. A WEAK STRETCHED-OUT VORT LOBE IN
THIS SOUTHWESTERLY FLOW MOVES OVER THE AREA SATURDAY AFTERNOON AND
EVENING. LOW POPS ARE CONFINED TO THE HIGHER TERRAIN WITH THIS
SYSTEM. NO MENTION OF THUNDER AS THE BC WAVE SHOULD DRY OUT OUR
LOW LEVEL MOISTURE SOMEWHAT...LIMITING INSTABILITY.

SUNDAY...ATTENTION THEN TURNS TO THE WEST AS ANOTHER PACIFIC
SYSTEM IS SET UP TO REPLACE THE ONE CURRENTLY OVER NEVADA. MODELS
CURRENTLY DONT DIG THIS SYSTEM QUITE AS FAR SOUTH AS THE CURRENT
ONE. THIS SHOULD SPELL A BETTER CHANCE OF PRECIPITATION FOR OUR
AREA. GOOD DIFLUENT SOUTHERLY FLOW AHEAD OF THIS SYSTEM ALWAYS
CATCHES OUR ATTENTION. TIMING OF THE ASSOCIATED SHORT WAVES IS
DIFFICULT AT THIS POINT. BUT FOR SUNDAY FEEL THAT THE BEST CHANCE
OF CONVECTION IS OVER THE OREGON HIGHLANDS DURING THE
AFTERNOON...MOVING INTO THE SOUTHERN BASIN DURING THE LATE
AFTERNOON AND EVENING. HAVE POPS IN ALL AREAS BUT CONFINED THE
THUNDER TO THE SOUTHERN ZONES FOR NOW.

MONDAY...THINGS START TO GET REAL INTERESTING. UPPER LOW OFF THE
OREGON COAST GIVING US VERY NICE SOUTHEASTERLY FLOW..WITH GOOD
MOISTURE FROM THE SOUTH. THIS HAS THE POTENTIAL FOR A GOOD WRAP-
AROUND BRAND OVER US. SOUTHEASTERLY FLOW INTO THE CASCADES ALSO
RAISES THE POTENTIAL FOR HEAVY PRECIPITATION THERE. GFS MODEL HAS
BEEN FAIRLY CONSISTENT ON THIS SCENARIO FOR THE PAST FEW RUNS.
WILL LEAVE POPS IN THE CHANCE CATEGORY BUT RAISE THEM TO NEAR
LIKELY AND ADD THUNDER TO ALL ZONES.  RJ

MONDAY NIGHT THRU FRIDAY...EARLY PART OF THE WORK-WEEK CONTINUES TO
REMAIN UNSETTLED AS LARGE CUT OFF LOW EXPECTED TO HOVER PARTLY OVER
EASTERN OREGON AND SOUTHWEST IDAHO MOVES SLOWLY GETS STEERED TO THE
EAST BY THE SOUTHERN BRANCH OF THE FLOW OVER THE WESTERN US.
BLOCKING RIDGE PATTERN WITH AXIS ALIGNED UP AND DOWN OVER THE BC
PROVINCE REMAINS OVER THE NORTHERN BRANCH FOR A TIME. THE EXPECTATION
IS THAT THE CUT OFF LOW WILL ACT LIKE A FERRIS WHEEL AND SPIN MINOR
SHORTWAVES AROUND ITS PERIPHERY. THEREFORE IT IS REASONABLE TO EXPECT
A FEW OF THESE SHORTWAVES TO GET PUSHED UP INTO EASTERN WASHINGTON
AND NORTHERN IDAHO IN SUCH A WAY TO MAKE ANY STORMS THAT FORM IN AND
SOUTH OF OUR REGION TO THE NORTH AND NORTHWEST WITH TIME. 850MB
THETA-E SHOWS ADEQUATE MOISTURE GETTING WRAPPED AROUND THE LOW AND
OVER IDAHO SO THE MOISTURE SHOULD BE THERE...THE SHORTWAVES SUPPLY
THE LIFT...AND THE INSTABILITY SHOULD ALSO BE THERE DUE TO THE
PRESENCE OF THE UPPER LEVEL CUT OFF LOW COOLING UPPER LEVEL
TEMPERATURES AND LOW LEVEL WARM AIR ADVECTION AND DAYTIME
HEATING INCREASING THE LAPSE RATES. WILL DECREASE POPS FROM WEST TO
EAST WITH TIME IN THE TUESDAY AND WEDNESDAY TIME PERIOD AS THE CLOSED
LOW MOVES FURTHER AWAY AND SHORTWAVE RIDGING MOVES OVERHEAD.
DRY FORECAST DUE TO THE SHORTWAVE RIDGING PERSISTS INTO
THURSDAY. GFS HAS BEEN DELAYING ONSET OF NEXT PACIFIC FRONTAL SYSTEM
SO FOR NOW HAVE IT ONLY AFFECTING THE CASCADES FRIDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
SPOKANE        46  64  45  63  46  62 /  40  10  20  20  30  50
COEUR DALENE  47  63  45  63  45  61 /  70  20  20  20  30  40
PULLMAN        47  58  43  61  47  59 /  60  10  20  20  30  50
LEWISTON       51  66  47  67  50  63 /  70  10  20  20  40  50
COLVILLE       44  72  44  68  43  65 /  30  10  20  20  30  50
SANDPOINT      46  65  45  64  44  61 /  70  20  30  30  30  40
WALLACE        44  59  42  60  42  56 /  80  30  40  30  30  50
MOSES LAKE     48  72  45  69  47  66 /  10  10  10  20  40  50
WENATCHEE      51  72  50  70  51  65 /   0  10  10  20  40  50
OMAK           47  74  45  70  46  65 /  10  10  10  20  30  50

&&

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