Debris Flow in Washington, March 27, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
451 PM PDT SUN MAR 27 2011

.SYNOPSIS...
A WET AND COOLER THEN NORMAL SPRING WEATHER PATTERN CONTINUE OVER
THE PACIFIC NORTHWEST THIS WEEK. PERIODS OF PRECIPITATION
WILL FALL MAINLY AS MOUNTAIN SNOW AND VALLEY RAIN...BUT WITH A
CHANCE OF OVERNIGHT LIGHT WET SNOW ACCUMULATIONS IN THE VALLEYS
AND HIGHER PLATEAUS OF THE COLUMBIA BASIN.

&&

.DISCUSSION...
TONIGHT AND TOMORROW...COLD POOL ALOFT REFLECTED BY KOTX SOUNDING
SHOWING 500MB TEMPS OVERHEAD NEAR -30C INTO TOMORROW. RESULTING
LAPSE RATES ARE SOMEWHAT CONDITIONALLY UNSTABLE AND RUNNING
SLIGHTLY ABOVE 7 DEG C/KM. TRIGGERING MECHANISMS THAT COULD BE
UTILIZED TO PRODUCE CONVECTIVE RAIN AND SNOW SHOWERS COULD EITHER
BE OROGRAPHIC OR A MESOSCALE FEATURE EXPECTED TO ROTATE AS IT
MOVES THROUGH IN A WEST TO EAST FASHION AND PRIMARILY INFLUENCE
SOUTHEAST WASHINGTON AND NORTHERN IDAHO INTO TOMORROW. SNOW LEVELS
NOT VERY USEFUL WITH SPRINGTIME CONVECTION BUT HAVE TRIED TO SHOW
THIS BY UTILIZING VERY LOW ONES OR REMOVING THEM WHEN POSSIBLE
WITH THE IDEA THAT SNOW ACCUMULATIONS OVERNIGHT IN ANY
LOWLAND/VALLEY AREA COULD LINGER FOR A FEW HOURS BUT DURING THE
DAY IT IS LESS LIKELY TO OCCUR. FORECAST TEMPERATURES REMAIN A BIT
ON THE COLD SIDE OF NORMAL FOR THIS TIME OF YEAR GIVEN THE
TROF/COLD POOL SOLUTION DESCRIBED ABOVE. /PELATTI

MONDAY NIGHT THROUGH WEDNESDAY...THROUGH THIS TIME PERIOD THE
FORECAST WILL GO THROUGH A TRANSITION PERIOD. WEAK RIDGING LATE ON
MONDAY WILL QUICKLY BREAK DOWN MONDAY NIGHT AND ALLOW YET ANOTHER
FAST MOVING AND WEAKENING UPPER LEVEL LOW TO TRACK INTO BRITISH
COLUMBIA. BEHIND THIS UPPER LEVEL LOW THE FLOW WILL BECOME
WESTERLY AS WEAK HIGH PRESSURE SLOWLY BUILDS ALONG THE COAST.
AMPLE MOISTURE WILL MOVE IN OFF THE PACIFIC KEEPING AT LEAST SOME
CHANCE OF PRECIPITATION IN THE FORECAST.

MONDAY NIGHT AND TUESDAY..THE UPPER LEVEL FLOW WILL TURN
SOUTHWESTERLY MONDAY NIGHT AND TAP INTO AMPLE PACIFIC MOISTURE.
PW'S WILL INCREASE TO ABOVE A HALF INCH. LIFT WILL BE PROVIDED BY
THE COMBINATION OF ISENTROPIC UP- GLIDE ALONG THE 290-295KT
SURFACE AND UP-SLOPING FLOW INTO THE HIGHER TERRAIN. WARM OVER-
RUNNING PRECIPITATION WILL BEGIN ALONG THE CASCADE CREST BETWEEN
09-12Z AND THEN SLOWLY MOVE INTO THE AREA TUESDAY MORNING. THE
FOCUS OF THE PRECIPITATION WILL BE ACROSS THE NORTHERN AND EASTERN
HIGHLANDS. THE LOWER EAST SLOPES AND THE DEEP BASIN WILL MOST
LIKELY GET SHADOWED OUT BY THE SOUTHWEST FLOW BUT MANY AREAS WILL
SEE SOME LIGHT PRECIPITATION. THERE IS NO CLEAR CUT SURFACE COLD
FRONT WITH THIS SYSTEM...ALTHOUGH A VERY WEAK FRONT IS DISCERNIBLE
AT BETWEEN 7-5H. WHILE INSTABILITY WILL BE WEAK TUESDAY AFTERNOON
PRECIPITATION WILL TURN FROM STRATIFORM TO CONVECTIVE...NOT THAT
IT WILL BE THAT NOTICEABLE.

TUESDAY NIGHT INTO WEDNESDAY...THE FLOW BECOMES WESTERLY ALLOWING
FOR INCREASE PACIFIC MOISTURE TO STREAM INTO THE REGION. NO STRONG
LIFTING OR FORCING MECHANISM ARE EXPECTED. HOWEVER THE SHEAR
AMOUNT OF MOISTURE WILL KEEP HIGH POPS AND AMPLE PRECIPITATION IN
THE FORECAST. WESTERLY FLOW IS NOT CONDUCIVE FOR MUCH
PRECIPITATION FOR THE LOWER EAST SLOPES AS THIS FLOW SHADOWS OUT
THESE AREAS. HOWEVER THE NORTHERN AND EASTERN MOUNTAINS AND THE
CASCADE CREST SHOULD GET AN EXTENDED PERIOD OF LIGHT PRECIPITATION.

SNOW LEVELS WILL BE FLUCTUATING BY QUITE A BIT...BUT EXPECT MAINLY
RAIN FOR MOST OF THE LOWER ELEVATION....WITH A PERIOD OF RAIN/SNOW
MIX AT NIGHT AND SNOW ABOVE 3000-3500 FEET FOR THE MOUNTAINS. BY
WEDNESDAY AFTERNOON SNOW LEVELS WILL RISE ABOVE 4000 FEET FOR THE
ENTIRE FORECAST AREA. /TOBIN

WEDNESDAY NIGHT THROUGH SUNDAY...THE MODELS ARE IN GOOD AGREEMENT
OF A LOW PRESSURE SYSTEM IN THE GULF OF ALASKA TO BEGIN THE
EXTENDED PERIOD. A MOIST WESTERLY FLOW IS AIMED AT SOUTHERN
BC...WASHINGTON...AND NORTH IDAHO. MODELS ARE STRUGGLING WITH THE
EXACT PLACEMENT OF AND TIMING OF BOTH THE MOIST BAROCLINIC
BOUNDARY THAT SETS UP...AND A COLD FRONT PASSAGE. ALL IN ALL...A
WET PERIOD LOOKS TO BE IN STORE WED NGT/THU...AND POSSIBLY FRIDAY
FOR THE CASCADE CREST AND MOUNTAINS OF NORTH IDAHO. SNOW LEVELS
LOOK TO INCREASE TO 5-6K FEET WEDNESDAY NIGHT AND THURSDAY AHEAD
OF THE COLD FRONT SO A PERIOD OF WARMER TEMPERATURES IS EXPECTED.
THEN AFTER THE COLD FRONT PASSAGE THURSDAY NIGHT OR FRIDAY...SNOW
LEVELS WILL FALL BACK DOWN TO THE HIGHER VALLEYS AND MOUNTAINS AS
THE TROUGH AXIS MOVES INLAND PROVIDING AN UNSTABLE AND SHOWERY AIR MASS
OVER THE AREA. DOWNSLOPE FLOW OFF THE CASCADES WED NGT THROUGH
SATURDAY SHOULD KEEP MOST OF THE COLUMBIA BASIN AND LEE SIDE
CASCADE VALLEYS DRY. A DRY PERIOD IS POSSIBLE FOR ALL AREAS ON
SUNDAY AS THE TROUGH DEPARTS AND A SHORT WAVE RIDGE MOVES OVER THE
AREA PER 12Z GFS AND ECMWF MODELS...BUT GIVEN THE PROGRESSIVE FLOW
PATTERN CONFIDENCE ON THE TIMING OF THIS DRY PERIOD IS LOW. JW

&&

.AVIATION...
BANDS OF SHOWERS WILL ROTATE NORTH INTO EASTERN WASHINGTON AND NORTH
IDAHO THROUGH 18Z MONDAY AS A LOW PRESSURE SYSTEM MOVES INTO OREGON.
THE GREATEST CONCENTRATION WILL OCCUR OVER SOUTHEAST
WASHINGTON...INCLUDING KPUW WHICH WILL BE IN CLOSEST PROXIMITY TO
THE LOW.  IN ADDITION SNOW LEVELS WILL BE NEAR 2000-2500 FEET IN
THIS AREA RESULTING IN -SN AT KPUW WITH CIGS BECOMING IFR AND VSBYS
MVFR.  THIS AREA OF LOW LEVEL MOISTURE OVER SE WASHINGTON IS SHOWN
BY MODELS TO ADVECT NORTH INTO KGEG/KSFF/KCOE BTWN 8-18Z WITH
IFR/MVFR STRATUS EXPECTED.  ALL AREAS WILL SEE IMPROVEMENT BY 19Z
MONDAY AS THE LOW PRESSURE SYSTEM DEPARTS AND CLOUD BASES RISE.  JW

&&

.PRELIMINARY POINT TEMPS/POPS...
SPOKANE        33  48  35  45  36  50 /  60  20  20  70  30  40
COEUR D'ALENE  31  48  33  43  34  48 /  60  30  20  80  30  50
PULLMAN        32  48  35  46  36  51 /  80  20  10  70  40  40
LEWISTON       36  55  38  54  38  57 /  70  30  10  50  30  40
COLVILLE       32  52  33  49  35  51 /  50  30  20  80  30  60
SANDPOINT      32  46  32  42  34  45 /  50  40  20  80  40  60
KELLOGG        30  44  31  41  33  44 /  70  50  20  80  60  60
MOSES LAKE     32  56  36  56  37  58 /  50  10  50  30  10  10
WENATCHEE      32  53  38  53  38  57 /  70  10  60  20  10  10
OMAK           33  55  35  52  35  55 /  60  10  60  50  10  20

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SPOKANE WA
1002 AM PDT SUN MAR 27 2011

IDZ001>004-026-027-WAZ031>038-041>044-281715-
NORTHERN PANHANDLE-COEUR D'ALENE AREA-IDAHO PALOUSE-
CENTRAL PANHANDLE MOUNTAINS-LEWISTON AREA-
LEWIS AND SOUTHERN NEZ PERCE COUNTIES-NORTHEAST BLUE MOUNTAINS-
LOWER GARFIELD AND ASOTIN COUNTIES-WASHINGTON PALOUSE-
MOSES LAKE AREA-UPPER COLUMBIA BASIN-SPOKANE AREA-
NORTHEAST MOUNTAINS-OKANOGAN HIGHLANDS-WENATCHEE AREA-
EAST SLOPES NORTHERN CASCADES-OKANOGAN VALLEY-WATERVILLE PLATEAU-
1002 AM PDT SUN MAR 27 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH IDAHO...
NORTH CENTRAL IDAHO...CENTRAL WASHINGTON...EAST CENTRAL
WASHINGTON...NORTH CENTRAL WASHINGTON...NORTHEAST WASHINGTON AND
SOUTHEAST WASHINGTON.

.DAY ONE...TODAY AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

A SERIES OF STORMS WILL PASS THROUGH THE REGION THROUGH MID WEEK.
MOTORISTS PLANNING TO TRAVEL OVER THE PASSES IN NORTH IDAHO AS
WELL AS THE PASSES IN CENTRAL AND EASTERN WASHINGTON SHOULD
ANTICIPATE INTERMITTENT WINTER DRIVING CONDITIONS. NO MAJOR SNOW
STORMS ARE ANTICIPATED AT THIS TIME...BUT SLUSHY SNOW ACCUMULATIONS
WILL MAKE DRIVING SLIPPERY FROM TIME TO TIME...ESPECIALLY ABOVE
3000 FEET.