Severe Thunderstorm Warning 21, NWS Boise, ID

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE BOISE ID
350 AM MDT THU AUG 6 2009

.SHORT TERM...TODAY THROUGH FRIDAY...VERY POTENT SYSTEM FINALLY
MAKING ITS WAY ONSHORE AND IT IS HEADED STRAIGHT FOR OUR AREA. WE
WILL SEE PERIODS OF SHOWERS AND THUNDERSTORMS...SOME WITH HEAVY
RAIN...FROM THIS AFTERNOON RIGHT ON THROUGH FRIDAY. WITH SO MUCH
RAINFALL COMING...WE HAVE DECIDED TO DROP THE RED FLAG WARNING.
TEMPS WILL BE MUCH COOLER TODAY THAN IN RECENT DAYS OWING TO THE
CLOUD COVER AND RAIN COOLED AIR. A COLD FRONT WILL BECOME WELL
ORGANIZED ON OUR EASTERN BORDER THIS AFTERNOON. TONIGHT WILL BE
STORMY AND COOL...WITH WIDESPREAD RAINFALL AND NUMEROUS
THUNDERSTORMS. FRIDAY WILL BE A RECORD SETTING DAY WITH COOL
MAXIMUM TEMPERATURES. AT THIS TIME...IT APPEARS THAT HIGHS WILL BE
IN THE 40S AND 50S IN THE MTNS AND IN THE 60S IN THE LOWER
ELEVATIONS. THIS COOL AIR WILL BE PROVIDED BY THE UNUSUALLY STRONG
UPPER LEVEL STORM SYSTEM...COMBINED WITH CLOUDY SKIES AND MORE
RAIN COOLED AIR. WE HAVE CONSIDERED ISSUING A FLOOD WATCH FOR OUR
HIGHER TERRAIN...BUT WILL LET THE SERVICE HYDROLOGIST MAKE THAT
CALL DURING THE DAY. HIS EXPERTISE WILL BE CRITICAL IN MAKING THIS
DECISION. OVERALL...IT LOOKS LIKE WE MAY HAVE WIDESPREAD RAINFALL
AMOUNTS OF OVER AN INCH...WITH LOCAL MAXIMA OVER 2 INCHES. WINDS
WILL BE AN ISSUE THIS AFTERNOON... ESPECIALLY IN SOUTHERN OWYHEE
AND TWIN FALLS COUNTIES. OUR CURRENT FORECAST DOES NOT WARRANT A
WIND ADVISORY...BUT IT IS CLOSE. IF THERE IS INTERACTION WITH A
CONVECTIVE COMPLEX THIS AFTERNOON... ADVISORY LEVEL WINDS COULD
RESULT. WINDS WILL BE HIGHER THAN NORMAL AGAIN FRIDAY...MAKING THE
COOL WEATHER SEEM EVEN COOLER.

THERE IS A SEVERE WEATHER THREAT TODAY...MAINLY IN OUR SOUTHWEST
IDAHO COUNTIES. INSTABILITY WILL BE ABOUT AS HIGH AS WE EVER GET
THIS AFTERNOON. CAPE VALUES NEAR OR OVER 2000 WILL OCCUR...
ESPECIALLY IN THE WESTERN MAGIC VALLEY WHERE THE GREATEST SEVERE
WEATHER THREAT EXISTS. THIS IS ONE OF THOSE RARE DAYS WHERE WE SEE
SUPERCELL THUNDERSTORMS...JUST LIKE THEY DO OUT IN THE PLAINS. AND
ALTHOUGH THE THREAT IS STILL QUITE SMALL...WE NEED TO MENTION
TORNADOES AS A POSSIBLE THREAT BECAUSE OF THE COMBINATION OF SHEAR
AND INSTABILITY.

.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...WIDESPREAD
PRECIPITATION WILL PERSIST FRIDAY NIGHT AS THE COLD UPPER LEVEL
TROUGH REMAINS OVER IDAHO. ON SATURDAY...THE TROUGH WILL DRIFT
EASTWARD...CONFINING INSTABILITY SHOWERS TO SW IDAHO. HAVE
MAINTAINED FORECAST OF THUNDERSTORMS SATURDAY EVENING BUT HAVE
DECREASED PROBABILITY TO SLIGHT CHANCE DUE TO MARGINAL
INSTABILITY PARAMETERS. GENERALLY WARMER AND DRIER ACROSS SE ORE
AND THE WRN SNAKE PLAIN ON SATURDAY...BUT HIGHS STILL
APPROXIMATELY 15 DEGREES BELOW NORMAL. WARMING TREND WILL CONTINUE
SUNDAY AND MONDAY AS HEIGHTS REBOUND IN RESPONSE TO THE DEPARTING
TROUGH. BY WEDNESDAY...FLOW ALOFT WILL BECOME SOUTHWESTERLY /AHEAD
OF AN APPROACHING PACIFIC SYSTEM/ AND TEMPERATURES WILL WARM TO
NEAR NORMAL VALUES.

&&

.AVIATION...ISOLATED MVFR SHOWERS/THUNDERSTORMS WILL BECOME
SCATTERED IN NATURE BY LATE MORNING. BY 21Z THIS AFTERNOON...SHOWERS
AND EMBEDDED THUNDERSTORMS WILL BECOME WIDESPREAD ACROSS SE ORE AND
SW ID. EXPECT LOCAL IFR IN HEAVY RAIN AND WIDESPREAD MOUNTAIN
OBSCURATION THROUGHOUT THE AFT/EVE. LIGHT TO MODERATE WEST WINDS
- WITH 30-35 KT GUSTS NEAR KTWF AND KJER. ERRATIC AND EVEN
STRONGER GUSTS ARE LIKELY IN THE VICINITY THUNDERSTORMS.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
OR...NONE

&&

WEATHER.GOV/BOISE

SHORT TERM...SP
LONG TERM....MT
AVIATION.....MT

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BOISE ID
619 AM MDT THU AUG 6 2009

IDZ011>016-028>030-ORZ061>064-071230-
WEST CENTRAL MOUNTAINS-LOWER TREASURE VALLEY ID-BOISE MOUNTAINS-
UPPER TREASURE VALLEY-SOUTHWEST HIGHLANDS-WESTERN MAGIC VALLEY-
CAMAS PRAIRIE-OWYHEE MOUNTAINS-SOUTHERN TWIN FALLS COUNTY-
HARNEY COUNTY-BAKER COUNTY-MALHEUR COUNTY-
LOWER TREASURE VALLEY OR-
619 AM MDT THU AUG 6 2009 /519 AM PDT THU AUG 6 2009/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL
IDAHO...SOUTHWEST IDAHO...WEST CENTRAL IDAHO...NORTHEAST OREGON
AND SOUTHEAST OREGON.

.DAY ONE...TODAY AND TONIGHT
A STRONG FALL-LIKE UPPER LEVEL STORM SYSTEM WILL APPROACH
SOUTHEAST OREGON AND SOUTHWEST IDAHO TODAY. THUNDERSTORMS WILL BE
WIDESPREAD TODAY AND TONIGHT...AND HEAVY RAIN IS POSSIBLE FROM
THIS AFTERNOON THROUGH TONIGHT. IN ADDITION...SEVERE THUNDERSTORMS
ARE POSSIBLE TODAY AND TONIGHT. THE STORM PREDICTION CENTER HAS
PLACED MOST OF THE AREA IN THE SLIGHT RISK CATEGORY...SOMETHING
THAT ONLY HAPPENS TO US A FEW TIMES A YEAR. THIS AFTERNOON AND
TONIGHT THERE IS A RISK OF HAIL...DAMAGING WINDS...AND EVEN A
TORNADO. THE WESTERN MAGIC VALLEY HAS THE BEST CHANCE OF SEEING
SEVERE THUNDERSTORMS...BUT IN OUR OPINION ALL AREAS RUN AT LEAST A
SLIGHT RISK. THE STRONG UPPER LEVEL STORM SYSTEM WILL PASS OVER
THE AREA TONIGHT...BRINGING MUCH COOLER TEMPERATURES WITH IT.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY
WITH COOL AIR FROM THE UPPER LEVEL SYSTEM IN PLACE...HIGHS IN THE
VALLEYS ON FRIDAY WILL BE IN THE 60S...WITH 40S AND 50S IN THE
MOUNTAINS. HEAVY RAIN IS POSSIBLE FRIDAY...BUT WILL TAPER OFF
FRIDAY NIGHT INTO SATURDAY. A WARMUP WILL BEGIN SATURDAY...AND WILL
LAST WELL INTO NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...
ALL INFORMATION ON THUNDERSTORMS AND HEAVY RAIN WILL BE GREATLY
APPRECIATED. PLEASE CALL LOCAL LAW ENFORCEMENT OR THE NATIONAL
WEATHER SERVICE OFFICE IN BOISE. WE THANK YOU FOR YOUR ASSISTANCE.

SP