Severe Thunderstorm Warning 177, NWS Cheyenne, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
345 PM MDT WED SEP 3 2008

.SHORT TERM...TONIGHT THROUGH FRIDAY AFTERNOON.

TONIGHT...AS PROMISED BY THE NAM AND GFS AND AS SEEN IN VISIBLE
SATELLITE IMAGERY AND SURFACE OBSERVATIONS...LOW LEVEL CONVERGENCE
AXIS HAS FORMED ALONG THE INTERSTATE 25 CORRIDOR AND THE SPINE OF
THE LARAMIE RANGE. BASED ON CONVECTIVE PARAMETERS...EXPECTING
ISOLATED TO SCATTERED THUNDERSTORMS TO DEVELOP THROUGH EARLY EVENING
ALONG THE LOW LEVEL CONVERGENCE AXIS AND THE NORTH TO SOUTH PORTION
OF THE INTERSTATE 25 CORRIDOR...THEN STORMS PROPAGATING EAST THROUGH
LATE EVENING INTO OUR NORTHERN AND EASTERN COUNTIES. AN ISOLATED
STRONG TO SEVERE THUNDERSTORM WILL BE POSSIBLE WITH LIFT AIDED BY
SHORTWAVE TROUGH MOVING ACROSS AT PEAK HEATING ALTHOUGH CAPE WILL BE
MARGINAL. THUNDERSTORM EXPECTED TO END AROUND MIDNIGHT AS NOCTURNAL
INFLUENCES TAKE OVER AND LIFT FROM SHORTWAVE TROUGH ENDS IN THE
SUBSIDENT SECTOR OF THE SHORTWAVE TROUGH.

THURSDAY...DECENT LOW LEVEL CONVERGENCE AXIS DEVELOPS ACROSS
SOUTHEAST WYOMING. HOWEVER...WITH LIMITED LOW AND MID LEVEL MOISTURE
AVAILABILITY...ONLY EXPECTING ISOLATED TO SCATTERED AFTERNOON
SHOWERS AND THUNDERSTORMS ACROSS CONVERSE AND NIOBRARA COUNTIES OF
WYOMING. MAXIMA IN THE 60S TO LOWER 70S PER THICKNESSES NEAR 5670
METERS.

THURSDAY NIGHT...IMPRESSIVE SHORTWAVE TROUGH ALOFT MOVES ACROSS
WYOMING WITH LOW AND MID LEVELS OF THE ATMOSPHERIC COLUMN
SATURATING. WILL GO NEAR 100 PERCENT RAIN CHANCES AFTER MIDNIGHT
ACROSS OUR SOUTHERN COUNTIES...WELL ABOVE GUIDANCE VALUES...AS
ATMOSPHERIC COLUMN IS SATURATED...DECENT LIFT PROVIDED BY DYNAMICAL
LIFT AND UPSLOPE LIFT. NO TIME TO PLAY IT SAFE AND CONSERVATIVE WITH
POPS. ALL AREAS SOUTH OF A RAWLINS TO SCOTTSBLUFF LINE WILL GET
DECENT MEASURABLE RAIN AFTER MIDNIGHT. AREAS OF FOG ALSO IN AREAS
THAT RECEIVE LIMITED OR MINIMAL RAIN.

FRIDAY...SHOWERS WILL DECREASE IN AREAL COVERAGE FROM WEST TO EAST
AS LIFT WANES AND LOW AND MID LEVELS DRY OUT. REFRESHINGLY COOL DAY
FOR COOL WEATHER LOVERS AND NOT SUCH A PLEASANT DAY FOR WARM WEATHER
ENTHUSIASTS WITH MAXIMA WELL BELOW NORMAL PER 1000-500 MB
THICKNESSES AROUND 5580 METERS.   *RUBIN*

.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...
IMPROVING CONDITIONS FRIDAY EVENING BEHIND SYSTEM EXITING TO THE
SOUTHEAST.  MODELS ARE STILL SHOWING SOME DISCREPANCIES OVER THE
WEEKEND.  12Z GFS RUN IS NOW FASTER SHOWING NEXT SHORTWAVE TROUGH
MOVING DOWN ON NW FLOW ALOFT SATURDAY MORNING...BRINGING COOL AND
SHOWERY WEATHER SATURDAY FOR AT LEAST THE EASTERN CWA AND THEN A DRY
AND NOT AS COOL SUNDAY.  THIS MODEL RUN LOOKS TO BE AN OUTLIER AT
THIS POINT AND THOUGH THERE ARE MINOR DIFFERENCES AMONG THEM...A
COMBO OF NAM/ECMWF/CANADIAN IS PREFERRED.  LATTER MODEL RUNS HOLD
BACK MORE SHORTWAVE ENERGY OVER SW CANADA SATURDAY MORNING...AND
THIS PATTERN HAS BEEN MORE CONSISTENT AND IS WHAT IS REFLECTED IN
OUR GOING FORECAST.  THIS WOULD MEAN A DRY/MILDER SATURDAY AND THEN
CHANGING WX SATURDAY NIGHT BEHIND A COLD FRONT WITH COOLER/SHOWERY
CONDITIONS SUNDAY AS SHORTWAVE ENERGY RACES SE ACROSS MT/WY AND
ACROSS THE NORTHERN PLAINS STATES.  RISING UPPER HEIGHTS AND
SLIGHTLY BACKING FLOW ALOFT WILL MEAN DRY CONDITIONS MON AND TUE.
ALTHOUGH WED WILL REMAIN MILD...NEXT SYSTEM COMES INTO PLAY LATE.

&&

.AVIATION...SCATTERED THUNDERSTORMS WILL PRODUCE ISOLATED MVFR
THROUGH MIDNIGHT TONIGHT ALONG AND EAST OF INTERSTATE 25. OTHERWISE
VFR TONIGHT.

VFR ON THURSDAY.

IFR AND LIFR DEVELOPING FROM NORTH TO SOUTH THURSDAY NIGHT WITH IFR
AND LIFR BECOMING WIDESPREAD IN SHOWERS...LOW CLOUDS AND AREAS OF
FOG.   -RUBIN

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.

&&

SHORT TERM/AVIATION...RUBIN
LONG TERM...JLH

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHEYENNE WY
1000 AM MDT WED SEP 3 2008

NEZ001>003-019>021-054-055-WYZ059>070-041130-
SIOUX-DAWES-BOX BUTTE-SCOTTS BLUFF-BANNER-MORRILL-KIMBALL-
CHEYENNE-CONVERSE-NIOBRARA-SOUTHWEST CARBON-NORTH CARBON-
SNOWY RANGE-NORTH LARAMIE RANGE-LARAMIE VALLEY-LARAMIE RANGE-
PLATTE-GOSHEN-CHEYENNE FOOTHILLS-PINE BLUFFS-
1000 AM MDT WED SEP 3 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN NEBRASKA
PANHANDLE AND SOUTHEAST WYOMING.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WILL DEVELOP THIS AFTERNOON ALONG THE
LARAMIE RANGE AND INTERSTATE 25 CORRIDOR AND THEN PROPAGATE EAST
ACROSS EASTERN WYOMING AND THE WESTERN NEBRASKA PANHANDLE THIS
EVENING. THE VAST MAJORITY OF THUNDERSTORMS WILL BE
NON-SEVERE...ALTHOUGH A FEW SEVERE THUNDERSTORMS WILL BE POSSIBLE
ALONG AND EAST OF INTERSTATE 25 THIS AFTERNOON AND EVENING.
THUNDERSTORMS WILL DIMINISH AROUND MIDNIGHT. THUNDERSTORM MOVEMENT
WILL BE NORTHEAST AT 25 MPH.

A FEW OF THE THUNDERSTORMS WILL BE STRONG AND A FEW POSSIBLY
SEVERE...PRODUCING HAIL UP TO PENNY SIZE AND WIND GUSTS IN EXCESS OF
60 MPH.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A FEW THUNDERSTORMS WILL BE POSSIBLE ON THURSDAY AFTERNOON AND
EVENING MAINLY IN THE SOUTHEAST HALF OF THE REGION.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY NOT BE NEEDED TODAY AND
TONIGHT...SINCE THE COVERAGE OF STRONG TO SEVERE THUNDERSTORMS WILL
BE LIMITED.

&&

THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC...AND
CLIMATE INFORMATION IS AVAILABLE ON THE WEB AT...
HTTP://WEATHER.GOV/CHEYENNE

RUBIN

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHEYENNE WY
510 PM MDT WED SEP 03 2008

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0501 PM     HAIL             DULL RESERVOIR          43.41N 104.95W
09/03/2008  M0.50 INCH       CONVERSE           WY   CO-OP OBSERVER

&&

MWEILAND

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE CHEYENNE WY
544 PM MDT WED SEP 3 2008

WYZ060-040145-
NIOBRARA-
INCLUDING THE CITY OF...LUSK
544 PM MDT WED SEP 3 2008

...STRONG THUNDERSTORMS WERE OVER PARTS OF NIOBRARA COUNTY...

AT 530 PM...STRONG THUNDERSTORMS WERE LOCATED IN A LINE
EXTENDING FROM NORTH CENTRAL NIOBRARA COUNTY TO SOUTHWEST
NIOBRARA COUNTY. THE LINE OF STRONG STORMS WAS MOVING TO THE
EAST AT 30 MPH.

AT 527 PM...WIND GUSTS TO 40 MPH AND PEA SIZED HAIL WAS
REPORTED 8 MILES TO THE NORTH OF LANCE CREEK. ALSO...AT 537
PM...WIND GUSTS BETWEEN 40 AND 50 MPH WERE OBSERVED 11 MILES
TO THE NORTHEAST OF LANCE CREEK. LANCE CREEK IS 25 MILES TO
THE NORTHWEST OF LUSK.

THOSE STRONG STORMS WILL PRODUCE A PERIOD OF HEAVY RAIN...WIND
GUSTS TO BETWEEN 40 AND 50 MPH...SMALL HAIL AND DEADLY LIGHTNING.
THE LINE OF STORMS WILL MOVE TO A NORTHEAST NIOBRARA COUNTY TO
NEAR LUCK AROUND 615 PM AND SHOULD SLOWLY WEAKEN DURING THAT
TIME.

WEILAND

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHEYENNE WY
546 PM MDT WED SEP 03 2008

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0532 PM     HAIL             8 N LANCE CREEK         43.14N 104.64W
09/03/2008  M0.25 INCH       NIOBRARA           WY   TRAINED SPOTTER

            WIND GUSTS TO 30 AND 40 MPH. LIGHT RAIN.

0535 PM     TSTM WND GST     LANCE CREEK             43.02N 104.64W
09/03/2008  E40.00 MPH       NIOBRARA           WY   TRAINED SPOTTER

            FAIRLY GOOD RAIN.

0536 PM     TSTM WND GST     11 NE LANCE CREEK       43.13N 104.49W
09/03/2008  E50.00 MPH       NIOBRARA           WY   TRAINED SPOTTER

            ESTIMATED TO BE 40 TO 50 MPH GUSTS. SOME RAIN.

&&

BCHAPMAN