Damaging Wind in Wyoming, August 29, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
203 AM MDT THU AUG 29 2002

MCS FINALLY EXITING JOHNSON COUNTY AGAIN THIS MORNING. LUCKILY THE
HEAVIEST RAIN FROM THIS SYSTEM WAS A LITTLE NORTH OF WHERE THE
HEAVIEST RAIN FELL TWO NIGHTS AGO. NOW WE HAVE TO DEAL WITH UPPER LOW
OVER IDAHO AND APPROACHING SHORTWAVE OVER NORTHERN UTAH. I BELIEVE
THE AVN HAS A BETTER HANDLE ON THIS UTAH FEATURE WHICH APPEARS TO
RIDING ON TOP OF SPEED MAX ROTATING NORTHWARD OUT OF ARIZONA AND
SOUTHERN UTAH. THE AVN DEPICTS THE CURRENT AREA OF LIFT QUITE NICELY
AND SHOWS LEFT EXIT REGION DIVERGENCE MOVING INTO SOUTHWEST WYOMING
AROUND 12Z AND MOVING RAPIDLY ACROSS THE CENTRAL PART OF THE COWBOY
STATE BY 18Z. WILL HAVE TO BEEF UP THUNDERSTORM CHANCES ALONG ITS
PATH AND REMOVE AFTERNOON WORDING AS CONVECTION WILL NOT BE LIMITED
TO AFTERNOON HEATING. OTHER QUESTION IS WILL SEVERE WEATHER BE A
THREAT ONCE AGAIN TODAY? WE WONT HAVE THE ORGANIZED UPSLOPE FLOW WE
HAD YESTERDAY BUT WE SHOULD HAVE SOME LOW LEVEL CONVERGENCE WHERE
DEVELOPING SOUTH OR SOUTHWEST FLOW HITS MORE MOIST SOUTHEAST OR EAST
FLOW IN CENTRAL WYOMING. BEST THREAT AREA WILL PROBABLY BE FROM
EASTERN FREMONT AND NATRONA NORTHWARD INTO JOHNSON AGAIN.

DRIER MORE STABLE AIR SHOULD TAKE OVER ON FRIDAY BUT NEXT TROUGH
BRUSHES THE NORTH ON SATURDAY FOR AT LEAST SOME THREAT UP THERE.
WE MAY EVEN SEE SOME CONVECTION IN THE NORTHWEST AS EARLY AS
FRIDAY NIGHT. LOWER RELATIVE HUMIDITIES AND INCREASING SOUTHWEST WIND
OVER OUR SOUTHWEST FIRE ZONES MAY RESULT IN CRITICAL FIRE CONDITIONS
ON FRIDAY. SYSTEM EXITS ON SUNDAY WITH WEAK FRONTAL BOUNDARY
PASSING THROUGH. BEST CHANCE FOR THUNDERSTORMS WILL MOST LIKELY BE
ACROSS OUR EASTERN ZONES WITH BEST INSTABILITY AND POSSIBLY WEAK
CONVERGENCE ALONG FRONTAL BOUNDARY. THE AVN SHOWS ANOTHER SHORTWAVE
MOVING ACROSS MONTANA ON MONDAY WITH NORTHERN WYOMING GETTING CLIPPED
ONCE AGAIN. WILL NOT INTRODUCE PRECIPITATION JUST YET. RIDGE IS THEN
FORECAST TO MOVE IN TUESDAY WITH NEXT PACNW TROUGH DEVELOPING AROUND
MIDWEEK WITH POTENTIAL FOR MORE THUNDERSTORM DEVELOPMENT IN THE WEST
BY WEDNESDAY.

.RIW...NONE.

SKRBAC

WYZ001>015-017-019-020-022>028-292130-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
1140 AM MDT THU AUG 29 2002

...POTENTIAL FOR HAIL AND HEAVY RAINS FROM THUNDERSTORMS THIS
AFTERNOON AND EVENING...

THE GREATEST THREAT OF SIGNIFICANT SEVERE WEATHER EXTENDS EAST OF A
LINE FROM JACKSON TO BIG PINEY TO GREEN RIVER TO FLAMING GORGE. THIS
INCLUDES YELLOWSTONE NATIONAL PARK...PARK COUNTY...TETON
COUNTY...SUBLETTE COUNTY...SWEETWATER COUNTY...FREMONT COUNTY...
NATRONA COUNTY...HOT SPRINGS COUNTY...WASHAKIE COUNTY...BIG HORN
COUNTY...AND JOHNSON COUNTIES.

WINDS GUSTING TO 60 MPH AND HAIL UP TO AN INCH IN DIAMETER COULD
OCCUR WITH THE STRONGER STORMS. ADDITIONALLY...ISOLATED STORMS COULD
PRODUCE VERY HEAVY RAIN WHICH CAN CAUSE FLASH FLOODING ON ALREADY
SATURATED SOILS.

TWO AREAS OF STORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON. THE
FIRST AREA WILL BE IN NORTHWEST WYOMING. STORMS IN THIS AREA WILL
MOVE NORTH NORTHEAST AT 25 MPH. THE SECOND AREA OF STRONG STORMS WILL
MOVE NORTH FROM SOUTHERN WYOMING. THESE STORMS ARE EXPECTED TO MOVE
NORTH AT 20 MPH.

MOST LOCATIONS WILL RECEIVE RAINFALL OF LESS THAN ONE HALF
INCH...HOWEVER ISOLATED LOCATIONS COULD RECEIVE OVER AN INCH AS
LOW LEVEL MOISTURE REMAINS HIGH. IN ADDITION...SOILS THAT ARE ALREADY
SATURATED IN SPOTS DUE TO THE HEAVY RAINS EARLIER THIS WEEK...HAVE
THE POTENTIAL FOR FLASH FLOODING.

WCJIN-WYNW-WYNE-WYSW

MLC