Severe Thunderstorm Warning 2, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
230 PM MST MON FEB 14 2000

PER WATER VAPOR...UPPER LOW SPINNING EAST ACROSS SOUTH CENTRAL
OREGON AT 20Z.  LARGE WARM ADVECION CLOUD SHIELD OVER MONTANA AND
WYOMING AFTER LEAVING 6 TO 12 INCHES OF SNOW OVER FAR WEST VALLEYS
AND WEST MOUNTAINS THIS MORNING.  NEXT AREA OF PRECIPITATION MOVING
INTO EASTERN IDAHO ASSOCIATED WITH STRONG LIFT/INSTABILITY AHEAD OF
OREGON SHORTWAVE.  RADAR/LIGHTNING DATA SHOWING SOME 45+ DBZ
RETURNS AND NUMEROUS LIGHTNING STRIKES OVER SOUTHWEST IDAHO.
WIDESPREAD SNOWFALL WILL RETURN TO THE FAR WEST BY ISSUANCE WITH
HEAVIEST BAND OF SNOWFALL REACHING WESTERN BORDER AROUND 02Z.  ETA
SEEMS TO BE TRACKING VORT CENTER BEST BASED ON EXTRAPOLATION...
TAKING IT INTO NORTH CENTRAL WYOMING BY 06Z AND TO EASTERN WYOMING
BORDER AT 12Z.  ALSO ETA SURFACE PROGS PREFERRED AS LATEST SURFACE
ANALYSIS SHOWS LOW CENTER...BIGGEST PRESSURE FALLS OVER IDAHO
PANHANDLE NEAR ETAS 00Z POSITION.  SURFACE LOW THEN REDEVELOPS EAST
OF DIVIDE JUST NORTH OF SHERIDAN AT 15/06Z AND THEN QUICKLY MOVES
SOUTHEAST INTO SOUTH DAKOTA.  WITH TROUGH PASSAGE IN THE FAR WEST
LATE THIS EVENING...NEGATIVE LI/S REMAIN OVER AREA ALONG WITH
OROGRAPHIC LIFT AND HIGH OMEGA VALUES...BUT HEAVIEST SNOWFALL WILL
OCCUR UPSTREAM OF TROUGH AXIS THIS EVENING.  WILL KEEP CURRENT WINTER
STORM WARNINGS AND ADVISORIES GOING THROUGH THE NIGHT IN WESTERN
ZONES WITH ONLY CHANGE TO DROP ZONE 10 OUT OF HIGHLIGHTS.  IN EAST
MAIN PROBLEM WILL BE WINDS WHICH HAVE JUST BEGUN TO PICK UP IN MOST
AREAS AND STILL HOLDING OUT FOR CODY AND SOME OTHER NORTHERN ZONES.
HIGH WINDS ALREADY VERIFIED IN WARNED ZONES 14 AND 15 TODAY WITH MID
LEVEL WINDS AND SUBSIDENCE PROGGED TO INCREASE THROUGH THIS
EVENING. THEREFORE WILL KEEP HIGH WIND WARNING GOING THROUGH THE
EVENING WITH DECREASING WINDS AFTER TROUGH PASSAGE AROUND
MIDNIGHT.  DRYING AND SUBSIDENCE BEHIND EXITING SHORTWAVE TUESDAY
FOR MOSTLY SUNNY WITH SOME LINGERING WIND MAINLY RKS AND CPR.
A SHORTWAVE IS PROGGED TO MOVE THROUGH COLORADO TUESDAY NIGHT WITH
SOME LIFT/DYNAMICS OVER SOUTHWEST/SOUTHCENTRAL WYOMING AND WILL ADD
SCATTERED POPS TO THIRD PERIOD THERE.  AFTERWARDS...WEDNESDAY LOOKS
BENIGN ALTHOUGH AVIATION IS COVERING JUST ABOUT THE ENTIRE ROCKY
MOUNTAIN REGION WITH CLOUDS AND PRECIPITATION BETWEEN WEAKENING
UPPER LOW MOVING INTO CALIFORNIA IN SOUTHERN STREAM AND WEAK TROUGH
OVER MONTANA IN NORTHERN STREAM.  MRF MOVES A BACKDOOR COLD FRONT
THROUGH THE STATE WEDNESDAY NIGHT AND THURSDAY BUT CONFIDENCE IS
LOW IN UPPER LEVEL PATTERN THAT LOOKS CHAOTIC...SPLITTING NORTHERN
STREAM ENERGY INTO SEVERAL PIECES.  GENERALLY DRY FORECAST FRIDAY
AND SATURDAY.

.RIW...WINTER STORM WARNING FAR W MTNS THROUGH TNGHT...ZNS1>3..6..
17..19. SNOW AND BLOWING SNOW ADVSRY FAR W VALLEYS AND EASTERN WIND
RIVER MTNS THROUGH TNGHT...ZNS 7..11..16..18..20. HIGH WIND WARNING
NATRONA CNTY AND GREEN MTNS THIS EVG...ZNS 14..15.

AEM