Southwest flow ahead of an approaching Pacific storm system produced high wind over central Wyoming in response to a strengthening pressure gradient.
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The episode as NWS RIW wrote it up.
Southwest flow ahead of an approaching Pacific storm system produced high wind over central Wyoming in response to a strengthening pressure gradient.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Riverton, WY wrote its last area forecast discussion before the first event at Dec 19, 3:30 PM MST, 9 hours 30 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 330 PM MST WED DEC 19 2007 .SHORT TERM...TONIGHT THROUGH SATURDAY AREA OF OPEN CELLULAR CONVECTION IN THE EASTERN PACIFIC QUITE IMPRESSIVE ON IR SATELLITE IMAGERY THIS AFTERNOON. LARGE AREA OF ISENTROPIC UPGLIDE BEGINNING TO MOVE THROUGH OREGON DURING THE DAY RAPIDLY SPREADING EASTWARD THIS AFTERNOON. THIS AREA OF LIFT WILL BRING WIDESPREAD SNOWFALL TO WESTERN WYOMING BEGINNING THIS EVENING. DECIDED TO UPGRADE THE WINTER STORM WATCH TO TO A WARNING GIVEN THE CURRENT PACIFIC MOISTURE TRAJECTORY...APPROXIMATELY 12 HOURS OF GOOD ISENTROPIC UPGLIDE TONIGHT AND THURSDAY MORNING...LEFT FRONT QUAD JET DYNAMICS (115 KT) CONSISTENTLY FORECAST BY THE GFS AND ECMWF WHICH WILL MOVE OVER THE STATE DURING THE DAY THURSDAY...OROGRAPHIC EFFECTS...STEEP LAPSE RATES FOR SCATTERED TO NUMEROUS HEAVY SNOW SHOWERS THURSDAY AFTERNOON AND EVENING...NEAR MAXIMUM DENDRITIC SNOW GROWTH POTENTIAL...AND FRONTOGENESIS TAKING PLACE AROUND MID-DAY THURSDAY. THE LARGE UPPER TROUGH RESPONSIBLE FOR THE SIGNIFICANT SNOWFALL IS MOVING SOMEWHAT SLOWER THAN EXPECTED SO PUSHED THE START OF THE WARNING BACK SIX HOURS TO 06Z THURS. THE STRENGTHENING COLD FRONT TAKING SHAPE OVER THE WEST THURSDAY WILL SHIFT SOUTHEAST DURING THE DAY...BRINGING GOOD SNOW CHANCES TO SWEETWATER COUNTY DURING THE AFTERNOON AND SOUTHERN NATRONA COUNTY DURING THE EVENING HOURS. TRAILING FRONTOGENESIS OCCURS JUST AHEAD OF THE UPPER LEVEL TROUGH AXIS OVER YELLOWSTONE PARK AND POINTS EAST THURSDAY EVENING. THE FRONT PUSHES SOUTHWARD THROUGH THE BIG HORN BASIN THURSDAY NIGHT AND THROUGH THE WIND RIVER BASIN EARLY FRIDAY MORNING...BRINGING SNOW CHANCES TO AREAS EAST OF THE DIVIDE IN UPSLOPE FLOW. THE UPSLOPE FLOW SHIFTS SOUTH DURING THE DAY BRINGING GOOD SNOW CHANCES TO NATRONA COUNTY FRIDAY AFTERNOON. STRONG SOUTHWEST WIND THROUGH THE WIND CORRIDOR FROM THE RED DESERT EAST THROUGH CASPER WILL CONTINUE AHEAD OF THIS TROUGH TONIGHT THURSDAY EVENING BEFORE SHIFTING TO THE NORTH FRIDAY MORNING. IN THE CODY FOOTHILLS...STRONG SOUTHWEST WIND OF 20 TO 40 MPH WITH LOCAL GUSTS TO 50 MPH ARE POSSIBLE TONIGHT THROUGH THURSDAY MORNING AS AT LEAST TWO DISTINCT MOUNTAIN WAVES MOVE DOWN THE EAST SLOPE OF THE ABSAROKA MOUNTAINS. .LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY BACKING FLOW AND WEAK ISENTROPIC UPGLIDE RETURN TO THE FAR WEST SATURDAY AS UPPER RIDGE ESTABLISHES BRIEF PRESENCE OVER NORTHERN ROCKIES BEFORE BEING FLATTENED BY NEXT INCOMING TROUGH. EC AND OPS GFS ALONG WITH ITS ENSEMBLES BEGAN TO SHOW INCREASING SPREAD AS EARLY AS SATURDAY NIGHT WITH VARIOUS OUT OF PHASE SOLUTIONS BY MONDAY. FORECAST WEIGHTED TOWARD A CONTINUATION OF SPLIT FLOW REGIME WITH NEXT SERIES OF PACIFIC TROUGHS AS DEPICTED BY THE EC RATHER THAN A STRONGER NORTHERN STREAM WITH MORE CONSOLIDATED ENERGY PLOWING ACROSS NORTHERN ROCKIES BEFORE SPLITTING DOWNSTREAM IN THE PLAINS AS DEPICTED BY THE GFS. FIRST SHORTWAVE IN THIS NEXT SERIES WILL DIVE ACROSS MONTANA INTO THE HIGH PLAINS SUNDAY BRINGING INCREASING CHANCES OF SNOWFALL TO THE WEST IN NORTHWEST FLOW WHILE KEEPING CENTRAL AREAS WELL-MIXED WITH FRONTAL PASSAGE AND VIGOROUS NW FLOW. AFTERWARDS...EC PATTERN LOOKS VERY SIMILAR TO PATTERN OF LAST SEVERAL DAYS WITH NEXT SYSTEM SPLITTING ALONG THE COAST MONDAY AFTERNOON WITH NORTHERN BRANCH OF SYSTEM BRUSHING AREA CHRISTMAS DAY. THE THIRD SYSTEM IN THIS SERIES EXPECTED TO FORM SW LOW NEAR LAS THURSDAY. AFTER SUNDAY...A RELATIVELY MILD AIRMASS TO DOMINATE WITH H7 TEMPS BETWEEN -4C AND -8C. BASIN AND VALLEY INVERSIONS SHOULD BE MUCH LESS PRONOUNCED THROUGH NEXT WEEK AFTER GOOD MIXING SCENARIO SUNDAY QUICKLY FOLLOWED BY THIS MILDER AIRMASS. MAINLY THE FAR WEST WILL CONTINUE TO SEE CHANCES OF SNOW THROUGH THE PERIOD WITH LIGHT ACCUMULATIONS. && .AVIATION... A WINTER STORM PROMISES TO IMPACT THE WESTERN THIRD OF THE FORECAST AREA OVERNIGHT...BRINGING IFR TO LIFR CONDITIONS AT KJAC AFTER 06Z THIS EVENING. HAVE CONTINUED TRENDING THE CEILINGS DOWN THROUGH THE EVENING HOURS...WITH SNOW ACTIVITY DEVELOPING ACROSS KJAC...KBPI... AND KPNA DURING THE OVERNIGHT HOURS. IFR TO LIFR CONDITIONS TO CONTINUE ACROSS IMPACTED AIRPORTS THROUGH THURSDAY MORNING AND AFTERNOON. KRKS MAY DEVELOP SNOW DURING THE AFTERNOON HOURS OF THURSDAY AS THE SNOW MOVES EASTWARD. STRONG WINDS WILL CONTINUE ACROSS KCPR THROUGH THURSDAY AS WELL...WITH SPEEDS INCREASING DURING THE LATE MORNING AND EARLY AFTERNOON HOURS. && .FIRE WEATHER... SIGNIFICANT SNOWFALL IS EXPECTED IN THE VALLEYS AND MOUNTAINS OF WESTERN WYOMING TONIGHT THROUGH THURSDAY EVENING. WEST AND SOUTHWEST WINDS WIND INCREASE IN THE CODY FOOTHILLS TONIGHT. STRONG WEST WINDS WILL CONTINUE IN THE WIND CORRIDOR FROM THE RED DESERT TO CASPER THROUGH THURSDAY EVENING. && .RIW WATCHES/WARNINGS/ADVISORIES... SNOW ADVISORY FROM 11 PM THIS EVENING TO 11 PM MST THURSDAY FOR WYZ001-002-014>016-025-027. WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 PM MST THURSDAY FOR WYZ012-013-023-024. && SHORT TERM...CHURCH LONG TERM...AEM AVIATION...BRANHAM FIRE WEATHER...CHURCH
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 339 PM MST WED DEC 19 2007 WYZ001>020-022>030-201200- ABSAROKA MOUNTAINS-BIGHORN MOUNTAINS SOUTHEAST- BIGHORN MOUNTAINS WEST-CASPER MOUNTAIN-CODY FOOTHILLS- EAST SWEETWATER COUNTY-FLAMING GORGE- GREEN MOUNTAINS AND RATTLESNAKE RANGE-JACKSON HOLE-LANDER FOOTHILLS- NATRONA COUNTY LOWER ELEVATIONS-NORTH BIG HORN BASIN- NORTHEAST JOHNSON COUNTY-OWL CREEK AND BRIDGER MOUNTAINS- ROCK SPRINGS AND GREEN RIVER-SALT RIVER AND WYOMING RANGES- SOUTH LINCOLN COUNTY-SOUTHEAST BIG HORN BASIN- SOUTHEAST JOHNSON COUNTY-SOUTHWEST BIG HORN BASIN-STAR VALLEY- TETON AND GROS VENTRE MOUNTAINS-UPPER GREEN RIVER BASIN- UPPER GREEN RIVER BASIN FOOTHILLS-UPPER WIND RIVER BASIN- WIND RIVER BASIN-WIND RIVER MOUNTAINS EAST-WIND RIVER MOUNTAINS WEST- YELLOWSTONE NATIONAL PARK- 339 PM MST WED DEC 19 2007 ...A WINTER STORM WARNING IS IN EFFECT FOR PORTIONS OF WESTERN WYOMING FOR TONIGHT AND THURSDAY... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...THIS EVENING AND TONIGHT A SIGNIFICANT SNOW STORM IS EXPECTED OVER WESTERN WYOMING TONIGHT AS A POTENT PACIFIC STORM SYSTEM APPROACHES THE AREA. SNOWFALL RATES OF ONE INCH PER HOUR ARE POSSIBLE TONIGHT ALONG WITH THE POTENTIAL FOR OVER A FOOT OF SNOW OVER THE TETONS WELL AS ACROSS THE WYOMING AND SALT RIVER RANGES TONIGHT. 6 INCHES OF SNOW IS EXPECTED ACROSS THE GROS VENTRE RANGE TONIGHT. 3 TO 4 INCHES OF SNOWFALL IS ALSO EXPECTED TONIGHT ACROSS THE NORTHERN JACKSON AND STAR VALLEYS ALONG WITH 1 TO 3 INCHES OF SNOWFALL ACROSS THE SOUTHERN PORTION OF THESE VALLEYS. TOGWOTEE...TETON AND SALT RIVER PASSES ARE EXPECTED TO BECOME SNOW COVERED AND SLICK TONIGHT. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH WEDNESDAY SNOWFALL IS EXPECTED TO CONTINUE ACROSS WESTERN WYOMING THURSDAY ALONG WITH TOTAL SNOW ACCUMULATIONS OF UP TO 18 INCHES ACROSS THE TETONS AS WELL AS OVER THE WYOMING AND SALT RIVER RANGES BY EVENING. UP TO 12 INCHES OF SNOWFALL ARE EXPECTED OVER THE GROS VENTRE RANGE. A TOTAL OF 8 INCHES OF SNOW IS POSSIBLE ACROSS THE NORTHERN JACKSON AND STAR VALLEYS ALONG WITH THE POTENTIAL FOR UP TO 4 INCHES OF SNOWFALL ACROSS THE SOUTHERN PORTION OF THE JACKSON AND STAR VALLEYS BY THURSDAY EVENING. LIGHT SNOW IS EXPECTED EAST OF THE DIVIDE FRIDAY MORNING BEFORE .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT ANY SNOWFALL AMOUNTS TO THE NATIONAL WEATHER SERVICE THROUGH THE EVENING AND ON WEDNESDAY MORNING. TEAM RIVERTON
The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2007Every state in 2007This day in weather historyWarnings in Wyoming, December 2007
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 65551.