Issued by NWS Cheyenne, WY
000 FXUS65 KCYS 112018 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 218 PM MDT SAT OCT 11 2008 .SHORT TERM...TONIGHT THROUGH MONDAY AFTERNOON. TONIGHT...EXPECTED WEATHER TODAY AND TONIGHT IS ONE REASON WHY THE WEATHER BUSINESS IS SO CHALLENGING AND EXCITING. AT 138 PM...WINDS AT LARAMIE AIRPORT WERE SOUTHEAST AT 38 MPH GUSTING TO 56 MPH. 2 PM TEMPERATURES ACROSS SOUTHEAST WYOMING AND WESTERN NEBRASKA WERE IN THE 30S. MSAS INDICATES A DEEP SURFACE LOW ACROSS WESTERN COLORADO WITH AN IMPRESSIVE WARM FRONT EXTENDING NORTHEAST FROM THE LOW ACROSS NORTHWEST COLORADO AND SOUTH CENTRAL WYOMING. WEATHER CHANGES AND APPROACHING STORM SYSTEM PRODUCING NICE 3 MILLIBAR THREE HOURLY PRESSURE FALL COUPLET ACROSS SOUTHEAST WYOMING AND NORTHERN COLORADO. VISIBLE SATELLITE IMAGERY SHOWS LIGHTNING ASSOCIATED WITH SCATTERED THUNDERSTORMS ACROSS SOUTHERN COLORADO AND NORTHERN NEW MEXICO. POWERHOUSE CLOSED AND STACKED TROUGH ALOFT MOVES TO NORTHERN UTAH THIS EVENING. MEANWHILE...IMPRESSIVE SHORTWAVE TROUGH MOVES ACROSS WYOMING ACTING ON DEEP MOIST LAYER TO PRODUCE WIDESPREAD PRECIPITATION. BOTH NAM AND GFS INDICATE SIGNIFICANT QPF AMOUNTS THIS EVENING ACROSS WESTERN WYOMING. WITH DECENT LIFT COMBINED WITH DEEP SATURATED LAYER...HAVE UPGRADED THE WINTER WEATHER ADVISORY TO A WINTER STORM WARNING FOR THE LOWER ELEVATIONS OF SOUTHERN CARBON COUNTY. DECENT QPF AMOUNTS WILL FALL AFTER MIDNIGHT ACROSS EASTERN WYOMING AND WESTERN NEBRASKA. BASED ON CURRENT TEMPERATURES AND DEWPOINTS...BELOW MODEL GUIDANCE...SNOW WILL DEVELOP SOONER THAN EXPECTED...ESPECIALLY ACROSS THE PLAINS OF EASTERN WYOMING. BASED ON EXPECTED SNOWFALL CHANGEOVER...HAVE HOISTED A WINTER WEATHER ADVISORY FOR TONIGHT FOR THE EASTERN PLAINS OF WYOMING AND NORTHWEST NEBRASKA. ALTHOUGH SNOWFALL AMOUNTS WILL BE LIMITED...THIS WILL BE THE FIRST SIGNIFICANT SNOWFALL OF THE SEASON...THUS IT WOULD BE QUITE PRUDENT TO ALERT OUR CUSTOMERS WITH THE ISSUANCE OF A WINTER WEATHER ADVISORY. 500-300 MB AND 700-500 MB QUASIGEOSTROPHIC FORCING PRODUCING LIFT WILL DRAMATICALLY END AROUND 6 AM SUNDAY. BASED ON THE TRACK OF THE UPPER TROUGH EXPECT SNOWFALL AMOUNTS ACROSS CARBON COUNTY TO RANGE FROM 2 TO 6 INCHES IN THE LOWER ELEVATIONS WITH 5 TO 10 INCHES IN THE MOUNTAINS. THE NORTHERN LARAMIE RANGE OF SOUTHERN CONVERSE AND NORTHERN ALBANY COUNTIES WILL SEE SNOWFALL AMOUNTS OF 10 TO 15 INCHES OVERNIGHT. SUNDAY...RAPID CESSATION OF THE SNOW WILL OCCUR AFTER DAWN WITH STRONG DOWNWARD MOTION INDICATED BY 500-300 MB AND 700-500 MB QUASIGEOSTROPHIC FORCING. RAW AND CHILLY DAY WITH DAYTIME MAXIMA RANGING FROM THE 30S WEST TO NEAR 50 EAST. SUNDAY NIGHT...SHEARED UPPER TROUGH AXIS STRETCHES FROM EASTERN MONTANA THROUGH WESTERN WYOMING TO SOUTHERN UTAH. DRIER GFS SOLUTION LOOKS BETTER THAN THE WETTER NAM WHICH SHOWS QPF ACROSS OUR SOUTHEAST COUNTIES. NAM QPF LOOKS OVERDONE BASED ON VERTICAL MOTION FIELDS. THUS WILL KEEP OUR COUNTIES DRY. MONDAY...STARK CONTRAST IN NAM AND GFS GUIDANCE MAXIMUM HIGH TEMPERATURES. COMPROMISE IN ORDER BASED ON 1000-500 MB THICKNESS TRENDS. DRY DAY WITH LIMITED LOW AND MID LEVEL MOISTURE AVAILABILITY. RUBIN .LONG TERM...MON NIGHT THRU SAT...LINGERING SRN PART OF UPPER TROF FINALLY MOVES OUT OF THE AREA BY TUE MRNG. COULD BE SOME PCPN THAT SPILLS NEWD OUT OF CO INTO FAR SE PART OF AREA MON NIGHT INTO TUE MRNG...WILL SEE HOW LATER MODEL RUNS HANDLE SITUATION. FLAT UPPER RIDGE SPREADS OVER AREA FOR TUE NIGHT INTO WED AHEAD OF NEXT WEAK UPPER TROF. TEMPS TO REBOUND BY WED. MODELS START DIFFERING WITH THIS NEXT TROF BY THU AS ECMWF IS SLOWER AND MORE AMPLIFIED THAN GFS. HAVE PLAYED THINGS WITH A COMPROMISE FOR NOW. FRI AND SAT STILL LOOKING WARMER AND DRY AS MDT-STG UPPER RIDGE BUILDS INTO THE REGION. && .AVIATION...WIDESPREAD IFR AND LIFR TONIGHT. CEILINGS AND VISIBILITIES IMPROVING TO VFR AND MVFR SUNDAY MORNING AND VFR SUNDAY AFTERNOON. VFR SUNDAY NIGHT. RUBIN && .CYS WATCHES/WARNINGS/ADVISORIES... WY...WINTER STORM WARNING UNTIL 6 AM SUNDAY FOR WYZ061-WYZ062-WYZ063- WYZ064. WINTER STORM WARNING FROM 6 PM SATURDAY TO 6 AM SUNDAY FOR WYZ059. WINTER WEATHER ADVISORY FROM 6 PM SATURDAY TO 6 AM SUNDAY FOR WYZ060-WYZ065-WYZ066-WYZ067-WYZ068-WYZ069-WYZ070. NE...WINTER WEATHER ADVISORY FROM 6 PM SATURDAY TO 6 AM SUNDAY FOR NEZ001-NEZ002-NEZ003. && $$ SHORT TERM/AVIATION...RUBIN
