120 FXUS65 KCYS 210500 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 1000 PM MST WED FEB 20 2013 .AVIATION...06Z TAF ISSUANCE... IFR CEILINGS AND MVFR OR IFR VISIBILITIES IN LIGHT SNOW AND FOG WILL CONTINUE ACROSS MUCH OF THE CWA THROUGH AT LEAST THURSDAY MORNING. CEILINGS AND VISIBILITIES WILL BE HIGHER OVER THE LOWER ELEVATIONS OF CARBON AND ALBANY COUNTIES. CEILINGS WILL SLOWLY LIFT OVER THE CWA THURSDAY AFTERNOON AND EARLY THURSDAY NIGHT AS THE STORM SYSTEM MOVES FURTHER EAST. VFR CONDITIONS WILL RETURN SLOWLY TO THE REGION THURSDAY NIGHT AND FRIDAY MORNING FROM WEST TO EAST. THE MOUNTAINS WILL BE OBSCURED THROUGH THURSDAY NIGHT. WESTERLY SURFACE WINDS WILL GUST AS HIGH AS 45 KNOTS FRIDAY NIGHT AND SATURDAY IN AREAS ALONG AND WEST OF THE LARAMIE RANGE. && .PREVIOUS DISCUSSION.../ISSUED AT 755 PM MST WED FEB 20 2013/... .DISCUSSION... THE FREEZING DRIZZLE OVER THE SOUTHEAST PART OF THE CWA HAS BEEN MIXING WITH OR EVEN CHANGED OVER TO ALL SNOW AS OF 0230Z. BAND OF ACCUMULATING SNOW DEVELOPED EARLIER THIS EVENING OVER NORTHEAST COLORADO AND HAS MOVED TO THE NORTHWEST. HOURLY RATES AT KIBM HAVE BEEN BETWEEN ONE QUARTER AND ONE HALF INCH PER HOUR. THAT BAND SHOULD CONTINUE TO LIFT NORTHWEST THROUGH EARLY THURSDAY MORNING. THAT BAND MAY WEAKEN AFTER THAT TIME AS THE MORE SIGNIFICANT BAROCLINIC BAND CONTINUE TO DEVELOP OVER CENTRAL COLORADO. THAT BAND IS AIDED BY THE LOW LEVEL THETA RIDGE AXIS... SURFACE CONVERGENCE AND DEEPER MOISTURE ALL OF WHICH ARE AND WILL BE CLOSER TO THE CURRENT EASTERN ARIZONA UPPER LOW. THAT BAND SHOULD GENERALLY REMAIN TO THE SOUTH AND EAST OF THE CWA. SNOW AMOUNTS OUTSIDE OF THE SOUTHEAST QUARTER OF THE CWA MAY BE A BIT LOWER THAN IN CURRENT FORCAST. HOWEVER...DUE TO THE POTENTIAL WITH THE INITIAL SNOW BAND HAVE ADJUSTED ONLY SLIGHTLY IN A RECENT UPDATE. && .PREVIOUS DISCUSSION.../ISSUED AT 529 PM MST WED FEB 20 2013/... .DISCUSSION... LIGHT FREEZING DRIZZLE CONTINUES EARLY THIS EVENING EAST OF A KEAN TO KCYS LINE. REPORTS INDICATE THAT SOME SMALL FLAKES HAVE BEEN STARTING TO FALL IN THAT AREA. THAT TREND SHOULD CONTINUE FOR THE NEXT FEW HOURS AS TEMPERATURES ALOFT SLOWLY COOL. RADAR RETURNS FROM THE KCYS RADAR HAVE INCREASED TO THE SOUTH AND EAST OF KCYS AND CLOUD TOPS HAVE BEEN COOLING. THE FREEZING DRIZZLE HAS MADE SOME BRIDGES...WALKWAYS AND METAL OBJECTS WERE SOME SLICK...BUT CONDITIONS DO NOT SEEM TO WARRANT AN ADVISORY AT THIS TIME. THE REDUCED VISIBILITIES IN THE FOG WERE PERHAPS THE WORST CONDITIONS AT THIS TIME. THE PRECIPITATION SHOULD CONTINUE TO SPREAD OVER THE REST OF THE CWA THIS EVENING...WITH THE FOCUS STILL ON THE SOUTHEAST PART OF OF THE CWA FOR THE POTENTIAL FOR HEAVIER SNOW. WILL TAKE A CLOSER LOOK AT SNOW FOR TONIGHT AND THURSDAY SOON. IN A RECENT UPDATE HAVE ADJUSTED POPS AND MADE MINOR CHANGES TO THE FIRST PERIOD OF THE FORECAST. && .PREVIOUS DISCUSSION..../ISSUED AT 449 PM MST WED FEB 20 2013/... .AVIATION...00Z TAF ISSUANCE... CLOUD BASES AND VISIBILITIES WILL CONTINUE TO LOWER OVER THE CWA THIS EVENING. CURRENT IFR CONDITIONS FROM KCYS TO LIBM WILL SPREAD NORTH...WITH IFR CEILINGS AND VISIBILITIES IN LIGHT SNOW AND FOG WIDESPREAD BY 04Z OVER THE SOUTHEAST HALF OF THE CWA. OVER THE REST OF THE CWA...MVFR CONDITIONS WITH PERIODS OF IFR CONDITIONS WILL DEVELOP BY 04Z. THE LOW CEILINGS AND VISIBILITIES WILL PERSIST FOR MUCH OF THURSDAY WITH SOME SLIGHT IMPROVEMENT IN THE LATE AFTERNOON. VFR CONDITIONS WILL RETURN SLOWLY TO THE REGION THURSDAY NIGHT AND FRIDAY MORNING FROM WEST TO EAST. THE MOUNTAINS WILL BE OBSCURED THROUGH THURSDAY NIGHT. ICING WILL BE A CONCERN THROUGH 15000 FEET MSL TONIGHT. THIS WILL ESPECIALLY BE THE CASE THROUGH 03Z SOUTH OF A KEAN TO KAIA LINE WHERE FREEZING DRIZZLE WILL CONTINUE. && .PREVIOUS DISCUSSION.../ISSUED AT 327 PM MST WED FEB 20 2013/... .UPDATE... HAVE RECEIVED REPORTS OF FREEZING DRIZZLE FROM LAW ENFORCEMENT AND WEATHER SPOTTERS IN PINE BLUFFS AND CARPENTER RESPECTIVELY. ALSO SEEING FREEZING DRIZZLE ON WEBCAMS IN THE SOUTHERN NEBRASKA PANHANDLE. HAVE UPDATED THE FORECAST TO HIT FREEZING DRIZZLE HARDER. VERY WELL MAY NEED AND WINTER WEATHER ADVISORY FOR THE FREEZING DRIZZLE IF IT BEGINS TO IMPACT GROUND SURFACES. THERE WAS A REPORT OF AN ACCIDENT IN THE PINE BLUFFS AREA DUE TO SLIPPERY CONDITIONS...OF COURSE THERE IS A WINTER WEATHER ADVISORY ALREADY IN PLACE FOR THAT AREA. ONCE THE SUN SETS...ROADS COULD BECOME SLIPPERY EVEN FASTER AND ROAD SURFACE TEMPERATURES DROP BELOW FREEZING. && .PREV DISCUSSION... /ISSUED 304 PM MST WED FEB 20 2013/ SHORT TERM... KEPT WINTER WEATHER ADVISORY GOING FOR THE SOUTHERN NEBRASKA PANHANDLE AND EXTREME SOUTHEAST WYOMING THROUGH 3 PM THURSDAY AFTERNOON. LOOKED AT DELAYING THE START OF THE ADVISORY UNTIL 5 PM THIS EVENING AS THE MAIN AREA OF SNOW IS STILL SEVERAL HOURS SOUTH OF THE FORECAST AREA...BUT AS THE VTEC CODE WILL SHOW A CANCELLED ADVISORY...DECIDED TO KEEP THE ADVISORY AS IS. ALSO THERE IS THE POTENTIAL FOR FREEZING DRIZZLE DEVELOPING ANY TIME THIS AFTERNOON. BOUNDARY LAYER IS BECOMING SATURATED AT THIS TIME AND THIS MOISTURE IS MOVING WESTWARD ACROSS SOUTHEAST WYOMING. MODEL SOUNDINGS CONTINUE TO SUGGEST THE POTENTIAL FOR FOG AND FREEZING DRIZZLE...MAINLY THE EVENING WITH THE GREATEST RISK OVER SOUTHEAST WYOMING INTO THE LARAMIE RANGE. WEST OF THE LARAMIE RANGE THREAT FOR FREEZING DRIZZLE VERY LOW. WILL HAVE TO KEEP A CLOSE EYE ON VISIBILITIES AND WATCH FOR ANY DRIZZLE FORMATION THIS EVENING AS THIS COULD PROMPT A WINTER WEATHER ADVISORY BEING ISSUED FOR SOME AREAS ALONG AND EAST OF THE LARAMIE RANGE. AS THE UPPER LEVELS BEGIN TO SATURATE...FREEZING DRIZZLE THREAT SHOULD SUBSIDE. SNOW AMOUNTS LOOKING ON TRACK WITH THE PREVIOUS FORECAST...OF COURSE WITH THE UPPER LEVEL LOW FARTHER SOUTH THAN THE MODELS WERE SHOWING SEVERAL DAYS AGO...TOTAL SNOW AMOUNTS WILL NOT BE AS HIGH AS ONCE EXPECTED. SNOW AMOUNTS OVER SOUTHEAST WYOMING WILL MAINLY BE IN THE 1 TO 3 INCH RANGE. MAY NOT SEE MUCH IN THE WAY OF SNOW OVER NORTHERN CONVERSE AND NORTHERN NIOBRARA COUNTIES WITH THIS SYSTEM. ALSO...RAWLINGS MAY NOT SEE MUCH IN THE WAY OF SNOW ACCUMULATIONS EITHER. THE SNOWY AND SIERRA RANGES ARE GENERALLY EXPECTED TO SEE ACCUMULATIONS LESS THAN 6 INCHES. MAINLY 2 TO 4 INCHES OVER THE NEBRASKA PANHANDLE WITH 4 TO 6 INCHES LIKELY NEAR THE COLORADO BORDER. CONVECTIVE SNOW IS STILL A POSSIBILITY OVER THE NEBRASKA PANHANDLE THIS EVENING WHICH COULD PRODUCE HIGHER SNOW RATES AND AMOUNTS...BUT BASED ON CURRENT SATELLITE AND RADAR IMAGERY...IT APPEARS THE STRONGER CONVECTION WILL BE SOUTH OF THE FORECAST AREA. IF ANYTHING FORECAST ERROR WOULD FAVORS LOWER SNOW AMOUNTS SHOULD CONVECTION SOUTH OF THE AREA ROB MOISTURE. WINDS NOT EXPECTED TO BE A BIG CONCERN WITH THIS SYSTEM...MAY SEE SOME GUSTS TO 25 MPH OVER THE PANHANDLE AND FAR SOUTHEAST WYOMING. THIS COULD PRODUCE SOME BLOWING AND DRIFTING SNOW. SNOW SHOULD TAPER OFF DURING THE DAY THURSDAY ALTHOUGH SOME LIGHT SNOW COULD HANG ON INTO THURSDAY EVENING OVER THE NEBRASKA PANHANDLE. DRY FRIDAY WITH A RIDGE BUILDING OVER THE AREA...BUT COULD SEE A FEW SNOW SHOWERS INTO THE MOUNTAINS. HIGH WINDS A POSSIBLE IN WIND PRONE AREAS LATE FRIDAY NIGHT THROUGH SATURDAY MORNING. MAY SEE GUSTS TO NEAR 60 MPH AROUND ARLINGTON AND INTO THE SOUTHERN LARAMIE RANGE. LONG TERM...SATURDAY THROUGH TUESDAY... FAST MIDLEVEL WESTERLY FLOW COMBINED WITH A STRONG LLVL GRADIENT COULD PRODUCE SOME HIGH WINDS IN THE WIND PRONE AREAS OF SOUTHEAST WY ON SAT MORNING. THE GFS SHOWS 700MB WINDS AROUND 45-50 KTS. THE ELEVATED WESTERLY WINDS WILL CONTINUE THROUGH THE AFTN IN ADVANCE OF A FROPA ON SAT NIGHT. THE COLD FRONT IS ASSOCIATED WITH A PRETTY STRONG UPPER LEVEL TROUGH DIGGING INTO THE INTERMOUNTAIN WEST DURING THE DAY...THAT THEN MOVES QUICKLY ACROSS THE CWA WITH THE TROUGH AXIS ACROSS EASTERN COLORADO BY SUNDAY AFTN. YESTERDAY THERE WAS ABOUT 12 HOURS TIMING DIFFERENCE BETWEEN THE GFS AND ECMWF WITH THIS SYSTEM...HOWEVER THOSE DIFFERENCES HAVE GENERALLY BEEN RESOLVED WITH TODAYS MODEL RUNS. THE ECMWF HAS HIGHER QPF AMOUNTS THAN THE GFS BUT BOTH MODELS INDICATE WIDESPREAD SNOW SUNDAY MORNING THROUGH THE EVENING. WITH THE MIDLEVEL LOW CLOSING OFF/DEEPENING OVER WESTERN KANSAS ON SUN NIGHT...WOULD LIKELY SEE SOME PRETTY STRONG NORTHERLY WIND GUSTS OVER THE PANHANDLE. SHORTWAVE RIDGING MOVES OVERHEAD FOR MONDAY BEFORE ANOTHER PROGRESSIVE SYSTEM IMPACTS THE REGION BY LATE TUESDAY. AT LEAST AT THIS TIME...THE LONG RANGE MODELS ARE LESS BULLISH ON PRECIP WITH THIS SYTEM THAN THE SUNDAY STORM. LITTLE ABOVE NORMAL TEMPS EXPECTED THROUGH THE EXTENDED AS LOWER HEIGHTS/THICKNESSES WILL DOMINATE THE PATTERN. AVIATION...18Z TAF ISSUANCE... WIDESPREAD IFR/VFR CIGS ACROSS THE PLAINS THIS AFTERNOON. KCYS HAS CLEARED OUT OVER THE PAST HOUR BUT LOW CLOUDS ARE QUICKLY MOVING WESTWARD AND KEPT THIS SITE IN IFR THROUGH THE AFTERNOON. SNOW WILL BEGIN TO DEVELOP OVER THE SOUTHERN PANHANDLE AND EXTREME SOUTHEAST WY AROUND 00-03Z AND THEN CONTINUE THROUGH THURS MORNING. SOUTHEAST WIND GUSTS TO 25 KTS WILL BE POSSIBLE IN THE PANHANDLE THIS AFTERNOON BEFORE BECOMING MORE EASTERLY AND WEAKENING DURING THE OVERNIGHT HOURS. FIRE WEATHER... NO FIRE WEATHER CONCERNS THE NEXT SEVERAL DAYS. SNOW EXPECTED OVER MUCH OF THE AREA WEDNESDAY NIGHT INTO THURSDAY MORNING. ANOTHER SYSTEM MAY BRING SNOW TO THE AREA THIS WEEKEND. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...WINTER WEATHER ADVISORY UNTIL 3 PM THURSDAY FOR WYZ119. NE...WINTER WEATHER ADVISORY UNTIL 3 PM THURSDAY FOR NEZ003-NEZ019- NEZ020-NEZ021-NEZ054-NEZ055. && $$ SHORT TERM/FIRE WEATHER...LIEBL LONG TERM/AVIATION...FINCH UPDATE...WEILAND