Issued by NWS Cheyenne, WY
000 FXUS65 KCYS 152015 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 215 PM MDT WED OCT 15 2008 .SHORT TERM...TONIGHT THROUGH FRIDAY... FAIRLY FAST WESTERLY FLOW ALOFT WILL BECOME MORE NORTHWEST BY THURSDAY NIGHT AS HEIGHTS RISE THROUGH FRIDAY NIGHT OVER THE ROCKIES. A BROAD RIDG ALOFT WILL BE OVER THE ROCKIES BY 12Z SATURDAY. MODELS DEPICT SEVERAL WEAK SHORTWAVE TROUGHS WILL MOVE ACROSS THE CWA TONIGHT AND THURSDAY. THE SHORTWAVE TROUGHS WILL BRING MAINLY AND HIGH LEVEL CLOUDS OVER MAINLY OF THE NORTH PART OF THE CWA DURING THAT TIME. A WEAK FRONT WILL MOVE ACROSS THE REGION LATE THURSDAY. WIND SPEEDS ALOFT INCREASE AND THE SURFACE PRESSURE GRADIENT TIGHTENS LATE TONIGHT AND CONTINUE FOR THURSDAY. THE RESULT WILL BE AN INCREASE IN WIND SPEEDS OVER THE CWA...ESPECIALLY ALONG AND WEST OF THE LARAMIE RANGE. WINDS SHOULD DIMINISH SOME FOR THURSDAY NIGHT AND FRIDAY. WILL LEAVE THE CWA DRY FOR NOW...ALTHOUGH LIGHT PRECIPITATION IS POSSIBLE OVER THE HIGHER ELEVATIONS OF THE SNOWY RANGE ON THURSDAY. TEMPERATURES WILL WARM UP TO 10 DEGREES AHEAD OF THE FRONT ON THURSDAY AND THEN SEVERAL DEGREES WARMER FOR FRIDAY. WESTERLY SURFACE PRESSURE GRADIENT WILL KEEP LOWS ABOVE NORMAL FOR TONIGHT THROUGH FRIDAY NIGHT. .LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY... THE RIDGE ALOFT WILL BE OVER THE ROCKIES THROUGH SATURDAY BEFORE BEING FLATTENED BY A SHORTWAVE TROUGH MOVING ACROSS SOUTHERN CANADA SUNDAY AND SUNDAY NIGHT. THE MODELS DO BRING A 300 MB JET SEGMENT AND WEAKER SHORTWAVE ENERGY OVER THE CWA SUNDAY THROUGH MONDAY. A COLD FRONT BACKS INTO THE CWA AS WELL SUNDAY. MODELS...ESPECIALLY THE 00Z ECMWF DEVELOP QPF BEHIND THE FRONT WHICH LINGERS IN THE UPSLOPE WIND FLOW THROUGH MONDAY. AT THIS TIME WILL INTRODUCE LOW POPS BEHIND THE FRONT...AND MOVING FROM NORTH TO SOUTH...SUNDAY THROUGH MONDAY. LOW CLOUDS WILL BE A POSSIBILITY LATE SUNDAY NIGHT AND MONDAY MORNING AND AGAIN LATE MONDAY NIGHT AND TUESDAY MORNING. TEMPERATURES WILL BE MILD THROUGH SATURDAY NIGHT AHEAD OF THE FRONT WITH READINGS FALLING TO AROUND NORMAL FOR SUNDAY AND MONDAY. A LARGE AMPLITUDE SHORTWAVE TROUGH WILL AFFECT THE CWA TUESDAY AND WEDNESDAY AFTER MOVING IN FROM THE PACIFIC. IN FACT...THE GFS AND ECMWF CLOSE OFF A DEEP UPPER LOW NEAR THE FOUR CORNERS AREA ON WEDNESDAY. THE 12Z GFS HAS BEEN CONSISTENT IS BEING FURTHER EAST WITH THE SHORTWAVE TROUGH AND UPPER LOW AND PLACES THE FEATURE OVER CWENTRAL KANSAS 00Z THURSDAY. BASED ON DISCUSSIONS FROM HPC WILL FAVOR A COMPROMISE TIMING OF THE UPPER LOW FOR TUESDAY AND NEXT WEDNESDAY. THE RESULTING SURFACE UPSLOPE AND INCREASED MOISTURE AND CYCLONIC FLOW ALOFT SHOULD PRODUCE SOME PRECIPITATION OVER ESPECIALLY THE SOUTH HALF OF THE CWA TUESDAY AND WEDNESDAY. AT THIS TIME THE TEMPERATURES LOOK TO BE WARM ENOUGH FOR THE PRECIPITATION TYPE TO BE MAINLY IN THE FORM OF RAIN BELOW 9000 FEET MSL. THE ASSOCIATED SURFACE COLD FRONT WILL MOVE ACROSS THE CWA TUESDAY OR TUESDAY NIGHT WITH BELOW NORMAL TEMPERATURES BEHIND THE FRONT. && .AVIATION...VFR CONDITIONS WILL CONTINUE ACROSS THE CWA THROUGH FRIDAY NIGHT. AN EXPECTED INCREASE IN THE WINDS FOR LATE TONIGHT AND THURSDAY...MAINLY ALONG AND WEST OF THE LARAMIE RANGE WILL PRODUCE GUSTS AS HIGH AS 35 KNOTS. TURBULENCE BELOW 700 MB CAN BE EXPECTED THROUGH THURSDAY WITH WEAK MOUNTAIN WAVE ACTIVITY NEAR THE MOUNTAINS. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...NONE. && $$ WEILAND
