000 FXUS65 KCYS 072148 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 248 PM MST SAT NOV 7 2009 .SHORT TERM...WATER VAPOR LOOP SHOWS A SHORTWAVE DIGGING INTO THE INTERMOUNTAIN WEST THIS AFTERNOON. MSAS SFC PRESSURE ANALYSIS SHOWS WIDESPREAD PRESSURE FALLS ACROSS THE ROCKIES AHEAD OF THE WAVE...WITH LEESIDE SFC TROUGH BECOMING APPARENT. BREEZY SOUTHERLY SFC WINDS HAVE BECOME WIDESPREAD ACROSS THE CWA THIS EARLY AFTERNOON AS THE LEE TROUGH DEEPENS. A PLUME OF MID AND HIGH LEVEL MOISTURE IS MOVING THROUGH THE ROCKIES IN STRONG SOUTHWEST FLOW ALOFT THIS AFTERNOON...SO HAVE PARTLY CLOUDY SKIES WITH EMBEDDED MOUNTAINS WAVES WHICH CAN BE SEEN ON VISIBLE SATELLITE IMAGERY. TEMPS ACROSS THE BOARD ARE ONCE AGAIN MILD...ALTHOUGH COOLER THAN PREVIOUS DAYS. AS THE UPPER LEVEL WAVE MOVES ACROSS NORTHERN WYOMING...EXPECT OROGRAPHIC SHOWERS TO INCREASE THROUGH THE EVENING. TEMPERATURES IN THE HIGH TERRAIN BASED ON MESOWEST SITES ARE WARM ENOUGH TO SUGGEST A MIX OF RAIN/SNOW INITIALLY WHICH SHOULD CHANGE OVER TO ALL SNOW AS TEMPS COOL OVERNIGHT. ACCUMULATIONS SHOULD REMAIN LIGHT OVERALL. ANOTHER SHORTWAVE WILL MOVE ACROSS THE REGION OVERNIGHT WITH A DRY COLD FRONT MOVING THROUGH THE EASTERN ZONES EARLY SUNDAY MORNING. TEMPS WILL AGAIN BE COOLER TOMORROW AND NW WINDS WILL INCREASE BEHIND THE FRONT AS HIGH PRESSURE AT THE SFC BUILDS ACROSS THE INTERMOUNTAIN WEST. 12Z NAM SHOWS MUCH STRONGER WINDS THAN EITHER THE GFS...ECMWF OR CANADIAN MODELS SO WILL RELY MORE ON THE MODEL CONSENSUS THEN THE OUTLIER NAM. IT SHOULD STILL BE A BREEZY DAY ACROSS THE EASTERN ZONES THOUGH WITH LOCAL SPOTS GUSTING 30 MPH IN SOUTHERN PORTIONS OF SOUTHEAST WYOMING AND THE NEBRASKA PANHANDLE. YET ANOTHER SHORTWAVE WILL MOVE ACROSS THE REGION SUNDAY NIGHT INTO MONDAY. WITH LOW LEVEL UPSLOPE WINDS IN PLACE ACROSS THE SOUTHERN CWA IN ADDITION TO SUPPORT FROM THE UPPER WAVE...WILL SEE PRECIPITATION ACROSS THIS AREA INCREASE IN COVERAGE THROUGH THE NIGHT. WILL SEE SNOW IN THE HIGHER ELEVATIONS WITH RAIN OR A RAIN/SNOW MIX LIKELY FURTHER EAST AS THICKNESSES DO NOT DECREASE SUBSTANTIALLY WITH THE PASSING WAVE. TOTAL PRECIP ACCUMULATIONS SHOULD BE LIGHT AS THE UPPER LEVEL SUPPORT QUICKLY TRANSLATES EAST OF THE AREA BY MONDAY AFTERNOON AND UPSLOPE FLOW WEAKENS. && .LONG TERM...MONDAY NIGHT THROUGH SATURDAY... UPPER RIDGE AXIS WILL MOVE EAST OUT ONTO THE CENTRAL PLAINS MONDAY NIGHT...TURNING THE MID/UPPER-LEVEL FLOW SOUTHWESTERLY INTO THE INTERMOUNTAIN WEST. THIS PATTERN WILL INDUCE THERMAL RIDGING ACROSS THE REGION...WHICH WILL BE MAXIMIZED LATE TUESDAY. BENIGN CONDITIONS WILL OCCUR FOR MONDAY NIGHT THROUGH TUESDAY...WITH TEMPERATURES WARMING BACK ABOVE NORMAL AFTER A COOLER MONDAY. MEDIUM RANGE DETERMINISTIC MODEL OUTPUT FROM 12Z ARE BECOMING MORE CONGRUENT FOR THE WEDNESDAY THROUGH FRIDAY TIMEFRAME...BUT THEN BECOME OUT OF PHASE BY THE WEEKEND. UPPER LOW WILL DIG INTO THE ERN PACIFIC EARLY WEDNESDAY...WITH INITIAL SHORTWAVE ENERGY REACHING THE ID/WY BORDER BY LATE WEDNESDAY. THE ECMWF WAS THE SLOWEST WITH THIS ENERGY... HOLDING IT BACK NR THE CASCADES BY THIS TIME. CONTINUED THE EARLIER THINKING OF SPREADING PRECIPITATION CHANCES FIRST INTO THE SNOWY/SIERRA MADRES ON WEDNESDAY...THEN OUT INTO LOWER ELEVATIONS OF CARBON AND ALBANY COUNTIES WEDNESDAY NIGHT...AND FINALLY OUT ONTO THE ERN PLAINS BY THURSDAY. THE GFS/GEM SUPPORT THE IDEA OF BRINGING THE MAIN TROUGH INTO WRN WY BY EARLY FRIDAY...ALTHOUGH THE GEM CLOSES IT OFF OVER IDAHO. MEANWHILE...THE ECMWF WOULD SUGGEST A SPLIT FLOW PATTERN...WHICH IF VERIFIES WOULD LIMIT PRECIPITATION CHANCES ACROSS THE REGION. SO...ALLOWING FOR SOME UNCERTAINTY IN THE PATTERN...HAVE INCREASE PRECIPITATION CHANCES SOME DURING THE THURSDAY NIGHT THROUGH FRIDAY PERIOD. LIKEWISE...AFTER ABOVE AVERAGE TEMPERATURES TUESDAY AND WEDNESDAY...COOLER TEMPERATURES ARE IN STORE FOR THURSDAY THROUGH SATURDAY. PREFRONTAL WINDS INCREASE ABOVE 50 KNOTS AT H7 LATE WEDNESDAY/EARLY THURSDAY...SO THIS PERIOD WILL HAVE BE MONITORED CLOSELY FOR THE POTENTIAL FOR HIGH WINDS AT THE SURFACE. INITIAL PRECIPITATION WILL LIKELY BE IN THE FORM OF RAIN AT ALL LOWER ELEVATIONS THROUGH THURSDAY...WITH BEST COLD AIR ADVECTION AND ANY POTENTIAL CHANGE-OVER HOLDING OFF UNTIL DURING THE DAY ON FRIDAY. && .AVIATION...A WEAK DISTURBANCE WILL DRAG A WEAK...AND MOSTLY DRY...COLD FRONT THROUGH THE REGION TONIGHT. ONLY IMPACT AT AREA TERMINALS WILL BE A WIND SWITCH FROM PREDOMINATELY S/SE EAST OF THE LARAMIE RANGE...AND SW WEST OF THE LARAMIE RANGE...TO AN EVENTUAL NORTHWEST BEHIND THE FRONT. BROUGHT CIGS DOWN SOMEWHAT OVERNIGHT...BUT MAINTAINED VFR CONDITIONS AT ALL TERMINALS. CIGS WILL BEGIN TO INCREASE DURING THE DAY ON SUNDAY...AS THE UPPER LEVEL DISTURBANCE DEPARTS. && .FIRE WEATHER...NORTHWEST WINDS WILL INCREASE EARLY SUNDAY ACROSS EASTERN ZONES AND WILL CONTINUE THROUGH THE EVENING. SOME AREAS COULD SEE GUSTS AROUND 30 MPH...WITH STRONGEST WINDS IN EXTREME SOUTHEAST WYOMING AND THE SOUTHERN NEBRASKA PANHANDLE. WITH COOLER TEMPS BEHIND A FRONT MOVING THROUGH THE AREA TONIGHT...MINIMUM RELATIVE HUMIDITIES SHOULD REMAIN IN THE 20S AND 30S IN THIS AREA FOR SUNDAY. WILL SEE PRECIPITATION INCREASE IN COVERAGE SUNDAY NIGHT INTO MONDAY AS AN UPPER LEVEL WAVE MOVES ACROSS THE REGION. WILL SEE SNOW IN THE MOUNTAINS WITH MAINLY RAIN OR A RAIN/SNOW MIX IN THE LOWER ELEVATIONS OF WYOMING AND THE NEBRASKA PANHANDLE. OVERALL ACCUMULATIONS OF PRECIPITATION WILL BE LIGHT THROUGH EARLY MONDAY AFTERNOON. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...NONE. && $$ SHORT TERM/FIRE WEATHER...RJM LONG TERM/AVIATION...HAHN