754 FXUS65 KCYS 270004 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 604 PM MDT THU SEP 26 2013 .SHORT TERM...(THIS EVENING THROUGH FRIDAY) ISSUED AT 424 PM MDT THU SEP 26 2013 THE DEEP UPPER LEVEL TROUGH WILL SLOWLY MOVE TOWARD THE FORECAST AREA TONIGHT...WITH THE TROUGH AXIS MOVING OVERHEAD FRIDAY EVENING. THE SLOW MOVEMENT OF THE TROUGH WILL ALLOW ENERGETIC SOUTHWEST FLOW TO REMAIN OVERHEAD TONIGHT AND FRIDAY...WITH THE SURFACE CYCLONE OVER EASTERN COLORADO DEEPENING AND REMAINING RELATIVELY STATIONARY AS THE UPPER TROUGH APPROACHES. EASTERLY SURFACE WINDS OVER THE EASTERN PLAINS WILL BACK TO BECOME MORE NORTH-NORTHEAST TONIGHT AS THE SFC BOUNDARY OVER EAST CENTRAL WYOMING SLIDES SOUTHWARD ACROSS THE FORECAST AREA AS A WEAK COLD FRONT. EXPECTING WIDESPREAD RAIN SHOWERS AND HIGH ELEVATION SNOW OVER WESTERN PORTIONS OF THE FORECAST AREA TONIGHT NEAREST THE BEST AVAILABLE MOISTURE PLUME AND AS MODERATE OROGRAPHIC AND ISENTROPIC LIFT RESIDE OVER THIS AREA. LOOKING AT SNOW ABOVE 8500 FEET WITH A MIX OF RAIN AND SNOW DROPPING TO 6000 FEET THROUGH THE NIGHT. ACCUMULATIONS OF 1 TO 2 INCHES ARE POSSIBLE AT THE HIGHER ELEVATIONS WITH LESS ELSEWHERE. MAIN AREA OF UNCERTAINTY AT THIS POINT WILL BE IN WESTERN CONVERSE COUNTY AS THIS AREA WILL BE ON THE BOUNDARY OF COLDER AIR...SO COULD SEE ALL SNOW IN THIS AREA AS WELL. FORECAST SOUNDINGS SHOW MORE OF A SLEET PROFILE IN THIS AREA HOWEVER...BUT ANY COOLING OF THE PROFILE MORESO THAN EXPECTED COULD SWITCH PRECIP TO ALL SNOW. FOR FRIDAY...THE TROUGH AXIS WILL BEGIN TO MOVE OVERHEAD LATER IN THE DAY WHILE THE MAIN COLD FRONT MOVES EAST ACROSS THE FORECAST AREA AFTER NOON. AGAIN...WITH THE SLOWER MOVEMENT OF THE ENTIRE SYSTEM...THE MOISTURE PLUME LOOKS TO ALIGN BETTER WITH THE SFC BAROCLINIC BAND AND ENERGY ALOFT IN THE LATE MORNING THROUGH EARLY EVENING. LOOKING AT A GOOD CHANCE FOR RAIN ACROSS THE EASTERN PLAINS BEGINNING THROUGH THIS TIME AS A RESULT. DO EXPECT RAIN AND HIGH ELEVATION SNOW TO CONTINUE AT TIMES OVER THE HIGH COUNTRY AS WELL...BUT BEST FORCING WILL SHIFT EASTWARD SO WILL BE LIGHTER RAIN AND SNOW RATES AS THE DAY PROGRESSES. LIKELY AN ADDITIONAL 1 TO 2 INCHES OF SNOW IS POSSIBLE IN THE MOUNTAINS ABOVE 8500 FEET THROUGH EARLY FRIDAY EVENING. FORECAST SOUNDINGS CONTINUE TO SHOW THE POSSIBILITY FOR A FEW FLAKES TO MIX IN WITH THE RAIN SHOWERS DOWN TO AROUND 6000 FEET ALONG THE INTERSTATE 25 CORRIDOR...BUT THE COLDEST AIR MAY NOT ADVECT INTO THIS AREA IN TIME TO SEE MUCH MORE THAN THAT. BEST FORCING AND DEEPEST MOISTURE WILL QUICKLY SHIFT EAST FRIDAY EVENING AND NIGHT WITH PRECIP LOOKING TO END THROUGH THIS TIME. THE OTHER CONCERN WITH THIS SYSTEM WILL BE THE SFC WINDS. LOOKS TO BE A TYPICAL BORA SITUATION SETTING UP WITH THE CAA STRENGTHENING THROUGH THE DAY AND AS SFC HIGH PRESSURE BUILDS IN BEHIND THE FRONT INCREASING THE PRESSURE GRADIENT FROM WEST TO EAST. THEREFORE...EXPECTING TO SEE A STARK INCREASE IN WESTERLY LLVL WINDS BEHIND THE FRONT...WITH WIND PRONE AREAS SEEING THE HIGHEST SPEEDS AS WOULD BE EXPECTED. WOULD NOT BE SURPRISED FOR SUSTAINED 25 TO 35 MPH WITH GUSTS APPROACHING 50 TO 55 MPH IN THE AFTERNOON IN THESE AREAS ALONG AND WEST OF THE LARAMIE RANGE. THESE WINDS WILL EASE SLIGHTLY OVERNIGHT BUT WILL STILL SEE ELEVATED SPEEDS PERSIST AS THE PRESSURE GRADIENT IS SLOW TO WEAKEN. THIS SHOULD KEEP OVERNIGHT TEMPERATURES FROM PLUMMETING IN THE POST FRONTAL ENVIRONMENT...BUT LIKELY WILL DROP BELOW FREEZING IN THE HIGH VALLEYS OUT WEST THAT SEE WEAKER WINDS. SATURDAY WILL REMAIN COOLER IN THE POST FRONTAL ENVIRONMENT WITH CONTINUED WINDY CONDITIONS ALONG AND WEST OF INTERSTATE 25. MUCH DRIER AIR WILL BE OVERHEAD SO NOT EXPECTING ANY PRECIPITATION. .LONG TERM...(SATURDAY NIGHT THROUGH THURSDAY) ISSUED AT 424 PM MDT THU SEP 26 2013 QUIET AND WARM WEATHER IS EXPECTED THROUGH THE MIDDLE OF NEXT WEEK WITH ALL MODELS IN AGREEMENT...SHOWING ZONAL FLOW ALOFT ACROSS THE FORECAST AREA. THE ONLY FORECAST CONCERN THROUGH TUESDAY WILL BE GUSTY WESTERLY WINDS ACROSS SOUTHEAST WYOMING WITH GUSTS UP TO 45 MPH POSSIBLE. OTHERWISE...TEMPERATURES WILL INCREASE INTO THE UPPER 60S TO UPPER 0S ACROSS SOUTHEAST WYOMING BY MONDAY WITH HIGHS AROUND 80 OVER THE PANHANDLE OF NEBRASKA. UPPER LEVEL FLOW WILL BECOME MORE SOUTHWESTERLY BY THE MIDDLE OF THE WEEK AS A SERIES OF UPPER LEVEL DISTURBANCES PUSH ACROSS THE NORTHERN ROCKIES. THIS WILL RESULT IN SLIGHTLY LOWER TEMPERATURES...BUT TEMPS WILL REMAIN NEAR OR SLIGHTLY ABOVE NORMAL TUESDAY AND WEDNESDAY. MOSTLY CLEAR SKIES ARE EXPECTED THROUGH WEDNESDAY BEFORE THE NEXT PACIFIC COLD FRONT MOVES EASTWARD BY LATE NEXT WEEK. MODELS ARE STRUGGLING WITH THE TIMING OF THIS FRONT AND ASSOCIATED TROUGH...SO WILL KEEP POP AROUND 20 PERCENT FOR NOW ACROSS MOST OF THE FORECAST AREA THURSDAY AND THURSDAY NIGHT. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY AFTERNOON) ISSUED AT 551 PM MDT THU SEP 26 2013 EAST OF THE LARAMIE RANGE...VFR CONDITIONS WILL PREVAIL THIS EVENING...WITH DETERIORATING CONDITIONS DUE TO PRECIPITATION SPREADING INTO AREAS WEST OF THE LARAMIE RANGE. GENERALLY MVFR CIGS/VSBYS ARE FORECAST AT KRWL AND KSAA...WITH THE MOUNTAINS BECOMING OBSCURED. MOIST UPSLOPE FLOW WILL BRING MVFR TO IFR CIGS/VSBYS TO AREAS EAST OF THE LARAMIE RANGE LATE TONIGHT AND FRIDAY MORNING. && .FIRE WEATHER... ISSUED AT 424 PM MDT THU SEP 26 2013 A STRONG STORM SYSTEM WILL BRING WIDESPREAD RAIN AND HIGH ELEVATION SNOW TONIGHT THROUGH FRIDAY EVENING. PRECIPITATION TYPE WILL BE IN THE FORM OF SNOW ABOVE 8500 FEET BEGINNING LATE THIS EVENING...WITH A MIX OF RAIN AND SNOW IN THE HIGH VALLEYS DOWN TO AROUND 6000 FEET. PRECIPITATION WILL THEN SPREAD EASTWARD THROUGH LATE FRIDAY MORNING AND AFTERNOON...MAINLY IN THE FORM OF WETTING RAINS ACROSS THE EASTERN PLAINS. TEMPERATURES WILL BE MUCH COOLER FRIDAY THROUGH SATURDAY AS THIS SYSTEM MOVES ACROSS THE REGION...WITH GUSTY WEST TO NORTHWEST WINDS DEVELOPING BEHIND A COLD FRONT MOVING FROM WEST TO EAST FRIDAY. MILD TEMPERATURES WILL RETURN FOR SATURDAY ALONG WITH DRY CONDITIONS. WESTERLY WINDS WILL REMAIN GUSTY AT TIMES ESPECIALLY ACROSS SOUTHEAST WYOMING...BUT HUMIDITIES WILL REMAIN ABOVE 20 PERCENT. BREEZY TO WINDY CONDITIONS WILL PREVAIL SUNDAY AND MONDAY...ALONG WITH CONTINUED DRY AND MILD CONDITIONS. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...NONE. && $$ SHORT TERM...RJM LONG TERM...TJT AVIATION...JAMSKI FIRE WEATHER...RJM