FXUS65 KCYS 181538 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 938 AM MDT THU MAR 18 2010 .UPDATE... MADE SOME TWEEKS TO TEMPERATURES THIS MORNING ALONG WITH CLOUD COVERAGE. UPDATED FORECAST OUT. WAITING FOR NEW MODEL RUN TO DETERMINE HOW TO PROCEED WITH OUR WINTER STORM. WILL MAKE FINAL DECISION AROUND NOONTIME OR SO. CLAYCOMB && .PREV DISCUSSION... /ISSUED 328 AM MDT THU MAR 18 2010/ SHORT TERM...TODAY THROUGH FRIDAY NIGHT... QUIET START TO THE DAY TODAY WILL CHANGE RAPIDLY DURING THE AFTERNOON AND EVENING AS UPPER TROF MOVES INTO THE NORTHERN ROCKIES TODAY WHILE STRONG SFC COLD FRONT DROPS SOUTH ACROSS THE CWA THIS AFTERNOON. MAX TEMPERATURES OVER THE NORTHERN CWA WILL BE REACHED EARLY THIS AFTERNOON THEN BE STEADY OR SLOWLY FALL. MUCH COLDER AIR WILL THEN SPREAD ACROSS THE CWA TONIGHT AND FRIDAY WITH A SECONDARY SURGE ARRIVING FRIDAY NIGHT KEEPING QUITE COOL TEMPERATURES IN PLACE THROUGH SATURDAY. MAIN DILEMMA WITH FORECAST IS THE AMOUNTS OF EXPECTED SNOWFALL ACROSS THE CWA IN POST FRONTAL UP-SLOPE REGIME TONIGHT INTO FRIDAY. MODELS HAVE SHOWN A TREND OF BRINGING THE SYSTEM THROUGH A LITTLE FASTER AND THUS QPFS HAVE TRIMMED. AREA OF BEST SNOWFALL TONIGHT INTO FRIDAY MORNING APPEARS TO BE OVER AN AREA FROM THE LARAMIE VALLEY EASTWARD ACROSS THE LARAMIE RANGE INTO THE ADJACENT HIGH PLAINS WHERE BEST MOISTURE AND JET DYNAMICS SHOULD BE CO-LOCATED WHILE AMOUNTS OVER THE FAR NRN CWA AND THE PANHANDLE NOT SO HIGH NOW. ALSO...MODELS HAVE BACKED OFF ON SFC WINDS SOMEWHAT WITH STRONGEST WINDS JUST AFTER FRONTAL PASSAGE THEN TAPERING DOWN SOME. AFTER COORDINATION WITH SURROUNDING OFFICES HAVE CHANGED WINTER STORM WATCH TO A SNOW ADVY FOR THE NEB PANHANDLE AND FAR NORTHERN PORTIONS OF THE CWA WITH SOME MINOR ADJUSTMENT OF TIMING. DONT SEE MUCH IN THE WAY OF SNOW OVER CARBON COUNTY THUS WILL DROP THE WATCH THERE. WILL HOLD ONTO REMAINDER OF WATCH IN AREA WHERE HEAVIEST SNOWFALL SEEMS TO BE TARGETING NOW BUT DELAY START UNTIL MID EVENING WHEN PCPN SHOULD BEGIN ARRIVING. SNOWFALL SHOULD TAPER OFF FROM NORTH TO SOUTH FRIDAY MORNING AND AFTERNOON WITH MOSTLY SCATTERED SNOW SHOWERS OVER MAINLY HIGHER TERRAIN BY FRIDAY EVENING. LONG TERM...SATURDAY THROUGH WEDNESDAY NIGHT... SURFACE HIGH PRESSURE WILL BE IN PLACE ACROSS SOUTHEAST WYOMING AND THE WESTERN NEBRASKA PANHANDLE AS AN UPPER LEVEL RIDGE AXIS WILL BE ALIGNED OVER THE GREAT BASIN. TEMPERATURES SATURDAY WILL STILL BE AROUND 10 TO 15 DEGREES BELOW NORMAL. SUNDAY CONTINUES TO APPEAR WARMER...WITH ABOVE NORMAL TEMPERATURES AND DRY CONDITIONS. MONDAY WILL BE THE WARMEST DAY OF THE PERIOD AHEAD OF THE NEXT WEAK DISTURBANCE WHICH WILL AFFECT NORTHERN AND WESTERN ZONES BY MONDAY EVENING WITH A CHANCE OF SHOWERS. LATEST MODEL RUNS FROM THE GFS AND EUROPEAN MODEL ARE SHOWING THIS UPPER TROUGH IN THE NORTHERN BRANCH OF THE JET STREAM DIGGING ACROSS THE GREAT BASIN MONDAY NIGHT...AND FORMING A CLOSED LOW NEAR THE FOUR CORNERS AS THE TWO BRANCHES OF THE JET STREAM MERGE BY LATE TUESDAY. THIS SYSTEM BRING A COLD FRONT SOUTH ACROSS THE AREA EARLY TUESDAY WITH BELOW NORMAL TEMPERATURES EXPECTED TUESDAY AND WEDNESDAY. PRECIPITATION CHANCES WILL BE SLIGHTLY GREATER TUESDAY THAN WEDNESDAY AS THE UPPER LEVEL SUPPORT FOR PRECIPITATION IS EXPECTED TO BE SOUTH OF THE FORECAST AREA BY THE DAYLIGHT HOURS WEDNESDAY. THIS IS A CHANGE FROM RECENT MODEL RUNS WHICH PLACED A CLOSED LOW FEATURE OVER THE FOUR CORNERS AREA...BUT BOTH THE GFS AND EUROPEAN MODELS ARE SHOWING THIS TREND. THIS WILL LEAD TO A WARMING TREND INTO THE END OF NEXT WEEK...WITH THE UPPER LOW GENERALLY MOVING EAST ACROSS NEW MEXICO AND INTO TEXAS. AVIATION... MVFR CEILINGS AND VISIBILITIES WILL DEVELOP ALONG AND NORTH OF A LINE FROM NEAR RAWLINS TO CHADRON LATE THIS AFTERNOON AS A STRONG COLD FRONT MOVES ACROSS THE AREA. IFR CEILINGS AND VISIBILITY WILL THEN BECOME LIKELY ACROSS THE ENTIRE AREA TONIGHT AS SNOW ACCUMULATIONS WILL BECOME LIKELY. THE LAST AREA TO DEVELOP IFR CONDITIONS WILL BE NEAR SIDNEY NEBRASKA...WITH IFR EXPECTED TO DEVELOP AROUND 9 PM MDT. FIRE WEATHER... NO CONCERNS THROUGH FRIDAY WITH MUCH COOLER TEMPERATURES AND SNOWFALL. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...WINTER WEATHER ADVISORY FROM 6 PM THURSDAY TO 6 AM FRIDAY FOR WYZ101-WYZ102. WINTER WEATHER ADVISORY FROM 6 PM THURSDAY TO 1 PM FRIDAY FOR WYZ103. WINTER WEATHER ADVISORY FROM 9 PM THURSDAY TO 1 PM FRIDAY FOR WYZ108. WINTER STORM WATCH FROM 9 PM THURSDAY TO 1 PM FRIDAY FOR WYZ104- WYZ105-WYZ106-WYZ107-WYZ110-WYZ112-WYZ114-WYZ115-WYZ116- WYZ117-WYZ118-WYZ119. NE...WINTER WEATHER ADVISORY FROM 6 PM THURSDAY TO 6 AM FRIDAY FOR NEZ002-NEZ095. WINTER WEATHER ADVISORY FROM 9 PM THURSDAY TO 6 AM FRIDAY FOR NEZ003-NEZ096. WINTER WEATHER ADVISORY FROM 9 PM THURSDAY TO 1 PM FRIDAY FOR NEZ019-NEZ020-NEZ021-NEZ054-NEZ055. && $$ SHORT TERM/AVIATION...CLAYCOMB LONG TERM...