609 FXUS65 KCYS 070312 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 912 PM MDT THU JUN 6 2013 .UPDATE... ISSUED AT 912 PM MDT THU JUN 6 2013 SHORTWAVE MOVING THROUGH NORTHWEST FLOW IS KICKING OFF A FEW RAIN SHOWERS AND SPRINKLES OVER FAR WESTERN PORTIONS OF THE FORECAST AREA AT THIS TIME. AS THE WAVE SHIFTS EAST SHOULD SEE THIS ACTIVITY FOLLOW BUT AS IT GETS EAST OF THE LARAMIE RANGE THIS ACTIVITY SHOULD STRUGGLE TO SURVIVE. MOST MEASURABLE PRECIPITATION WHICH WILL BE MINIMAL SHOULD BE FOUND OVER THE MOUNTAINS OVER THE NEXT 6 HOURS OR SO. NOT MUCH INSTABILITY TO WORK WITH AN FORCING RATHER WEAK...ALSO THE LOW LEVELS ARE DRY SO MUCH MOISTURE WILL EVAPORATE BEFORE REACHING THE GROUND...ESPECIALLY IN LOWER ELEVATIONS. WILL UPDATE THE FORECAST FOR THIS SHOWER ACTIVITY FOR TONIGHT...OTHERWISE FORECAST PRETTY WELL ON TRACK. && .SHORT TERM...(TONIGHT THROUGH FRIDAY NIGHT) ISSUED AT 330 PM MDT THU JUN 6 2013 CUMULUS CLOUDS HAVE BECOME MORE WIDESPREAD THIS AFTERNOON BUT SO FAR RADAR RETURNS HAVE BEEN MINIMAL. THE LAPS ANALYSIS SHOWS VERY WEAK INSTABILITY (100-200 J/KG OF CAPE) AS SFC DEWPOINTS HAVE DRIED OUT A BIT MORE THAN FCSTED. HAVE A SLIGHT CHANCE OF SHOWERS AND TSTMS ALONG THE LARAMIE RANGE THROUGH THE EVENING...BUT NOT REALLY EXPECTING MUCH PRECIP WITH THE DRY BOUNDARY LAYER. WEAK SHORTWAVE CURRENTLY SEEN ON SATELLITE IMAGERY OVER EASTERN IDAHO WILL MOVE SOUTHEASTWARD OVER THE CWA BY TONIGHT. MAIN EFFECT FROM THIS SYSTEM WILL BE AN INCREASE MIDLEVEL CLOUD COVER AND SOME SPRINKLES. STRONGER SHORTWAVE IS STILL ADVERTISED TO MOVE INTO MONTANA ON FRIDAY AND THEN INTO THE NORTHERN PLAINS BY FRIDAY NIGHT. PRESSURE FALLS IN ADVANCE OF THIS SHORTWAVE WITH CAUSE A SFC TROUGH TO DEVELOP OVER THE PLAINS OF SOUTHEAST WY BY THE AFTN. SOUTHERLY WINDS TO THE EAST OF THIS TROUGH WILL RESULT IN SOME MOISTURE ADVECTION WITH DEWPOINTS CLIMBING INTO THE MID 40S. THE GFS AND NAM BOTH SHOW BETTER INSTABILITY THAN THIS AFTN AS CAPE VALUES RISE INTO THE 500-1000 J/KG RANGE...ESPECIALLY OVER THE NEBRASKA PANHANDLE. WITH MODERATE NORTHWESTERLY MIDLEVEL FLOW...0-6 KM SHEAR VALUES ARE AROUND 40 KTS. SOME OF THE STRONGER STORMS ON FRIDAY AFTN COULD PRODUCE SMALL HAIL. THE LIMITING FACTOR FOR STRONGER TO SEVERE CONVECTION IS MARGINAL LOW LEVEL MOISTURE (AND RESULTANT INSTABILITY) AS THE MOISTURE ADVECTION IS LIMITED TO REALLY ONLY 12 HOURS BEFORE CONVECTION INITIATES. SHOWERS AND TSTMS COULD LINGER INTO THE EARLY NIGHT IN THE NEBRASKA PANHANDLE BEFORE THE UPPER LEVEL SHORTWAVE AND SFC TROUGH AXIS PASSES OVERHEAD BY EARLY SATURDAY MORNING. SOME BREEZY NORTHWEST WINDS WILL BE POSSIBLE ACROSS SOUTHEAST WY ON FRIDAY NIGHT...WITH GUSTS LIKELY REMAINING BELOW 35 MPH. .LONG TERM...(SATURDAY THROUGH THURSDAY) ISSUED AT 330 PM MDT THU JUN 6 2013 MEDIUM RANGE MODELS REMAIN IN EXCELLENT AGREEMENT THROUGH A MAJORITY OF THE FCST PERIOD. THE MAIN CHANGE FROM YESTERDAY HAS BEEN A SLIGHT SWD SHIFT IN THE TRACK OF A STRONG MIDLVL SHORTWAVE DIGGING SEWD ACROSS THE NORTHERN HIGH PLAINS EARLY IN THE PERIOD. AN ASSOCIATED SFC COLD FRONT WILL SWING ACROSS THE CWA ON SAT AFTN...WITH LLVL CONVERGENCE AND UPPER-LEVEL SUPPORT IN THE RIGHT EXIT REGION OF THE H25 JET CONTRIBUTING TO A SLIGHT CHANCE OF SHOWERS OR ISOLATED TSTMS. SIGNIFICANT HEIGHT RISES CAN BE EXPECTED FROM LATE IN THE WEEKEND INTO EARLY NEXT WEEK AS THE UPPER TROUGH DEPARTS TO THE EAST. GFS AND ECMWF BOTH SUGGEST H7 TEMPS APPROACHING 18 TO 20 DEG C WITH THICKNESSES NEAR 588 DM OVER FAR SOUTHEAST WY AND THE SOUTHERN PANHANDLE BY MON AND TUE. WITH MODELS BEGINNING TO SUGGEST A STRONGER AND MORE PERSISTENT RIDGE ALOFT...THE TREND IN THE GUIDANCE HAS DEFINITELY BEEN WARMER OVER THE LAST 24 TO 48 HOURS. POTENTIAL IS STILL THERE FOR NEAR RECORD HIGHS ON MON WITH MID AND UPPER 90S POSSIBLE IN THE PLATTE RIVER VALLEY. THE NEXT MIDLVL SHORTWAVE EJECTS NORTHEAST ACROSS THE GREAT BASIN ON MON AND TUE...WITH SFC WINDS STARTING TO TRANSPORT MORE IN THE WAY OF LLVL MOISTURE INTO AREAS ALONG AND EAST OF THE LARAMIE RANGE. FCST SOUNDINGS SHOW INVERTED-V TYPE PROFILES...FAVORING HIGH BASED TSTMS. MAY SEE SOME DECENT INSTABILITY ON MON AND TUE ALONG WITH INCREASING SHEAR...SO SEVERE STORMS WOULD BE POSSIBLE. STOUT CAPPING WILL PROBABLY KEEP CONVECTIVE COVERAGE LIMITED THOUGH. UPPER-LEVEL RIDGING WILL KEEP THINGS DRY ON WED AND THU. THE OVERALL PATTERN IS FAVORABLE FOR GUSTY WINDS TO THE WEST OF THE LARAMIE RANGE THROUGH MOST OF THE PERIOD WITH DEEP AFTN MIXING. && .AVIATION...(FOR THE 00Z TAF ISSUANCE) ISSUED AT 533 PM MDT THU JUN 6 2013 VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD. MIDLEVEL CLOUDS WILL BE ON THE INCREASE AFTER 06Z WITH A WEAK SHORTWAVE. WINDS THROUGH TONIGHT AND EARLY FRIDAY WILL GENERALLY BE LESS THAN 15 KTS. && .FIRE WEATHER... ISSUED AT 330 PM MDT THU JUN 6 2013 FIRE WEATHER CONCERNS ARE MINIMAL DUE TO NON-CRITICAL FUELS AND GREENUP. TEMPERATURES WILL CONTINUE TO WARM INTO THE WEEKEND AND EARLY NEXT WEEK AS A RIDGE OF HIGH PRESSURE BUILDS OVER THE INTERMOUNTAIN WEST. WIDESPREAD TEMPERATURES IN THE 80S WILL BE POSSIBLE OVER THE WEEKEND AND THEN INTO THE 90S BY EARLY NEXT WEEK. THE VERY WARM TEMPERATURES WILL CAUSE MINIMUM AFTERNOON HUMIDITIES TO FALL INTO THE 15-20 PERCENT RANGE DURING THE WEEKEND OVER THE LOWER ELEVATIONS...THEN INTO THE 10-15 PERCENT RANGE BY EARLY NEXT WEEK. BREEZY WEST-TO-SOUTHWEST WINDS WILL ALSO BE POSSIBLE MAINLY OVER SOUTHEAST WYOMING DURING THE AFTERNOONS FROM SUNDAY INTO THE WEEKEND. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...NONE. && $$ UPDATE...LIEBL SHORT TERM...FINCH LONG TERM...HAMMER AVIATION...TJT FIRE WEATHER...FINCH