Area forecast discussion National Weather Service Goodland Kansas 227 am MDT Monday may 20 2013 Short term...(today and tonight) issued at 227 am MDT Monday may 20 2013 Vertically stacked low will continue over the Dakotas today and tonight before finally moving east Tuesday night. A weak vorticity lobe will move over the forecast area this morning bringing scattered showers especially north of Interstate 70. Expect the air mass to be only slightly unstable this afternoon with convective available potential energy around 300 j/kg...but unstable enough to keep mention of thunderstorms in the forecast. Low level trajectories continue to bring cold air advection across the region...and expect afternoon temperatures to reach only the upper 60s and lower 70s. Decent 850-700 mb flow will mix to the surface which will produce northwest winds 15-30 knots especially over the northern half of the forecast area. For tonight...another weak shortwave will advect over the area...so will continue with a slight chance of showers. Temperatures will be a few degrees cooler than lows this morning...mainly in the lower to middle 40s. Long term...(tuesday through sunday) issued at 227 am MDT Monday may 20 2013 Tuesday...models show weak upward vertical motion with the final shortwave from this system...but the air mass in the low levels will continue to dry. Model soundings indicate saturation will not occur below 600 mb by the afternoon. The air mass will also be relatively stable...so will keep the forecast dry after 18z. 850 mb temperatures warm a few degrees celsius by Tuesday afternoon... but surface winds do not support a massive warm/up. Tuesday night and Wednesday night...500 mb ridge will build over the High Plains as Dakota low ejects east and the next system moves over the Pacific northwest. Expect warm air advection to begin in earnest Wednesday as surface winds become southeast. Will keep the forecast dry as subsidence inhibits synoptic scale lift. Thursday through Sunday...at the start of the period a low amplitude upper level ridge is situated over the area. By Thursday the ridge axis shifts east of the forecast area as an upper level trough deepens across the western Continental U.S.. Friday and Saturday...subtle middle/upper height falls commence as aforementioned western Continental U.S. Trough moves slowly east and begins influencing our weather. Surface Theta-E values increase as south/southeast low level trajectories favor northwest movement of moisture into the area. This is coincident with the strengthening/sharpening of Lee side trough/dryline. Medium range models indicate a series of shortwaves rotating around the trough to the west and these will enhance convective development over our area and necessitate daily slight to chance probability of precipitation. GFS ensemble members diverge over the weekend leading to some uncertainty beyond Friday. Nevertheless... medium range models all generally favor a southwest to northeast upper flow pattern with subtle embedded shortwaves impacting the area over the weekend and even beyond. && Aviation...(for the 06z tafs through 06z Monday night) issued at 1131 PM MDT sun may 19 2013 VFR conditions should prevail at both kgld and kmck terminals through the taf period...though brief MVFR conditions couldnt be completely ruled out if a moderate rain shower moves over kmck. Rain showers currently over central/western Nebraska rotating south along western extent of upper level system...and should move over kmck through the early part of the taf period and within vicinity of kgld. Current short range guidance favors this activity diminishing between 12z-15z before additional showers/thunderstorms redevelop over the region by the afternoon. Confidence was too low in coverage during the day Monday...so limited mention of vcsh through the early evening. Gusty westerly winds will continue at kmck through the taf period due to proximity of upper low center and stronger gradient. Westerly winds around 10kt at kgld will increase after sunrise with gusts to 30kt and then decrease around sunset Monday. && Gld watches/warnings/advisories... Kansas...none. Colorado...none. NE...none. && $$ Short term...Mentzer long term...Bowers aviation...Dr