585 FXUS63 KLSX 101130 AFDLSX AREA FORECAST DISCUSSION...UPDATED AVIATION NATIONAL WEATHER SERVICE ST LOUIS MO 530 AM CST Mon Nov 10 2014 .SHORT TERM: (Through Late This Afternoon) Issued at 424 AM CST Mon Nov 10 2014 Relatively strong and gusty southerly winds can be expected today due to a tight surface pressure gradient ahead of a developing low pressure system over the Plains, and a strong southwesterly low level jet. Unseasonably warm temperatures can be expected today due to strong low level warm air advection and only some high level clouds to hinder solar insolation. Prefer the warmer GFS MOS guidance for high temperatures today. GKS .LONG TERM: (Tonight through Sunday) Issued at 424 AM CST Mon Nov 10 2014 A surface low will develop in southeast IA and northern IL ahead of a shortwave and drag a strong cold front southeastward through our forecast area tonight and Tuesday morning. A northeast to southwest band of mainly light rain is expected along and just behind this front and ahead of a shortwave which will move eastward through our area late tonight and Tuesday morning. Strong low level cold air advection is expected late tonight and Tuesday behind the 850 mb trough and surface cold front leading to rapidly falling temperatures late tonight across northeast and central portions of MO and west central IL, and little if any diurnal rise in temperatures on Tuesday. It appears that most of the rain will end by the time the air is cold enough to support snow, although could not rule out a brief period of light snow or flurries before the precipitation ends across northeast MO and west central IL late tonight and early Tuesday morning. Most of the rain should shift southeast of our forecast area by Tuesday afternoon with a large and strong 1045-1050 mb surface ridge building southeastward into our area from the northern Plains. An unseasonably cold weather pattern is expected as an upper level low moves across the northern Plains and Great Lakes region and as this cold air mass plunges southeastward into the region. The models indicate a long period of low level cold air advection with the 850 mb temperatures progressively lowering down to around -12 degree C across our area by Thursday. Highs only in the 30s with lows in the upper teens to mid 20s will be common beginning Tuesday night and continuing through the remainder of the work week. Slightly warmer temperatures are expected for Saturday as the surface ridge weakens and shifts east of our area with surface winds becoming southerly on the backside of the ridge. The models were generating some qpf over our area Saturday afternoon through Sunday morning, although there were differences in timing of precipitation, and surface temperatures. The GFS model was a little warmer and had most of the precipitation across the northern half of our forecast area late Saturday night and Sunday morning associated with a northern stream shortwave. The ECMWF model was a little colder and had most of the precipitation associated with a southern stream shortwave with its qpf mainly Saturday afternoon and evening. Due to the model uncertainties for now will just include slight chance to chance pops for Saturday through Sunday with a precipitation type of snow, except rain or snow Saturday afternoon with temperatures potentially warming up to near 40 degrees. GKS && .AVIATION: (For the 12z TAFs through 12z Tuesday Morning) Issued at 518 AM CST Mon Nov 10 2014 Current data from the regional radar wind profiles and model soundings are indicating a south southwesterly low level jet of 35-40 kts which is contributing to LLWS. This LLWS should cease by 15z or so as the low levels mix and southerly surface winds increase with gusts of 25-28 kts. Winds will diminish around sunset. VFR flight conditions are expected until a strong cold frontal passage overnight at KUIN and KCOU, and near daybreak Tuesday in metro St. Louis. This cold front will be accompanied by MVFR cigs and gusty northwest winds. There could also be some spotty showers along and behind the front, but the probability is too low to mention in the TAFS at this time. Specifics for KSTL: Current data from the regional radar wind profiles and model soundings are indicating a south southwesterly low level jet of 35-40 kts which is contributing to LLWS. This LLWS should cease by 15z or so as the low levels mix and southerly surface winds increase with gusts of 25-28 kts. Winds will diminish around sunset. VFR flight conditions are expected until a strong cold frontal passage near daybreak Tuesday (11-12z). This cold front will be accompanied by MVFR cigs and gusty northwest winds. There could also be some spotty showers anytime from around 10-18z, but the probability is too low to mention in the TAFS at this time. Glass && .LSX WATCHES/WARNINGS/ADVISORIES: MO...NONE. IL...NONE. && $$ WFO LSX