National Weather Service Text Product
AFOS product AFDLSX
Dates interpreted at 00:00 UTCDisplaying AFOS PIL: AFDLSX
Product Timestamp: 2019-11-26 05:31 UTC
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193 FXUS63 KLSX 260531 AFDLSX Area Forecast Discussion...Updated National Weather Service Saint Louis MO 1131 PM CST Mon Nov 25 2019 .UPDATE... Issued at 1051 PM CST Mon Nov 25 2019 Raised overnight lows by a few degrees due to increasing cloud cover and winds becoming southeast to south as stalled frontal boundary lifts northward. Still expect scattered showers will develop and track to the north as this front lifts northward through the day on Tuesday. Best chances of rain will be north of the I-70 corridor. 00z model runs as well as latest HRRR/experimental HRRR develop a north/south line of storms during the evening hours over central MO and track east between 00z and 06z Wednesday, so raised pops to categorical a bit further west during this period. Byrd && .SHORT TERM... (Through Late Tuesday Night) Issued at 217 PM CST Mon Nov 25 2019 Increasing cloudiness can be expected later tonight with spotty light rain possible late tonight/early Tuesday morning, mainly across southeast MO and southwest IL as low-mid level warm air advection increases over our area well ahead of a developing low pressure system in the Lee of the Rockies. The coverage of showers will increase on Tuesday as the upper level trough moving into the northern Plains takes on a more negative tilt with increasing upper level divergence over our area. With the surface low tracking northeastward through northwestern MO and eastern IA Tuesday evening our forecast area will be in the warm sector of the storm system with any wintry precipitation remaining north and northwest of our forecast area. Deep layer wind shear will increase Tuesday night as a 100 kt plus mid level speed max moves through the region south-southeast of the upper level low. It appears that there will be enough low level moisture and instability for the development of not only thunderstorms, but possibly also severe storms as well mainly Tuesday evening. Some of the CAMS develop low-topped supercells across southwest MO, ahead of the approaching cold front extending south of the surface low, which congeal into a line of storms which race eastward through our area Tuesday evening. The primary threat will be damaging winds, but isolated tornadoes can not be ruled out. The showers and storms should shift east of our forecast area by early Wednesday morning. Very strong and gusty winds can be expected particularly late Tuesday night and Wednesday morning after the passage of the cold front due to a tight surface pressure gradient south of the deepening surface low. A wind advisory may be needed for much of the area Tuesday night and Wednesday. GKS .LONG TERM... (Wednesday through Next Monday) Issued at 217 PM CST Mon Nov 25 2019 Colder, but dry conditions can be expected Wednesday and Wednesday night as a surface ridge shifts eastward through the region, while an upper level ridge builds over the central US. Precipitation will spread eastward into much of our area on Thanksgiving due to increasing low-mid level warm air advection, and as a southwesterly low level jet brings increasing low level moisture into our area. Very dry air initially in the surface/boundary layer will slow the onset of the precipitation, while evaporative cooling may result in a brief period of snow or sleet Thursday morning, but the precipitation type should change over to liquid rain Thursday afternoon. Prefer the operational GFS and ECMWF model solutions which have consistently had the higher QPF over southern portions of MO and IL over the NAM which has the better QPF further north which would lead to a greater potential of wintry precipitation. The precipitation will become lighter and may shift south of our forecast area Thursday night, but will ramp up again on Friday as another storm system develops and moves eastward into the Plains. The track of the surface and upper level low is even further northwest than the Tuesday/Tuesday night low pressure system so precipitation type should be liquid rain for our area. The dry slot south of the upper level low will shift northeastward into our area on Saturday with most of the rain shifting east of our forecast area by Saturday night. Colder conditions can be expected Saturday night and Sunday after passage of the cold front, and with a deep upper level low just north- northeast of our area. Some of the model guidance hints at the possibility of light snow, mainly for northeast MO and west central IL late Saturday night and Sunday on the backside of the low pressure system. GKS && .AVIATION... (For the 06z TAFs through 06z Tuesday Night) Issued at 1051 PM CST Mon Nov 25 2019 A stalled frontal boundary remains over the St. Louis metro area as of 05z Tuesday. Increasing low level moisture and weak WAA will be a bit slower moving in than thought, so the ceilings will not lower to MVFR/IFR til mid morning on Tuesday. Otherwise, deepening surface low in the leeside of the Rockies will begin to lift northeastward by midday Tuesday, lifting stalled frontal boundary back to the north as a warm front. Best chances of showers and storms will be north of warm front especially over KUIN Tuesday afternoon. Then as main system approaches region, will see a line of convection develop and slide east across region between 00z and 06z Wednesday. As for winds, they will veer back to the south and increase once front slides northward. Winds will be sustained between 15 and 20 kts with gusts as high as 30 kts. SPECIFICS FOR KSTL: A stalled frontal boundary remains over the St. Louis metro area as of 05z Tuesday. Increasing low level moisture and weak WAA will be a bit slower moving in than thought, so the ceilings will not lower to MVFR/IFR til 14z Tuesday. Otherwise, deepening surface low in the leeside of the Rockies will begin to lift northeastward by 18z Tuesday, lifting stalled frontal boundary back to the north as a warm front. Best chances of showers and storms will be north of St. Louis metro area Tuesday afternoon, so just kept vicinity thunderstorm mention for this period. Then as main system approaches region, will see a line of convection develop and slide into metro area after 02z Wednesday. As for winds, they will veer back to the southeast to south and increase once front slides northward. Tuesday afternoon/evening, winds will be sustained between 15 and 20 kts with gusts as high as 30 kts. Byrd && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX