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Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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749 FXUS63 KLSX 061944 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 244 PM CDT Sat Jul 6 2024 .KEY MESSAGES... - Above normal temperatures will return on Sunday along with a chance of primarily afternoon thunderstorms across parts of central and northeast Missouri and west-central Illinois. - Shower and thunderstorm chances will increase and expand to the entire CWA Sunday Night through Tuesday, with the greatest chances (40-60 percent) Sunday night and Monday. - Depending on the track, the remnants of tropical cyclone Beryl could bring rain to parts of southeast Missouri and southern Illinois Wednesday and Wednesday night. && .SHORT TERM... (Through Late Sunday Afternoon) Issued at 227 PM CDT Sat Jul 6 2024 A few pinhead showers/sprinkles have developed across northeast MO and west-central IL. These are shallow and high-based and aren`t expected to amount to much and overall will individually be rather short-lived this afternoon. All in all it appears we should have a rather quiet weather night with lower than normal dew points/humidity for early July. Surface high pressure presently centered in southwest MO will slowly retreat eastward. An MCS is expected to organized across the Plains and move east into northwest MO and southwest IA later tonight. Presently it looks like sufficient low-level moisture return and instability will not be available on the backside side of the retreating high to sustain it as it moves towards north-central MO and thus weakening and dissipation is anticipated. The residual boundary, and a vort max or a left-over MCV is expected to be the catalyst for our first chance of showers and thunderstorms on Sunday. This should mainly be across central and northeast MO and west-central IL on Sunday afternoon, and will be aided by the return of low-level southerly flow in the wake of the retreating high and the accompanying WAA, moisture transport and instability. Otherwise Sunday should be the warmest day for the upcoming week (above normal temps) due to the southerly flow and warmer temps aloft. Glass && .LONG TERM... (Sunday Night through Next Saturday) Issued at 227 PM CDT Sat Jul 6 2024 More active weather will ensue Sunday Night into the first half of the upcoming week. While there are some subtle differences in vort max positions in the model guidance, the overall trend remains the same, with the positively-tilted upper trof slowly progressing eastward into the mid-upper MS Valley Monday-Monday night. A series of vort maxes within the southwest flow ahead of the trof, lift via the southwesterly LLJ, and frontal forcing associated with the advancing cold front will result in scattered-numerous showers and thunderstorms impacting mainly central and northeast MO and west- central IL late Sunday night. This overnight activity could persist and slowly move eastward through the day on Monday, or weaken early in the morning with new development ensuing in the afternoon along the boundary capitalizing on diurnal heating/instability. There remains some uncertainty with the longevity and footprint of precipitation/POPs Tuesday into Wednesday. The slowly progressive upper trof will weaken and move across the mid-upper MS Valley Tuesday into early Wednesday, eventually becoming absorbed into the southern extent of an upper trof centered in eastern Canada. Besides the initial cold front passage late Monday Night, there are less well-defined signals of a second boundary/cold front moving across the area on Tuesday associated with the upper trof axis and it`s passage. This later boundary and trof would support a continue threat of showers and thunderstorms across primarily the southeast half of the CWA on Tuesday, peaking in the afternoon with diurnal heating/instability. IF we see any impacts from the remnants of TC Beryl, at this time they look to be mainly across southeast parts of the CWA. The recurving remnants of Beryl are forecast to track from east TX across the lower MS Valley late Tuesday through Wednesday Night. The mean track of the superensemble would have the remnant low passing near the bootheel, however the track spread is such that it could be further north or south. The current forecasted impacts would be a slug of mid-high level tropical moisture and attendant rainfall across SE MO/SRN IL including parts of the southern CWA. We continue to have a sizable footprint of POPs Tuesday, and the new forecast has a bit larger footprint Tuesday Night-Wednesday night centered through SE MO and SRN IL to account for the potential for Beryl. The current guidance from the 100 member LREF suggests the greatest threat of attendant excessive rainfall appears to be south of the CWA. Ensemble guidance continues to show that during the later half of the upcoming week there will be a weakness in the mid-upper flow across the central U.S. with strong upper ridges centered in the western Atlantic and Intermountain West. This weakness could be the reflection of a weak upper trof dropping southeastward from the Plains or just an area of relatively lower heights with an embedded weak upper low. Either way there is no strong signal for organized precipitation, but perhaps some isolated diurnal activity. There shouldn`t be any extreme temperatures Tuesday through Friday. Tuesday and Wednesday look like the "coolest" days with largely below normal temps with highs Thursday-Friday within a few degrees of normal, and the NBM max temperature distribution continues to show a very small IQR. Greater summer heat could return by next weekend as there are some signals that by next weekend the western ridge may attempt to build into the mid MS Valley. Glass && .AVIATION... (For the 18z TAFs through 18z Sunday Afternoon) Issued at 1215 PM CDT Sat Jul 6 2024 VFR flight conditions are expected through the forecast period. Diurnal cumulus clouds are expected this afternoon with some high clouds late tonight. Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX