Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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704 FXUS63 KLSX 010335 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1035 PM CDT Sun Jun 30 2024 .KEY MESSAGES... - Pleasant summer conditions will linger through at least Monday as temperatures will be 5-10 degrees below normal. - Hot and humid conditions return Tuesday into Wednesday. The pattern becomes active once again Tuesday night onward with several rounds of showers and thunderstorms. Locally heavy rainfall will be possible as well. && .SHORT TERM... (Through Late Monday Night) Issued at 243 PM CDT Sun Jun 30 2024 Strong surface ridge continues to build into the region this afternoon with much drier air filtering in. By tonight as the flow becomes easterly, will see dewpoints dip down into the mid 40s to mid 50s with the driest air mainly along and east of the Mississippi River. This area is co-located with ridge axis and lightest winds, so low temperatures will be in the low to mid 50s, with 55 to 60 for areas west of the Mississippi River. Will be close to record lows, mainly at Quincy (52 in 1988) and St. Louis (56 in 1937), while Columbia`s record low (45 in 1892) will be hard to break. Monday will be another below normal day with highs only in the mid 70s to low 80s. In the meantime, as the surface ridge slides off to the east and upper ridge begins to build in, some weak shortwaves try to undercut the surface ridge. A number of the latest CAMs develop scattered showers especially over portions of central Missouri on Monday. However, the latest forecast soundings for KCOU have a lot of dry air in the low levels, thus confidence is low for any precipitation on Monday and kept mentionable POPs to our west. Otherwise, with southerly flow returning to the central CONUS, plenty of moisture is drawn northward into Kansas and western Missouri during the day on Monday. Temperatures begin a slow moderation by Monday night, but lows will still be slightly below normal in the low to mid 60s. Byrd && .LONG TERM... (Tuesday through Next Sunday) Issued at 243 PM CDT Sun Jun 30 2024 The ridging pattern will continue to shift eastward this week while another broad upper trough slides east along the U.S./Canadian border. The return of low level moisture to the forecast area will be a bit slower with mid to upper 70s dewpoints not returning to the entire region until Wednesday. Otherwise, highs on Tuesday will be in the upper 80s to mid 90s, with heat index values 100-105 across portions of central/northeast MO Tuesday afternoon where dewpoints will be in the low to mid 70s. The far eastern portions of the forecast area will still see pleasant conditions on Tuesday with dewpoints only in the upper 50s to low 60s. In the meantime, as the cold front associated with the trough slides east into central IA and northwestern Missouri by Tuesday evening, south to southwest low level jet will ramp up to 30-40kts ushering in copious amounts of moisture (PWATs 2-2.5", well over 90th climatological percentile in latest NAEFS/GEFS). The latest deterministic and ensembles now have similar location and timing of the front with convective initiation developing ahead of the front over Iowa late Tuesday afternoon, then moving into northeast MO/west central IL after 03z Wednesday. With increasing MU CAPEs (2000-3000 J/kg) as well as increasing deep layer shear (0 to 6km 30-40kts, though parallel to the boundary) and decent convergence along the front, could see some strong to severe storms move into northeast MO/west central IL during the late evening. However, a majority of the latest deterministic as well as ensembles have instability weaken across the forecast area during the late evening/overnight hours, so confidence is low on how far south the strong to severe storms will make it. So will continue to monitor over the next couple of days. The front could hang up over the region through at least Friday, including the Fourth of July, so will see several rounds of showers and storms. The latest deterministic as well as ensembles have differences in location, timing and strength with each wave, but are coming into better agreement that the strongest shortwave will move through late Wednesday night into Thursday morning. There will be plenty of upper ascent over the surface boundary, all within a region of deep layer moisture. Also, PWAT values will still be around 2-2.5 inches, which points to heavy rainfall the night of the 3rd and heading into the 4th. Beyond Friday, the latest deterministic and ensembles have some agreement with upper trough shifting off to the east with surface ridge building in once again by next weekend. Byrd && .AVIATION... (For the 06z TAFs through 06z Monday Night) Issued at 1033 PM CDT Sun Jun 30 2024 Dry northeast winds on the periphery of a departing surface high will promote VFR conditions through the TAF period. A few weak showers may impact central Missouri late Monday morning, but the anomalously- dry air will work strongly against any rain reaching the ground. MRB && .CLIMATE... Issued at 344 AM CDT Sun Jun 30 2024 Record Lows 7/1 St. Louis 56 in 1937 Columbia 45 in 1892 Quincy 52 in 1988 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX