Key Messages

• Above normal temperatures will continue for the next several days with the hottest conditions forecast on Tuesday and Wednesday.
• Chances (30-60%) of showers and thunderstorms each day will be mainly confined to parts of northeast Missouri and west- central Illinois near a stalled front.

Short Term

A weak cold front continues to move southeast, now located near a KVIH>>K3LF line as of 1900 UTC. There has not been much, if any, convective activity along this front due to strong capping. This boundary will clear the southeastern CWA close to midnight, with light northwest winds in its wake. Low-level moisture convergence increases after midnight, mainly across eastern Kansas. Widespread showers and thunderstorms are expected on the nose of this jet, with activity moving east/southeast with time. That means that most, if not all, of these showers/storms should stay to our west/southwest. However, parts of central Missouri may be on the far northeastern periphery and this is where low (20-30+%) chances of showers and perhaps a few thunderstorms exists late tonight into early Sunday morning.

Forecast uncertainty increases heading into Sunday afternoon, with deterministic models (including CAMs) showing a wide range of solutions. There does look to be two separate areas of somewhat more focused forcing: 1) northeast Missouri/west central Illinois where weak low-level moisture convergence and low/mid level frontogenesis resides and 2) far southern Missouri near the surface front and downstream of a midlevel shortwave. Nothing looks too widespread (or significant) in either zone, but this is where the highest (30-50%) PoPs reside. Activity should wane Sunday evening with loss of daytime heating, before the low-level jet kicks up again near the Missouri-Kansas border. Similar to tonight, much (if not all) of this activity Sunday night should stay to our west but may clip far western and/or northern section of the CWA.

Long Term

(Monday - Thursday Night)

The quasi-stationary front is expected to quickly lift north of the area on Monday as cyclogenesis commences across the central Plains. Very anomalous mid/upper level ridging is forecast to amplify across the mid south early/mid week. In fact, 500-hPa heights of 594+ dm would be record-breaking for this time of year. In addition, 850-hPa temperatures climb back above +20C (>99th percentile). The latest EPS Extreme Forecast Index (EFI) is also picking up on this heat, showing EFI values of 0.8-0.9 for high temperatures Tuesday and Wednesday, with even a slight Shift of Tails (SOT). This air mass does seem capable of threatening record highs (upper 90s to around 100 degrees) Tuesday and Wednesday, though it will depend on cloud cover and rain chances. Speaking of which, a cold front is likely to stall out near or just north of our CWA on Tuesday. This front may serve as the focus for showers and thunderstorms each day, with any widespread activity creating debris clouds which ultimately could impact temperatures over much of the area. Therefore, widespread mid 90s are not a given, though confidence does increase the farther south you head within the region.

A likely scenario may be for each successive round of convection to help help augment the boundary and help ooze it southward. This points to a gradual "cool" down heading toward late week into next weekend. Temperatures each day get more uncertain due to the high variability in the location of the front, and the fact that clouds and showers/storms near the boundary may enhance the temperature gradient from north to south.

Aviation

A weak front is moving through the area, with west/southwest winds veering to the north/northwest in its wake. Showers and thunderstorms overnight tonight into Sunday morning are expected to stay west/southwest of the central Missouri terminals.

Watches & Warnings

MO...None. IL...None.