St. Louis (LSX) — the National Weather Service forecast in plain English · Plaincast

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A cold high pressure system will bring dry weather and below normal temperatures to the region through the weekend into early next week. Temperatures will slowly climb back to around seasonal normals by the middle of next week.

Short Term

A high amplitude blocky pattern is setting up across the CONUS with a deep long wave trough over the eastern U.S., a ridge over the Plains, and another trough west of that. The eastern trough is dragging a high pressure system southward from Canada into the Mississippi Valley with what looks like the coldest temperatures so far this season. Upstream temperatures across Iowa and southern Minnesota topped out in the upper 30s to mid 40s Thursday afternoon, and this air is moving into the Mid Mississippi Valley today. Guidance is giving us highs in the mid 40s today, and this looks reasonable given the upstream temperatures, accounting for a bit of airmass modification and somewhat stronger insolation with less cloud cover today.

Winds will diminish tonight as the high continues building into the Midwest, and the latest model guidance shows a mostly clear to clear sky. The light winds and lack of cloud cover will be ideal for radiational cooling which will allow temperatures to drop into the low to mid 20s across most of the area. Wouldn't be surprised to see upper teens in some of our cold spots like Rosebud MO. temperatures rebound into the 40s again Saturday afternoon under full sunshine and light winds with the ridge axis overhead.

Long Term

The upper pattern translates slowly east Sunday into next week with the upper level ridge moving across the Midwest into the Great Lakes Region by midweek. Meanwhile, the surface high drifts southeast into the Ohio Valley by Monday, and then continues into the Mid Atlantic Region by Wednesday and Thursday. Temperatures across the Mid Mississippi Valley will slowly warm back to near seasonal normals in the mid 50s by Tuesday/Wednesday according to the the blend-of-models forecast. This is backed up by the LREF, which is showing very similar temperatures through the period. The interquartile range of temperatures in the ensembles is also very tight through midweek, 2- 3 degrees through Tuesday, and only 3-5 degrees on Wednesday and Thursday. This lends a high degree of confidence to the forecast through the period. There won't be any chance for precipitation under the influence of the surface high and upper level ridge through Wednesday. However, global deterministic guidance shows a short wave trough moving through the Great Plains late Wednesday and into the upper Midwest on Thursday. The low level reflection of the trough pushes another cold front into the Midwest with some modest low level moisture return ahead of it. The the blend-of-models forecast paints 20-30 chance of rain over much of the area Thursday, and around 30% of the LREF members have precipitation for our area as well, so the the blend-of-models forecast's chance of rain seem reasonable.