General Discussion: A booming start to the week! Monday kicks off this week with a low pressure system passing over Missouri, bringing a few showers and thunderstorms along with. These showers will be leaving after 3 pm, and in total will bring 1/4" to 1/2" of rain. Things should dry out for Tuesday, but Tuesday night another low pressure system will bring in even more showers and thunderstorms. Peeks of sunshine are possible for Wednesday morning into the daytime, but storms and rain move back in during the day. These showers may even continue on into Thursday, and total accumulations will be .5" to 1" of rain. Temperatures this week will be closer to average, cooling down from this past weekend. Highs should stay in the 70's while lows will range from mid 50s to low 60s.
Forecasters: Cade, Baker, Travis
Date Issued: 10/11/21 10:00 AM CST
Technical discussion:A low level jet brings in a fair amount of moisture and warm temperatures making for a pretty wet week. The main concern for this time period is the low pressure system moving out of the area Monday afternoon with another low close behind it. This will allow for a low level jet to carry in a vast amount of moisture thick air and warmer temperatures triggering more rain and possible thunderstorms late Tuesday. Both the GFS and NAM have the low pressure system moving out of the area Monday afternoon; however, when compared to upper level water vapor satellite imagery, the GFS did better at resolving the upper level atmosphere pattern. Also, by looking at MOS for KCOU the NAM looked to be too warm by the end of our forecast period.
The GFS 250 hPa heights show a low pressure system moving across the area Monday shifting the winds westerly. High values of wind divergence suggests convergence near the surface and rising motion in between. A small ridge follows the low pressure system out of the Middle Mississippi Valley, that is absorbed into a larger low pressure system over the Rockies.
The GFS 500 hPa has large amounts of vorticity and spin that will give way to rising motion in the atmosphere. A smaller ridge moving in behind the low pressure system will keep things calm going into Tuesday. The high values of vorticity surrounding the upper level low over the Rockies moves across the Central Plains bringing back forcing for lift in the atmosphere Wednesday.
The GFS 700 hPa map of RH shows Monday's low pressure system bringing in saturated air that will help the development of showers across Missouri. Behind the low Monday afternoon, the atmosphere drys out and stays that way into Tuesday in association with the ridge mentioned above. Saturated air returns with the low pressure system off the Rockies Tuesday night into Wednesday.
The GFS 850 hPa winds show a strong LLJ setting up ahead of Tuesday night's LPS. This will supply moisture for widespread rain continuing into Wednesday. Moisture transport vectors at 850 hPa show the greatest magnitude of transport over Missouri from Wednesday at 06Z to 21Z. GFS soundings back this up with a saturated profile at these times as well. The K-indices > 35 and PW > 1.5" supports widespread heavy rain. By Wednesday afternoon total precip accumulation could approach 1.5". At the surface, WAA solenoids behind the exits of Monday's LPS will not allow temperatures to drop much, if at all.