Wednesday Night- Thunderstorms throughout the evening, a few of which may be strong to severe. Low: 46-50
Primarily, the 18z GFS model run from 04.07.2021 was used for this forecast due to its superior handling of the intensity and location of the low pressure system currently affecting our area. GEFS and SREF plumes were used to assist in forecasting the temperatures as well as the rain totals.
As of 18Z Wednesday, there is a jet streak at the 250 mb level located to our southwest. High levels of divergence at this level can be seen in the area for the rest of Wednesday evening as the low pressure system moves through Missouri. Divergence levels will begin to decrease as the low moves to the north and east. As this low pressure system moves out of our aea, it will be replaced by another shortwave trough at the 250 mb level overnight Friday and into Saturday.
A similar story plays out at the 500 mb level. Central Missouri will see an abundance of vorticity over the next few days. Vorticity will be advected into the area during the mid afternoon on Wednesday. After the first shot of thunderstorms on Wednesday, the vorticity will continue to stick around as the convective rain switches over to stratiform rain during the overnight hours. The second wave of vorticity associated with the second low pressure system can be expected by the morning hours of Saturday.
The 700 mb level shows that the atmosphere is very moist in our region over the next couple of days. Relative humidity values of ~90% are present Wednesday evening. However, drier air at this level will move in during the overnight hours in conjunction with the dry conveyor belt of this system. The dry slot should be expected during the pre-dawn hours of Thursday, and will correspond with the switch over from convective rain to stratiform rain. Friday will see much drier air at this level as we will have westerly winds. However, those winds will begin to back in advance of the system that will move through during the overnight hours of Friday into Saturday. The backing winds will then advect moisture into the area allowing for the potential for rain overnight.
At the 850 mb level, we will see a line of elevated omega values corresponding to the first wave of convective rain during the early evening on Wednesday. At this time, Mid-Missouri will have almost completely saturated air at the 850 mb level. This moisture will stick around throughout Thursday, but will start to dry out as the first low pressure migrates out of our area. Friday will be much drier and have winds out of the west. However, our winds at this level will shift again overnight Friday into Saturday. The backing winds will supply the area with more moisture at the 850 level as a line of heightened omega values moves through during the pre-dawn hours of Saturday.
At the surface, we will see a cold front pass through the region Wednesday evening. The frontal passage will contribute to the ~ 10° temperature drop that we will see between Wednesday and Thursday. We will also have a wind shift at the surface from winds out of the south to winds largely out of the west. As for precipitation totals, we should see the heaviest rain move though Wednesday evening. We can expect around 0.5” - 1.0” inches of rain on Wednesday evening and an additional 0.5” of rain throughout the day on Thursday. Another 0.25 - 0.5” of rain can be expected Saturday morning. Therefore, Columbia could receive a total of roughly 1” - 2” of rain through the end of the forecast period.