Saturday: Mostly cloudy. Showers and thunderstorms in the late afternoon. High: 79
Saturday Night: Cloudy. Lingering showers and thunderstorms. Low: 63
Football fans should prepare to be disappointed as game time weather looks to be wet. Unsettled weather will bring with it cloudy skies and chances of rain all weekend. However, widespread heavy rain doesn't look to be a huge concern. More likely, on and off scattered showers and thunderstorms may cause some headaches for fans hoping to tailgate or spectate. Game day Saturday morning will start off with patchy fog and scattered showers. We may see some dry time and even peaks of sunshine throughout the day. Rain chances decrease into Saturday night and Sunday, but passing showers can not be ruled out. Another morning of patchy fog is likely on Sunday. Mostly cloudy skies will keep temperatures from going above the upper 70s. Total rainfall accumulations should stay near 0.5 inches.
- Millsap, Ethridge
Forecasters: Millsap, Ethridge, Travis
Date Issued: 10/1/21 5:45 PM CST
Unsettled weather will bring with it repeating wet and dry periods throughout the weekend. The main concern for this forecast is the upper-level shortwave trough that will bring with it multiple chances for scattered showers/thunderstorms. Model consensus and continuity has been less than great for the past several runs. While both the GFS and NAM had a decent handling of the upper-level pattern when compared to GOES WV imagery, the two models differed significantly on precip accumulations, and daytime highs. The NAM had a better handling on initial conditions than its considerably warmer GFS counterpart. As such, went primarily with 12z NAM guidance. Consulted SREF plumes to diagnose model continuity within the NAM.
NAM upper-level plots of 250-hPa heights, wind, and divergence show a persistent meriodional setup over the CONUS with an amplified ridge over the Mississippi River valley at the time of initialization. An upper-level, cut-off low over the Four Corners region will make its way east over the weekend. As it marches towards the Midwest, low will get absorbed into the larger-scale flow and deamplify into a shortwave trough by the time it reaches the Midwest. Increased divergence ahead of the negatively tilted trough hints at sufficient forcing for ascent over the area by 18z on Saturday.
500-hPa heights and absolute vorticity tell a similar tale. Increasing PVA will bring broad circulation into mid-Missouri come Saturday afternoon, supporting the forcing for ascent seen at 250-hPa. Dynamically speaking, Saturday looks to be the most impressive for widespread precipitation.
NAM 700-hPa RH and omega shows quite the mess for the duration of the forecast period. Widespread saturation of the mid-levels of the atmosphere exists over the majority of Mississippi River Valley until the upper low pushes off to the east by Sunday evening. The greatest plume of saturated air is temporally collocated with the impressive dynamics mentioned above. As such, the greatest chance for precipitation looks to be between 17z and 22z Saturday.
850-hPa height and winds show a less impressive setup than the upper-levels. The lack of a LLJ Friday night into Saturday would suggest an insufficient supply of moisture to support a complete washout with high accumulation totals. A similar story of unimpressive features continues at the surface. MSLP and 1000-500-hPa thickness show a lack of WAA ahead of this system (suggesting moisture advection may be lacking as well). A cold front albeit a weak one is evident from MSLP and surface winds passing through the area by 18z Saturday. The weak nature of this front with little post frontal CAA seen in the aforementioned surface plots will result in very little temperature change.
NAM soundings show persistent deep saturation beginning Friday night and continuing into Sunday afternoon. However, a fully saturated column is only present for 21z Saturday. These profiles look more consistent with frequently passing scattered showers. Throughout the day, Saturday, the NAM soundings favor a destabilizing atmosphere with CAPE values peaking near 1000 J/kg. This is considerably less aggressive than the less stable GFS soundings. The magnitude of destabilization will be heavily dependent on the extent of sunshine on Saturday. If overcast conditions dominate, CAPE values will remain on the low end. Nevertheless, sufficient instability exists to support convection Saturday into Saturday night. PWATs near 1.5 inches suggest that rain will likely be heavy at times. A quick look at both HRRR and NAM simulated reflectivity support the soundings profiles' suggestions of a much more widely scattered event. Widespread heavy rain looks to stay off to the southeast. A look at SREF dprog/dt shows a telling story of discontinuity between runs. What started as favoring a washout in older runs has trended towards a more widely scattered event. The NAM proper still favors higher accumulations near 0.4 inches with a sharp gradient to the SE. The GFS and GEFS members, on the other hand, are much less aggressive with totals sticking closer to 0.25 inches. Accumulations will be heavily dependent on the intensity of the showers/thunderstorms that move over the rain gauge at Sanborn.
The NAM is much slower to dry out the atmosphere behind the weak cold front than the GFS. As such, lingering showers and thunderstorms look possible Saturday night and into the day Sunday, but overall chances for precip diminish considerably compared to Saturday.