Current Conditions at Sanborn Field
Friday Night: Clear. Low: 61
Saturday: Sunny in the morning. Clouds increasing in the afternoon. High: 84
Saturday Night: Cloudy. Low: 60
Sunday: Cloudy with showers tapering off after sunrise. Becoming partly cloudy. High: 72
Sunday Night: Few clouds. Low: 54
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Discussion:
The potential for some rain returns to campus this weekend. Saturday will still feel quite summer-like before clouds start to build in by the afternoon hours. A cold front will approach the region late Saturday night bringing with it the chance for rain that will continue overnight and into Sunday morning. A wet start to the day will give way to lower temperatures and a clearing sky by Sunday afternoon. Temperatures will feel very fall like, dropping into the lower 50s Sunday night into Monday morning.
Travis
Forecasters: Allen, Labit, Easter, Travis
Date Issued: 09/09/2022 6:30PM CDT
After an extended period of persistence-dominant forecasting, some excitement returns to the region in the form of some much needed rainfall. Went with a blend between the 12z GFS and the 18z NAM due to discrepancies between precip onset and exit.
A long wave trough has progressed southeast and will continue to propagate east throughout the forecast period. Embedded within, a shortwave will eject out of the Upper Plains states and into the Midwest. Dynamic forcing with this system is certainly not in short supply as the upper-level jet stream begins to reintroduce itself to the Mid-Mississippi River Valley after a long summer slumber up north. A maximum in vorticity and positive vorticity advection (PVA) will provide ample upper-level dynamic support for upward vertical motion (UVM). There seems to be some disconnect between the NAM and GFS regarding the exact timing at which these factors move in and out. The GFS favors an earlier solution with greatest forcing present between Sunday at 06 and 12 UTC while the NAM a later one: between 09z and 15z UTC.
Moisture looks to be the limiting factor in terms of system performance. Weak low-level winds and the absence of a LLJ indicate notably inefficient moisture transport/availability. Soundings as well as NAEFS Situational Awareness table for precipitable water (PW) both show near-median values of 1.5". A lack of moisture transport is due to the position of a cutoff low that has been situated over the Gulf Coast. As such, mid-Missouri has been in a weak easterly flow in the lower levels. Additionally, this system has kept moisture advection confined to the eastern side of the Appalachian Mountains. Deterministic totals range between 0.25" and 0.50" while the National Blend is significantly lower at less than 0.10". Current thinking is that if a line of heavy rain can hold together by the time it reaches mid-Missouri, totals will be closer to the deterministic solutions. If it can't then there's a potential for laughably lackluster amounts.
Finally, instability is virtually nonexistent. CAPE in the double digits and unimpressive lapse rates is where uncertainty comes into play. Lift near a surface cold front arising from the dynamic sources mentioned earlier as well as the presence of mid- and low-level WAA will be responsible for supporting precipitation development. The lack of any instability and significant low-level moisture convergence leaves the concern that the line of precipitation will fall apart overnight by the time it reaches mid-Missouri.
As the surface front passes, the showers will move east out of the region by late morning and the sky will gradually clear by the late afternoon. The NAM showed moisture and forcing sticking around later in the morning: evidence of possible, lingering, isolated showers. Nevertheless, By Sunday night, the sky will be largely clear allowing temperatures in the post-frontal air mass to drop into the lower 50s.
Travis
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