Current Conditions at Sanborn Field

Thursday: Partly cloudy, mostly in the afternoon. High: 56

 

Thursday Night: Partly cloudy. Low: 38

 

Friday: Mostly cloudy. High: 43  

Friday Night: Partly cloudy. Low: 28

Saturday: Mostly sunny. Increasing clouds in the evening. High: 43

 

 

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Discussion:

 

Say goodbye to the warm, sunny days! Cooler, fall weather is back. Clouds will linger for the forecast period, though rain is not expected. Friday night will be the coldest we've had in awhile, getting down to below freezing! Saturday brings a quick glimpse of the sun before clouds return in the evening. 

 

- VanUnnik

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Forecasters: McDonald, VanUnnik

Date Issued: 11/11/21 10:00 AM CST

Technical discussion:   

The 06z GFS was used for our forecast today, as it initialized current and recent conditions better than the NAM, specifically in regards to overnight low temperatures.

At 250 mb we can see that Missouri is caught right in the middle of a negatively tilted trough, situated at the bottom of it’s dip into the Midwestern US. Far away from the center of the low on the Minnesota-Wisconsin border, the flow into Missouri remains continuous but weaker from west to east, as most of the stronger winds are close to the low’s center. This pattern will break at Saturday 06z as the trough shifts to become more positively tilted, directing the diving flow of the trough Northwest into Missouri with an associated jet streak that looks to strengthen into Sunday. 

Vorticity also looks to be continuous over this period, as 500 mb findings show vorticity wrapping around the center of the low, swinging in and out of Missouri as the trough slowly shifts its axis and direction northeastward. Active weather caused by this vorticity will likely be to our east, as the region of maximum lifting and vorticity is east of Missouri’s position at the bottom of the trough - this will give us increasing cloud cover, but not precipitation through Friday night. Saturday 15z will provide a brief break in the vorticity, reducing clouds for a few hours before the influence of another negatively tilted trough to the west brings it’s eastern side to Missouri, providing a more significant chance of rain into Sunday morning 

700 mb relative humidity will remain high through Saturday 00z, and cloud cover will slowly increase as the moisture continues to linger for the next 48 hours. However, at Saturday 03z, pockets of dry air wrapping around an occluded front will open up a period of drier conditions for most of that day. Even while humidity is continuously high before Saturday 03z, omega values are very low and do not show any indicators of powerful uplifting. This should bring more sunshine to the region for Saturday and eliminate an already low probability of rain thus far.

Cold air advection was immediately noticeable on the 850 mb chart, brought on by the influence of the low over Minnesota-Wisconsin, which is much more pronounced at this level. Winds shift decisively to the west at this point, wrapping cooler air from the low’s center into Missouri and keeping temperatures steadily below average. Solenoids are also very well formed initially at Thursday 12z, and stay tightly packed and high in number through Saturday 03z, lining up with timing of decreasing vorticity, omega, and humidity. 

GFS soundings display only marginal amounts of moisture, enough for cloud formation but not quite enough for a confident forecast of precipitation. 

Future forecasters should pay attention to the following trough moving into Missouri late Saturday night, which looks put the state on the eastern side of it’s axis where active weather will be much more likely. 

 

- McDonald