Wednesday September 25th Morning Forecast

Wednesday: Partly cloudy. High: 76°F

Wednesday Night: Clear. Low 55°F

Thursday: Increasing clouds. High: 77°F

Thursday Night: Mostly cloudy. Low: 58°F

Friday: Overcast. High: 77°F

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General Discussion:

Moisture levels are expected to drop, bringing drier conditions on Thursday. Clouds in the mid and upper atmosphere will limit significant radiational cooling Thursday night. However, some clearing will allow for patchy fog development, mainly in river valleys, similar to this morning. Temperatures will rise into the upper 70s heading into the weekend, driven by mostly sunny skies and warm air advection from a high-pressure ridge centered to our west-northwest over the Great Plains.

– McCurdy, Peine

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Forecasters: McCurdy, Brucker, Latlip, Peine

Date Issued: 09/25/2024 9:00 A.M.

Technical Discussion:

Key Messages:

• Minimal cloud coverage is expected in the lower levels today, with some upper-level clouds present. Temperatures will reach the late September average in the upper 70s by the weekend.

• Tropical Cyclone (TC) Helene is projected to make landfall along the Big Bend of Florida before being absorbed by the upper-level low over the southern Mississippi Valley, potentially bringing rain to our region this weekend.

To construct this forecast, we referenced both the GFS and NAM models, which provided insight into evolving weather patterns for the upcoming week.

The cutoff low over central MO/IL will break away from the jet stream by 00Z Thursday, lingering over the MO/IL/KY region until fully separated. It will continue drifting southward along the Mississippi River by Friday morning, breaking the high-pressure ridge over the central Plains into two distinct centers of high pressure—one to the west and one to the north of the cutoff low. This setup will result in the cutoff low diving south, with its trajectory affecting the trajectory of TC Helene.

Both models (GFS and NAM) show consistent agreement up to this point, but significant differences arise once TC Helene begins interacting with the low. The NAM suggests a stronger TC Helene, which could bring more moisture into the area, leading to increased cloud cover across central Missouri. However, the NAM is known to overestimate hurricane strength. The GFS, on the other hand, predicts a weaker Helene, allowing the upper-level low to push further east into the Ohio River Valley by 15Z Saturday. Given these discrepancies, temperatures could vary from the mid-60s to mid-70s over the weekend, with a slight preference towards warmer conditions. With the current forecast leaning towards the GFS due to the NAM’s bias with moisture, Friday will be mostly cloudy with a slight chance for scattered showers. The chance for rain increases Friday night into Saturday and should be monitored by future shifts.

– McCurdy, Peine