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Tuesday Night: Small chance (20-30%) of measurable snowfall. Low: 24°F
Wednesday: Sunny. High: 39°F
Wednesday Night: Clear. Low: 24°F
Thursday: Sunny. High 53°F
Thursday Night: Small chance (20-30%) of rainfall. Low: 38°F
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General Discussion:
Unseasonably hot temperatures usher into the Ohio and Mississippi River Valley this afternoon. An approaching storm system will bring a strong cold front through Mid-Missouri later this evening. Strong northerly winds of 25 mph, with gusts up to 40 mph will plummet temperatures to the mid-20s by the overnight hours. A light dusting of snow will occur behind the front, but there will be little to no accumulation. Temperatures will rebound back into the 50s for Thursday, where another warming trend is expected.
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Forecasters: Yost, Thee
Date Issued: 2/27/2024 6:00 PM CST
Technical Discussion:
Key Messages:
- Small chance (20-30%) of post-frontal snow accumulation Tuesday night into Wednesday morning.
- Large temperature drop into the 20s associated with frontal passage.
- Small chance (20-30%) of rain Thursday night into Friday morning.
A strong surface cyclone currently tracks north of Missouri towards the Ohio River Valley and southern Great Lakes region. The strong thermal/pressure gradient and associated WAA regime ahead of the cyclone reinforced the the unseasonably hot temperatures throughout the CWA this afternoon. A strong cold front lagging behind the surface low is draped from portions of eastern IA into northwestern MO. Temperatures in southeast MO (ahead of the cold front) are experiencing mid-80s, while northwest Missouri (post-front) are in the low-40s. This temperature gradient highlights the intensity of the front, and the expected temperature drop later this evening. Visible satellite imagery displays a moist prefrontal air mass, represented by the abundant cloud cover. Conversely, post-frontal cloud cover is sparse. These differing air masses will interact throughout tonight for convective initiation, but mid-Missouri will remain outside the threat as the severe threat extends into the Ohio River Valley and Great lakes region. The main focus will revolve around the major temperature drop this evening, and the small chance of snow.
A dynamic upper-level set-up is currently brewing across the Central Plains. The high-amplitude trough and associated surface cyclone will generate severe weather of all modes this evening into the overnight hours across portions of the Ohio River Valley into the Great Lakes region. Model guidance displays jet stream phasing over portions of the Mississippi and Ohio River Valley this evening. An intensifying jet streak (160kts) rounds the base of the high-amplitude trough which will interact with the warm-sector overnight. Convective initiation is expected in southeast MO this evening ahead of the aforementioned cold front. Despite the unstable atmosphere in place, the lack of high-quality moisture will result in no convective initiation within the CWA this evening. However, post-frontal forcing and moisture return will bring a small chance (20-30%) of snow accumulation tonight. An intense LLJ of 60kt wind speeds will aid in sufficient wrap-around moisture. Therefore, higher-quality moisture will be in place after the frontal passage in central MO. Model guidance suggests the cold front sweeping through mid-Missouri around 00Z-03Z. A tight thermal/pressure gradient will accompany the post-frontal air mass and generate strong northerly winds of 25kts, and gusts up to 40kts. Model soundings suggest enhanced air mass modification by 09Z Wednesday, displaying saturation and sub-freezing temperatures across the vertical profile. Accumulation is not expected to amount to much considering the moist air mass does not maintain itself very long, and warm soil temperatures will be present. Two to three hours of light snowfall is expected at the max, so a small chance (20-30%) of measurable accumulation is expected overnight tonight, mainly on grassy surfaces.
By Wednesday morning, an upper-level ridge and associated surface anticyclone will linger to the northwest and advect cool, dry air into the region. The surface high will traverse the Central Plains and central MO throughout Wednesday contributing to sunny sky conditions and below average (avg. high 50) temperatures. The surface anticyclone will shift winds back to the south by Thursday morning (12Z), which will aid in a quick temperature rebound to annual averages (avg. high 50). The WAA regime will not be very impressive and will not exhibit moisture return. Therefore, sky conditions will remain sunny through Thursday afternoon.
At the same time, an upper-level shortwave will traverse the Central Plains and induce lee-cyclogenesis on the Rockies Thursday night. This will generate subtle moisture return Thursday night, and induce the redevelopment of cloud cover. Once the shortwave pivots over the CWA, subtle forcing for ascent will allow for a shallow moist layer to form. Model soundings exhibit a lot of dry air, and the GEFS/NAM plumes suggest a trace of accumulation. Therefore, we have opted for a 20-30% chance of measurable accumulation. With temperatures returning to annual averages at this point, we can expect rain as the p-type.
-Yost