Thursday Afternoon, 13 March, 2025 Forecast – 6:00 PM CDT
Thursday Night: Mostly Clear. Low: 58oF
Friday: Sunny and Windy with evening T-storms likely. High: 83oF
Friday Night: Partly Cloudy. Low: 51oF
Saturday: Increasing Clouds. High: 60oF
Saturday Night: Partly Cloudy. Low: 33oF
GENERAL DISCUSSION
A MODERATE RISK of severe weather is outlined over portions of eastern Missouri and western Illinois for Friday evening into early Saturday morning as severe weather is expected to move into the Midwest. At this time, the expected hazards are damaging winds, embedded tornadoes with a strong tornado possible, and locally heavy rain. During the day Friday, temperatures are expected to exceed 80o F with winds being around 20-25 MPH with gusts as high as 30 MPH possible. A broken line of severe thunderstorms will impact Columbia by 5 PM Friday evening. Cooler air will infiltrate the forecast area in the wake of this severe weather event, contributing to a weekend cooling trend, before a weak cold front moves in Saturday evening. Though no precipitation is expected, the cooling trend will continue as high temperatures Sunday is anticipated to not exceed 55o F.
KEY MESSAGES
– Damaging winds and a couple tornadoes are anticipated for Friday as a Moderate Risk exists for the eastern half of the forecast area.
– A cooling trend is expected for the weekend bringing temperatures 15 degrees cooler.
– A weak cold front will move through mid-Missouri Saturday night, bringing cooler temperatures for Sunday.
TECHNICAL DISCUSSION
Missouri is currently subject to ridging as seen from 300 MB. Combined with wind barb direction, this ridging contributes to increased warm air advection into the forecast area, bringing high temperatures warmer than previously forecast. This ridging progresses eastward overnight while a significant trough traverses the western United States. This trough is going to be the weather maker for Friday evening into Saturday morning.
Strong southerly winds will infiltrate Missouri Friday, as the trough begins to take on a negative tilt by Friday 12Z. This will bring wind speeds up to 20 knots with gusts as high as 30 knots as the day progresses. Friday, for the most part, will remain sunny and warm, bringing temperatures as high as 82° F, with these strong winds possibly enhancing warm air advection (and concurrently enhancing the warm sector) into mid-Missouri. As Friday evening draws near, the ingredients begin to fall in place for a regional outbreak of severe weather.
Diffluence begins to overspread the region as the day goes on, increasing confluence at the surface and upward motion throughout the atmosphere. By 21Z, the low level jet begins to increase with southerly winds as high as 50-60 knots overspreading the region, as seen at 850 MB. This will increase the transport of Gulf moisture into the area, though the best moisture will remain along the Mississippi River region and towards southeastern Missouri into southern Illinois. Although a strong low level jet exists over the forecast area, moisture still remains a concern with the best values being concentrated around the Missouri bootheel and points south and east. Bootheel dew point values are anticipated to be around a 10 degree difference compared to the mid-Missouri region. This is due to the positioning of the trough and its associated wind vectors, mainly bringing in dryer air from the desert southwest along the Highway 50 corridor and points northward.
Regardless, initiation is anticipated to occur along and east of the Interstate 49 corridor around 20Z-21Z, along a stout dry line positioned poleward, which will be the main forcing mechanism for the severe weather event. The moisture gradient is strong, with a 20-30 degree dew point difference between the moist and dry side, especially being prominent towards the Ozark Plateau. The storm mode is expected to begin as semi-discrete before transitioning into a QLCS set up as it moves towards the Mississippi River valley region. The QLCS nature can be contributed to very steep lapse rates, with values expected to be around 7.5 and 8° C / km, as well as the stout moisture gradient, resulting in a strong forcing mechanism. The initial semi-discrete nature can bring damaging winds, hail between quarter and half-dollar size and the chance of a strong tornado as it moves into a region of favorable wind shear. Around Columbia and points east, wind shear is ample in nature, with model sounding guidance suggesting values of 60-75 knots of surface to 6km shear, as well as consistent 250+ m^2 / s^2 of storm relative helicity. Models disagree on whether or not LCL positioning will remain on the high or lower side, with the CAMs airing on the lower side, which can increase tornadic potential for mid-Missouri.
The storms are expected to hit Columbia around 0Z Saturday, with damaging winds, a couple tornadoes and local heavy rain being the expected hazards. The rain, combined with the severe wind gusts, can reduce visibility for the Friday evening commute for those going home to Kansas City or St. Louis this weekend. The storms will translate east very quickly, with consistent storm speeds of 60-70 MPH. Timing on when the storm mode will transition into linear is in the air at this time, but is expected to be linear by the time it crosses into Illinois around 3-4Z Saturday.
Cold air advection will move into the area concluding the severe weather event, with decreasing clouds as we head into Saturday morning. There will be an increase in moisture as Saturday progresses, leading to an increase in cloud cover. As the Friday trough dies off, another trough is expected to form along the Great Plains Saturday morning. It will intensify and begin to take on a negative tilt as Saturday evening draws closer. Paired hand-and-hand with this trough, a weak cold front is expected to move through mid-Missouri between 21Z Saturday and 0Z Sunday, though no precipitation is anticipated, due to a lack of surface level to 850 MB moisture. With 700 MB moisture being present, cloud cover will be expected to increase for the evening.
Conclusion of this cold front will bring further cold air advection from the north, as the trough translates east, dropping temperatures 20-30° lower than the high temperature seen today (measured at 81.7° F). In addition, the decrease in moisture (and in turn, cloud cover) will increase radiational cooling from the surface Saturday night, dropping low temperatures into the lower to mid 30s.
-Alcorn