Thursday: Partly Cloudy. High: 78
Thursday Night: Partly Cloudy. Low: 54
Friday: Partly Cloudy. High: 80
Friday Night: Mostly Cloudy. Low: 60
Saturday : Increasing Cloud Cover. High: 75
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Discussion:
Warm weather will continue on for the end of your week. However, be mindful that we could get rain on Saturday with a potential for thunderstorms.Forecasters: Hefner, Macko, Samson
Date Issued: 4/13/2023 10:00 AM CDT
Weather over Columbia will continue to be influenced by the Rex block pattern over the 250mb level. However, an upper-level trough moving east from the Inner-Mountain West region will bring more active weather to Missouri. During this forecast period, the GFS and NAM had general agreement in regards to flow patterns; however, any disagreement between the two models will be covered.
As the upper-level trough moves east, it will push the low-pressure system centered around Texarkana northeast, gliding it through the Ohio River Valley eventually into New England. As the this low moves, it should not have any effect on Columbia. However, as the upper-level trough moves closer to Columbia, it will start to amplify and develop a negative tilt. Amplification indicates a strengthening trough. The negative tilt indicates wind shear (winds changing direction with height), signifying an unstable atmosphere, and potential for severe weather (this will be covered more fully in a moment). The trough is expected to move into the Columbia area around 18Z Saturday. The first disagreement between the GFS and the NAM occurs around this time as the GFS resolves upper-level divergence beginning at 21Z and increasing in area on 00Z Sunday, while the NAM resolves a similar pattern 3 hours after the GFS begins. The upper-level divergence noted here indicates lower-level convergence, which in turn indicates atmospheric instability.
Continuing with atmospheric instability at the 500mb level, there is not a whole lot of vorticity affecting Columbia throughout the forecast period (Thursday 12Z to Sunday 00Z). Some brief bands pass through Columbia, but nothing substantial that would have a real impact on our weather. Although the trough noted above will bring with it intense circulation, it will not reach the Columbia area until after this forecast period ends.
Forcing at the 700mb level mirrors that of the 500mb level, with the most intense negative Omega occurring with passage of the trough (00Z Sunday). However, considerable negative Omega values do begin to appear over the Columbia area at 06Z Saturday persisting until passage of the trough. The negative Omega indicates lifting air parcels. This could aid in cloud formation and precipitation given the right amount of moisture. Which, at the 700mb level there is not a lot of moisture going on. There is a brief flash of moisture (relative humidity >65%) from 03Z to 18Z Friday (with the GFS resolving moisture ending at 12Z Friday, the discrepancy does not matter much because there is not any forcing mechanisms to do anything with the moisture available). For the rest of the period, the atmosphere is dry; however, the GFS resolves a small pocket of moisture at 21Z Saturday (the NAM does not). This disagreement could have more impacts due to the presence of negative Omega at this time. If there is moisture, clouds could form. However, I do not know if there is enough forcing to cause precipitation.
Moisture at the 850mb level is much more present that with the 700mb level. There are patchy areas of moisture starting at 09Z Friday and dipping inbetween moist and dry pockets of air until 18Z (the NAM start at 12Z, but the NAM's inherent moisture bias causes the GFS to appear more trustworthy) Saturday where moisture will continue to the end of the period. Moisture at this level could lead to cloud formation and if saturation is reached, precipitation could occur. The moisture will be supported by a low-level jet coming out of the Oklahoma-Texas Panhandle affecting the Columbia area 03Z Saturday fizzling out at 15Z Saturday.
The most significant feature coming out of surface analysis is a cold front passing through Columbia at 00Z Sunday. This cold front will lower surface temperatures and could influence our precipitation chances for Saturday evening. Since cold fronts due act as a forcing mechanism and there is moisture support at the 850mb level around the same time as the FROPA.
With the amount of divergence present at the end of the forecasting period (00Z Sunday). Consulting with GFS soundings at 21Z, MUCAPE value is 2418 J/kg, MUCINH of -28 J/kg, and a LI of -10. The CAPE value indicates moderate convection and there is not a lot of capping with a value of -28 J/kg. The LI makes thunderstorms appear even more likely. However, forcing at this time is rather weak with a large amount of positive Omega occurring, indicating falling air, at this time. The strong positive Omega throws into doubt whether or not a thunderstorms will occur at all. Additionally, all of the variables affecting thunderstorm chances significantly decrease within the next three hours of this sounding as the 00Z sounding has MUCAPE values of 221 J/kg, MUCINH values of 5 J/kg, and a LI of -2. Therefore, it seems imperative that future forecasting shifts be on the lookout for any changes in the atmosphere that might influence our thunderstorm chances.
-Samson
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