Current Conditions at Sanborn Field

 

Thursday: Light Rain. High: 55

 

      

Thursday Night: Showers. Low: 41

 

Friday: Rain. High: 46

Friday Night: Showers. Low: 40

Saturday: Scattered showers in the morning. High: 54

 

  

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Discussion: 

Our rain streak will continue until Saturday. Most of the rain will be limited to showers; however, on Friday we can expect moderate rainfall. Don't forget your raincoat or umbrella!

-Samson 

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Forecasters: Hefner and Samson

Date Issued: 03/23/2023 10:00AM CDT

Technical Discussion:

  

Rain will continue to be Columbia's biggest "issue" throughout this period, as we will continue to see showers from today until Saturday. For this forecasting shift, the 12Z run of the GFS model was used due to a more accurate moisture profile correlating to real-time observations compared to the moisture-rich NAM models.

Beginning at the 300mb-level, there is a trough, with no tilt, situated over the southwest United States connected to a low-pressure system centered over the northwest Four Corners region. The trough and associated low will deepen and amplify as they move eastward. The trough will tilt negatively at 21Z Thursday and begin to affect Columbia at 00Z Friday by increased upper-level divergence from 00Z Friday until 12Z Saturday, signifying low-level convergence. The trough's negative tilt indicates that the weather system is strengthening. This strengthening correlates with the amplification of the trough. There will be a powerful jet streak near the right entrance region which will aid upper-level divergence. Additionally, due to the jet streak being located on the right side of the trough, both it and the associated low will begin to deamplify as it passes through the mid-Mississippi Valley, eventually entering the Great Lakes region, where it will eventually die, leaving Columbia in zonal flow.

At the 500mb-level, spotty amounts of circulation occur over Columbia for the forecasting shift; however, a vorticity maximum will go over Columbia at 03Z Saturday, lasting until 21Z Saturday. This maximum is associated with the low-pressure system noted in the 300mb-level analysis, and the circulation will move out towards the Great Lakes region with the low. The resolved circulation will aid in vertical forcing in the atmosphere, which can play a role in precipitation intensity.

Relative humidity values at both the 700mb- and 850mb-level indicate a dry layer starting at 12Z Thursday, and an increase in moisture will begin at 21Z Thursday. However, a dry pocket of air remains over Columbia until 12Z Friday, which can create a brief pause in precipitation. The high moisture values (>65% relative humidity) will persist over Columbia, eventually drying out at 21Z Saturday.  If the moisture at this level reaches saturation, thanks to high negative Omega values, precipitation will occur, and the precipitation intensity will depend on forcing at this level. For the 850mb-level, high moisture values resolved except for one time period, 15Z Saturday, where there will be a brief dry pocket before returning to moist air. So, cloud cover and precipitation support will be present at the 850mb-level for almost the entire period.

These high negative Omega values correlate with high moisture values at the 700mb level at 18Z Friday until 03Z Saturday and again at 09Z Saturday until 15Z Saturday. The negative Omega seen from 03Z Saturday to 09Z Saturday is in conjunction with the vorticity max noted at the 500mb-level. This coupling of forcing mechanisms could lead to more intense precipitation at that time period. However, the highest Omega values are expected to occur on Friday at 18Z, and this lifting mechanism will cause the highest intensity of our expected rain for this time period.

Down at the surface level, cold FROPA occurred earlier than previous forecasting shifts expected. FROPA resulted in a rapid decrease in surface temperature which sparked our significant 10-degree change in the forecasted high for today. Surface winds have a mostly northerly component, combined with solenoids throughout the entire forecast period, CAA is anticipated. As a result, the CAA will bring us temperatures down into the 40s. Additionally, a mid-latitude cyclone will begin to affect the Columbia area around 00Z Saturday. The most significant impact of this cyclone will be on wind direction for Columbia. Columbia's position relative to the front will cause a westerly shift in winds. The cyclone, however, should not cause Columbia to experience more precipitation. The reason for this conclusion, is that the cyclone will be too far east of Columbia for any precipitation associated with the cyclone to have an effect.

Wrapping up this AFD with sounding analysis, GFS generated soundings resolved the heaviest precipitation occurring at 18Z Friday. Negative Omega values are the highest at this time period, and the atmosphere is saturated (dewpoint temperature is equal to air temperature) up until ~680mb-level. The atmosphere is also close to saturation until around the 200mb-level, indicating the presence of moisture far into the upper atmosphere.

Precipitation totals from now until Saturday are from 1.25" to 1.5". This was determined using SREF plume guidance and sounding analysis. 

-Hefner and Samson