Current Conditions at Sanborn Field

 

Thursday: Rain. High: 43

 

 

 

Thursday Night: Drizzle. Low: 34

Friday: Mostly cloudy. High: 47

Friday Night: Mostly cloudy. Low: 32

Saturday: Rain. High: 44

 

 

 

 

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Discussion:

Prepare for rainfall for today and Saturday. Rain today should begin at 3pm and 3pm on Saturday. Make sure to bring your umbrella/raincoat and take it easy on the roads.

-Samson

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Forecasters: Hefner, Macko, and Samson

Date Issued: 03/09/2023 10:00 AM CST

Technical Discussion:

 

Rain should be expected later today and on Saturday totaling from 0.1" to 0.25" of rainfall. For this forecast period, preference was shown to the GFS due to its better handling of observed upper-air conditions regarding geopotential height

To begin at the 300mb level, Columbia starts in zonal flow, indicating calm and stable atmospheric conditions. Zonal flow will last from 12Z to 18Z Thursday. From there, the air over Columbia will be influenced by a shortwave trough starting at 18Z. This trough will cause instability and help conditions allowing for precipitation on Thursday. The shortwave trough will begin to push out around 12Z Friday, leading Columbia into a ridge of high pressure. The ridge will transition us out of the unstable weather of the trough into calmer, stable conditions. Columbia will be under this ridge for most of the remaining forecast period; however, by about 00Z Sunday, Columbia will begin to be influenced by a trough generated by a low-pressure system in Canada. Though the atmosphere will shift between stability and instability, upper-level divergence stays at a minimum, not influencing the weather Columbia will experience over this forecasting shift. However, by the end of the shift (~21Z Saturday), significant upper-level divergence will build in, leading to lower-level convergence. This low-level convergence will lead to instability and the potential for more precipitation on Saturday.

Geopotential height contours at the 500mb level of the atmosphere follow a similar pattern to those of the 300mb level. Starting in zonal flow, transitioning to a shortwave trough, then to a ridge, then, at the end of the period, into a trough again. During the passage of the shortwave trough, vort maxes will remain north of Columbia, cycling through Iowa. Circulation over Columbia will remain close to zero, indicating that instability will be minimal. At the end of the period, when the trough indicated at the end of the forecast period begins to influence the Columbia area, circulation will begin to pass over (starting at 15Z and going through the end of the forecasting period).

The atmospheric forcing (or lack thereof) at the 500mb level is complemented by observed negative Omega values at the 700mb level. Significant negative Omega values will last from 12Z Thursday to 21Z Thursday, 00Z Saturday throughout the rest of the period (00Z Sunday). Negative Omega represents rising air and an unstable atmosphere. The timing of the observed negative Omega works well with relative humidity values as there are high relative humidity values (70-100%) from 12Z Thursday to 00Z Friday, a small pocket of moisture at 09Z Saturday, and 18Z Saturday until the end of the forecast period. Negative Omega forces air parcels upwards and when there is moisture in the atmosphere, clouds form and precipitation occurs if saturation is reached.

Moisture support in the atmosphere continues down to the 850mb level. As a result, high moisture values can be seen over Columbia from 12Z Thursday to 09Z Friday, 18Z Friday, and 15Z Saturday to the end of the period. In addition, the moisture in the atmosphere supports evidence for cloud formation and precipitation chances for Thursday and Saturday. The moisture at the 850mb level is brought in by two low-level jets, transporting moisture from the Gulf of Mexico into Missouri. The first is a relatively weak jet that brings in the initial moisture observed on Thursday. The latter is a much stronger low-level jet that brings in the final round of moisture on Saturday.

At the surface level, solenoids can be observed from 03Z Friday to the end of the forecast period. Solenoids indicate areas of cold- or warm-air advection. Surface winds at 03Z Friday contain a northern component. Wind direction shows colder air from the north blowing into Columbia, potentially lowering temperatures. The northerly wind component will shift to a southeasterly component at 15Z Saturday and remain so for the rest of the forecasting period. The shift in winds indicates warmer air from the south will be blowing into Columbia, potentially increasing surface temperatures. Winds for the forecasting period should remain calm; however, 15-knot (11 to 17 mph) winds are observed overnight Thursday (06Z Friday). So, it is reasonable to expect Thursday night to be windy.

Regarding precipitation forecasting, GFS soundings generated from SHARPpy resolve precipitation at 21Z Thursday, lasting until 03Z Friday (where it will likely transition into drizzle). Negative Omega values are weak, indicating that precipitation will be light. For the second round of rainfall, the GFS resolves saturation in the atmosphere on Saturday at 21Z and will last through the forecast period into Sunday. Forcing values are much stronger for this round of precipitation, so rainfall should be much more intense.

Cloud cover will be overcast Thursday and Thursday night in conjunction with rainfall. For Friday and Friday night, it is expected to be mostly cloudy as there will be a good amount of moisture in the atmosphere. However, the moisture will not reach saturation. For Saturday, expect overcast conditions again due to expected rainfall.

 

Temperatures were forecasted using previous forecast predictions and a mixture of the National Blend of Models and SREF plumes.

Future forecast shifts should be aware of a cold front passing through Columbia around 09Z Sunday.

-Samson