Current Conditions at Sanborn Field
Tuesday: Partly cloudy. High: 74
Tuesday Night: Cloudy. Low: 62
Wednesday Night: Cloudy. Low: 61
Thursday: Clearing sky. High: 71
Discussion:
The sun must have requested the day off tomorrow as clouds and the chance for rain tomorrow are the overarching themes of this forecast. Temperatures will cool down slightly after today, dipping a few degrees cooler into the upper-60s by tomorrow. Make sure to bring an umbrella tomorrow as we will see the best chance of rain for this forecast period, with the greatest chances of rain being between mid-morning and mid-afternoon. The possibility of thunderstorms will increase as we head into the afternoon hours before we experience a calm and cloudy night. Total rain accumulations are expected to range from 1/2" to 3/4". By Thursday, we will dry considerably and will get to see the sun once again.
- Macko
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Forecasters: Macko
Date Issued: 10/5/21 10:00 AM CST
Technical discussion:
This forecast was produced utilizing the NAM40 06Z run from October 5th, 2021. The NAM performed better compared to the GFS when modelling current conditions, with the NAM being only a degree cooler than the measured temperature at Sanborn Field. The GFS, on the other hand, was several degrees too cool. Overall, the NAM has been the most accurate when it comes to the weather system impacting us, and has been used in multiple prior forecasts as well.
At 250-mb, there is an moderate upper-level jet stream rounding a trough just to the south of Missouri. A portion of this jet stream covers areas of Missouri, including Columbia, and remains as such until late Wednesday afternoon. The upper-level trough initially south of Missouri will begin to push north overnight tonight, an indicator of the active weather we will see as soon as tomorrow morning. A much stronger jet stream is located off to our west and is expected to reach eastern Kansas late Thursday.
The NAM 500-mb indicates a slight to moderate amount of positive vorticity over the Columbia area today. The strongest vorticity will move in from the southeast tomorrow, implying that some thunderstorm development will be possible. By late Thursday, vorticity will dissipate.
The 700-mb model suggests that humidity will vary from 50% to 75% RH throughout the day today, with these values dropping even lower in the overnight hours tonight. By tomorrow morning, significant moisture is brought into the area via southerly flow, increasing the RH at 700-mb upwards of 95%. The RH will once again decrease as the evening begins, indicating that the air at this level has lost moisture. The 700-mb level will remain dry on Thursday, but an area of increased moisture will remain just off to the west. Vertical velocity at this level remains unimpressive throughout the majority of the forecast period, with only slight increases represented on Wednesday.
At 850-mb, a rather weak low-level jet (LLJ) is seen over the area from today into early Thursday morning, dissipating by sunrise. The relative humidity at this level is much more intriguing--RH values maintain a steady 95% RH from mid-morning to mid-afternoon tomorrow. Considering the high RH at 700-mb, rain is rather likely during this time period tomorrow. By early evening tomorrow, this level of the atmosphere will also begin to dry out, with significantly less moisture over Columbia by Thursday. Warm air advection (WAA) peaks over Columbia early tomorrow afternoon, further demonstrating the strong likelihood of both clouds and precipitation tomorrow, as well as the chance for thunderstorms.
At the surface, high dewpoint temperatures are to be expected primarily tomorrow. CAPE values are not particularly impressive early afternoon tomorrow at about 730 J/kg. However, this value nearly doubles by mid-afternoon tomorrow, reaching 1350 J/kg. PW values are around 1.5" for the majority of the day tomorrow with a K Index range of 30-35 throughout the day tomorrow. The lifted index is below zero around mid-morning, and it continues to decrease throughout the day, reaching as low as -5. The values of indices suggest that heavy rain is possible as the system moves through tomorrow, and that the thunderstorms developing in the afternoon have a moderate chance of being severe.
Forecasters for the next shift should further investigate tomorrow's convective potential as well as rainfall amounts due to the K value.
- Macko
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