Tuesday's increasing cloud cover will persist into the night, bringing an end to the clear skies. Beginning Wednesday morning, the sunny, unseasonably warm temperatures Mid-Missouri has seen for the past few days will leave as a cold front associated with a low pressure system moves through the area. Winds will begin to pick up ahead of this system before rain is expected on-and-off Wednesday and Thursday. Two waves of thunderstorms are possible with this system: one in the morning and one in the afternoon. These storms have the potential to be strong to severe, with the main threat being stronger wind and small hail. The rain will end late Wednesday evening, but pick up again after midnight. The rain continues into Thursday as Columbia sees a return to cooler temperatures. By Friday, the low pressure system has moved out of Mid-Missouri, so clearer skies and warmer temperatures will return.
This forecast was assembled using the 12Z run of the GFS, SREF and GEFS plumes for temperatures, GFS soundings, and the 19Z run of the HRRR for storm timing. The most recent runs of the GFS and HRRR had the most accurate initial conditions and consensus for Wednesday's system, and were chosen for this reason. GFS soundings were used to examine the potential threat for hail and minor tornadoes.
At the 250-mb level, divergence associated with a negatively-tilted trough will move into Missouri around 09Z Wednesday. The low pressure system at the base of the trough will break off and become a closed low by 00Z Thursday, and continue on a northeastward track, moving out of Missouri by 12Z Friday. While there will still be divergence in the region Friday, it is in much lesser amounts.
500-mb plots of heights and vorticity show the strength of the low impacting our area on Wednesday. By 09Z Wednesday, the first wave of vorticity moves through our forecasting area, allowing for storms in the early to mid-morning hours. This wave moves out of the area, but by 18Z Wednesday the majority of the vorticity associated with the low moves into our area, bringing with it the second opportunity for severe storms on Wednesday. The potential severity of these storms will be determined from examining GFS soundings. Missouri remains under the influence of this low for the entirety of Thursday providing support for the continued rain showers. By 12Z Friday, the abundant vorticity has moved out of the area, leaving cloudy skies and calmer conditions in its wake.
700-mb plots of relative humidity and heights demonstrate the timing and intensity of this precipitation event. Higher relative humidity values begin appearing in Mid-Missouri around 09Z Wednesday, which is when the first round of storms will pass through the area. This moisture lingers until around 00Z Thursday, providing a brief break from the rain before it returns around 09Z Thursday and stays throughout the remainder of the day. By Friday at 09Z, the high moisture values will move out of the area along with the low pressure system, allowing for clearer skies to return.
At the 850-mb level, heights, winds, and temperatures depict the passage of a cold front and the moisture transport associated with this system. A LLJ with south-southwesterly winds provides the moisture transport from the Gulf, giving this system plenty of available moisture. The passage of the low pressure system will shift the winds to a more westerly direction, one reason as to why cooler temperatures can be expected after Wednesday. Another shift in the winds south of the low indicate the passage of a cold front around 21Z Wednesday. The westerly winds will help move the moisture out of the area by Thursday evening, and by Friday all abundant moisture has left.
At the surface level, plots of MSLP, thickness, and winds display the passage of the cold front more clearly. The cold front passes around 21Z Wednesday. Strong pressure gradients ahead of the front support windy conditions. A small shortwave ridge enters the area on Friday, adding further support to the calm and clear conditions.
GFS soundings were used to determined the severity of Wednesday's two rounds of storms. Wednesday morning around 09Z, MUCAPE values are estimated at 1027 J/kg. However, soundings also indicate abundant downward motion, which could cause an updraft to not reach its highest potential. By 12Z, updrafts will dominate with MUCAPE values of 762 J/kg, where small hail could be a threat throughout the day. 3-6 hours later, shear values lie within 30-40 m2/s2, so with enough rotation, a spin-up tornado cannot be ruled out IF the atmosphere can recover after Wednesday morning's storms.