will be a good idea to keep that umbrella handy for the next few days
as a cold front brings more rain to Missouri. Rain will begin late
Wednesday morning and continue off and on into the afternoon. These
showers will not be severe, but there could be some rumbles of thunder
along with a flash or two of lightning. Showers continue into the
evening and overnight with increasing rainfall intensity bringing
moderate downpours at times. Again, nothing severe but the chance for
thunder and lightning are not ruled out. From there, a cool down begins
Thursday into the weekend. Thursday will be slightly cooler with a
chance for rain in the morning and mid to late afternoon, but dry during
mid-day. Showers taper off Thursday night into Friday morning where
there will be a dry end to the work week and temperatures will start
feeling more like fall. Rainfall accumulation through Friday looks to be in the range of 1.5 to 2 inches -- a quality late week soaking.
Forecasters: Kobielusz, Macko, Bongard
Date Issued: 10/13/21 10:00 AM CST
For this forecast, the 06Z run of the NAM40 was chosen. Both the NAM and the GFS performed similarly when locating the area of low pressure to the northwest, but the NAM was decided upon due to better modeled surface temperatures.
At 250-mb, the jet stream between the upper-level trough to the west and the upper-level ridge to the east begins to move into Missouri throughout the day and into the evening on Wednesday. The strongest portion of this jet will be seen over NW Missouri, although our forecast area will also fall under its influence today. In the overnight hours on Wednesday, the jet begins to move northward. The upper-level trough seen off to the west will slowly move eastward over the next several days before arriving Friday evening.
The 500-mb vorticity plot indicates that stronger vorticity moving in from the southwest will be located over the forecast area later Wednesday afternoon before dissipating once again. These greater vorticity levels could help support the development of thunderstorms during the afternoon hours. By Wednesday night, vorticity builds back up, with vorticity above the area around 09Z. The vorticity will maintain its magnitude until 18Z Thursday. The NAM indicates that this vorticity is likely to return by Friday afternoon.
At 700-mb, moisture is prevalent. Relative humidity values above the forecast area remain consistently above 90%, occasionally exceeding 95%. This trend extends to the end of the forecast period. Upward vertical velocity is expected throughout the day on Wednesday before downward motion is to be seen in the overnight hours. Vertical velocity becomes neutral overnight.
The 850-mb level of the atmosphere is also expected to be moist throughout the forecast period, with relative humidity percentages nearly identical to those indicated in the 700-mb discussion. For this reason, clouds and rainfall are the main focus of this forecast. No significant warm air advection or cold air advection was identified at this level. The area of low pressure first seen over Nebraska begins to move north throughout the day on Wednesday, crossing into Canada by midnight. By Friday, a positively-tilted trough will have reached mid-Missouri.
The NAM surface-level model suggested that much cooler temperatures are to be expected as the week goes on. However, these temperature drops were extremely significant. While cooler temperatures are anticipated, it is highly unlikely that the temperatures will fall so far as to be 20 degrees lower than previously forecasted as the cold front is not expected to pass through the area until Thursday afternoon.
Severe weather is not expected with the weather the region will be experiencing. MUCAPE values hit a maximum around 780 J/Kg around 18Z today, before falling to 200 J/Kg at 21Z. Low MUCAPE is expected before hitting zero towards the end of the forecast period. K-values remained in the 30s for Wednesday and Thursday, indicating rain may be heavy at times.
Future forecasters should further examine rainfall totals associated with the system that will be affecting the area tonight into tomorrow.