Friday Night - Chance of rain with decreasing clouds by sunrise. Low: 34-38
Saturday - Increasing clouds in the afternoon. High: 60-64
Saturday Night- Cloudy with a slight chance of rain. Low: 38-42
Monday- Sunny and windy. High: 46-50
For this forecast period the 12Z GFS model was used due a variety of reasons. Neither NAM or GFS handled current surface temperatures particularly well as both were trending colder than the current high of 48F at Sanborn Field. To break the tie SREF and GEFS plumes were analyzed and dProg/dt was utilized to determine that better consensus existed with the GFS. NAM was the colder of the two models and handled QPF of this weekends incoming system very poorly so the decision to use GFS was made. This model choice is a deviation from the morning forecast when NAM handled IC's better so larger changes in the forecast may be necessary.
Zonal flow aloft at 250 mb will transition to southwesterly flow this evening and overnight as the sub-tropical jet couples with the polar jet over the central Plains. Slight ridging over the Midwest and eastern half of the CONUS will preside tomorrow as a trough over the Rockies deepens the long wave flow. The meridional nature of the flow continues into Sunday when a ridge-trough-ridge pattern is created by Sunday evening. The easternmost ridge exits the CONUS Monday giving way to a way amplified ridge-trough pattern over the country. This will place mid-Missouri in a northwesterly flow aloft by the end of the forecast period.
500-mb analysis is active for the forecast period. Vorticity overhead today will erode to the east this evening. A very subtle shortwave riding the flow across the Midwest will bring some vorticity near the region tonight though this energy will stay mainly north of the area over Iowa. Slight ridging in the 500-mb flow Saturday will begin to push east tomorrow night as the amplifying long wave to the west begins its trek into the Central Plains tomorrow night. A secondary shortwave and possible cold front will traverse through the region Sunday.
700-mb and 850-mb charts as well as model sounding data were used to determine the nature of the lower levels this weekend. Moisture is apparent this evening over mid-Missouri but dries out considerably overnight. Due to this the chance of rain for this evening will be lowered significantly to maybe an isolated shower with little accumulation though confidence is low. South-southwesterly flow at 850 mb tomorrow will allow modest WAA to warm Saturday temperatures into the low 60's. This is thanks to an LLJ that will develop from Texas to Nebraska and begin to slide east as the second short wave and associated cold front begin their trek into the Midwest tomorrow evening. The column begins to moisten at first from the top down by 21Z tomorrow with some surface saturation by 03Z Sunday though the dry layer will persist.
While PWAT values will climb to around 0.7 Saturday night the dry layer in the middle of the profile looks to be strong enough to hamper precipitation chances with this frontal passage. A very slight chance of showers early Sunday morning will be left in the forecast though confidence is again low. Frontal passage will occur in mid-Missouri between 09-12Z Sunday morning pushing any usable moisture to the east drying the profile leading to a cloudy but dry Sunday. As the sun rises Monday morning the area will be in a post frontal regime as northwest flow presides giving way to a chilly but sunny Monday.