Thursday, April 11, 2019

Tonight - Mostly Cloudy. Low: 34-38

Friday - Mostly Sunny Skies. Breezy. High: 54-58

Friday Night - Clouds develop into morning hours. Low: 34-38

Saturday - Overcast with rain coming later in the night. High: 52-56

Sunday - Overcast with rain moving out in the late evening. High: 48-52

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Warm spring weather this week was short lived as Columbia, MO receives a cold front tonight and dries us out for the majority of the weekend. Temps drop more significantly than seen earlier this week tomorrow, however our conditions remain mostly sunny. This is all due to a low pressure system that moves out in the early morning hours of Friday. Saturday brings us similar conditions with cloud cover continuing to build into the later evening hours. Saturday night brings yet another low pressure system however this time it will produce a significant amount of rain through the night. This rain will continue through Sunday evening as temperatures continue to drop. Expected total amounts of rainfall will hover between .75" of an inch to 1.25" inches.
Forecasters: Myers and Doll
Issued: 4:25 p.m., 11 April 2019 

Technical Discussion (The nerdy stuff we are discussing in class!) 
Dry cool air creeps into Columbia, MO through the night due to the low pressure system seen north in Minnesota looking at the GFS model. Columbia, MO is currently in a wind advisory as the backside of the northerly system brings in the dry conveyor belt. When comparing the GFS and NAM models, both are in agreement in placement and development of the system overnight. However NAM has trace amounts of rain while GFS keeps Columbia dry through the night. This system develops into it's mature stage overnight bringing as the dry conveyor belt creeps in right behind the cold front dropping temperatures significantly. In terms of the flow through tonight, the deep central CONUS trough influences southwesterly winds bringing in the post frontal regime seen through central Missouri tomorrow morning. When looking at model sounding comparisons, NAM has a much deeper dry layer through the night from 850-mb to 450-mb while GFS keeps the dry layer from 750-mb to 600-mb. NAM overcomes this dry layer giving the trace amounts of rain by having the surface layer more saturated compared to GFS. 

Post frontal regime takes full effect tomorrow as the low pressure system moves out of Missouri by late morning according to the GFS model. Columbia, MO dries out quickly as the deep trough turns zonal cutting off life from the low pressure system over the Great Lakes. As Friday continues on, a very deep trough begins developing extending down to the Mexico border where the jet max at 250-mb gives Missouri its southwesterly flow throughout the day. As this trough deepens, it gains a combination of convection and moisture from the gulf of California beginning later Friday night.

As the trough begins developing in the GFS model over the morning hours from west Texas, central Missouri keeps receiving warm air advection in the mid-levels from the southwest along with moisture indicating cloud development Saturday morning. As the day continues on, GFS has the atmosphere saturated from the top layer of 200-mb, trickling down to 600-mb Saturday night. Surface winds through the day shift from northwesterly to easterly in the nightly hours. In terms of comparing the GFS sounding to the NAM, both models are in good agreement of the saturated layer, as well as the wind shift. However Saturday night, GFS has the wind shift from easterly to southwesterly beginning at 700-mb indicating a bigger CIN level to overcome for any developing storm-like conditions. NAM keeps the shift at 850mb giving more development to this low pressure system and higher rain totals. Rain will begin late Saturday night and continue heavy into the hours of Sunday.

The biggest thing to watch for in this low pressure system into Sunday is the development of a sizable CAPE layer. Vorticity of this system is significant with the highest seen value of 44mb/s over Columbia, MO in the early morning hours of the NAM model. With a sizable CIN layer however, this vorticity will not be enough to overcome and develop thunderstorm conditions. As the rain pours and continues, the low pressure system will enter into its mature stage as it moves out of central Missouri Sunday evening. Seen earlier this weekend, the cold dry air will follow suit to this development dropping our temps into the start of next week. Rain totals from Saturday to Sunday hover from an inch to an inch and a half according to the NAM, but half an inch to an inch according to the GFS. 

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