Friday, September 27, 2019

Friday - Increasing clouds with showers possible in the afternoon.  High: 80-84

Friday Night - Mostly cloudy with possible showers.          
Low: 66-70

  Saturday - Mostly cloudy with showers. 
High: 80-84

Saturday Night - Mostly cloudy with showers and thunderstorms.  Low: 71-73

Sunday - Partly cloudy with morning showers .
High: 84-88

Thanks to for the icons!

Currently a cold front is stalled over Iowa which sparked a few thunderstorms over northern Missouri into Illinois early this morning. This cold front will be the cause of storms that will move into our area later Friday night into Saturday. Heavy rainfall accumulations are not expected. Areas north of I-70 can expect to experience the most rainfall from this system. Saturday night some of these thunderstorms could be strong. By Sunday the rain should clear out and clouds should break up making for a mostly clear afternoon. Overall rainfall for the weekend will be between a quarter and a half inch.
Forecasters:   Taylor, Est   Lead Forecaster: Steward
Issued:  10:30 a.m. ; September 27,  2019

Technical Discussion (The nerdy stuff we are discussing in class!)

00Z NAM40 km chart analysis is showing a primarily zonal pattern at the 300mb level with a jet max within the base of the trough. On the 500mb level, vorticity couplets can be seen extending from the Southeastern CONUS through the Great Lakes area. The 700mb level is reflecting the 500mb level well, with increased moisture and a minor short wave trough upstream of the station. The 850/925mb level is showing moist air advection to the south of the station and is continuing to stack with the upper levels. TA high pressure system in the south eastern United States is causing moist air advection and increasing instability to push into the area, supported by the increasing gradient between the cP and mT air masses as seen on the NAM Theta-E products. 

00Z GFS model were showing a tenth of an inch precipitation through the current period, however no sensors around the region have reported precipitation as the Model solution continues to be overly aggressive. The NAM has continued to be show the boundary stalling north for multiple model runs and thus was the model of choice moving forward.

Fridays influence of the high pressure ridging will keep the boundary at bay concurring with the NAM solution.  Brief periods of showers will however move through, but will mostly manifest to the north.  Higher resolution modeling shows a few showers breaking through the wall of subsidence, but will be few and far between for any appreciable accumulations.

Saturday NAM guidance shows an increase in instability as the ridging dissipates and southerly flow increases with strengthening pressure gradient and moisture transport. This will coincidentally increase chances for showers and thunderstorms through the day Saturday with CAPEs approaching 2000J/kg
and linear wind shear with speeds increasing with height.   Storms are not anticipated to be severe with backing in the mid levels.  Saturday night shows the boundary moving through the area bringing with it the highest chance for Thunderstorms.  Exact timing of the boundary has been the most challenging part of the forecast. These are not expected to be severe as we will loose most of the instability after sunset.

Sunday, lingering showers will dissipate following the post frontal subsidence as well as clearing clouds.  Still a bit shaky on the QPF totals for the weekend, but a generous solution of a quarter to a half of inch seems reasonable for the period.

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