Wednesday, March 6, 2019

Wednesday Night - Increasing clouds, isolated snow showers by morning. Low: 22-26

Thursday -
 Mostly Cloudy, isolated rain/snow mix possible in the afternoon and evening. Accumulations less than 0.5 inches. High: 42-46

Thursday Night - Scattered mix of rain/snow possible. Accumulations less than 1 inch. Low: 29-33

Friday - Mostly cloudy. High: 46-50

Saturday - Rain and thunderstorms possible. High: 50-54

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Overnight lows will moderate after frigid temperatures earlier this week and only dip into the 20's after a warmer Wednesday afternoon. A mostly cloudy Thursday greets us tomorrow though afternoon highs will warm even more into the 40's ahead of frontal system that will bring a slight chance for a rain/snow mix overnight. No worries needed though as accumulations of any wintry precipitation are minimal. High temperatures on Friday will be seasonal (FINALLY!) as we continue the warming trend despite mostly cloudy highs. Clouds will thicken overnight Friday as the next frontal system will lead to a soggy Saturday. Thunderstorms are possible late morning through Saturday evening as this system makes its way through central Missouri. Highs Saturday will reach into the low 50's before the cold front makes its presence felt across the region.  
Forecasters: Bongard, and Hirsch
Issued: 3:35 p.m.March 6, 2019

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

GFS and NAM upper level charts depict an upper level ridge sliding into the central Plains tonight. This will shift the pattern over Columbia to a more zonal flow as the axis of the ridge propagates into the Midwest overnight. Vorticity and some low level moisture will advect into the northern Plains and ultimately into northern Missouri by 12Z Thursday morning as a shortwave ejects out of the northern Rockies. This will be the catalyst for some potential snow shower activity over northern Missouri. Some disagreement exists between models as NAM gives a slight chance at snow showers for central Missouri while GFS keeps all the snow north of the area through the early morning. NAM snow accumulations are little more than a dusting so chances for this actually occurring are minimal. Low level flow will shift to the southwest in response to the western flank of a large high pressure system over the southeastern. Warmer temperatures on Wednesday and this persistent southwest flow will keep low temperatures overnight much warmer than previous nights this week.

Thursday will be a mostly cloudy day as the system over the northern Plains develops a low pressure center over central Kansas by mid morning and slowly begins to spin toward the forecast area by evening. Zonal flow aloft thanks to a de-amplification of the invading ridge will help to progress this system through the area quickly. The flattening ridge is in response to a vigorous upper level trough digging into the northern Rockies from British Columbia, Canada. This trough will be the culprit responsible for a soggy weekend forecast. Low level moisture will stream into central Missouri from the south on the strength of continued southerly flow as a warm front lifts into the region Thursday evening. This will help to promote precipitation overnight Thursday as the frontal system pushes through the region. Precipitation type is still a bit murky with the 540 line meandering around central Missouri for the majority of Thursday night. Accumulations total are very low at less than 0.1 inches for both NAM and GFS so we do not anticipate a large impact from this system at this time.

A re-energized ridge sweeps into the region Friday morning and quickly begins to erode to the east by Friday afternoon as the trough over the northern Rockies begins to influence the central CONUS. Precipitation chances from the frontal passage Thursday night into Friday will diminish quickly after daybreak as the ridge treks into the central Plains eliminating any forcing mechanisms needed plus mid and upper level moisture. Wrap around low level moisture from the departing system will keep skies overhead mostly cloudy Friday. Vorticity associated with this system will eject into the central Plains by 06Z Saturday. Model sounding data is in agreement that the dry layer in the mid levels overhead will begin to erode from above and the trough and its associated frontal system influence the central Plains Friday night. By 03Z Saturday a low pressure center will form over southeastern Wyoming and begin to spin across southern Nebraska. Out ahead of this encroaching system southerly winds over the forecast area will stream copious amounts of moisture into the Midwest. 

Saturday will be a rainy day for Columbia as the upper level trough and associated frontal system embedded in the flow impact the area. Rain will begin Saturday morning as forcing from the oncoming system creates a rather large precipitation shield across the southern Plains and Midwest. The areas first chance at thunderstorms appears Saturday most likely around midday. The cold front associated with this system will provide the forcing needed to create some convective activity as the front wades into PWAT values of around an 1 inch and CAPE values of approximately 600 J kg-1. Model disagreement on precipitation timing exists with NAM pushing precipitation out of the area in the early afternoon with half an inch of QPE by midnight Saturday. GFS has double the accumulation and keeps precipitation over the area much longer with heavier 6-hourly QPE. As of now the SPC is not promoting a severe component to these storms though this should be monitored as we get closer to the weekend. Continued warm air advection through the early afternoon will top afternoon highs Saturday into the low 50's. 

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