Monday, April 29, 2019

Tonight - Cloudy with thunderstorms developing after midnight. Low: 56-60.

Tuesday - Cloudy with thunderstorms. Storms may be severe, especially after noon. Storms may produce heavy rainfall. High: 68-72.


Tuesday Night - Cloudy with thunderstorms ending by dawn. Storms may be severe, especially before midnight. Storms may produce heavy rainfall. L: 60-64.

Wednesday - Mostly cloudy with thunderstorms possible in the early afternoon. Storms may be severe. High: 72-76.

Thursday - Cloudy. High: 64-68.  

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A frontal boundary currently set up over Missouri will move very little between now and Wednesday, and it will act as the focus for several rounds of showers and thunderstorms during this period. Between Tuesday and Wednesday, there will be a heightened risk of severe thunderstorms, with large hail and damaging winds being the main threats. Additionally, any thunderstorms will have the potential to produce torrential rainfall, and with several rounds of thunderstorms in store, localized flooding is possible. By Thursday, the weather shouldn't be as severe as Tuesday and by the evening, skies should be mainly cloudy.

Forecasters: Danaher and Hirsch
Issued: 6:00 p.m., 29 April 2019

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

WPC recommended a non-NAM model blend because of greater surface pressure drops after Wednesday along the cold front into Ohio Thursday. Therefore, the GFS, SREF, and GEFS will be the models used throughout this forecast period.

Over the next couple days Columbia will mainly experience rain and high wind.
High winds will be the reason we are in the position of a severe thunderstorm from tonight leading into the rest of the forecast period. The jet core north of Missouri and the LLJ will be one of the many contributors that will help the low pressure system over upper Oklahoma and southwest of Texas will influence Missouri.

As Monday night approaches, rain is expected to fall around 03Z Tuesday according to GFS skew-T because of CAPE values at 603 J/kg, LI of negative 4C, CAP of 2C/750mb, negative omega ranging from 800mb to 500mb with the highest being 9 microb/s at 725mb, PW of 1.27", and complete saturation from 900 to 700mb. There is a dry slot between 700mb and 400mb, but forcing for ascent will continue to moisten the layer. By 09Z Tuesday, skew-T shows CAP reaching to 1C/725mb, CAPE increasing to 639J/kg, LI of negative 3C. Winds between 03Z Tuesday to 09Z Tuesday continue to show backing. This not only brings in CAA, but also the flow of moisture as we head into Tuesday for the continuation of severe weather. 

Throughout Tuesday, the flow of moisture occurs because of the LLJ. This will cause a warm front over Columbia as only a little bit of veering from 950mb to 790mb at 12Z Tuesday. However, within hours divergence aloft will sweep over Missouri around 15Z Tuesday causing the winds to shift to backing once again. It will not be until after 18Z Tuesday the warm front has shifted into Northern Missouri. GFS skew-T shows that winds at the surface will be around 40kts between 03Z Wednesday to 06Z Wednesday. This is mainly the reason why we are under a severe thunderstorm threat throughout Tuesday into the night according to the WPC. SREF also notices the threat because the most unstable CAPE happens between 18Z Tuesday to 00Z Wednesday with values at 1598 J/kg. On the other hand, GEFS shows values of CAPE below 1500J/kg and GFS skew-T at 00Z has shown CAPE values of 439J/kg, but with excellent negative omega from 650mb to 500mb with the highest at 600mb at 13 microb/s. So the ability of hail is unlikly while the wind is more so the problem due to the LLJ and south jet streak. Therefore, it does make sense to put out the severe warning due to high winds. However these high winds only last for a couple hours during the night so I believe the warning should be more towards Tuesday night.

By Wednesday, a lot of the convection has eased up. GFS Skew-T does not rule out the possiblity of thunderstorms as could be more into the afternoon. This is because CAPE continues to increase from 1000J/kg at 15Z Wednesday to 3000J/kg at 00Z Thursday, LI staying negative and CAP decreasing back to 0C as it stay between 900mb to 800mb. a dry slot forms and expands from 850mb to 350mb during 12Z Wednesday. Also, saturation continues from 12Z Wednesday to 03Z Thursday. It continues to be in the 700mb to 500mb layer. Only by 06Z Thusday is when the dry slot continues to shrink down to the surface. But it still is able to persist as not rain will fall from 06Z Thursday to 12Z Thursday.

By Thursday, the potential for severe thunderstorm is extremely small as little to no negative omega is present throughout the entire day. CAPE is available throughout 12Z Thursday to 00Z Friday. But without any forcing for ascent, it is unlikely any severe storm will occur over Columbia. However, a lot can change within a couple of days so the next forecast period should look more into it.

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