If you read the blog yesterday and follow us on social media, you are aware that the Mid-South and Lower Mississippi Valley are facing what could be the most significant severe weather event(s) since spring 2011. (NOTE that I am not comparing this to April/May 2011, just saying that we haven't seen anything like this SINCE then). I'll handle this day-by-day in an effort to be coherent and for you to glean the most information, bypassing the nitty-gritty details of the state of the atmosphere to focus on threats and possible timing.
At a high-level, the main setup is a developing upper level low of huge proportions setting up over the Plains and moving ever-so-slowly east into the Ohio River Valley the next few days, strong jet stream wind and screaming mid-level wind enhancing storm intensity, and abundant of moisture and instability (especially during peak heating) creating the environment capable of producing severe weather.
Sunday and Sunday Night
The day starts quiet, but becomes stormy pretty quickly - probably by late morning - as the first area of lift associated with an upper-level disturbance brings in enough instability to create thunder. This round may last into mid-afternoon and will probably NOT be severe, but it primes the pump. Main risks: lightning, gusty wind.A break will probably occur during the late afternoon/evening hours as storms explode over a Moderate Risk area in southwest MO, west AR, and the ArkLaTex. This area could be upgraded to a High Risk tomorrow. During the evening these storms, which will be capable of strong tornadoes, large hail, and high wind, move east and may coalesce into a squall line or MCS (mesoscale convective system) as they move towards the metro. We expect these storms during the overnight hours Sunday into Monday - perhaps late overnight (after midnight). The Moderate Risk currently extends to just west of the metro; we are in a Slight Risk.
Some weakening is expected as they move into our area due to less heating from the sun and more organized line(s) rather than individual supercells, but they definitely still bear watching. Main risks: damaging wind, large hail, isolated tornado, heavy rain, copious lightning. The probability of severe storms in the metro Sunday/Sunday night is 30% according to SPC (see below), with a 45% area just to our west and a 10% risk of significant severe weather (EF-2 tornadoes, 2" hail, 75 mph wind), thus the hatched area in the graphic.
Monday
Monday is the day of biggest concern, particularly areas along and east of the Mississippi River, which includes the entire metro. Once overnight storms move out, another break is expected in the morning, which (with some sun) will recharge the atmosphere. The impressive (or awful if you hate severe weather) dynamics of the atmosphere shift slightly east and are expected to be overhead the Mid-South. A Moderate Risk of severe weather exists along/east of the river, including the metro. By afternoon, perhaps early in the afternoon depending on morning heating, storms will begin firing right over our area. As opposed to Sunday night when storms will probably be more linear, Monday's storms will likely be dangerous supercells, capable of large hail, high straight-line wind, and perhaps strong tornadoes. These storms are most likely Monday afternoon and evening, probably ending by midnight.According to SPC, the severe weather probabilities Monday are 45% for severe weather and 10%+ for significant severe (EF-2 tornadoes, 2" hail, 75 mph wind). These probabilities could change. Anything much higher than this and a rare High Risk zone would be required. The potential limiting factor is overnight storms the previous night. If they linger into Monday morning and cloud cover sticks around, the threat could shift just to our east a bit. For now, we're in the Moderate Risk.
Tuesday
The risk on Tuesday appears to be lower than thought yesterday. It now appears that the main risk of severe weather will be to our east, more towards middle TN and AL, though a few showers or storms are possible Tuesday morning. The threat on this day is fairly uncertain though and will need to be updated as time gets closer. If the cold front that ends all of the severe weather threats comes through early Tuesday, we'll be fine. If it is delayed into the afternoon and more heating can occur, we'll be more at risk.Flash Flood Potential
A Flash Flood Watch has been issued from 7pm Sunday to 7pm Tuesday for the metro. Multiple rounds of storms, each capable of producing heavy rain, could compound issues related to excess water. Sunday starts with ground and streams fairly dry and capable of taking on some water. By Monday though, any downpours could cause flooding concerns. The Weather Prediction Center's graphic below for projected total rainfall through Tuesday morning shows widespread 2-4" rainfall totals and places that see several storms pass over in that period could see 4-6".
Safety Preparations
Being that this is the best chance of widespread severe weather we have seen in a few years, brushing up on severe weather safety is a necessity. See the graphic below for our suggestions, including what a safety kit should include.Always understand your risk and know what you will do no matter where you are during the period of potential severe weather. Plan it ahead of time.
Have multiple ways of receiving warnings. Don't count on sirens, especially if you typically have trouble hearing them indoors at your home/work. We highly encourage the use of smartphone apps as one of your "layers" of information. Of course, we highly recommend ours because we built it for you! Get more info on it's capabilities and then download it here.
In the MWN app, the most important thing you can do is purchase (one-time) StormWatch+ severe weather notifications. Program your location(s) and then leave it next to the bed overnight unsilenced. It WILL wake you up if a Severe T'storm or Tornado Warning activates while you are sleeping, but only if your programmed location(s) are in the warning polygon. For 1/3 the price of a Weather Radio (which we also recommend but isn't as precise), it could save your life and it definitely provides peace of mind.
If you have outdoor plans, games, practices, etc. Sunday PM or Monday PM, don't be complacent. They will likely be affected by storms. Don't be afraid to make the safe and wise move. We're delaying assembling our new trampoline until at least Tuesday, maybe Wednesday, because it would be stupid to have it destroyed by a storm in it's first week! Yes, the kids are upset. They'll get over it. :-)
Finally, we will bring your the absolute latest info, including nowcasting live during storms (without interrupting your favorite TV program) on Facebook and Twitter. We've talked about the issues with Facebook not showing you everything before. We aren't responsible if you miss something - it's best to go to directly to our FB page and refresh regularly or click "Get Notifications" on the Like button on our page if you want to see everything.
As always - be prepared, not scared. Though the risk is elevated, the chances of a tornado hitting your house, even in an outbreak, are small. With proper preparation, heeding all warnings appropriately, and taking cover if necessary, chances are you'll be in good shape.
Erik Proseus
MWN Meteorologist
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