With our first round of rain, we could begin to see scattered rain showers as early 10 PM. Most of the heavy constant rainfall won’t begin until after midnight. We expect a wet morning commute:
Thursday: Two Rounds of Rain & Storms – Wake Up 61° High 74°
The most recent SPC severe weather outlook has us very close the area alerted to significant severe weather potential.
A more localized view of us on that bubble:
On David’s unofficial SPC outlook translator, this is a “you have my attention” event, right on the border of “getting concerned”:
As David mentioned early, this event is nothing like the two earlier “slight” risk events that we have seen. In both those events, there was question as to whether or not severe weather would occur at all in the region. With this event, severe weather will be happening at some point tomorrow. The exact location of where it will happen is still TBD. We are expected to have all of the ingredients present for severe weather in the afternoon/evening hours. The question is if the moisture from the storms to our West reach our location in time to utilize those ingredients.
We are expecting two rounds associated with this weather event. First, in the early morning, main concern is flash flooding. Then, a break in the action, to allow for the atmosphere to potentially recharge. Second, later in the afternoon/early evening, our main concerns are damaging winds, more localized flash flooding, hail, and a tornado or two. Make note that all our hazard levels have increased through the day.
Round 1 – Early Morning
Timing: Rush hour primarily, expect it to take you a little longer to get to work
Main Concern: Localized Flash Flooding
NAM, GFS, and Euro are all taking the stance that we may have a few periods of showers in the early AM, but will get significant heavy downpour during morning rush hours:
While the models may not agree how, both of the scenarios will lead to localized flash flooding. Be safe and aware of your surroundings. If you see a flooded roadway, “Turn Around Don’t Drown!”
Lunchtime-ish Break in the Action
When the morning rain ends, weather nerds everywhere will be rushing to view the satellite trends (will the sun come out?), special weather balloon data (if NWS launches some), and the SPC’s RAP Mesoanalysis page, all of which will indicate whether the atmosphere is filling back up with instability/CAPE, shear, supportive wind fields, LCL heights, and other ingredients that will have to come together to set us up for severe weather ahead of an approaching cold front expected later in the day.
For example, here’s the NAM4 model for 4 PM Thursday, showing some sunshine, which suggests we’ll be recharging our CAPE/instability.
Round 2 – The Potential Severe Storms
Timing: Still a little too far out to tell. ETA late afternoon/evening/late
Based on the information from the NWS, estimate times are probably between 4 PM – 10 PM. I really do not see any storms developing much before 5 PM because that is when our atmosphere will be recharging.
All of the models seem to be agreeing that the rain will be here in the evening hours. How early or late is still undetermined and all the models vary at that point.
GFS thinks rain could start around 7 PM with the heavy, potentially severe storms right behind it:
The NAM holds off a bit, shows some showers going north of us and the main event not reaching us until after 9 PM.
Main Concern: Damaging Winds, Hail, Flash Flooding, a Tornado or two.
A lot of our concern about “how bad will it be” is still up in the air. The lull after the morning rain will be the key to our potential severe weather — will the atmosphere recharge? A strong southern wind will shove reinforcing warm air to recharge our atmosphere; however, if pockets of the region remain clouded over, or ongoing storms to the south cut off the good southern moisture transport, the threat will diminish. In addition, the upper level support of severe weather should be higher nearer to the Ohio River. The whereabouts of these gaps in co-located severe weather ingredients present the forecaster with the most uncertainty here — no one knows where they will develop — so absent that certainty SPC did not feel it appropriate to expand its risk area across I-65. I also think our risk is slightly lower because models suggest the storms will show up after dark. If storms show up after dark, less ingredients will be present.
Flooding concerns will remain through the evening hours. If we get one of those supercells “training” over our area, the already-saturated ground from the morning rain could set the stage for localized flooding. Most weather deaths and injuries occur from people in cars around flooded roads.
The majority of the threat does still remain to our west; however, these storms very easily with the right timing could develop and move into our region.
One forecast model, the usually-over-dramatic NAM4, is painting a grim, and frankly scary, severe weather setup tomorrow. The details of that aren’t helpful. It looks way too unrealistic; however, the other models are building a consensus that the storm potential is real. So, stay tuned.
We will be updating you throughout the day on Twitter at @NashSevereWx. Consult multiple reliable weather sources tonight and tomorrow.
When Will It End?
Rain should be gone by your drive to work on Friday.
Rain totals are expected to be around 1′ to 2″ when all is said and done. Local areas (especially in Williamson County) could potentially see up to 3″ of rain through this event.
This website supplements @NashSevereWx on Twitter, which you can find here.
Categories: Forecast Blogs