April 25th Forecast, Tornado Outbreak Expected

April 25 Day 2 Map

I’m still working on the forecast so I may make some changes to this. I really haven’t had much computer time yet. I have been focused on setting up equipment ever since I got off work so I can focus on forecasting in the morning.

Current surface observations show dewpoints in the mid to upper 60’s across Oklahoma and dewpoints approaching 70 in central Texas. Soundings from OUN and FWD show moisture is plenty deep. A southerly low level jet will continue to strengthen tonight and draw that moisture north into the central plains by tomorrow afternoon, so as expected there are no issues at all with moisture quality for tomorrow with dewpoints in the upper 60’s across the warm sector. Morning precipitation should not be an issue tomorrow with any cloud cover burning off through the day over the majority of the warm sector with temperatures rising into the upper 70’s, low 80’s ahead of the dryline. Any precip tonight/early tomorrow should be confined to the area along and north of the warm front and track off to the east tomorrow morning. This will leave an uncontaminated warm sector that should be strongly unstable by early afternoon.

Storm initiation time and convective evolution is a bit tricky still. I think the NAM is out to lunch with it’s precip output, so I want to look at that and short term models in the morning before getting into when storms will develop and convective evolution. Storm motions will be normal enough to the dryline tomorrow that storms should be somewhat discrete as they move off the boundary. With strong instability and around 50kts of deep layer shear, storms will quickly become supercells.

The NAM has taken a big turn for the better IMO today with shear profiles. Mid level winds aren’t nearly as backed while 850’s are more backed, giving us much better directional shear ahead of the dryline compared to what it showed in previous runs. Below is tonight’s NAM run of surface/850/500 crossover. I posted the same chart from the NAM the other day, so look back to that and you’ll see there is a significant improvement in directional shear with the latest NAM runs.

850-500 crossover

Directional shear was one of my big concerns regarding tornado potential with the dryline and that has largely been put to rest if the NAM is telling the truth. The 00Z GFS also shows solid directional shear, lending further credibility to the NAM solution. The directional shear isn’t quite as good as you go south into southern Oklahoma and north Texas, but the northern half of the dryline looks good where 925-850 winds are backing more.

The NAM is also showing stronger low level shear in it’s latest runs, which was also a concern with this setup. 1km SRH is strong enough through the afternoon for a tornado threat given the good thermodynamics in place, but around 00Z as the low level jet strengthens (850 winds nearing 50kts and 925 around 30kts), low level hodographs start to enlarge dramatically. 1km SRH is forecast by the NAM to be around 150-200 ahead of the dryline in Oklahoma/Kansas by 00Z and increases to 250 by 03Z as low level winds ramp up. Given the thermodynamics in place, that is easily into strong tornado territory. Below is a forecast sounding/hodograph for Wichita at 00Z. Not bad.

Sunday Wichita hodograph

The tornado threat will increase through the evening and likely peak near dark. Strong long-track tornadoes will be possible with any discrete storms, especially over the area I hatched in red on the map.

Now for a few problems… Unfortunately at the same time as low level shear improves towards dark, mid and upper level winds start to back, giving hodographs an S shape. Still, I think given the solid thermodynamics, any discrete storm ahead of the dryline later in the day will pose a strong tornado threat. I don’t think this will be a big problem since the models haven’t been showing mid/upper winds backing until late in the day. My other big concern is about convective evolution, especially over the dryline bulge area where storms tend to pack in quick with hard negative tilt troughs. I’ll hold off until morning to get into those details though. Convective evolution/coverage could certainly trim the threat area tomorrow. The paramaters seem to be there, so that’s kind of the last hurdle to clear. Again that will be a big focus of my morning forecasting so check back for updates. Other than that I think we are in pretty good shape given the improvement to shear profiles in the latest model runs (assuming they’re telling the truth).

Alright, it’s 12:15 and time for me to calm down and get ready for bed. The subtle uptick in directional shear and low level shear in the latest runs is the difference between a moderate and high risk to me with this setup. If that holds I would probably expect a high risk over a portion of the dryline and up to the triple point. We may not see it in the earliest outlook since the models have just recently been trending shear up, but if it holds through morning and convective evolution looks to be favorable for discrete storms late in the day, I think we’ll see a high risk. I’ll check data first thing tomorrow morning and update regularly. I should be at home most of the morning forecasting, so I’ll be posting a lot I imagine. I haven’t picked an exact target yet, but I’m leaning towards starting out near the OK/KS border and playing south central Kansas. I will keep Wichita in range tomorrow since I feel like there is a strong tornado threat. Gotta protect the home town lol. Alright, check back in the morning for an update.

 

 

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One Response to April 25th Forecast, Tornado Outbreak Expected

  1. Dave says:

    Decided to stay back in California for this one…hopefully I do not regret it lol! With so many unknowns right up to the day of the event and not having a multi-day event it was hard to pull the trigger. Anyhow…good luck out there and safe chasing!

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