Monday, February 27th
Hello all, hope you had a great weekend. Weekend forecast worked out great !! We got our flurries/light snow patches on Saturday followed by the huge warm up yesterday. Looking forward… active weather once again in the forecast starting overnight Tuesday into Wednesday – with yet another batch of stormy weather possible Friday night. I’m not going to touch on Friday night but I am going to get into the Tuesday night/Wednesday event… so, here we go.
No worries through early tomorrow (Tuesday) evening. Here’s the NAM prog valid 7pm EST Tuesday…
The above chart shows a strong upper system poised in the central plains with its surface low in central NE and the retreating warm from extending southeast across the MO valley into the TN valley. Strong WAA on a strengthening LLJ will be overspreading our region as Tuesday night wears on. Here’s the vertical sounding progged tomorrow evening at 7pm… no problems as we’re still very much capped aloft but it does show increasing amounts of low level moisture.
Quite the change… this sounding is showing a classic thermal structure for elevated storms. If the H9 parcel is lifted it is free to go. I’ve highlighted the positive area on the sounding showing the CAPE / instability aloft. Now look at the wind field on the far right of this chart. VERY impressive warm air advection pattern with strong shear values in place. This is telling us that the storms that fire later Tuesday night into early Wednesday morning should become organized and will be capable of producing hail. We will have to watch for any storms that may occur close to the surface warm front as it will be possible for those to be rooted a bit closer to the surface and as a result some of the wind energy could reach the ground in the form of damaging wind gusts and even a few tornadoes given the strength of the low level wind fields (0 to 1 k shear: 50kts + and 0 to 1 k SRH’s: through the roof !! in excess of 600 from the Ohio River and pts north).
By Wednesday morning (7am EST), the surface warm front is progged to be well north of the Ohio River. Here’s the NAM charts for both 7am and 1pm EST Wednesday…
What we think may happen in this scenario is the overnight Tuesday batch of possibly severe storm lifts north with the retreating warm front. As indicated on the chart(s) above, we will be in the warm sector through early afternoon. Provided the overnight convection does clear the area, we will likely see some breaks in the overcast allowing for the instability to once again increase by midday Wednesday. Here’s the NAM’s instability chart valid 1pm EST Wednesday.
CAPE values of 500 to 1000. As shown on the NAM’s progged 4-panel chart (just before the instability chart above and valid at 1pm EST Wed.), the cold front/dry line will be sweeping east across the region, a strong H5 shortwave / vort trough rotating across the region – all point towards the possibility of a second round of thunderstorms Wednesday afternoon. Vertical shear profiles still strong but more unidirectional indicating this second possible batch of storms would have more of the straight line wind and hail threat… As always, we’ll watch it close.