Stx_Thunder

Posting these H7 and 850Mb temp profiles from 0Z GFS, NAM runs tonight for visual reference on why ETX icing, is bound to be majorly impactful Saturday night. As long as 850Mb - 700Mb layer warm-rain processes don't get too much in the way.

0Z GFS, NAM runs tonight appear to be coming in line with 1 - 2 in. total icing, in ETX this weekend. Either way, things are definitely still looking highly impactful there.

I certainly understand there's many people out there who just want to know what's actually going to happen in weather, nothing else. And that's personally fine with me. But it's always better when people would like to (or are willing, more specifically), learn about the meteorological science & parameters in order to really understand what *can* happen. Especially nowadays where it seems like every year we pass now has its own bizarre pattern or systems that are getting more complicated to break down in meteorology.

The primary forcing aloft from the parent mid-level trough out west isn't forecast by the reliable models to start overspreading the state until later today - tonight. Which is why I've been stating the main deal (especially for convective ice/sleet) is going to be Saturday night. It's common to have "lull" or large gap areas of little or no precip between lead shortwave activity like what's ongoing in the state tonight. I have not seen the RRFS in action at all for winter wx events yet. But it does have its moments for MCS (mesoscale convective system) propagation through the state in the spring time.

Already seeing lightning activity ongoing over the Big Bend region (west of Del Rio) for the past 2 hours now. 12Z HRRR showing an MCC or small MCS tracking into STX ahead of the surface front later tonight. Which definitely has the possibility to be strong/severe if the storms out there can organize. Already seeing some favorable signs outside here in STX with all the darker mid-level cloud bases and structures before sunset. -- I do need to mention another highly underlooked instability parameter that will in fact be another major contributing factor to the wintry convective onslaught tomorrow (aside from substantial deep-layer shear closer to 100 knots on Euro & NAM), is steep mid-level lapse rates. CRP and HOU sites showing -6 to -7 C on upper-air obs data today. And Euro model systems continue to project those in the state through tomorrow night.

Was there also CG lightning going on up there back then that night? It was just incredible when I saw 2 simultaneous CG strikes (likely positive-charged because they were pretty thick bolts), in just over 35 F wx about a mile from my backyard down here. I didn't have access to detailed lightning strike data online back then.

Yes. Very, significant LIs for this kind of scenario. Just about every single parameter I can think of is lined up for a (possibly) catastrophic ETX ice storm. I don't want to overstate myself, but I feel even these most reliable winter wx models are still underdoing the accumulation potential with such a powerful incoming SS trough for this winter wx setup. That's also why I still would not let my guard down at all. Even in CTX or Austin/San Antonio region.

Same here, definitely. HRRR does tend to overdo things. Particularly when it's convective, as I've seen over the years. But even NAM, which is typically very conservative with any kind of overrunning convective instability (especially in these polar/arctic air masses), has joined that party. It's even been showing significant 850Mb instability (negative LIs) over ETX in more recent runs for Saturday night.

'Would not necessarily underestimate FZRA accumulation potential, even up there. Models have been honing in on a pretty powerful incoming SS trough out west into the state Saturday night. So the 850Mb - 700Mb southerly flow regime from S - ETX is quite likely to be significant. Even the NAM 3km runs (which always does best with these incoming shallow Arctic airmass scenarios), has been consistent on showing the 850Mb front still hung up close to DFW until late Saturday night. Which makes lots of sense in this case.

Finally... NWS got smart in ETX. I'm actually a bit surprised they went ahead and put out the IS warnings now. Since they initially just went with WS alerts.

Icing potential is definitely still there in Austin this weekend, and even San Antonio area at least to an extent. I have family in Austin region and would definitely still tell them to be prepared nonetheless (even though the much more significant or damaging ice impacts are likely to remain in ETX). NAM, alongside GFS models typically do best at least with ice/sleet accumulations in the state from what I've seen in past years. European (ECMWF) model isn't as reliable with accumulations in TX as it tends to stay too warm on surface temps.

'Hope ETX people are prepped by early tomorrow! Only thing I'm seeing now that could potentially interfere major icing or FZRA accumulation is the warm-rain processes from all the WAA occurring in the 850Mb - 700Mb layer Saturday night ahead of the SS trough. But below 850Mb - sfc is looking cold enough by later in the night to prevent that for most of the region.

Elevated wintry thunderstorms are looking pretty likely now in ETX (where it's most probable to occur), with lots of 850Mb - 700Mb WAA there. Euro is even showing unusually decent 850Mb instability from around Tyler area and south Saturday night. With lifted-index values down to -3. Definitely would not rule out a sig amount of CG lightning with those kind of instability values. Quite unstable and abnormal with this Arctic airmass setup. This is looking to be similar to the post-frontal Arctic airmass convective event in the state back in March 2014. Where even though sfc temps were above freezing in the 30s, I still had some pretty strong storms in STX with substantial CG lightning activity that one night. Which I had never experienced before.

0Z NAM was showing at least close to 1" icing in ETX. GFS was going all the way up to 2". Even just 1 inch icing is more than enough to cause major impacts & power outages.

ETX icing threat is looking real now with an R. I feel that an Ice Storm watch/warning is easily warranted now (rather than a Winter wx one in this region), as the incoming SS mid-level trough out west is trending more intense and diving abnormally further south into MX than I had suspected. Even on NAM, the H5 trough axis taking on at least a neutral (N-S) tilt. Which will definitely strengthen the mostly south flow WAA regime over ETX ahead of it (possibly up to 60 knots), in the 850Mb - 700Mb layer. Which is most critical for precip type. Even in STX, would not rule out at least a few elevated supercell storms with so much incoming dynamics aloft Saturday night (behind the surface front). But even in ETX, thunder ice/sleet is looking very likely now at least in a scattered storm variety.