David Reimer

The high risk 'bust' of 2017 is flashing in my mind in regards to Saturday. Conditions certainly do set up to support a significant severe weather event, but I'm not sure which mode will be dominant. A QLCS would result in plenty of damaging winds, hail, and brief tornadoes while a semi-discrete supercellular mode would probably have a substantial tornado threat. Lousiana is pretty much doomed at this point since timing is set up to support both modes out that way. I'm just not sure we'll get it done in East Texas before we veer or have VBV issues. Hopefully, we get more answers than questions with the 0Z model suite. We'll also have to see how far west the threat sets up on Saturday considering the slowing trend in data over the last day.

Have some minor ice accumulations on elevated objects like trees and light posts. Looks like the heavier rain rates earlier this afternoon helped prevent more in the way of ice accumulation. We did have sleet for a while, but the rain just washed it away. It's harder to get ice accumulation this late in the season without temperatures in the 20s during the day. I'm curious if the OKC metro will see any bridge icing tonight with the freezing drizzle.

I wouldn't mind a switchover to sleet and snow in OUN at this point. This FZRA garbage needs to stop. We're starting to lose trees and I really don't want to flirt with power outages. It's all fun and pretty until the power goes out

Hope Y'all up in Tulsa get some good snow out of this! Looks like we're pretty locked in here in OUN (famous last words), so it would only be fitting for TSA to get some love too.

It's being discussed internally (NWSChat), but we'll see what actually comes out with the afternoon package.

Digging into the 0Z NAM shows a potentially nasty situation across Central Oklahoma on Thursday. It does have temperatures hovering near freezing, but if those were one to two degrees too warm, somebody would be getting a nasty ice event. FWIW the 0Z HRRR out to 12Z Thursday is even slower than the NAM with the upper-level low.

What a let down after 0Z guidance last night for Central Oklahoma. Another big bust.

After the early December model clusterbomb, I certainly understand offices being skeptical. Assuming deterministic models and their ensembles come into decent agreement tonight I'd expect various winter weather products to be issued by the midnight crews. Texas/Oklahoma offices have been great with the collaboration conferences this year, so whatever eventually gets issued will be done in a regional fashion with the morning forecasts.

I'll probably hit the wind threat in my forecasts tomorrow with a low-chance of a rain/snow mix as precipitation ends from west to east across Central/Eastern OK into Texoma. I won't even mention accumulations (if at all) until Wednesday at the earliest. A cold core upper low is a weatherman's woe - and usually, do produce big surprises in the winter precipitation department. Combined with the anticipated wind, it wouldn't take much snow to create 'official' blizzard conditions in a few spots.

06Z NAM gives OKC 1.8"-2" of liquid QPF between 15Z Saturday and 03Z Sunday. That would be an insane amount of sleet and/or snow. FWIW the NAM decided to give OKC 26" of snow this run. It has the backside snow dropping 1-2" an hour snowfall well into the evening.

0Z NAM was a bit warmer for Central Oklahoma. That would keep the heaviest ice on the northern side of I-44 corridor (a 20-30 mile shift north). It also drops an insane amount of snow on the back of the slow. FWIW: It gives Shamrock, Texas almost 30" of snow. At least a foot across most of Oklahoma (north of the freeze line). Let's see what the 06Z HRRR going out to 6 AM Friday has for surface temperatures. 0Z GFS was a good sign for snow lovers. I'm glad y'all up in SW MO are going to get some (based off this run).

Area Forecast Discussion National Weather Service Norman OK 332 PM CST Mon Dec 3 2018 .DISCUSSION... Obviously the primary focus is on a potentially impactful winter weather event late this week into the weekend. A more more detailed discussion of the meteorology, uncertainties, confidence, etc., can be found below, but first a few key points: - Dry/uneventful weather with below normal temperatures and a gradual warming trend through mid-week. - Next round of precipitation expected to start Thursday, with coverage/probabilities increasing substantially Thursday night into Friday, lasting through Saturday. - Shallow cold surface layer starts to transition rain into freezing rain and sleet Thursday night into Friday across at least the northern 2/3rds of the area. A transition to snow is expected deeper in the colder air across northern Oklahoma. - As cold advection continues and sub-freezing temperatures deepen with cooling aloft Friday night into Saturday, snow will become the dominate precipitation type across at least the northwest half of the area. - Given the uncertainties we just have two rather vague graphics out on precipitation type for now, and are beginning to message safety/preparedness. *The above describes the most likely scenario. Although confidence at this time range is slightly above average, there are still aspects of this system that are quite uncertain--especially temperatures. Meteorological Analysis: WV loop and 500-mb analysis show broad cyclonic flow across much of the country. A departing shortwave that was accompanied by a period of ascent and deeper mid-level saturation has moved east of the area. Periods of mid-level radar returns from virga, or perhaps brief non-measurable precipitation have ended as a result. An extensive area of low stratus from the northern Plains and Midwest slowly crept southward through across northern Oklahoma this morning and has halted near I-40 this afternoon. To its north, temperatures are colder than previously anticipated, with only modest warming across southern portions of the area that have been mostly clear. Northerly winds will decrease tomorrow and become light or even become southerly across western sections of the area. Temperatures should be slightly warmer, though southerly warm advection/downslope regime is not expected to kick in for a more significant warmup. Meanwhile, another weak perturbation in west-northwesterly flow aloft should bring additional mid-level cloud cover to mainly norther portions of the area, probably oriented along a ~500-mb frontogenesis band oriented west-northwest to east-southeast across the area. This saturation shouldn`t be deep enough for precipitation but similar to this last system, some virga or perhaps very light non-measurable precipitation may occur. Again, this should be close to the Kansas border. Wednesday, southwesterly 850-mb flow strengthens and we should warm to at least early December climo temperatures. It`s possible temperatures could exceed current forecast values which were not changes from model consensus blends. Northern stream shortwave activity will send a cold surge(s) southward toward the area late in the week. The first cold front is expected to move through later in the day Thursday. Precipitation chances near/ahead of the front should be minimal until large scale ascent increases markedly toward the predawn hours Friday morning, and especially during the day Friday. Thermal profiles in forecast soundings suggest light freezing rain where temperatures fall below freezing Thursday night. This would be generally near and north of the I-40 corridor, most likely. On Friday, deepening/digging mid-upper low will move east across Baja California. Mid-level height falls and large scale ascent will increase across the area. Isentropic ascent will strengthen as southerly flow increases atop cold shallow air mass in response to entrance region of powerful upper jet shifting northeastward. The degree of cold air at the surface will dictate precipitation type. Models have been fairly consistent with the track of deep low to our south and enhancement of north-northeasterly surface flow maintaining these cold surface temperatures. But details with magnitude of upstream cold air will be better understood once model run-to-run consistency with northern stream shortwave activity improves. The most optimal icing setup for our area happens with a pronounced northern stream wave that is able to dislodge a significant artic air mass and send it south before a lagging southern stream system approaches our area. In this case, the two waves aren`t in phase optimally and the cP surge(s) aren`t particularly cold. So, efficient icing from low-mid 20F temperatures isn`t expected. Rather, some impacts in the form of elevated surfaces accumulating ice may occur, but rather inefficiently as much of the freezing rain should occur with fairly warm temperatures right around freezing. It`s worth noting that most deterministic and ensemble guidance is still fairly tightly clustered on storm total QPF ranging from around 2.0" in the southeast to around 0.5" in the northwest. So, confidence in the synoptic scale pattern and probabilities of precipitation are above normal for this time range. It`s the temperature forecast, and how critical it will be given the position of the 32F line that is less confident. Here are a couple possible scenarios that could deviate from current expectations: 1) If northern stream shortwaves are more optimally timed and more substantially amplified sending colder air southward, icing potential will increase. This is the worst case scenario for impacts, but seems unlikely at this point. 2) If the southern stream system digs further and closes off more, thereby slowing some, we could see more significant preceding warm advection and more of the area receiving rain. This is the best case scenario for impacts as rain-ice-snow transition would be quicker. The 03.12 ECMWF was slightly slower/deeper and warmer which would support scenario #2 above, but unfortunately this appears to be an outlier among its ensembles when we compare to the ECMWF-ensemble mean. So it doesn`t appear to be a trend that we can lock onto at this point. BRB

Well, that was a rather interesting last two hours in D/FW...

This evening's 0Z NAM, 3KMNAM, and GFS indicate the potential for a significant ice storm across parts of the Big Country, Northwest Texas, into portions of Oklahoma. I haven't looked farther north/east. I wouldn't be surprised to see some winter storm watches (prelude to any ice storm warnings) in the Tuesday morning packages.

I'm getting pictures of accumulating sleet and light snow on cars and elevated objects in North Dallas and up in McKinney (380/75 area). Minor accumulations, but enough to keep roads wet. Wet roads with temperatures falling into the mid-20s in the next few hours could cause a flash-freeze (similar to what happened in BHM and ATL a few years back). That's my big worry for the next few hours. Anything that falls, even with surface temperatures below freezing, will probably melt as it hits surface roads and bridges. Soil temperatures are still around 40 degrees. That sleet/snow melts and makes the roads wet. Once surface temperatures fall to 25-26 degrees (or lower) those wet spots could easily flash-freeze into pure ice, especially on bridges and elevated roadways (which D/FW does not have a shortage of).

D/FW is going to have some really big problems if that sleet doesn't stop in the next hour. Lots of pictures coming in showing wet roads (since sleet/snow melting on contact). All that is going to flash-freeze once we get into the middle 20s, which is only 2-3 hours away.

The HRRRx (the HRRR experimental version) has done well in the past; so it is definitely worth watching as we get in operational range of the current HRRR. Remember that with surface temperatures falling into the 20s it won't take much precipitation to cause major travel problems. I'm also concerned with the potential for enhanced sleet bands across South-Central Texas. Some models have been hitting Austin and San Antonio pretty hard with sleet on Tuesday.

The benefit of living in Norman is one doesn't really have to "go out" per say. Just chill at home till 3-4PM. If it looks like storms may pop, drive an hour. Otherwise, continue on your day.

Sunday is crap. High signal from CIPS of severe from OK up to IA, but the tornado output is almost completely blank. Another good day to sit at home (or near it). Veered LLJ, marginal moisture return in terms of depth, and timing issues.

It'll Ben interesting to see what impact, if any, the very warm GOM SSTs have on moisture return.

My concern level is going up for this evening in the Big Country into North Texas. Several high-res models start popping off storms near the warm front. If the HRRR is correct the highest threat will be around the D/FW Metroplex in the middle of a playoff game. Others are a bit further south and west.

This scenario would probably result in a decent severe weather threat for parts of Dixie Alley.

It used to be the same way back on EasternWX many years ago. Not much to talk about in the summer.

Perhaps instead of cluttering a thread that will undoubtedly go in the archive with an off-topic discussion on sheltering practices, it would be better to just create a separate thread for that?

I was around for May 4, 2007 when the Greensburg, KS Tornado struck. I remember seeing an image of the Normalized Rotation (NROT) in 3D and thought it couldn't get any more impressive then that. I was wrong... This is as the tornado was passing over Tuscaloosa. I've never seen such a violent, deep mesocyclone indicated like this before using this product.