Weekend Severe Weather Threat

[DNewman]

Can anyone who is experienced in severe weather forecasting help me with the weekend forecast for severe weather for Texas? Some meteorologists and even the weather channel has expressed the fact that there is the potential for severe weather this weekend, especially for the Dallas area. How does the potential for a severe weather outbreak look? Could we see tornadoes here as well? Please keep me updated ASA you find new information, because this weekend looks like a possible opportunity for Texas twisters especially with all the warm moist and unstable air I place!

 

[Bob Hartig]

Dominique, this far from the weekend, I doubt that anyone on Stormtrack can give you any better insights than you've already gotten from listening to the the meteorologists you've mentioned and from The Weather Channel. It's just too far out to say with any certainty what, if anything, will happen, or where.

If you're not familiar with the SPC Convective Outlooks, then they would be a great place for you to start learning more about the language and the reasoning of severe weather forecasting. Here is the link: http://www.spc.noaa.gov/products/outlook/ I'm pointing you there because I think you need to start asking some other questions besides whether there will be tornadoes and where they might be. You've already gotten the weather report; you don't need anyone here to repeat it for you. What you now want to start considering is why there's talk of a possible severe event this weekend. In other words, if you're truly interested in storm chasing and severe weather, then you need to start learning about forecasting--about the four ingredients of instability, moisture, lift, and wind shear; and about the tools of the trade that forecasters use to determine whether and where those ingredients might combine to produce storms and possibly tornadoes, as well as what could keep that from happening. "Why?" and "How?" are important questions for you to start dealing with. And the SPC link I've provided is a good way to get started. The site is updated several times each day, so check it out often. Make sure you READ THE DISCUSSIONS, and watch how they change as the weekend draws closer.

Here is another excellent site where you can learn tons about forecasting principles: http://www.theweatherprediction.com/habyhints/

I hope this helps. Good luck!

 

[Andy Wehrle]

I've been following the model output for this weekend on the UCAR site. Severe weather certainly looks like a possibility, but in my non-expert opinion it doesn't scream tornado outbreak because there appears to be very little turning with height (500 and 850mb wind barbs are almost parallel over the warm sector). There also doesn't appear to be a well-defined surface low, the map doesn't mark the position of one and you have to infer it from the surface wind barbs. Of course, that can always change (in either direction).

 

[Jim Parsons]

Check out some of Tim Vasquezs books on weather....I would start with his "Storm Chasing Handbook". http://www.weathergraphics.com/chasing/

 

[Timothy Finn]

I'm watching this too. I'm planning on going after this if it holds together. The big thing to remember with models this far out, you know where to watch to see if it looks like it will come together or if it will fall apart.

As Andy mentioned, it can go either way this far out, and for me, that's part of the fun. You can watch it come together, get excited, and form a chase strategy, or you can watch it come undone, and analyze the atmosphere to see why it bombed.

Tim

 

[DNewman]

Well Bob I am already quite knowledgable about severe weather, and the various websites for weather updates and valuable information about weather and have done my own research for years especially when it comes to severe weather. I was just asking around to get the publics opinion about the possible severe weather this weekend, and t see what they could have come up with themselves. Its always good to get a second opinion,and It is not that I wanted anyone to repeat the same information to me again because that obviously wouldn't make any sense.But thanks anyway.

 

[DNewman]

I will definitely be analyzing this system as the days progress. Thanks.

 

[Timothy Finn]

I will be more anxious to share strategies and thoughts once this comes into the range of NAM. I've always been sort of leery of GFS.

Tim

 

[Skip Talbot]

Well Bob I am already quite knowledgable about severe weather, and the various websites for weather updates.

I don't think it was anyone's intentions to say, "hey, just go look at SPC." We don't know what level of forecasting knowledge you have and are trying to get you engaged in the forecast discussion.

Could we see tornadoes here as well? ... looks like a possible opportunity for Texas twisters especially with all the warm moist and unstable air I place!

You've mentioned half the ingredients necessary for severe weather. What are the other two? The GFS is showing a positively tilted trough over the southwestern states this weekend with broad southwest flow over Texas and a dryline over central Texas. *If* that verifies, how would that factor into these other two ingredients? As far as tornadoes are concerned, we're looking at a few more parameters like LCL height, low level instability, low level speed and directional shear, boundary locations, and others. While the forecast models can get a decent idea of what the overall pattern might be, they have trouble resolving the finer details this far in advance, and these details play a big part in the tornado potential. This morning's GFS shows southwest flow along the dryline, which will negatively affect low level directional shear for any storms initiating on the dryline. Yesterday it was showing southeast surface winds along the Red River, which would positively affect the low level directional shear. You're definitely on the right track by noticing this upcoming weather system and the need to see how it develops. At almost a week out, however, it's still way too early to be looking at the tornado potential for this setup, given that the models are changing the surface pattern from run to run. I think you can really start seriously gauging the tornado potential for a region maybe 3 days out. For the Dallas area in particular, I think you'll have to wait until Sunday to really tell.

Based off of this morning's GFS, I'd say northeast Texas on Sunday looks like the best bet for supercells, give or take about 400 miles (because the surface features are bouncing around) as the models are forecasting modest, but adequate amounts of instability, a well defined dryline, and strong midlevel flow over this corner of Texas. As far as tornadoes, there may be anywhere from zero to several, but I'd lean toward fewer given the veered wind profile. What about Dallas? You'll want to watch where that dryline's position is being plotted for Sunday afternoon/evening. It's going to move around as the event approaches, and if you're west of it, I think you can rule Dallas out of the severe weather threat.

 

[Bob Hartig]

Well Bob I am already quite knowledgable about severe weather, and the various websites for weather updates and valuable information about weather and have done my own research for years especially when it comes to severe weather. I was just asking around to get the publics opinion about the possible severe weather this weekend, and t see what they could have come up with themselves. Its always good to get a second opinion,and It is not that I wanted anyone to repeat the same information to me again because that obviously wouldn't make any sense.But thanks anyway.

Dominique, I can see how my post may have seemed patronizing to you, and I apologize if parts of it offended you. To be clear, my intention was simply to be helpful, not put you down. Since your original post doesn't speak in terms of what you yourself have observed in the forecast models using terminology that is common to forecast discussions on this forum, it was natural for me to think you might need to get better acquainted with forecasting concepts in order to interact meaningfully with such discussions. If you're already conversant with the various forecast maps and key concepts of ingredients-based forecasting, then I encourage you to share your own thoughts as the models progress, similar to what Andy and Skip have done. Right now, as has been pointed out, the models are bound to slosh around, and we're still waiting on the NAM to kick in.

On a personal level, I learn as much from interacting with forecast discussions as anyone. I'm keen on helping others learn simply because I know how steep my own learning curve was for many years and how much I have yet to learn.

 

[Skip Talbot]

Check out the difference between this morning's and this evening's GFS runs.

That kind of run to run inconsistency is why we generally wait until the event is within a couple days before we seriously start gauging the tornado potential. The dryline plotted in the first plot is now being plotted as a surging cold front, way east of Dallas and northeast Texas. Tomorrow it might be back in Texas again. When the NAM is in range and the GFS aligns with its solution, I think we'll have a better idea of what's going to happen.

 

[Bob Hartig]

Yesterday's 18Z GFS was the last of the bullish CAPE displays. Today's 00Z and 6Z are a world of difference, pushing instability much farther south with a cold front surging toward the Gulf of Mexico. This morning's run locates the dryline in extreme southern TX, with the CF eventually dominating. This is a scenario similar to what NOGAPS has been portraying for a couple days, and it has been less exuberant with the instability. I have to confess that I'm only just getting acquainted with this model since it became a part a of the F5 Data suite a few days ago. It's interesting to see the GFS coming into alignment with it.

The 12Z run is just beginning to show up. Now to see how this morning's sounding affects the picture.

 

[DNewman]

Thanks for the valuable weather info. I guess I shouldn't have come off sounding so uneducated about severe weather in my first post.Anyway I will definitely be tracking the weather situation to unfold for this weekend. Right now the runs and models are just all over the place, and I can certainly agree with you Skip about those GFS runs. It looks to be right now the way some of the latest runs projects, is that there may be a severe threat beginning as early as Saturday night. But again well blow that bridge up when we get there. One thing that ill have to get more familiar with though Bob are the Z time frame, it's so confusing to me trying to remember what each number represents in normal time and with seasonal changes as well. I don't know why SPC and NWS meteorologists use this instead of regular time. It seems much easier.

 

[Skip Talbot]

it's so confusing to me trying to remember what each number represents in normal time and with seasonal changes as well. I don't know why SPC and NWS meteorologists use this instead of regular time. It seems much easier.

Z is +6 right now, and +5 when we change the clocks. Those are the two adjustments you have to remember living in the central time zone. Instead of constantly trying to subtract whenever you see a Z time, if you look at enough weather maps, it becomes automatic in your head (you think, "0z, oh that's 7pm"), or you automatically associate 0z with the evening and 12z with the morning, 18z with noon and 6z with midnight. They use this time zone because it keeps everyone on the same page. It seems easier to you to always use central time, because that's what you're always dealing with. Meteorologists, aviation, and military, however, are constantly working between different timezones, so it would be more difficult for them to use the local time. Meteorologists from all over the world don't want to screw around with whatever local timezone some other meteorologist is on, so they all use the same time. You'll notice that the NWS does use local times for their watch and warning products because those are being consumed by the public.

 

[Andy Wehrle]

GFS is indicating very meager moisture return into the warm sector of this system, except right along the Gulf Coast which is well removed from the strongest upper-level flow. Too bad this isn't May or June and the 65 degree line isn't pulled up as far north as Madison under those 80+ kt southwesterlies at 500mb!

Edit: NAM is no better on dewpoints and shows ZILCH for CAPE at 0Z Sunday (7 PM Saturday).

Edit #2: I made the mistake of ignoring the model output for 12Z (84-hour NAM) since that is not the preferred diurnal timeframe for severe weather, but upon looking at that it does show considerable improvement in dewpoint and CAPE valid for 12Z Sunday morning (over the lower Mississippi Valley and ARKLATX). One more run and it'll be in for Sunday afternoon/evening...