2018 severe wx/chase season discussion

[Todd Lemery]

I plan on heading down this coming Wednesday with the GFS pegging a slow moving low (like Mark referenced) possibly making chaseable days Thurs, Fri, and Sat. The biggest selling point for me this far out is GFS and CFS starting to agree on moisture return and I haven’t been out yet, missing the last setup that I just couldn’t go to. It’s a dart throw farther down the line, but CFS is hinting at some more Northern opportunities possibly starting as soon as the 15th.

 

[Quincy Vagell]

It looks like the atmosphere is making baby steps toward a more active pattern. Despite increased activity, it looks like the next week will probably run near or slightly below average with respect to climatology. That could change if the pattern late this week looks more significant.

Shortwave energy is progged to pivot from the northern/central Plains into the Midwest/Great Lakes around the middle of this week. Tuesday may feature some localized and/or sporadic severe, but limited boundary layer moisture and capping suggests that this will probably not feature any "enhanced" chase prospects. Wednesday looks a bit more interesting, in a northwest flow regime, coincident with improved boundary layer moisture and at least modestly favorable deep layer wind fields. With that said, the mid-Mississippi Valley/Ohio Valley region looks favored, which may be out of range for those who want to stay focused on the Plains for the days following. Thursday looks like a transition day, but details are tough at this point. Maybe it features isolated severe in the High Plains or even along a warm front farther east, but only time will tell.

Friday-Saturday looks more likely to feature at least one, if not two chase-worthy setups in the Plains. Details will certainly change, but a positively tilted trough is modeled to swing from the Four Corners region into the High Plains through the period. The setup is not all that different from last week, although the speed of the system looks faster and troughing not as vigorous.

Medium to long-range trends for the following week (especially mid to late next week) are increasingly encouraging. Perhaps the Lower 48 will finally be moving into a pattern with more consistent/substantial troughing across the West. It's been a long time coming, but in a way, it's better to see this pattern during the second half of May, rather than earlier in the season.

Anyone with chasecations scheduled for this week should enjoy at least a chase or two; possibly more if things work out just right. Next week looks even more active and although it's tough to say for late May, climatology and ensemble data suggest the signs are encouraging.

Thoughts about the chase tours:
Even though this year has been quieter than most, even climatology suggests that April through the first week of May is risky at best when it comes to anything more than isolated chase setups in the Plains. Anyone who chasecations or participates in a tour this early in the year should be advised that even climatology suggests that half or more of days between April and the first week of May will not be chase days. The only year in recent memory that I can think of that featured consistent early May activity was 2007. Even this year was a bit of an anomaly with having 3-4 chase days in a row in the Plains. Late April is usually active (not this year), but that activity is most consistently found over poor chase terrain, from the Ozarks into Dixie. It's not common for extended chase periods until at least the second week of May.

Bottom line, if you're going to block out a week in late April/early May, be ready for some backup plans with sight seeing, checking out restaurants, etc. I would hope that the tour groups are aware of climatology. I'm sure they are and after all, they probably make money anyway, even if a tour group doesn't see much for a week, since they're usually booked well in advance.

 

[Brett Roberts]

Thoughts about the chase tours:
Even though this year has been quieter than most, even climatology suggests that April through the first week of May is risky at best when it comes to anything more than isolated chase setups in the Plains. Anyone who chasecations or participates in a tour this early in the year should be advised that even climatology suggests that half or more of days between April and the first week of May will not be chase days. The only year in recent memory that I can think of that featured consistent early May activity was 2007. Even this year was a bit of an anomaly with having 3-4 chase days in a row in the Plains. Late April is usually active (not this year), but that activity is most consistently found over poor chase terrain, from the Ozarks into Dixie. It's not common for extended chase periods until at least the second week of May.

Bottom line, if you're going to block out a week in late April/early May, be ready for some backup plans with sight seeing, checking out restaurants, etc. I would hope that the tour groups are aware of climatology. I'm sure they are and after all, they probably make money anyway, even if a tour group doesn't see much for a week, since they're usually booked well in advance.

This bears repeating: if you're booking a chasecation or tour months in advance, and you're only going to be out 7-10 days or less, it makes no sense to go earlier than mid-May. The ramp up in consistent Plains chase opportunities in a typical year just between May 1 and May 15 is very steep; and that's saying nothing of how profoundly unreliable any given period in April is, speaking from climo.

It seems like folks who are new to chasing and live far from the Alley have a tendency to gravitate toward this late April/early May period for their first foray into the hobby. This is strange to those of us who have been chasing for awhile; the only hypothesis I can come up with is that a few legendary days -- namely, 4/26/91 and 5/3/99 -- completely dominate the public consciousness surrounding Plains chasing. To reiterate what Quincy said, I can't think of a truly memorable, quality chase sequence in the first week of May for the past eleven years. Plenty of years are almost completely dead.

 

[Eric Bucsela]

This bears repeating: if you're booking a chasecation or tour months in advance, and you're only going to be out 7-10 days or less, it makes no sense to go earlier than mid-May. The ramp up in consistent Plains chase opportunities in a typical year just between May 1 and May 15 is very steep; and that's saying nothing of how profoundly unreliable any given period in April is, speaking from climo.

It seems like folks who are new to chasing and live far from the Alley have a tendency to gravitate toward this late April/early May period for their first foray into the hobby. This is strange to those of us who have been chasing for awhile; the only hypothesis I can come up with is that a few legendary days -- namely, 4/26/91 and 5/3/99 -- completely dominate the public consciousness surrounding Plains chasing. To reiterate what Quincy said, I can't think of a truly memorable, quality chase sequence in the first week of May for the past eleven years. Plenty of years are almost completely dead.

Public perception of April as “Tornado Month” might simply follow from the fact that tornadoes rarely make the news unless they cause fatalities. Tornado deaths peak in April (mainly in populous eastern states).

 

[John Homenuk]

This bears repeating: if you're booking a chasecation or tour months in advance, and you're only going to be out 7-10 days or less, it makes no sense to go earlier than mid-May. The ramp up in consistent Plains chase opportunities in a typical year just between May 1 and May 15 is very steep; and that's saying nothing of how profoundly unreliable any given period in April is, speaking from climo.

It seems like folks who are new to chasing and live far from the Alley have a tendency to gravitate toward this late April/early May period for their first foray into the hobby. This is strange to those of us who have been chasing for awhile; the only hypothesis I can come up with is that a few legendary days -- namely, 4/26/91 and 5/3/99 -- completely dominate the public consciousness surrounding Plains chasing. To reiterate what Quincy said, I can't think of a truly memorable, quality chase sequence in the first week of May for the past eleven years. Plenty of years are almost completely dead.

Yeah, this is a great point. This was my first year planning an actual chasecation but there was never any doubt in my mind that it would be targeted near Memorial Day. The increase in activity on a regional scale is so dramatic during that time frame when compared with dates earlier in the month. From a logistical standpoint it offers a much higher percentage chance of at least seeing something (structure, supercells, etc) as opposed to a higher percentage of a complete whiff earlier in the month.

I also think you're on to something with folks looking for the grand slam days that have come a bit earlier as of late.

 

[Paul Knightley]

Both CFS and ECMWF continue to show an active MJO starting up and then moving toward phase 2 mid-late month, with ECMWF doing this more quickly. Analogues suggest that a western US trough is favoured in such a scenario, so it could well be that mid-late May shapes up to be quite active.

 

[Andy Wehrle]

After waffling to a disgusting massive western ridge/very anemic H5 flow south of the Canadian border pattern for awhile, CFS last couple runs is back to showing a fair amount of potential for my window (May 18-26).

This may be better suited to another thread, but my curiosity is piqued by many of the CFS supercell composite maps showing a large spike at 06Z vs. the preceding 00Z map (scrub through the current 00Z 05/7 run on the COD website and you'll see what I mean, although I've seen this on many prior runs before).

I know the model is quite coarse even compared to the operational globals (GFS and EURO), but what exactly is it seeing with such a sharp spike in values well removed from the diurnal peak for severe weather? Is it even capable of resolving things like increasing CINH/ decoupling boundary layer after dark? If this kind of solution holds, should it be taken seriously as representative of a significant late night severe threat?

 

[John Homenuk]

Evening EPS against the 1962/1958 analog package that we discussed a while back. Pretty cool to see this. Having it come to fruition is a whole other battle

 

[John Homenuk]

After waffling to a disgusting massive western ridge/very anemic H5 flow south of the Canadian border pattern for awhile, CFS last couple runs is back to showing a fair amount of potential for my window (May 18-26).

This may be better suited to another thread, but my curiosity is piqued by many of the CFS supercell composite maps showing a large spike at 06Z vs. the preceding 00Z map (scrub through the current 00Z 05/7 run on the COD website and you'll see what I mean, although I've seen this on many prior runs before).

I know the model is quite coarse even compared to the operational globals (GFS and EURO), but what exactly is it seeing with such a sharp spike in values well removed from the diurnal peak for severe weather? Is it even capable of resolving things like increasing CINH/ decoupling boundary layer after dark? If this kind of solution holds, should it be taken seriously as representative of a significant late night severe threat?

I'd assume the model is showing the last 6 hours of SCP, no? If that is the case, perhaps it's going with the maximum SCP from 00z-03z-ish? That might help to explain some of the issue but it still doesn't make a ton of sense as the highest values still typically come from 21z-00z anyways. Just brainstorming.

 

[Jeff House]

If it is not a 6-hour max, low level jet is the only thing I can think of for 06Z Supercell Comp ramping up on the CFS. Otherwise, it's American mid-range modeling, lol! What would the ECMWF say?

Speaking of the ECMWF, I'm looking forwrad to its weekly product tonight. Ensembles alone show variability the next 15 days. Plains has a system this weekend, but Sunday is Mother's Day. Late next week should have another. Hints of more show after May 21.

MJO and Pacific convection is still a mess. Need the Central Pac to quiet down, and that IO convection to come out into the West Pac. Still it's May. If the Plains has systems, the Plains will have at least some action.

 

[Mark Blue]

This is strange to those of us who have been chasing for awhile; the only hypothesis I can come up with is that a few legendary days -- namely, 4/26/91 and 5/3/99 -- completely dominate the public consciousness surrounding Plains chasing.

Even more of an outlier event was Hesston on 3/13/90, but chase tours don’t operate that early, although Roger Hill will run a short notice tour no matter what time of the year it is. Another early May significant event was the May 6, 1975, Omaha tornado, yet another event prior to chase tours. These dates probably aren’t at the forefront of anyone’s mind though since they were so long ago. I guess the Super Outbreak is another early event from April 3, 1974. Maybe the folks who go on these early tour slots are the same ones who would bet on the 99-1 odds horse named Instilled Regard at the Kentucky Derby last weekend!

 

[Andy Wehrle]

I believe I've posted this before but growing up and getting interested in severe weather/chasing in the '90s definitely skewed my perception that April should be much more prime season in the southern Plains than it really is. 1990-93 all had some notable outbreaks in different regions/at different times of the year but of course Andover, Red Rock, the turnpike tornado of 4/26 plus the Pond Creek, OK tornado of 4/12/91 were the ones that filled TV and home video documentaries, and were prominently discussed in publications such as Grazulis' The Tornado: Nature's Ultimate Windstorm and Bluestein's Tornado Alley: Monster Storms of the Great Plains.

Add in other historic and devastating April events discussed by those and other giants of severe weather research such as the Red River Valley outbreak (4/10/79), Woodward (1947), and...yeah.

 

[Brandon Centeno]

After waffling to a disgusting massive western ridge/very anemic H5 flow south of the Canadian border pattern for awhile, CFS last couple runs is back to showing a fair amount of potential for my window (May 18-26).

This may be better suited to another thread, but my curiosity is piqued by many of the CFS supercell composite maps showing a large spike at 06Z vs. the preceding 00Z map (scrub through the current 00Z 05/7 run on the COD website and you'll see what I mean, although I've seen this on many prior runs before).

I know the model is quite coarse even compared to the operational globals (GFS and EURO), but what exactly is it seeing with such a sharp spike in values well removed from the diurnal peak for severe weather? Is it even capable of resolving things like increasing CINH/ decoupling boundary layer after dark? If this kind of solution holds, should it be taken seriously as representative of a significant late night severe threat?

Consider the formula:
SCP = (muCAPE / 1000 J kg-1) * (ESRH / 50 m2 s-2) * (EBWD / 20 m s-1)

You’ll notice there is no CIN factor. MUCAPE can be very high even in a strongly capped 06z profile. The calculation for CFS likely also uses 0-3 km SRH instead of ESRH, and 0-6 km BWD. The culmination is very high values at 06z in certain cases. This is not a depiction of sig severe threat overnight typically, but just noise brought upon by the LLJ, paired with strong (but capped) potential instability associated with the EML.

 

[Brandon Centeno]

Re: early season, I definitely think there is an allure to the strong waves of April, the potential for violent tornadoes, etc among many. Early season offers some very strong systems, though instability and abundant moisture rarely come by.

 

[Warren Faidley]

Interesting note. The GFS has formed a tropical system off the Yucatán Peninsula over several runs (on and off). It's way out there in la la land at 300+ hours, but interesting to watch, especially if something did form further north and alter Gulf trajectories, as one run of the GFS showed a day or two ago. With a low shear environment like last year, who knows.