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DanLarsen34

January 10-11 Severe Weather Threat

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Thought I’d get a thread going for January 10-11. SPC already has 15% threat areas for next Friday and Saturday, January 10-11, for much of the gulf coast. Threat starts in the Texas, Arkansas, and Louisiana area on Friday, then shifts to Mississippi and Alabama on Saturday. Could this be our first severe weather event of the decade?

478702A8-DFC6-498E-81C0-FE1FAC406DA0.gif

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As mentioned above, SPC has added a 30% contour for Friday for the Arklatex region. Discussion shows they’re quite bold on the warm sector that will be in place that day. Instability/shear combo will be quite impressive 
 

Saturday stays at 15%, but the risk area has been expanded a bit with SPC hinting at a possible upgrade in the next outlook. 

700113DE-3F22-4AB0-9716-88583E81D60A.gif

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Pretty neat that there's a legit EML for this one . . . could favor a more discrete storm mode than is typical for outbreaks this time of year.

 

180871_trj001.gif

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As mentioned above, I’m pretty impressed with the forecasted EML on Friday. Several point soundings indicate 700-500 mb lapse rates exceeding 8 C/km and a pretty notable cap early on which could help limit junk convection.

It remains to be seen how the wind fields evolve, but just seeing that capping/steep lapse rates in conjunction with a seasonably moist warm sector with mid-upper 60s dewpoints has me raising eyebrows.

I also have concerns about overnight Friday into Saturday morning, as the trough swings negative tilt and the wind fields really ramp up across the Lower Mississippi and Tennessee Valleys. That actually may end up being the best juxtaposition of strong low level shear and rich low level moisture, but obviously there are still changes ahead. Overnight sig severe and Dixie is tailor made in the cold season (see 12/16/19 and 1/21-22/2017 for a couple of recent examples).

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As an interesting side note, you can use the PivotalWeather ECMWF clickable soundings to check for severe weather parameters. 

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The lapse rates on the GFS for Friday afternoon/evening in the Arklatex/lower MS Valley made me sit up and take notice. Those are often the make-or-breaker in low-CAPE cool season setups.

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2 hours ago, cheese007 said:

30% contour added for Saturday. Severe season looking to be off to one hall of an early start

Pretty sizable risk area at that.
 

Friday’s outlook has shifted west towards the Dallas/Fort Worth area and I-35. 

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Big sig severe contour in the southern portion of the enhanced risk. Includes 7 million+ folks. 30% across MS/AL for D4 as well

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Probably stating the obvious here, but the ceiling of Friday and Saturday is going to hinge on storm mode. Both days have the potential for discrete convection ahead of an intense QLCS. Any discrete cells on either day would be capable of producing significant tornadoes. 
 

Either way, we’re looking at a pretty significant two day period for severe weather.

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41 minutes ago, DanLarsen34 said:

Probably stating the obvious here, but the ceiling of Friday and Saturday is going to hinge on storm mode. Both days have the potential for discrete convection ahead of an intense QLCS. Any discrete cells on either day would be capable of producing significant tornadoes. 
 

Either way, we’re looking at a pretty significant two day period for severe weather.

Yeah I think this is worth highlighting - we'll have at least a handful of tornado reports but like always in this region, storm mode is king, and will be the difference in determining if this is a memorable vs. a unremarkable event.

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Friday afternoon over E. Texas, EHI ticked up again on the 12Z NAM but VBV is quite pronounced above 850mb in forecast soundings from the most unstable areas. That's not a look for sustained open warm sector tornadic supercells. There could be some pretty potent QLCS tornadoes though with the amount of turning below 850mb.

nam_2020010812_060_31.09--96.23.png

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15 minutes ago, Bob's Burgers said:

The euro is the new hype machine lol

 

 

euro stpmax.png

Still quite a bit of VBV in this sounding.  Shear profiles are progged to improve somewhat through the day Saturday in southern parts of MS/AL and the Florida panhandle. I think that's where/when any long-track, EF3+ supercell tornadoes will be with this event if things stand as they are.

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12 minutes ago, CheeselandSkies said:

Friday afternoon over E. Texas, EHI ticked up again on the 12Z NAM but VBV is quite pronounced above 850mb in forecast soundings from the most unstable areas. That's not a look for sustained open warm sector tornadic supercells. There could be some pretty potent QLCS tornadoes though with the amount of turning below 850mb.

nam_2020010812_060_31.09--96.23.png

On this point: The storm mode is definitely an issue, but given the strength of the low level jet, this could still be a prolific tornado producer. We’re looking at 850 mb winds between 60-80 knots Friday and Saturday (latter values have popped up for Saturday across Alabama). Several embedded tornadoes, including significant tornadoes, are a distinct possibility. 
 

Some of the CAPE and STP values showing up in Texas on Friday are crazy for early January too. I think the CAPE record for this time of the year in the Dallas area was set around Christmas of 2016 in a similarly anomalous winter set-up. 

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Yeah, you never know when those embedded tornadoes get strong. Think El Reno and Rushton, LA from last year -- both killer EF-3's in squall lines at night. 

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One thing to keep an eye on is the mean wind being very close to or on the hodograph. That will cause storms to have trouble turning right and starting to strongly rotate.

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Strange that there's no mention of this potentially significant severe set up in the Southeastern Forum. They're all worried about some flurries around the 15th or something.

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Area Forecast Discussion
National Weather Service Birmingham AL
607 AM CST Wed Jan 8 2020
Friday will mark the beginning of an extended period of unsettled
weather as a trough strengthens and becomes increasingly dynamic
over Texas and New Mexico. Strengthening southerly flow will lead
to isentropic lift as a warm sector begins to advance northward.
Widespread showers with isolated embedded elevated thunderstorms
are expected across much of the forecast area on Friday.

As the upper-level trough transitions from a neutral to negative
tilt Friday night, rapid pressure falls are expected near the
Mississippi River at 6 AM Saturday. An extremely strong low-level
jet is anticipated in advance of a well-organized QLCS, with mid
to upper 60s dewpoints overspreading the forecast area by noon
Saturday. As it stands, a significant severe weather event appears
likely beginning as early as 9 AM in our western counties. SBCAPE
is currently modeled at 500-1000 J/kg by most model guidance, but
my hunch is that these values may be a little on the low side due
to the effects of erroneous-looking QPF as noted in the ECMWF
data. Even taking CAPE a face value, strong forcing combined with
extreme low-level winds and wind shear would result in a QLCS
capable of producing widespread damaging winds and embedded
tornadoes. The ECMWF shows a wide swath of 70-80 kt 700mb winds
with pockets up to 100 kts, meaning that a derecho cannot be ruled
out particularly across our northwestern counties. The potential
for supercells ahead of the QLCS will depend on the state of the
warm sector. If the warm sector is relatively uncontaminated and
the current timing holds true, temperatures would rise into the
70-74F range during the late morning and early afternoon hours,
aiding in the formation of cellular convection ahead of the QLCS.
In order for any cellular activity to become tornadic in the
presence of extreme wind shear, robust updrafts will be required.
Otherwise, these updrafts will be torn apart.

This system should exit the area late Saturday afternoon or
Saturday evening, and dry conditions expected on Sunday with the
exception of a slight chance of showers across our southeastern
counties. Here the front is expected to stall and return northward
as a warm front Sunday afternoon into Monday. Showers and embedded
thunderstorms should expand in coverage and move northward to
near I-59 on Monday. These high rain chances will continue into
Tuesday across most of the forecast area.

87/Grantham

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What BMX said is very true.  The QLCS comes through too early Saturday for heating to be maximized with current timing so warm sector updrafts may not be robust enough to survive. This a could result in a very impressive QLCS and I personally think (Currently) damaging winds/embedded tors are the greatest threat Saturday. 

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