Severe WX January 10-12, 2020 Severe Weather Forecast Thread

[Richardjacks]

The Euro keeps saying Mississippians should find a bunker Friday night, yeesh. Remains the most aggressive model. NAM doesn't want to bring dews in as far as the Euro thinks into AL which makes me question isolated cell potential buuuut that's just the NAM for now I think; the timing also says late morning but WAA would override time of day with a system this potent.

right, we are in the long range for NAM still, I would not let my guard down, as the NAM could be underplaying moisture return for Alabama.

 

[WesL]

Just wanted to add this GFS run to the forum so we would have it for the future. Highly encourage everyone to save this type of data as an attachment so that we can always refer to it later on. Linking to a website is great but as time goes on those links will expire and go away.




NAM

 

[Equus]

I need to start throwing the huge stash of model runs/soundings/radar images that always accumulates on my phone after a big event online somewhere for future reference honestly... I oughta go do that sometime

 

[SilentShadow87]

So is it all hinging on the dews making it far enough east at this point?

 

[Equus]

Looking like it... NAM vs Euro on that, at this point; BMX saying cellular activity hinges on that, and actually using the word derecho now

From BMX:

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 tothe 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.

 

[Gail]

I'm in a weird area where I'm on the tip of the Jackson, Memphis, and Birmingham NWS coverage areas (far Northern Lowndes County, MS). I'm technically in the Jackson coverage area, but I check all three. The word Derecho has me nervous. Last time we had one, we were without power for about three weeks. If that ice storm in voodoo land does happen to verify (doubt it will), we're out of luck since our entire house is electric - heat and oven. :-/ Maybe a generator would be a good investment?

 

[Equus]

I live in a house deep in the woods surrounded by tall white oaks, some still with root damage from construction, and a fragile maple and pine directly west of the house, so I'm always on edge in big wind events. Derecho in March 2013 took down about two dozen trees (a domino effect starting with the pines, of course) very close to the house.

 

[Kory]

UKMET is quite cellular. Begins to pivot the trough negatively tilt and then ejects its a little slower. Allows for upper level winds to veer and storm mode to change.

 

[ARCC]

So is it all hinging on the dews making it far enough east at this point?

No, problems with lapse rates and mid-level warm air/capping.

 

[darkskys25]

UKMET is quite cellular. Begins to pivot the trough negatively tilt and then ejects its a little slower. Allows for upper level winds to veer and storm mode to change.

Euro and ukmet vs the nam and gfs. I think thats why everyone is so torn. I mean at face value this looks very significant but it seems to hinge on the orientation of the trough and how fast it rotates out. I think the most likely solution is a qlcs but nothing extreme. I think the trough is too progressive to allow for a quality warm sector needed for a hi end event. When you look at the upper dynamics of the euro its pure weather porn. But the gfs and nam i think bring us back to reality. I guess we will know more when looking at the hi res models when they come out. The main event i think is the qlcs and if its significant or not. Tornadoes will def be possible in the line given more robust instability. Otherwise this isnt a high end event imho.

 

[Equus]

I dunno the GFS has been sleeping a little on these cold season events, Euro definitely is painting armageddon and is surely overdoing it but probably closer to in between the two extremes. Totally can see the NAM solution of less instability but the Euro did pretty well with 12/16 (which the GFS basically slept on) so I'm not gonna let down my guard just in case

 

[ARCC]

I dunno the GFS has been sleeping a little on these cold season events, Euro definitely is painting armageddon and is surely overdoing it but probably closer to in between the two extremes. Totally can see the NAM solution of less instability but the Euro did pretty well with 12/16 (which the GFS basically slept on) so I'm not gonna let down my guard just in case

Looking at the 12z Euro soundings across central MS, the NAM is actually slightly more impressive. Neither painting anything extreme.

 

[Equus]

Even the GFS is showing reasonable soundings with believable instability now so I think we may be starting the slow march towards a better consensus, now we look for the timing to line up and wait on the CAMs lol

 

[Kory]

Euro and ukmet vs the nam and gfs. I think thats why everyone is so torn. I mean at face value this looks very significant but it seems to hinge on the orientation of the trough and how fast it rotates out. I think the most likely solution is a qlcs but nothing extreme. I think the trough is too progressive to allow for a quality warm sector needed for a hi end event. When you look at the upper dynamics of the euro its pure weather porn. But the gfs and nam i think bring us back to reality. I guess we will know more when looking at the hi res models when they come out. The main event i think is the qlcs and if its significant or not. Tornadoes will def be possible in the line given more robust instability. Otherwise this isnt a high end event imho.

The NAM and GFS *ARE* high end QLCS parameters. The euro and UKMET indicate more cellular. This will be significant.

 

[Xenesthis]

The NAM and GFS *ARE* high end QLCS parameters. The euro and UKMET indicate more cellular. This will be significant.

Kory,
How far north do you think this threat for tornadoes will get?

 

[darkskys25]

The NAM and GFS *ARE* high end QLCS parameters. The euro and UKMET indicate more cellular. This will be significant.

I

The NAM and GFS *ARE* high end QLCS parameters. The euro and UKMET indicate more cellular. This will be significant.

Depends on your definition of high end. I think of high end a solid moderate or high risk. I think thats very debatable.

 

[Kory]

You won’t need raging CAPE values to get the 70-80kt LLJ to the surface. You might need a little bit more CAPE than currently projected over the warm sector north of 20/59 to get supercells to maintain their updrafts from getting ripped apart.

300-600 J/KG CAPE as is shown ahead of the line will be more than enough to yield a high end damaging wind threat.

It is such a backwards way of thinking that linear threats are less threatening. The morning round of 4/27 had not a single discrete cell yet was quite destructive. I do not think the instability will be as high as that event but some of the shear values we are seeing are quite comparable.

 

[akt1985]

Birmingham is mentioning a Derecho, I thought those primarily occurred during the warm season.

 

[Equus]

As long as the parameters are met season wouldn't seem to be a big issue; with near 100kt 700mb winds and unseasonably high dew points I'd say we've got a good shot at hitting derecho qualifications somewhere.

On that note, if those parameters stay intact I fully expect a 45/hatch moderate risk for wind on Saturday. A derecho forecast usually calls for probs that high, though any uncertainty that a derecho may not develop would probably hold it at 30. The only real question at this point is the possibility for discrete development which might also up the tornado probs. Given the prolific tornado production of QLCS with hodos like are being modeled, even as high as a 10-15% would probably be a safe bet at the heart of the QLCS regardless of supercell development.

 

[andyhb]

Birmingham is mentioning a Derecho, I thought those primarily occurred during the warm season.

Serial derechos, those that usually are generated by a squall line, are more common when jet dynamics are intense, e.g. in the cold season and early spring.