Apr. 2-4 Severe Threat

[Hoosier]

Tuesday might have a shot at some severe in parts of the sub.  How much surface based CAPE is realized is questionable but it's a dynamic looking system with pretty decent mid level lapse rates.

[andyhb]

2 hours ago, Hoosier said:

Tuesday might have a shot at some severe in parts of the sub.  How much surface based CAPE is realized is questionable but it's a dynamic looking system with pretty decent mid level lapse rates.

Shortwave has shifted to be more amplified with time and it looks like at least seasonable moisture will be in place (also with a fairly healthy looking dryslot aloft in the morning associated with the EML). Definitely think there will be a threat, whether there's any tornado potential is up in the air. Should be at least a decent squall though.

[Quincy]

Lapse rates in the 0-3km layer look rather marginal in the 5.5-6 C/km range on the GFS and NAM. Will need better surface heating for larger low level CAPE profiles, as the GFS/NAM show temperatures struggling to reach the mid-60s north of the Ohio River. The 12z Euro is a bit more aggressive in low-level warming, though.

Regardless, deep layer shear is more than adequate for organized convection. Even though mid and upper level winds are largely unidirectional, there is enough strength to the low-level wind profiles to support enlarged 0-3km hodographs, despite SSW/SW flow near the surface. 

The most realistic scenario at this point does look to be a squall line.

[Stebo]

27 minutes ago, Quincy said:

Lapse rates in the 0-3km layer look rather marginal in the 5.5-6 C/km range on the GFS and NAM. Will need better surface heating for larger low level CAPE profiles, as the GFS/NAM show temperatures struggling to reach the mid-60s north of the Ohio River. The 12z Euro is a bit more aggressive in low-level warming, though.

Regardless, deep layer shear is more than adequate for organized convection. Even though mid and upper level winds are largely unidirectional, there is enough strength to the low-level wind profiles to support enlarged 0-3km hodographs, despite SSW/SW flow near the surface. 

The most realistic scenario at this point does look to be a squall line.

You do realize that the GFS/NAM have been absolutely horrendous with surface heating all season thus far. I think you are putting too much merit in bad models with known bias.

[Sydney Claridge]

Though for what it's worth, it is interesting that today's 12Z and 18Z NAM runs are putting out some decent EHI values (2.5+) for central Ohio on Tuesday, with mid-to-upper 60s temperatures and upper 50s to low 60s dew points around Columbus.  There seems to be a little VBV though.

[HillsdaleMIWeather]

0Z GFS gets the sixties all the way into Michigan now

[RCNYILWX]

Definitely a rather interesting scenario on Tuesday. Globals are not in lock step on surface low placement, but good agreement on a strong 992-995 mb surface low with upper 50s-low 60s dews in warm sector. Just pattern wise that supports a severe risk in the region, but as others have written it remains to be seen if/what extent of tornado risk there is. Favor the ECMWF and probably even GEM thermals over the GFS.

 

Not putting too much/any stock in NAM depiction. It has a much messier surface low and thermal and moisture profiles reek of being compromised by snow cover put down tomorrow in parts of region that the model thinks will survive temps well into the 40s if not 50 on Monday. It's possible even that the surface pressure depiction is messed up by the thermal and moisture fields being contaminated.

 

Edit: image added from AWIPS of model snow depth on 00z 12km NAM valid 18z Tuesday. That's all you need to see to know that the model is out to lunch and hopelessly compromised for Tuesday's system. When the model can't properly resolve the warm sector because it has phantom snow cover in the warm sector, you can't trust the rest of its solution when trying to assess severe potential.

 

 

 

 

[Stebo]

18 minutes ago, RCNYILWX said:

Definitely a rather interesting scenario on Tuesday. Globals are not in lock step on surface low placement, but good agreement on a strong 992-995 mb surface low with upper 50s-low 60s dews in warm sector. Just pattern wise that supports a severe risk in the region, but as others have written it remains to be seen if/what extent of tornado risk there is. Favor the ECMWF and probably even GEM thermals over the GFS.

 

Not putting too much/any stock in NAM depiction. It has a much messier surface low and thermal and moisture profiles reek of being compromised by snow cover put down tomorrow in parts of region that the model thinks will survive temps well into the 40s if not 50 on Monday. It's possible even that the surface pressure depiction is messed up by the thermal and moisture fields being contaminated.

 

Edit: image added from AWIPS of model snow depth on 00z 12km NAM valid 18z Tuesday. That's all you need to see to know that the model is out to lunch and hopefully compromised for Tuesday's system. When the model can't properly resolve the warm sector because it has phantom snow cover in the warm sector, you can't trust the rest of its solution when trying to assess severe potential.

 

 

Wow that NAM depiction is big time trash, that snow is easily going to melt right after it falls tomorrow. I would be shocked if anything is on the ground by Monday late afternoon.

[RCNYILWX]

Wow that NAM depiction is big time trash, that snow is easily going to melt right after it falls tomorrow. I would be shocked if anything is on the ground by Monday late afternoon.

Yeah it's a major problem with that model. At least we know the source of the error and that it should be discounted until it realizes there's won't be any snow on the ground in that area on Tuesday.

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[Stebo]

1 minute ago, RCNYILWX said:

Yeah it's a major problem with that model. At least we know the source of the error and that it should be discounted until it realizes there's won't be any snow on the ground in that area on Tuesday.

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I would imagine that the models might ramp this up very quickly especially late tomorrow if the trough is ejecting in the manner shown now. I would be curious if the other ensemble members for the SREF suffer the same snow depth issue as the 12k NAM.

[cyclone77]

6 minutes ago, Stebo said:

Wow that NAM depiction is big time trash, that snow is easily going to melt right after it falls tomorrow. I would be shocked if anything is on the ground by Monday late afternoon.

It would be pretty cool if you could have the option of running the NAMs without the simulated snow cover to see a direct side by side comparison with everything else being equal.  The interesting thing about the NAMs faulty depiction of snow cover is it shows how much the skin layer, and resulting boundary layer has on the overall synoptic setup.  Luckily we won't have this problem too much longer, unless this snowy pattern persists into May and June.  

[Stebo]

1 minute ago, cyclone77 said:

It would be pretty cool if you could have the option of running the NAMs without the simulated snow cover to see a direct side by side comparison with everything else being equal.  The interesting thing about the NAMs faulty depiction of snow cover is it shows how much the skin layer, and resulting boundary layer has on the overall synoptic setup.  Luckily we won't have this problem too much longer, unless this snowy pattern persists into May and June.  

I am shocked how much it has lasted already and especially how far south.

[cyclone77]

The marginal on the day 3 will likely need to be bumped quite a bit northward to cover more of central into east-central IL, northern half of IN, and parts of southern MI in coming outlooks.  I'd side with the slower Euro as well over the speedy GFS.  The Euro has surface cape up near 1000J/kg in the warm sector as far north as the I-80 corridor in the LOT cwa.

[Hoosier]

1 hour ago, cyclone77 said:

The marginal on the day 3 will likely need to be bumped quite a bit northward to cover more of central into east-central IL, northern half of IN, and parts of southern MI in coming outlooks.  I'd side with the slower Euro as well over the speedy GFS.  The Euro has surface cape up near 1000J/kg in the warm sector as far north as the I-80 corridor in the LOT cwa.

Agree on it coming north.

[Hoosier]

11 hours ago, RCNYILWX said:

Definitely a rather interesting scenario on Tuesday. Globals are not in lock step on surface low placement, but good agreement on a strong 992-995 mb surface low with upper 50s-low 60s dews in warm sector. Just pattern wise that supports a severe risk in the region, but as others have written it remains to be seen if/what extent of tornado risk there is. Favor the ECMWF and probably even GEM thermals over the GFS.

 

Not putting too much/any stock in NAM depiction. It has a much messier surface low and thermal and moisture profiles reek of being compromised by snow cover put down tomorrow in parts of region that the model thinks will survive temps well into the 40s if not 50 on Monday. It's possible even that the surface pressure depiction is messed up by the thermal and moisture fields being contaminated.

 

Edit: image added from AWIPS of model snow depth on 00z 12km NAM valid 18z Tuesday. That's all you need to see to know that the model is out to lunch and hopelessly compromised for Tuesday's system. When the model can't properly resolve the warm sector because it has phantom snow cover in the warm sector, you can't trust the rest of its solution when trying to assess severe potential.

 

 

 

 

Interesting.  I am wondering just how far north the surface low/warm front will get in the LOT cwa... the cold lake at this time of year sometimes tries to hang it up near/south of I-80 at any excuse imaginable but we aren't dealing with a weak system in this case.

[RCNYILWX]

The marginal on the day 3 will likely need to be bumped quite a bit northward to cover more of central into east-central IL, northern half of IN, and parts of southern MI in coming outlooks.  I'd side with the slower Euro as well over the speedy GFS.  The Euro has surface cape up near 1000J/kg in the warm sector as far north as the I-80 corridor in the LOT cwa.

 

Completely agree with your thoughts, including on favoring slower Euro. While Broyles may have referenced the GFS soundings in his typical outlook writeup approach, the actual outlook makes it appear likely he heavily based it off the NAM. I sent out a internal collaboration chat to neighboring offices referencing the spurious snow cover messing up the NAM solution and included SPC on it and did get a reply from SPC thanking me for that info on the NAM.

 

Wish I had provided more direct input for the outlook, would've suggested a marginal into the LOT CWA for starters with the day 3. With a strong surface low tracking overhead and sufficient instability for at least some thunder threat across most or all of northern IL, not even having general thunder northwest of I-55 is questionable at best.

 

 

 

[RCNYILWX]

Interesting.  I am wondering just how far north the surface low/warm front will get in the LOT cwa... the cold lake at this time of year sometimes tries to hang it up near/south of I-80 at any excuse imaginable but we aren't dealing with a weak system in this case.

I have the same concern about how far north the warm front gets, though it appears a pretty safe bet at least southern/southeastern 1/3 to 1/2 of CWA will spend some time in the warm sector.

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[cyclone77]

6 minutes ago, RCNYILWX said:

 

Completely agree with your thoughts, including on favoring slower Euro. While Broyles may have referenced the GFS soundings in his typical outlook writeup approach, the actual outlook makes it appear likely he heavily based it off the NAM. I sent out a internal collaboration chat to neighboring offices referencing the spurious snow cover messing up the NAM solution and included SPC on it and did get a reply from SPC thanking me for that info on the NAM.

 

Wish I had provided more direct input for the outlook, would've suggested a marginal into the LOT CWA for starters with the day 3. With a strong surface low tracking overhead and sufficient instability for at least some thunder threat across most or all of northern IL, not even having general thunder northwest of I-55 is questionable at best.

 

 

 

Yeah it certainly looks like a good chance for elevated storms well north of the warm front.  Maybe even some elevated hailers if we can build enough MUCAPE.  GFS and NAM are both showing a nice plume of mid-level LR feeding right into northern IL/southeast WI Tuesday.  The NAM even has a plume of LRs over 9.4 C over parts of the north half of IL at 15z Tue lol.

[Quincy]

The 700-500mb lapse rate progs are very impressive. The 3km NAM shows a widespread area in the warm sector with 700-500mb lapse rates in excess of 8 C/km. The 00z ILN sounding climatology data suggests lapse rates steeper than 8 C/km move into the 99th percentile. 

Two convective regimes seem most probable, with any prefrontal convection posing the greatest severe risk. Even setting aside low-level thermodynamics, the 3km NAM shows some sort of pre-frontal trough feature that some discrete/semi-discrete convection forms along. This isn't exactly the same setup as Alabama on March 19th, but the mid and upper level thermodynamics would easily support significant (>2 inch) hail, particularly with any pre-frontal, discrete convection. 

Even in a worst case scenario, given the degree of deep layer shear and substantial low-level shear (35-45 knots in the 0-1km layer), one could see damaging winds, isolated hail and brief, QLCS tornadoes with a squall line, immediately ahead of a cold front. The wild card seems to be how much convection is able to initiate in the open warm sector, as well as how far north a warm front lifts.

The image below shows an icon with 8.5 C/km lapse rates and this is actually over southeastern Indiana, not ILN, as was previously mentioned. The lapse rates down in the lower Ohio Valley move into the 8.5-9 C/km range, which is highly unusual, if it verifies.

[snowlover2]

From Reed Timmer.

Quote

SEVERE WEATHER: Here is my updated target area for severe weather, isolated #tornado potential for Tuesday afternoon, April 3. > 60F dew points could surge as far north as western OH by late afternoon with a 60-70 knot LLJ. If current models verify, I'll be targeting somewhere between western KY and southwest OH, but definitely subject to change.

 

[HillsdaleMIWeather]

[Sydney Claridge]

The 0z NAM and the NAM 3K model seem to be ramping up the parameters from SE Indiana into Central Ohio, including an area of 2000+ J/Kg SBCAPE (and MLCAPE on the NAM 3k) centered on the Columbus area at peak heating.  Also 4.0+ 0-3km EHI over a broad area of Central Ohio.

That said, the GFS places the highest CAPE over SE OH.  Now whether we can get any storms to take advantage of these parameters is another question, as it seems that the main line of storms will reach Ohio after peak heating.

[Hoosier]

We have a day 2 enhanced risk.

[Jackstraw]

Will be amazing if I can get in a local chase 48hrs after 6 inches of snow.  Pretty decent hodo's from central IN south and east into OH on the 12z 3K NAM late tomorrow afternoon.

[andyhb]

I am not really understanding the reasoning in the new D2 outlook. Warm temperatures aloft...what? This looks like a pretty typical case for steep mid level lapse rates. The 500 mb temperatures are below -15˚C across guidance and I don't really see any reason for substantial WAA aloft. I also don't see a whole lot of capping on forecasting soundings that would prevent storms going up ahead of the front providing there's enough ascent ahead of the trough axis.

[tornado_junkies]

12 minutes ago, andyhb said:

I am not really understanding the reasoning in the new D2 outlook. Warm temperatures aloft...what? This looks like a pretty typical case for steep mid level lapse rates. The 500 mb temperatures are below -15˚C across guidance and I don't really see any reason for substantial WAA aloft. I also don't see a whole lot of capping on forecasting soundings that would prevent storms going up ahead of the front providing there's enough ascent ahead of the trough axis.

With that being said, do you feel as though their probabilities are accurate in the new Day2 outlook?

[andyhb]

Just now, tornado_junkies said:

With that being said, do you feel as though their probabilities are accurate in the new Day2 outlook?

Probabilities seem fine, although I think I'd shift them a bit north too (closer to the track of the surface low).

[tornado_junkies]

Just now, andyhb said:

Probabilities seem fine, although I think I'd shift them a bit north too (closer to the track of the surface low).

I agree, especially if something like the HRW NMMB verifies. 

[Hoosier]

Yeah, I'm not really seeing the warm air aloft concern.  There's a bit of a warm layer around 850 mb but nothing significant and it gets eroded.

[tornado_junkies]

13 minutes ago, Hoosier said:

Yeah, I'm not really seeing the warm air aloft concern.  There's a bit of a warm layer around 850 mb but nothing significant and it gets eroded.

The trio of hi-res models (WRF-ARW, NMMB, and WRF-NSSL) all show some kind of discrete/semi-discrete activity by mid to late afternoon in the Northern KY/Ohio vicinity along the northward advancing warm front. Forecast soundings in the region certainly would support some tornado potential if this were indeed to verify.