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February 27-28 Severe Threat


pen_artist
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Large Day 4 slight risk.

...DISCUSSION...
   ...Tuesday/Day 4 and Wednesday/Day 5...
   An upper-level trough is forecast to move across the central U.S. on
   Tuesday, as an associated mid-level jet moves from the southern
   Plains into the mid Mississippi Valley. Moisture advection, ahead of
   a cold front, will likely take place from the Ark-La-Tex
   northeastward into the southern Great Lakes. In spite of abundant
   cloud cover, some destabilization is forecast across the moist
   sector ahead of the front. The ECMWF has MLCAPE generally peaking in
   the 500 to 1000 J/kg range along parts of the moist axis by
   afternoon. As thunderstorms develop ahead of the front during the
   late afternoon and early evening, a severe threat is expected from
   the Ozarks northward into the southern Great Lakes. Wind-damage, and
   perhaps a few tornadoes would be possible with supercells and/or the
   stronger bowing line segments.

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06Z GFS presents the area roughly near Ottawa-Streator, IL as a possible chase target. FH090 00Z sounding shows a stout low-level inversion but it ought not to be as strong during the preceding couple of hours. There's decent streamwise vorticity in the low levels and a solid westerly component to the 500mb flow.

The higher-end scenarios with this setup don't look to be panning out at this point, but the atmosphere keeps trying to tell me it only takes one (storm) in the sweet spot.

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00z Euro if anything upped the ante a bit, assuming we can trust its dew points. Liking the south third of LOT and points south where the near or over 50 J/kg 0-3 km CAPE is progged.

Also of note, the Bunkers right moving vectors are less crazy than you'd think they'd be for a cold season setup, so anything prior to sunset should be chaseable without having to speed as much.



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24 minutes ago, RCNYILWX said:

00z Euro if anything upped the ante a bit, assuming we can trust its dew points. Liking the south third of LOT and points south where the near or over 50 J/kg 0-3 km CAPE is progged.

Also of note, the Bunkers right moving vectors are less crazy than you'd think they'd be for a cold season setup, so anything prior to sunset should be chaseable without having to speed as much.


 

Euro definitely the most ominous solution of all the models. Lapse rates are good esp for this north and this time of year thanks to that EML. This def bears some similarities to 2-28-17 though for that event we had a well defined wf up this way. I like that sfc winds are south to even slightly backed. Shear isn't crazy but definitely sufficient with that cape profile. Definitely am still worried about cap holding till cf moves in. That dewpoint depression and/or dryline feature could help fire storms ahead of cf if there's enough convergence on it and cap can break. Good thing is storms would likely be discrete. Sfc low is strong but wish it was more compact and not stretched out. Definitely not a perfect setup but definitely one worth chasing. 

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Euro definitely the most ominous solution of all the models. Lapse rates are good esp for this north and this time of year thanks to that EML. This def bears some similarities to 2-28-17 though for that event we had a well defined wf up this way. I like that sfc winds are south to even slightly backed. Shear isn't crazy but definitely sufficient with that cape profile. Definitely am still worried about cap holding till cf moves in. That dewpoint depression and/or dryline feature could help fire storms ahead of cf if there's enough convergence on it and cap can break. Good thing is storms would likely be discrete. Sfc low is strong but wish it was more compact and not stretched out. Definitely not a perfect setup but definitely one worth chasing. 
Doing a deeper dive at the office now using ECMWF ERA5 reanalysis maps to look at antecedent conditions prior to some notable cool season events. This one definitely has questionable moisture with Gulf currently scoured out.

2017 not a bad comp w.r.t. Td over the GoM within this range of the event, though it had a better sfc pattern for more rapid moisture advection with the primary CO low a good deal stronger and a much stronger surface high (1035 mb) off the east coast.

Some other notable cool season events, November 17th, March 15, 2016, March 27, 1991 to name a few, had much better source region moisture present.

What Tuesday does have is exceptionally steep mid-level lapse rates as you mentioned with cold -15 to -20 C h5 temps. Seeing how February 8th performed with relatively questionable moisture quality, the cold mid-level temps/steep mid-level LRs could help compensate for the potentially middling moisture quality. We're concerned here that if the sun breaks out at all on Tuesday, Td could mix out substantially especially with northward extent.

Perhaps a narrow zone near the warm frontal zone is best bet where you can pool the moisture with a longer residence time and pump up the 3CAPE to the 50+ threshold. Still thinking southern LOT CWA and points south with this in mind.


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6 minutes ago, RCNYILWX said:

Doing a deeper dive at the office now using ECMWF ERA5 reanalysis maps to look at antecedent conditions prior to some notable cool season events. This one definitely has questionable moisture with Gulf currently scoured out.

2017 not a bad comp w.r.t. Td over the GoM within this range of the event, though it had a better sfc pattern for more rapid moisture advection with the primary CO low a good deal stronger and a much stronger surface high (1035 mb) off the east coast.

Some other notable cool season events, November 17th, March 15, 2016, March 27, 1991 to name a few, had much better source region moisture present.

What Tuesday does have is exceptionally steep mid-level lapse rates as you mentioned with cold -15 to -20 C h5 temps. Seeing how February 8th performed with relatively questionable moisture quality, the cold mid-level temps/steep mid-level LRs could help compensate for the potentially middling moisture quality. We're concerned here that if the sun breaks out at all on Tuesday, Td could mix out substantially especially with northward extent.

Perhaps a narrow zone near the warm frontal zone is best bet where you can pool the moisture with a longer residence time and pump up the 3CAPE to the 50+ threshold. Still thinking southern LOT CWA and points south with this in mind.

 

Totally agree 100%. Last second moisture return esp in cold season always is a concern. Afraid moisture may be too shallow and can mix out easily like you said. It's too bad all winter we avoided big scouring cf's in Gulf overall but now that severe wx is upon us we are getting them. Ha. But as you said lapse rates will really help. Hodos have great low level curvature so wouldn't take much to produce tornadoes if storm mode avoids being too linear. I feel like wf will be very in play for your area. 

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9 hours ago, RCNYILWX said:

Doing a deeper dive at the office now using ECMWF ERA5 reanalysis maps to look at antecedent conditions prior to some notable cool season events. This one definitely has questionable moisture with Gulf currently scoured out.

2017 not a bad comp w.r.t. Td over the GoM within this range of the event, though it had a better sfc pattern for more rapid moisture advection with the primary CO low a good deal stronger and a much stronger surface high (1035 mb) off the east coast.

Some other notable cool season events, November 17th, March 15, 2016, March 27, 1991 to name a few, had much better source region moisture present.

What Tuesday does have is exceptionally steep mid-level lapse rates as you mentioned with cold -15 to -20 C h5 temps. Seeing how February 8th performed with relatively questionable moisture quality, the cold mid-level temps/steep mid-level LRs could help compensate for the potentially middling moisture quality. We're concerned here that if the sun breaks out at all on Tuesday, Td could mix out substantially especially with northward extent.

Perhaps a narrow zone near the warm frontal zone is best bet where you can pool the moisture with a longer residence time and pump up the 3CAPE to the 50+ threshold. Still thinking southern LOT CWA and points south with this in mind.

 

It's interesting, when they initially put out the Day 4-8 areal highlights on Thursday, SPC seemed pretty confident that moisture return would be less of an issue with this setup than would be expected for the time of year. What changed?

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1 hour ago, Stevo6899 said:

Not sure anyone could predict some areas (detroit) could have just as many severe watches as winter storm watches djf. Only recall maybe one with the Jan 9-11 event but think maybe southern areas of the metro didn't even get a wsw with that event.

We had multiple winter weather advisories in January but no warnings. I believe a winter storm watch for something? But I really don't expect a severe thunderstorm watch out of this. We will see. 

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An El Niño Febnado?

SUMMARY...
   Scattered strong to severe thunderstorms, associated with large hail
   (some near 2 inch diameter), damaging gusts, and a few tornadoes
   will be possible from late Tuesday afternoon, into the evening and
   overnight from parts of the mid Mississippi Valley, and southwestern
   Great Lakes.

   ...Mid-MS Valley/Southwest Great Lakes Vicinity...

   An upper trough over the northern Rockies/Intermountain West will
   shift east on Tuesday, becoming oriented from the Upper MS Valley
   and Mid-MO Valley by Wednesday morning. Fast deep-layer
   southwesterly flow ahead of this feature will overspread the Ozark
   Plateau into the Great Lakes. At the surface, a low will deepen as
   it shifts east from MN toward southern Ontario. A cold front
   attendant to the low will quickly shift east/southeast across the
   Plains and the Mid/Upper MS Valley during the afternoon and into the
   overnight period. Initial thunderstorm activity may develop in warm
   advection regime near the quasi-warm front/moisture gradient from
   northern IL into IN/NW OH/southern MI around 21-00z. Additional
   activity will then develop along the cold front as it develops east
   and the main upper wave ejects into the region around 00-03z.

   Warm advection and southerly low-level flow ahead of the front will
   allow for modest airmass modification into the Midwest. However,
   forecast dewpoints are only expected to reach into the 50s to near
   60 F. Nevertheless, a plume of steep midlevel lapse rates will
   overspread the IL/IN/MI/OH vicinity from afternoon into the evening.
   This will support modest destabilization with MLCAPE generally
   forecast to be less than 1000 J/kg, though a narrow corridor of up
   to 1500 J/kg MLCAPE may be possible for a brief period around 00z.
   Forecast soundings across the region indicate most of available
   instability will be located above the 850-700 mb layer. 

   Initial thunderstorm activity may be slightly elevated as some
   forecast soundings indicate a warm nose between 850-700 mb during
   late afternoon/early evening. Nevertheless, effective shear greater
   than 50 kt, and enlarged low-level hodographs becoming elongated
   above 3 km indicate initial supercells will be possible near the
   quasi-warm front/moisture gradient from northeast IL into northern
   IN and vicinity. With most instability focused above the 850-700 mb
   layer, and in conjunction with poor boundary-layer dewpoints, the
   tornado risk may be somewhat lower than typically expected given
   shear profiles in the 0-2 km layer. Nevertheless a couple tornadoes
   are possible, especially if greater moisture than forecast can make
   it this far north. Large hail, with a few instances near 2 inch
   diameter, will be possible with any semi-discrete supercells, along
   with damaging gusts. 

   Once linear forcing along the front increases in the 00-03z period,
   a line of storms is forecast to develop east from the Mid-MS Valley
   toward the Lower OH Valley during the nighttime hours. Damaging
   gusts will be the main concern with this activity.

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NAM initiates convention around 23z but much further west toward Peoria. NAM doesn’t seem to be “off the charts” like the HRRR but still a good tornado potential across the 5% area SPC has outlined. I’ll let the experts dive deeper into the setup. 

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Recent CAM/short-range guidance seems to be on the upswing for tomorrow's threat. For one, that subtle embedded wave aloft that induces surface cyclogenesis along the surface trough seems to be returning (e.g. the earlier Euro runs) that could increase the low level wind response. The RAP in particular has a fairly potent surface cyclone and pseudo-dryline. Moisture seems sufficient across most models as well.

I'd be wary of the HRRR overmixing and being too far east at this range. The MPAS from NSSL also seems to have an issue with that, although it has improved from the 00z to the 12z run.

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1 hour ago, andyhb said:

Recent CAM/short-range guidance seems to be on the upswing for tomorrow's threat. For one, that subtle embedded wave aloft that induces surface cyclogenesis along the surface trough seems to be returning (e.g. the earlier Euro runs) that could increase the low level wind response. The RAP in particular has a fairly potent surface cyclone and pseudo-dryline. Moisture seems sufficient across most models as well.

I'd be wary of the HRRR overmixing and being too far east at this range. The MPAS from NSSL also seems to have an issue with that, although it has improved from the 00z to the 12z run.

Yeah, I thought the same after today's 12Z HRRR run. 18Z seems to be an improvement although not quite ideal.

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