2021-04-27 EVENT: TX/OK/KS

Apr 10, 2008
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Tulsa, OK
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A significant severe weather episode appears to be in store for Tuesday, April 27, 2021 across much of the southern and central Plains. Model data has been persistent ejecting a strong large scale trough from the southern Rockies into the Plains Tuesday 4/27. Strong WAA will transport a moist boundary layer north across the plains in advance of an eastward surging dryline. The nose of a strong mid-level jet is forecast to overspread the warm sector by Tuesday afternoon creating an environment that would appear to favor intense supercells with all hazards likely.

There are some significant differences in the synoptic setup between various models. The GFS has shown quite a bit of inconsistency between runs while the ECMWF has shown remarkable run-to-run consistency. The ECMWF solutions show a more volatile environment featuring a sharp dryline across western OK with strong instability across the warm sector to the east with a strong southerly low-level jet in place. Forecast deep layer shear is quite impressive and mid-level flow is perpendicular to the dryline. This would favor supercells with an attendant threat for all hazards. In fact, the ECMWF solutions have a pretty high ceiling for tornadoes should it verify.

The GFS shows a less volatile environment with hints of meridional mid-level flow which would be more parallel to the dryline. The GFS has also been aggressive mixing the dryline much farther east into eastern OK compared to the ECMWF. I suspect the ECMWF will end up being more accurate assuming current trends in data continue, and this is reflected in SPC's Day 6 placement of severe probabilities.

Obviously the finer details of this upcoming event will not be resolved until the day of, but model trends do suggest this event could be rather significant, and depending on how things play out we could be looking at a tornado outbreak if full potential is realized.

Nebraska and perhaps Iowa may need to be added to the title at some point if severe probabilities end up being farther north than currently depicted.
 
Oct 10, 2004
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Madison, WI
It seems to me actually that the GFS has been quite consistent with its highly amplified trough and very meridional flow for next Tuesday-Wednesday, and despite a vast warm/moist sector over the central CONUS, large areas of it with minimal to nil SBCAPE, and wonky wind profiles in those areas that do have instability (one of which is pretty close to MBY, and I have Wednesday off, so I'm still keeping an eye on things). Would be nice to see it start caving toward the Euro at this point, though.

Edit: 12Z GFS is looking like a step in the right direction, the winds at 500mb stay a little more southwesterly rather than almost due southerly.
 
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Nojima B

Enthusiast
Apr 22, 2021
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Missouri
It seems to me actually that the GFS has been quite consistent with its highly amplified trough and very meridional flow for next Tuesday-Wednesday, and despite a vast warm/moist sector over the central CONUS, large areas of it with minimal to nil SBCAPE, and wonky wind profiles in those areas that do have instability (one of which is pretty close to MBY, and I have Wednesday off, so I'm still keeping an eye on things). Would be nice to see it start caving toward the Euro at this point, though.

Edit: 12Z GFS is looking like a step in the right direction, the winds at 500mb stay a little more southwesterly rather than almost due southerly.
Sorry to have to ask this, but what does MBY mean?
 
Apr 10, 2008
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Tulsa, OK
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Tuesday has trended way down from what we were looking at last week. Not sure what to think about chasing prospects at this point. SPC's day 2 outlook seems to side with the latest ECMWF data which is the most aggressive with severe potentials. Most of the other models depict a less favorable severe weather scenario. The data has been inconsistent and has varied from each run and each model. I am not sure yet I will chase Tuesday or wait for the next opportunity. It will likely be a morning decision.
 
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James Gustina

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Mar 9, 2010
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The spread on this one even just between the different flavors of the WRF is pretty nuts. This morning's 06Z HRRR points to cloud cover issues present throughout the day which tempers instability, with the 00Z runs of the NAM3K and all WRF members depicting the same issue in slightly different ways.

The 00Z Euro stayed pretty aggressive with its solution, with a broad area of favorable deep layer shears and MLCAPE values in that hatched corridor the SPC outlined reaching 1750-1900 j/kg by 00Z. Cloud cover or not, it looks like the southern half of the dryline is hinging on the development of a second surface low down the dryline along the I-20 corridor. The dryline setup/wind profiles look far more favorable in this scenario.

As it stands right now, it's going to be a game time decision on whether or not I try to roll out of work early for this one. With a fair number of people skipping 4/23, it'll likely still be crowded out in the Big Country regardless of model trends into this evening.
 
Feb 19, 2021
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Wichita
A couple of the global models forecast a weak impulse extending from approximately KLIC to KTCC at 18Z Tuesday. 500mb heights are forecast to fall 3dm in central Kansas in the afternoon. If that is a genuine feature combined with the 2000+j of energy forecast at KICT at 23Z Tuesday, south central KS and north central OK may be back in play.

I have attached the ECMWF instantaneous flash rate forecast for 8pm.

Again, this is highly conditional on the short wave being a genuine feature and instability being as high as forecast.
 

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Aug 9, 2012
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Galesburg, IL
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12z HREF showing a fairly nice swath of helicity tracks tomorrow afternoon/evening from the Colorado border east into NW KS/SW NE. Other models show a very narrow ribbon of mid 50s dew points in this area with easterly winds (narrow corridor of CAPE as well). I imagine there will be at least the potential of a landspout tornado or two early on and then evolving into hailers later on with good structure. Kind of an odd setup, but being in the high plains region, things don't exactly have to look "extreme" to get a nice storm/tornado combo. Probably where I'd target tomorrow. Something to keep an eye on. I'm likely not chasing, too far for a marginal setup and I already have a 9 day chasecation slated for mid to late May!

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