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Significant Severe Weather Event Possible Thursday, August 27, 2020


weatherwiz
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Finally...we've been waiting all summer for this but the potential exists on Thursday for a widespread...perhaps severe weather outbreak with widespread damaging winds and perhaps some tornadoes all possible. This is a rather delicate setup, however, all the ingredients are there. as always with this type of potential there are numerous caveats and the extent of the potential probably won't be known until early Thursday morning. 

1) Morning MCS - there likely will be an ongoing MCS to begin the day (riding along an instability gradient). This will certainly be one feature which complicates the forecast as we would ave to deal with cloud debris and likely subsidence behind the departing MCS. Subsidence can be good as it can help clear junk out faster, however, if it is too strong it can inhibit development later on. 

2) Lack of EML/steep lapse rates. lapse rates aren't horrific, but these setups tend to have their severe weather potential (magnitude) vastly increased when there is an EML involved. With that said, combination of temperatures well into the 80's...perhaps near 90 in spots and dewpoints perhaps into the 70's with high mixing ratios should contribute to near moderate instability (again...cloud debris will be a player here too). 

3) Rather strong shortwave approaching will be accompanied by anomalously strong mid-level flow with a west-to-northwest MLJ exceeding 50-60 knots with a low-level jet exceeding 30-35 knots. One caveat here is the BEST dynamics may push off the coast before we can crank again in the afternoon. 

This should be extremely fun to track the next few days with plenty to work out. It is extremely important to keep expectations in check b/c this is by far a lock and lots have to come together...but all the ingredients are there. 

Saturday has potential to be quite active as well.

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3 hours ago, weatherwiz said:

Finally...we've been waiting all summer for this but the potential exists on Thursday for a widespread...perhaps severe weather outbreak with widespread damaging winds and perhaps some tornadoes all possible. This is a rather delicate setup, however, all the ingredients are there. as always with this type of potential there are numerous caveats and the extent of the potential probably won't be known until early Thursday morning. 

1) Morning MCS - there likely will be an ongoing MCS to begin the day (riding along an instability gradient). This will certainly be one feature which complicates the forecast as we would ave to deal with cloud debris and likely subsidence behind the departing MCS. Subsidence can be good as it can help clear junk out faster, however, if it is too strong it can inhibit development later on. 

2) Lack of EML/steep lapse rates. lapse rates aren't horrific, but these setups tend to have their severe weather potential (magnitude) vastly increased when there is an EML involved. With that said, combination of temperatures well into the 80's...perhaps near 90 in spots and dewpoints perhaps into the 70's with high mixing ratios should contribute to near moderate instability (again...cloud debris will be a player here too). 

3) Rather strong shortwave approaching will be accompanied by anomalously strong mid-level flow with a west-to-northwest MLJ exceeding 50-60 knots with a low-level jet exceeding 30-35 knots. One caveat here is the BEST dynamics may push off the coast before we can crank again in the afternoon. 

This should be extremely fun to track the next few days with plenty to work out. It is extremely important to keep expectations in check b/c this is by far a lock and lots have to come together...but all the ingredients are there. 

Saturday has potential to be quite active as well.

Can't say I disagree with this notification effort thru yesterday's 12z...  00z, not so much in the Euro, but the GFS hangs on a bit...

But In the other thread, I mentioned a couple days ago that D5/6 looked like an "EOF1 bomb" potential for the upper MA to NE states... These baser kinematic structures you're honing in on were evidence back then and as of yesterday - by then D3 ...

Maybe like a last season 'threat hurrah' as the summer closes the books and we'll see if this new-ish complexion toward seasonal migration that the operational Euro GFS suddenly paint has legs... Could be a rush job - I think the GFS 528 dm double noded height core amid a continental scoped, sub polar vortex over JB is a bit hard to cough down in late August/early Sept... but, I also covet some personal "science fiction" plausibilities as to why the model is doing that, and it is rooted in evidence spanning the last 6 years...

Namely, we've been "continental folding" at transition seasons with unusual proficiency at the books ends of winter.  

That's John- labeling ...there's no actual identity of that in Meteorological/climate vernacular ...but, I call it that ...it's like super synoptic scaled "Kelvin-Helmholtz" effect. 

We have velocity surpluses in the mid and upper tropospheric ambience that is tending to kick in very early in transition season, and... lagging unsually long on the way out. The cause is the expanding HC...or in the case of Autumn, the HC expansion as a persistence on-going perpetuated state, is triggering gradient to increase very quickly as the sun's integrate insolation across the hemisphere begins to dim toward the ends of August and particularly...during Sep/Oct ...  This increased gradient is directly proportional to the surplus velocity. But why that is important is, the velocity of the jet is "folding" over the top mass of the R-wave fields, and this is increasing/enhancing trough node tendencies earlier in the year of eastern/southern Canada, and also... in May's ...  

This 'plausibility' is why we have since 2000 experience either synoptic scaled snow chances, or, ... packing pellet virga exploded CU cold waves in Octobers and May some 1/2 if not 2/3rds of the last 20 years worth of transition seasons ...either end. 

In between?  ...DJF/early M .... that HC stuff impinges a whole 'nother issue with raging jet velocities so extreme that it forcing a morphology of precipitation event structures.  

Anyway, this may seem to have nothing to do with Thursday at this point ...but, it does in the sense that the mechanics are perhaps being exaggerated over what is normal up our way...as these gradient rich events transpire through lingering seasonal warmth and dps... Outside the box thinking a little - 

In any case, the pattern looks in the 00z run by the Euro to have moved to more a NW flow with some positive shearing ...maybe more whisky line or even MCS-y

 

 

 

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I also wonder how the morning MCS potential influences things later in the day. Those are always a significant challenge...most times they completely kill potential, however, there are times they can enhance potential. 

1) Will there be s/w subsidence behind it? As explained before, this can be good in that it clears out cloud debris quicker, however, it can also be bad b/c if that subsidence can't be overcome later, convection becomes suppressed. 

2) MCSs can certainly leave behind residual boundaries and these can be a focal point for convection initiation and they can also locally enhance tornado potential...depending on how the storm motion is with respect to the boundary. 

3)Timing of the MCS...this is actually rather huge...is it bright and early or late morning.  

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All three days Thursday through Saturday look troublesome or certainly could turn out that way with that front oscillating in the area ... accentuated helictites long it with unusual thermal gradient for this time of the year either side is intriguing. 
 

Seems that EOF1swarm idea had shifted more to Saturday with organized cyclone mechanics in the area but the boundary  itself could be active for a couple days before that ...wherever ultimately sets up

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6 minutes ago, Typhoon Tip said:

All three days Thursday through Saturday look troublesome or certainly could turn out that way with that front oscillating in the area ... accentuated helictites long it with unusual thermal gradient for this time of the year either side is intriguing. 
 

Seems that EOF1swarm idea had shifted more to Saturday with organized cyclone mechanics in the area but the boundary  itself could be active for a couple days before that ...wherever ultimately sets up

Let's hope we can get at least one of these days to work out. I think historically when we seem to have these multiple days of potential we typically get one to work out. 

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10 minutes ago, weatherwiz said:

Let's hope we can get at least one of these days to work out. I think historically when we seem to have these multiple days of potential we typically get one to work out. 

Ha ha yeah this isn’t the panhandle of Texas from late April to early June when you have 45 straight days of visible crispy super cells rollin under the tropopause

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