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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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28 minutes ago, high risk said:

                My call (as well as LWX's high PoPs) is in big danger now of busting.     Pretty much all of the 00z CAMs now really mix out the moisture Sunday afternoon, and as a result, it's pretty tough to find more than very isolated showers/storms in any of the simulated reflectivity forecasts.

The ARW and NMMs have both been super paltry on sim reflectivity for multiple runs now. There was really only one long range HRRR run and one NAM nest run that got good storms into the area. Meh. 

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30 minutes ago, Kmlwx said:

The ARW and NMMs have both been super paltry on sim reflectivity for multiple runs now. There was really only one long range HRRR run and one NAM nest run that got good storms into the area. Meh. 

          Good point, although the lack of storms in the ARW is due to it dropping our dew points tomorrow afternoon into the 40s which has seemed really implausible to me.    Regardless of the magnitude, it certainly seems now like dew points will drop during peak heating tomorrow.

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I'm actually more interested in the meso-low in southwestern VA now than I am about any potential afternoon convection for the reasons stated above. Perhaps early morning downpours w/ something a little more (gusty winds). If there were a little bit more surface CAPE, it could be more interesting.

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9 hours ago, yoda said:

MRGL risk remains on new Day 1... 5 for both hail and wind

        I think they spelled out the competing factors quite nicely.     We want heating today, but too much heating is going to mix out the low-level moisture.     There is probably a combination of balance somewhere in there, and most guidance is showing at least a few widely scattered stronger cells later today.    

    I'm going to be watching the dew points closely.    I don't buy the low 50s shown by the HiResW ARW (which shows basically no storms), so if we stay stay in the mid 50s, I think we can crank out a few cells.    Anything above that probably increases the coverage (like the NAM Nest shows).

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4 hours ago, high risk said:

        I think they spelled out the competing factors quite nicely.     We want heating today, but too much heating is going to mix out the low-level moisture.     There is probably a combination of balance somewhere in there, and most guidance is showing at least a few widely scattered stronger cells later today.    

    I'm going to be watching the dew points closely.    I don't buy the low 50s shown by the HiResW ARW (which shows basically no storms), so if we stay stay in the mid 50s, I think we can crank out a few cells.    Anything above that probably increases the coverage (like the NAM Nest shows).

DP 49 at DCA

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2 hours ago, Kmlwx said:

The last two storm days we've had - yesterday and the day last week, really have featured some nice lightning and thunder. 

I had the windows open late Friday afternoon, and while we didn't get direct impacts overhead here, the storms just a couple miles to our west sent some nice, rolling peals of thunder as they passed by at the time. I miss hearing that throughout the winter months.

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All we've got for now - and really for the extended period as well...

D4-8 discussion excerpt

 

...DISCUSSION...
   Low/mid-level winds will likely strengthen across the Mid-Atlantic
   and Northeast on Day 4/Wednesday as an upper trough moves eastward
   across these regions. There is still some uncertainty regarding how
   much low-level moisture will be present ahead of a cold front. If
   enough boundary-layer instability develops by Wednesday afternoon,
   then strong/damaging winds appear possible with any storms that can
   develop along or ahead of the quickly moving front. At this point,
   confidence in organized severe convection producing a swath of
   damaging winds remains too low to introduce 15% severe
   probabilities. Still, some severe risk appears possible from roughly
   eastern NC to southern NY, and this region may need to be included
   in low severe probabilities in a subsequent outlook.
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3 hours ago, Kmlwx said:

All we've got for now - and really for the extended period as well...

D4-8 discussion excerpt

 

...DISCUSSION...
   Low/mid-level winds will likely strengthen across the Mid-Atlantic
   and Northeast on Day 4/Wednesday as an upper trough moves eastward
   across these regions. There is still some uncertainty regarding how
   much low-level moisture will be present ahead of a cold front. If
   enough boundary-layer instability develops by Wednesday afternoon,
   then strong/damaging winds appear possible with any storms that can
   develop along or ahead of the quickly moving front. At this point,
   confidence in organized severe convection producing a swath of
   damaging winds remains too low to introduce 15% severe
   probabilities. Still, some severe risk appears possible from roughly
   eastern NC to southern NY, and this region may need to be included
   in low severe probabilities in a subsequent outlook.

            It's not a pipe dream;  I'll say that.    It looks like there will be a line of forced convection just ahead of the front early Wednesday afternoon in an environment with fairly decent speed shear.     It should warm up to the mid to upper 60s ahead of the front, but dew points will struggle to reach the low 50s.      Forecast soundings have only a small amount of CAPE, but they show a strong inverted-V structure, suggesting some possibility of stronger wind gusts.    It's possible that SPC puts us in a day 3 MRGL, although I don't think it's anything close to a given.

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9 hours ago, high risk said:

            It's not a pipe dream;  I'll say that.    It looks like there will be a line of forced convection just ahead of the front early Wednesday afternoon in an environment with fairly decent speed shear.     It should warm up to the mid to upper 60s ahead of the front, but dew points will struggle to reach the low 50s.      Forecast soundings have only a small amount of CAPE, but they show a strong inverted-V structure, suggesting some possibility of stronger wind gusts.    It's possible that SPC puts us in a day 3 MRGL, although I don't think it's anything close to a given.

         SPC did give us the day 3 MRGL, and the 06z NAM nest shows the idea of the scenario described above with a strong line of convection moving through the area (not an event for the western folks) early Wednesday afternoon.

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One clear fail scenario being depicted is the front going through too early in the day, as shown in the 00z HRRR and 12/18z GFS.    If I had to wager, I'd say that the GFS is too fast, and the HRRR gets some indirect synoptic influence from the GFS, so that *might* explain why it looks similar.     But I'm not confident at all in saying that.    Ultimately, the later the front arrives, the better the chances of severe.

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9 hours ago, high risk said:

One clear fail scenario being depicted is the front going through too early in the day, as shown in the 00z HRRR and 12/18z GFS.    If I had to wager, I'd say that the GFS is too fast, and the HRRR gets some indirect synoptic influence from the GFS, so that *might* explain why it looks similar.     But I'm not confident at all in saying that.    Ultimately, the later the front arrives, the better the chances of severe.

Our area can do surprisingly well in setups like this. If we can manage some decent sun in the morning and get our CAPE over ~500 that can sometimes be just enough with a dynamic front.

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51 minutes ago, Eskimo Joe said:

Our area can do surprisingly well in setups like this. If we can manage some decent sun in the morning and get our CAPE over ~500 that can sometimes be just enough with a dynamic front.

        I agree fully.    Could be like that Sunday event in March when we had no lightning but had a bunch of wind reports.     I still think, though, that the timing is the biggest factor that is *potentially* working against us.    The HRRR is still faster with the front, and the better activity gets going just east of the area.   The latest NAM nest is still good verbatim, but it has notably sped up the front, relative to earlier runs.     A 1pm frontal passage vs an 11am passage could make all of the difference here.

 

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43 minutes ago, Yeoman said:

Our best storms come in June.. 

April can perform under the right circumstances.

I think April/May have slightly higher odds to go with in terms of things of the TOR variety. Probably into June too. But by June we tend to look for ring of fire type derecho stuff more so than tornadoes (other than an isolated event). All about lining up the shear that can be really good in spring with the instability that can be spectacular in the summer. 

By July we tend to be limited to the pulse severe stuff...don't get me wrong - a monster cell can blow up in July that delivers huge hail or major wind damage - but it's less likely to be the widespread mod risk type thing. 

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54 minutes ago, WxUSAF said:

Euro is a whole lotta nada

          The Euro is clearly in the "faster front camp".     Seems like the GFS/ECMWF/HRRR camp gets things going either just east or a good distance east of our area.   The NAM and several HiResWindows (some of which are initialized from the NAM...) have a slightly slower front which gives most of us east of the Potomac a good event.     A 1 or 2 hour change in the timing of the front is going to make a huge deal.

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4 minutes ago, high risk said:

          The Euro is clearly in the "faster front camp".     Seems like the GFS/ECMWF/HRRR camp gets things going either just east or a good distance east of our area.   The NAM and several HiResWindows (some of which are initialized from the NAM...) have a slightly slower front which gives most of us east of the Potomac a good event.     A 1 or 2 hour change in the timing of the front is going to make a huge deal.

Bet I know which camp wins out ;) 

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20 minutes ago, Kmlwx said:

April can perform under the right circumstances.

I think April/May have slightly higher odds to go with in terms of things of the TOR variety. Probably into June too. But by June we tend to look for ring of fire type derecho stuff more so than tornadoes (other than an isolated event). All about lining up the shear that can be really good in spring with the instability that can be spectacular in the summer. 

By July we tend to be limited to the pulse severe stuff...don't get me wrong - a monster cell can blow up in July that delivers huge hail or major wind damage - but it's less likely to be the widespread mod risk type thing. 

              I mostly agree with this.     April tends to struggle to generate much SVR here (even the best setups often leave the Mid-Atlantic in a cold air damming scenario), but there are notable exceptions.       And it certainly seems to be our best  month for hail.         It feels to me (and I'm too lazy to go check) that our best TOR threat here runs something like May 15-June 15 (maybe June 15 is a bit late, but I think you need to include at least the first 10 days of June), and after that, we get more of the linear or MCS severe threat.     But I may be speaking out of my @ss on this.  

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