2021 Mid-Atlantic Severe Weather - General Discussion

[yoda]

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

[osfan24]

Sun already peeking out.

[mattie g]

On 4/10/2021 at 7:03 AM, WeatherShak said:

From coastal Alabama this am. Friend camping in Gulf State Park




.

And she’s got crampons for fingernails. Perfect!

[high risk]

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).

[MN Transplant]

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

[high risk]

5 hours ago, MN Transplant said:

DP 49 at DCA

        Yeah, that was some impressive mixing, but the dews rebounded a bit right ahead of the storms.     I was thrilled to get a a nice storm here.

[Kmlwx]

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

[vastateofmind]

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.

[Kmlwx]

We may end up being at early May for any appreciable severe threat (or later). CIPS is pretty much dormant for any analog related risk to our area for the next 1-2 weeks. 

[NoVaWx]

Had a thunderstorm with hail. Pretty rare

[George BM]

20 minutes ago, NoVaWx said:

Had a thunderstorm with hail. Pretty rare

Same t-storm hit me here with small hail. Cold air aloft (500mb temps of -23 to -24C) definitely helped.

[FXW176]

Huh. That was cool.

[Kmlwx]

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.

[high risk]

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.

[high risk]

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.

[Kmlwx]

NAM nest sim reflectivity certainly could look worse. I'll take it given that I'm not expecting much to begin with. Could keep us semi satisfied while we wait for something bigger to track. 

[high risk]

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.

[Eskimo Joe]

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.

[Kmlwx]

The super long range 6z HRRR has the activity waiting to fire until mainly east of the Chesapeake. 6z NAM nest still looks decent for a line, though. 

[high risk]

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.

 

[Yeoman]

Our best storms come in June.. 

[WxUSAF]

Euro is a whole lotta nada

[Kmlwx]

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. 

[high risk]

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.

[Kmlwx]

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  

[high risk]

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.  

[George BM]

Soundings over the eastern shore, on the long range HRRR anyway, look good for severe wind potential as well as some hail with VERY steep LLLRs, 500-1000+ J/kg MLCAPE and 500mb temps (-20/-21C) w/ a LI around -4.

[George BM]

1 minute ago, high risk said:

              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.  

The May 15th-June 15th period actually happens to be the exact period I feel best about overall severe potential in these parts.

[Kmlwx]

1 hour ago, high risk said:

              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.  

I don't think you're ever talking out of your @ss when it comes to weather  

Then the fall has another window of sorts in September for some TOR related activity. This is of course ignoring any threat from tropical that could come August to October for the most part. 

Would seem to me that we are "due" (hate that term for the most part) for a derecho event. At least based on the average return periods for that type for stuff for the DC area. 

[Kmlwx]

Looking like the immediate DC-Balt corridor may be out of the game completely at this point. Thinking east of the Bay is where it's at. Oh well. We keep waiting for severe season!