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2020 Mid-Atlantic Severe Weather - General Thread


Kmlwx
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10 minutes ago, yoda said:

00z NAM showing ML Lapse Rates around 7.0 C/KM for Wednesday afternoon into the evening

         Soundings for Wednesday definitely look great.    Shoutout to Kmlwx for noting this threat way in advance.    While the dynamics as currently progged aren't great, a nearby front and small height falls could be enough.    If we can trigger storms, the setup for SVR will be pretty robust.

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21 minutes ago, high risk said:

         Soundings for Wednesday definitely look great.    Shoutout to Kmlwx for noting this threat way in advance.    While the dynamics as currently progged aren't great, a nearby front and small height falls could be enough.    If we can trigger storms, the setup for SVR will be pretty robust.

Seems like with a lack of forcing - we might have to rely on a cold pool getting established. Has obviously helped us before. We'll see - still far enough out that anything is on the table. 

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A bit north of us - @mappy is in the slight. Obviously expect tweaks as we get closer. D3 is an eternity away in severe forecasting. Do we all need a refresher that on June 29, 2012...DC proper was not even in the slight risk until the 20z update. Moderate not until the 01z update. 

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NAM nest at range has the timing not as favorable for us - by 0z (end of the run) the line is still up in PA for the most part. Would like to see that speed up a bit. It matches well with the SPC outlook of the best threat being to our north mainly. 

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Not really enthused with Wednesday. If you go back and look at all the the mid to higher range MCS / derecho events in the LWX CWA, they contained historically hot antecedent airmasses. That won't be the case this week. Unless there is a substantial cold pool or EML I would temper my expectations for this week.

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3 minutes ago, Eskimo Joe said:

Not really enthused with Wednesday. If you go back and look at all the the mid to higher range MCS / derecho events in the LWX CWA, they contained historically hot antecedent airmasses. That won't be the case this week. Unless there is a substantial cold pool or EML I would temper my expectations for this week.

I consider low to mid 90s a hot air mass with DPs near 70

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29 minutes ago, yoda said:

I consider low to mid 90s a hot air mass with DPs near 70

I agree with both of you. I think what @Eskimo Joe is pointing out - is that this isn't triple digit heat. So it won't be a 2012 style scenario. My expectations are a bit tempered because of that - but also because there seems to be a consistent signal to keep the main focus to our north and/or west. That's two easy ways we could underperform.The high end on this from SPC is probably a 30% wind enhanced. With the potential of good mid-level lapse rates - there could be a good hailer somewhere too. 

 

Our best hope for something more than meh is for a cold pool to establish very well and then to get a forward propagating MCS that sustains as it sags south

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1 minute ago, Kmlwx said:

I agree with both of you. I think what @Eskimo Joe is pointing out - is that this isn't triple digit heat. So it won't be a 2012 style scenario. My expectations are a bit tempered because of that - but also because there seems to be a consistent signal to keep the main focus to our north and/or west. That's two easy ways we could underperform.The high end on this from SPC is probably a 30% wind enhanced. With the potential of good mid-level lapse rates - there could be a good hailer somewhere too. 

 

Our best hope for something more than meh is for a cold pool to establish very well and then to get a forward propagating MCS that sustains as it sags south

Well I hope people aren't expecting 2012 to be walking through the door... cause that's just silly

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Just now, Kmlwx said:

I agree with both of you. I think what @Eskimo Joe is pointing out - is that this isn't triple digit heat. So it won't be a 2012 style scenario. My expectations are a bit tempered because of that - but also because there seems to be a consistent signal to keep the main focus to our north and/or west. That's two easy ways we could underperform.The high end on this from SPC is probably a 30% wind enhanced. With the potential of good mid-level lapse rates - there could be a good hailer somewhere too. 

On the plus side, it's good to see the complex / line being favored to go on the northern end of the subforum.  Historically, these things dive further south at the last minute. Re-analysis of the 2008, 2012, and 2013 events shows the meso guidance was too far north at HR 48+

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3 minutes ago, Kmlwx said:

This has been the most intriguing part to me - we don't normally get good hail results in SARS like this - 

Capture.PNG

Has this mainly been on the NAM?  Or has the GFS and EURO been having the same?

And those are some large matches by hail size... probably helped by the eastward moving EML with between 7.5 and 8.0 C/KM mid level Lapse rates 

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2 minutes ago, yoda said:

Has this mainly been on the NAM?  Or has the GFS and EURO been having the same?

And those are some large matches by hail size... probably helped by the eastward moving EML with between 7.5 and 8.0 C/KM mid level Lapse rates 

Mainly NAM - but even the GFS has printed out a few good hailer results here and there. 

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31 minutes ago, Eskimo Joe said:

History shows that in these parts if the GFS and Euro aren't on board, at least to a certain extent, then it's just the NAM being the NAM.

Indeed. GFS doesn't look "bad" - it's always lower end than the NAM on svr. 

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Afternoon AFD from LWX discussing severe for Wed to Fri time period:

By Wednesday, south southwesterly flow will continue to pump in
ample low level moisture across the area and much warmer
temperatures as 850 temps near 20C. High temperatures on
Wednesday will soar into the upper 80s to middle 90s, with heat
indices reaching the upper 90s near and south of the District.

At the same time a cold front will be dropping southward from
the Great Lakes and into Pennsylvania Wednesday afternoon and
evening. Instability will increase between 15-20k J/kg across
the area, as mid-upper level winds increase and turn westerly,
resulting in 40+ knots of shear. As the front inches southward
while coinciding with an approaching shortwave from the Ohio,
showers and thunderstorms are expected to encroach from the
north late Wednesday afternoon and Wednesday night. Question
remains how much southward progress the convective activity can
make into our CWA during this time before losing the support of
daytime heating. That being said, the threat for scattered
severe storms will exist across our far northern zones that hug
the Mason Dixon Line (SPC Slight Risk), with a more isolated
threat extending down to the I-66 corridor. Activity is expected
to wane Wednesday night with the loss of insolation, while
conditions remain warm and muggy with lows holding in the upper
60s to lower 70s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Area will remain in warm humid air mass through Sat morning. So, the
risk of t-storms will be present Thu and Fri with potential for
severe thunderstorms especially Fri. Only height rises are shown by
models through Friday, therefore, forcing will be driven by
mesoscale features hard to determine this far out. A cold front is
expected to finally push through the area Sat with enough dry air to
lower humidity and inhibit t-storm potential.

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