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Spring severe weather chatter


Ian

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    The reason, however, why that sounding is saturated is that the model is producing convective precip at that time.   A NAM sounding (and soundings from most models) will look very moist if convection has initiated at that point.

 

 

Messy. Not liking how the sounding is saturated -- Resembles what I saw on the soundings for this past Sunday. Wind field is kinda meh too.  This will probably be a non-event for most everyone here, except for the maybe the most northern folks in the subforum. 

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Model consistency is there for an event passing to our north and then north and east. We might get clipped. As mentioned above - if it comes south a bit we are golden. But it seems PA has been pretty steady in terms of being hit on the last few runs of the NAM. 

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   A big part of the problem is that the orientation of the system as currently progged puts our area in strong downsloping which really dries out the moisture and limits the cape, despite us likely heating into the 90's Saturday.    In addition, the more westerly component of the mid-level winds (as opposed to the northwest flow shown a few days ago) would seemingly limit storms in PA from dropping south into MD/VA.    And then, the front goes through just after 12z Sunday which couldn't be timed any worse for storm chances.

 

   Our best hope seems to be that the Friday late night / early Saturday activity in PA drops south (suggested by NAM nest) and leaves an outflow boundary sitting just to our northwest that can fire later Saturday, but again, the downsloping may wipe out that scenario too.

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   A big part of the problem is that the orientation of the system as currently progged puts our area in strong downsloping which really dries out the moisture and limits the cape, despite us likely heating into the 90's Saturday.    In addition, the more westerly component of the mid-level winds (as opposed to the northwest flow shown a few days ago) would seemingly limit storms in PA from dropping south into MD/VA.    And then, the front goes through just after 12z Sunday which couldn't be timed any worse for storm chances.

 

   Our best hope seems to be that the Friday late night / early Saturday activity in PA drops south (suggested by NAM nest) and leaves an outflow boundary sitting just to our northwest that can fire later Saturday, but again, the downsloping may wipe out that scenario too.

Thank you for the informative post!

Seems we just can't seem to buy a good trending severe event this spring/met summer so far. My trusty CFSv2 has some good instability days in the future ;) 

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     I like the 12z NAM nest better than I liked previous runs, but it's still not great.   It initiates a convective system over the Great Lakes later today and moves it into NY/PA Saturday with propagation or redevelopment on the outflow boundary allowing cells to push southward into southern PA and northern MD.     But the activity really falls apart as it tries to move towards DC/Baltimore/northern VA.   The strong downsloping is not our friend here.    These plots from the 12z NAM show 1)  the 10m winds and dew points, indicating drying over DC Metro/central and northern VA, and central MD from the westerly winds      2)   the impact on cape at 00z tomorrow with lousy instability in that same general area.     Instability is better in northern and especially northeast MD where the better chances remain.   If the dew points in our area don't drop, then any activity dropping out of PA would have a chance to remain strong further south.

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     I like the 12z NAM nest better than I liked previous runs, but it's still not great.   It initiates a convective system over the Great Lakes later today and moves it into NY/PA Saturday with propagation or redevelopment on the outflow boundary allowing cells to push southward into southern PA and northern MD.     But the activity really falls apart as it tries to move towards DC/Baltimore/northern VA.   The strong downsloping is not our friend here.    These plots from the 12z NAM show 1)  the 10m winds and dew points, indicating drying over DC Metro/central and northern VA, and central MD from the westerly winds      2)   the impact on cape at 00z tomorrow with lousy instability in that same general area.     Instability is better in northern and especially northeast MD where the better chances remain.   If the dew points in our area don't drop, then any activity dropping out of PA would have a chance to remain strong further south.

 

Is the cape on the 4km nam just never to be believed? Either way, it builds alot of cape north of 70

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   First, I may have caused confusion by discussing the NAM nest (NAM4) and then showing plots from the NAM parent.

 

   I tend not to use the nest for cape, as it only lightly invokes shallow convection (which mixes the lower levels), so it tends to be a bit warm and moist which can inflate the cape values.

 

   That said, even the parent NAM still has a lot of cape north of I-70.    It may be right;  places that don't mix out the low-level moisture tomorrow should have dew points well into the 60s with strong heating, so I would expect significant instability in those areas.

 

 

Is the cape on the 4km nam just never to be believed? Either way, it builds alot of cape north of 70

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   First, I may have caused confusion by discussing the NAM nest (NAM4) and then showing plots from the NAM parent.

 

   I tend not to use the nest for cape, as it only lightly invokes shallow convection (which mixes the lower levels), so it tends to be a bit warm and moist which can inflate the cape values.

 

   That said, even the parent NAM still has a lot of cape north of I-70.    It may be right;  places that don't mix out the low-level moisture tomorrow should have dew points well into the 60s with strong heating, so I would expect significant instability in those areas.

 

And is drying/instability the main variable with tomorrow? Or are we still in need of a mechanism to trigger storms (hence you mentioning possible boundaries doing the deed earlier)?

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An upper-level disturbance will pass by just to the north and east
during midday hours. A few popup showers and thunderstorms are
possible...especially across northeastern Maryland during this
time. Moderate instability and moderate shear profiles suggest
that there is a threat for thunderstorms to become severe with
locally damaging winds and large hail being the primary threats.
More showers and thunderstorms are expected to develop over
Pennsylvania ahead of a cold front Saturday afternoon. This
activity will steer toward our region due to the northwest flow
aloft...possibly impacting portions of our area late Saturday
afternoon into Saturday evening. Again...some of these storms have
the potential to be severe. The best chance for severe
thunderstorms will be across northern Maryland.

As of now...current thinking is that the downsloping westerly
flow will prevent thunderstorms potential severe weather for most
of the CWA...with the exceptions being across northern/northeastern
Maryland due to the reasons mentioned above.

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    It always feels good to see the LWX AFD agree with my take on the event.   :)

 

    You're right that there isn't really a great trigger for storms.   There may be a weak shortwave in the middle of the day, but the primary wave is way late and passes to our north, and the front doesn't make it until Sunday morning.   So, after the midday threat (probably northeast of here), we primarily need storms over PA to drop south into our area or at least leave a boundary close by, and that is possible given the northwest mid-level flow.      But they need to encounter strong instability over our area to survive, and it doesn't look like that will be in place.  But if it is, we could be in business.

 

    

 

And is drying/instability the main variable with tomorrow? Or are we still in need of a mechanism to trigger storms (hence you mentioning possible boundaries doing the deed earlier)?

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    It always feels good to see the LWX AFD agree with my take on the event.   :)

 

    You're right that there isn't really a great trigger for storms.   There may be a weak shortwave in the middle of the day, but the primary wave is way late and passes to our north, and the front doesn't make it until Sunday morning.   So, after the midday threat (probably northeast of here), we primarily need storms over PA to drop south into our area or at least leave a boundary close by, and that is possible given the northwest mid-level flow.      But they need to encounter strong instability over our area to survive, and it doesn't look like that will be in place.  But if it is, we could be in business.

 

Gotcha, well here's to hoping for a surprise, but it seems like a long shot at this point :(

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Some of the morning HRRR runs bring whatever drops south out of PA later deeper into central MD (and maybe even DC Metro) than had been suggested before weakening it.   The 6z NAM nest is somewhat on board too, although it's later.   I would normally dismiss the over-aggressive HRRR, but the parallel HRRR (which is very effective at mitigating the biases of the operational version) basically has the same idea.   They show the reduced cape over northern VA due to downsloping, but they maintain higher values across MD.   I'm still skeptical, but this idea can't totally be written off either.

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Great analysis the last couple days. Watched the few storms that fired in PA dry out as others mentioned would likely happen. That said, diminishing parameters failed those to the north today/tonight. We'll get ours eventually.

 

I agree. 

In 2024

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And now we start hunting for our next shot. This is getting a little old at this point. If you don't live near the M/D line in our area you pretty much have a whole lot of boredom lately. 

Give us a good areawide squall line with some embedded severe and I'd even be happy. Don't need a wedgefest. 

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This has been a pretty terrible storm season since March 1. Even for this area.

Sent from my iPhone using Tapatalk

Seems to be the norm of late. Never was a huge storm place but the last few years have really sucked.
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