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Kmlwx

2019 Mid-Atlantic Severe Wx - General Discussion

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Lots of the area covered in the Day 7 SPC outlook, 15%, looks like sloppy thirds from another eastern Plains/Dixie outbreak next week.

f3ede64984da7fb6b6da8defca4cd56e.jpg

```...DISCUSSION...
Medium-range models continue to depict progression of a highly
amplified upper trough across the U.S. through the Day 4-8 period.
While differences are rather substantial with respect to the initial
strength of this trough -- and thus its associated surface
reflection -- as it exits the Rockies and moves into the Plains Day
5 (Wednesday 4-17), evolution/progression of the upper system
thereafter is reasonably similar as it traverses the central and
eastern U.S. through the end of the period.

Given the amplitude of the trough, and accompanying/well-developed
surface system, a favorably strong wind field will accompany the
progression of this system, along with ample northward advection of
Gulf moisture. As such, it appears that a kinematic and
thermodynamic environment supportive of severe storms (and all modes
of severe weather) will exist each day -- and therefore 15% risk
areas are being added. Though model differences continue to cast
some uncertainty as to location of the daily risk, as well as the
magnitude, it appears that any risk Day 4 (Tuesday 4-16) will be
limited. Day 5 (Wednesday 4-17) however, as the upper trough
advances more fully into the central U.S., risk for severe weather
is evident from roughly the Mid-Missouri Valley south across eastern
portions of the Plains, and eastward to roughly the Mississippi
Valley. Day 6 (Thursday 4-18), the risk should extend from roughly
the Mississippi Valley to the Appalachians, and as far north as the
Midwest states. Day 7 (Friday 4-19), risk should exist primarily
east of the mountains. Finally, by Day 8 (Saturday 4-20), the front
will likely be advancing offshore, and thus diminished potential is
apparent.

..Goss.. 04/13/2019```

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@Kmlwx @high risk

SPC 12z HREF ensemble mean paints fixed layer STP of 4 to 7 across the region from around 03z to 08z MON

Also shows 40% or greater ensemble probability of fixed layer STP >3 from 03z to 08z MON

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18z HRRR at LR, so take it FWIW, but that radar image doesnt look good around 03z to 04z... string of sups

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So help me out guys. I just dodged tornadoes here in east Texas and for back to BWI tomorrow, landing around 9 pm. Am I going to be early enough to miss any potential severe ex?

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Interesting wording in the HWO about late tomorrow into tomorrow night.  Usually it says something like an isolated tornado is possible... but instead says this:

DAYS TWO THROUGH SEVEN...Sunday through Friday

Showers and thunderstorms are expected late Sunday through Sunday
night. Some thunderstorms will be capable of producing damaging
wind gusts or a tornado, as well as localized flooding from heavy
rain.

A Gale Warning may be needed for portions of the waters Monday and
Monday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is likely late Sunday or Sunday night.

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9 minutes ago, yoda said:

Interesting wording in the HWO about late tomorrow into tomorrow night.  Usually it says something like an isolated tornado is possible... but instead says this:

 

 

yeah, it says "a" tornado.

Possibly the only thing more fruitless than tracking snow in this region, is tracking severe. lol.

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1 minute ago, C.A.P.E. said:

yeah, it says "a" tornado.

Possibly the only thing more fruitless than tracking snow in this region, is tracking severe. lol.

But it says "some thunderstorms"... take out the damaging wind gusts part and it makes it seem like they are saying some thunderstorms will be capable of producing a tornado.  

I like that it says that spotter activation is likely too

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@high risk @Kmlwx @C.A.P.E. @Eskimo Joe

Excellently written updated evening AFD (posted at 951 PM) about the threat for late tomorrow into tomorrow night by the LWX mets... excellent points both for and against

Quote
SHORT TERM /12 PM SUNDAY THROUGH MONDAY NIGHT/...

Regarding severe potential Sunday afternoon and night, there are
several (very) favorable factors, but also a few notable limiting
factors.

1) Large, looping hodographs (indicative of low-level directional
and speed shear) strongly favors supercellular convection, with 0-
1/0-3 km SRH values of 250 to 400 m2/s2, respectively.

2) Mid/upper level diffluence and strong PVA ahead of a deep,
neutral to negatively-tilting upper shortwave; increasingly negative
tilt over time is evident in most guidance with a strong shortwave
rounding the base of a larger scale trough pivoting across the Great
Lakes Sunday night. This shortwave and its associated vortmax will
move directly over our area, but its exact strength and orientation
will be modulated by overnight convection over the Deep South, and
the finer scale evolution will likely play a role in storm mode over
the Mid-Atlantic (linear vs. supercellular vs. mixed).

3) A robust wind field is expected to result in 0-1/0-3/0-6 km bulk
shear of 50/65/90 kts (from a generally southwestward direction). At
first glance, this would be highly favorable for storm organization,
but if the aforementioned shortwave results in a line of convection
oriented more parallel to this low/mid level shear, or smaller
individual discrete cells are favored, there may be too much shear
given the more modest convective instability expected to be in
place, and this could disrupt some updrafts (too much horizontal
motion with not enough vertical motion to compensate). However, the
strong synoptic lift may make up for this, and if a line (or
cells/segments within a line) move orthogonal to the low-level wind
in a northeasterly direction, the effect of too much shear could be
offset.

4) The convective instability (CAPE) is expected to be modest,
generally 400-800 J/kg, but as mentioned previously this could be
offset by the strong synoptic lift.

5) The time of day is a limiting factor, and although most hi-res
guidance insists very little inhibition in the middle of the night
(along with increasing boundary-layer winds and CAPE after sunset,
which is a red flag that something a-typical is afoot), it is still
a touch more difficult to initiate new convection overnight. But the
overall environment suggests that at the very least existing
convection approaching from upstream should be able to largely
maintain itself well into the overnight.

6) The parent surface low will move across Ohio to over Erie
Pennsylvania, which is perhaps just a touch north and west of what
would be the absolute most ideal for severe weather, but not by
much. There may be a subtle split between more synoptic forcing to
the northwest and instability to the southeast, but not nearly
enough to negate the severe weather potential.

The main severe threats given the low-level wind field appear to be
damaging wind gusts and tornadoes, with hail a lesser threat
(especially if storms become more numerous/linear) given limited
CAPE to work with.

In addition to the severe potential, heavy rainfall will also
bring the threat for localized flooding. Given the very moist
airmass in place and climatologically high PWATs, as well as
the potential for training convection, flooding will be a
possibility. Much of the activity will be pushing east of the
metros and across the Bay around or just after daybreak Monday.
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52 minutes ago, Kmlwx said:

That is a heck of a write up - One of the best I've seen from LWX regarding severe weather in recent memory. 

Yep...just read it and agree ...incredible attention to details ..very descriptive..pretty deep stuff. 

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I'll agree with the props to LWX for the synopsis.      Looking at the early components of the 00z suite, the HRRR wants to initiate some convection during the late afternoon in the area that would have slightly better low-level instability to work with than later storms - this might be an earlier show, with lesser severe potential later at night.    The NAM nest avoids the earlier convection and has the show all being later at night, with an ominous radar showing cells and line segments.     That said, the cape is very tall and skinny, which reduces the severe potential at least a little, but the low-level shear is still very impressive.  

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54 minutes ago, high risk said:

I'll agree with the props to LWX for the synopsis.      Looking at the early components of the 00z suite, the HRRR wants to initiate some convection during the late afternoon in the area that would have slightly better low-level instability to work with than later storms - this might be an earlier show, with lesser severe potential later at night.    The NAM nest avoids the earlier convection and has the show all being later at night, with an ominous radar showing cells and line segments.     That said, the cape is very tall and skinny, which reduces the severe potential at least a little, but the low-level shear is still very impressive.  

This sounding is just WSW of DC in Fairfax County at 06z MON on the 00z NAM NEST:

2019041400_NAMNST_030_38.86,-77.35_sever

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You shouldn't be stuck, but there is likely to be two rounds of storms. Prefrontal storms will come through between 6 and 10 pm and then the frontal storms after 1am. 

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27 minutes ago, canderson said:

So what’s the over/under if my flight from Dallas lands at BWI at 8:55 pm?

I’m thinking I’ll be stuck here overnight.  

You'll be fine getting home.

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4 hours ago, showmethesnow said:

Nowhere near the experience and knowledge of those on here when it comes to severe but this coming Friday into Saturday has my interest somewhat.

That's what I get for scheduling a delivery of six cubic yards of mulch and a landscaping crew for my gardens this Friday.  Damn wedge tornado will probably suck up all my mulch.

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