2023 Mid-Atlantic Severe Wx Thread (General Discussion)

[high risk]

1 hour ago, Kmlwx said:

Too far out for now...but Sunday may have some potential - and does get a mention in the D4-8 outlook - but uncertainty is too high per their discussion (SPC). 

        The 500 mb forecasts look terrific for late Sunday, but I agree with SPC that the moisture ahead of the system right now looks iffy.    The weakening Saturday wave don't help things at all, as it disrupts what might be a longer period of southerly flow into our currently very dry air mass.

[mattie g]

On 4/6/2023 at 3:29 PM, NorthArlington101 said:

Meh, I know we love baseball but the sport has a historically tough time calling off games when needed. Not gonna complain about them being too cautious. The 1/14 stat is crazy to me.

Meh. Baseball sucks.

[Kmlwx]

Instability/moisture concerns ignored - CIPS is really highlighting the 120hr period 

[Kmlwx]

[yoda]

What exactly is a squeegee line lol

LONG TERM /SUNDAY THROUGH THURSDAY/...
A negatively tilted upper level trough will dig into the Ohio
River Valley on Sunday as the associated low moves over the Great
Lakes. A few models show the trough becoming cutoff as it moves
eastward creating uncertainty in the forecast. Either way, the
associated cold front will cross the region Sunday afternoon into
Sunday night bringing rain showers and thunderstorms. 12z
guidance from both the ECMWF/GFS have the front arriving in the
west of the Blue Ridge after 22z/6pm before pushing eastward
late Sunday night into early Monday morning. As for severe
weather, the threat is dependent on timing. The earlier the
front the more CAPE to work with compared to the latter. For
now, thinking a "squeegee line" of gusty showers and perhaps a
thunderstorm Sunday evening into Sunday night. CAPE values sit
between 400-800 j/kg with 0-6km bulk effective shear values
modeled at 45-60kts. Wind would be the primary threat from this
line as it pulls through. Much needed rain will also accompany
this boundary, but not enough to quell the current drought/fire
weather concerns.

[MN Transplant]

17 minutes ago, yoda said:

What exactly is a squeegee line lol

LONG TERM /SUNDAY THROUGH THURSDAY/...
A negatively tilted upper level trough will dig into the Ohio
River Valley on Sunday as the associated low moves over the Great
Lakes. A few models show the trough becoming cutoff as it moves
eastward creating uncertainty in the forecast. Either way, the
associated cold front will cross the region Sunday afternoon into
Sunday night bringing rain showers and thunderstorms. 12z
guidance from both the ECMWF/GFS have the front arriving in the
west of the Blue Ridge after 22z/6pm before pushing eastward
late Sunday night into early Monday morning. As for severe
weather, the threat is dependent on timing. The earlier the
front the more CAPE to work with compared to the latter. For
now, thinking a "squeegee line" of gusty showers and perhaps a
thunderstorm Sunday evening into Sunday night. CAPE values sit
between 400-800 j/kg with 0-6km bulk effective shear values
modeled at 45-60kts. Wind would be the primary threat from this
line as it pulls through. Much needed rain will also accompany
this boundary, but not enough to quell the current drought/fire
weather concerns.

Ha, interesting.  I would interpret this as a thin line with dry conditions behind.  It does look like DPs in the 20s/30s for Tuesday and Wednesday.

[nw baltimore wx]

14 hours ago, yoda said:

What exactly is a squeegee line lol

LONG TERM /SUNDAY THROUGH THURSDAY/...
A negatively tilted upper level trough will dig into the Ohio
River Valley on Sunday as the associated low moves over the Great
Lakes. A few models show the trough becoming cutoff as it moves
eastward creating uncertainty in the forecast. Either way, the
associated cold front will cross the region Sunday afternoon into
Sunday night bringing rain showers and thunderstorms. 12z
guidance from both the ECMWF/GFS have the front arriving in the
west of the Blue Ridge after 22z/6pm before pushing eastward
late Sunday night into early Monday morning. As for severe
weather, the threat is dependent on timing. The earlier the
front the more CAPE to work with compared to the latter. For
now, thinking a "squeegee line" of gusty showers and perhaps a
thunderstorm Sunday evening into Sunday night. CAPE values sit
between 400-800 j/kg with 0-6km bulk effective shear values
modeled at 45-60kts. Wind would be the primary threat from this
line as it pulls through. Much needed rain will also accompany
this boundary, but not enough to quell the current drought/fire
weather concerns.

They have them in Baltimore at the corner of Pratt St and the end of I 83.

[csnavywx]

Saturday looking halfway decent for southern areas. Tendency towards less AM precip and a bit of clearing ahead of the front. Timing is good. Probably around 500-1000 MLCAPE and great directional shear, DPVA and jet support ahead of a neg. tilt trough. Worth an extension of SLGT northwards. 

[yoda]

Pretty decent squall line I guess on 18z NAM NEST rolling through Saturday evening around dinnertime... looks like 18z NAM has same idea

[yoda]

14 hours ago, csnavywx said:

Saturday looking halfway decent for southern areas. Tendency towards less AM precip and a bit of clearing ahead of the front. Timing is good. Probably around 500-1000 MLCAPE and great directional shear, DPVA and jet support ahead of a neg. tilt trough. Worth an extension of SLGT northwards. 

Good call sir

Intriguing disco too 2/5/15

 Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0105 AM CDT Fri Apr 21 2023

   Valid 221200Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
   CAROLINAS INTO EASTERN VIRGINIA AND MARYLAND...

   ...SUMMARY...
   Scattered severe storms are expected from parts of the Carolinas
   into the Mid Atlantic Saturday afternoon and evening. Hail, damaging
   gusts, and perhaps a brief tornado will all be possible. A marginal
   severe threat could also develop in parts of Florida and in parts of
   Texas.

   ...Synopsis...
   A negative-tilt upper trough will swing northeastward across the OH
   Valley and across the Appalachians during the day, with strong
   height falls into the Mid Atlantic by late afternoon or early
   evening. To the west, moderate west/northwest flow aloft will
   persist over the southern Plains with an upper ridge over the West.

   At the surface, low pressure will gradually deepen as it moves
   across western NY into parts of southwest Ontario, with cold front 
   pushing rapidly east across the Carolinas, VA and PA during the
   afternoon. Ahead of the front, 50s F dewpoints will be common into
   PA and NJ, with 60+ dewpoints from southeast VA southward. Aiding
   moisture advection will be a 40+ kt low-level jet at 850 mb, which
   will also increase low-level shear.

   Elsewhere, moisture return will occur from Deep South TX up the Rio
   Grade Valley, reaching parts of central TX late as an east-west
   oriented cold front makes southward progress through the period.

   ...Carolina/Mid Atlantic...
   Heating and moisture advection will lead to a favorably unstable air
   mass for severe storms as the upper wave and surface trough push
   east during the afternoon. MLCAPE will exceed 1000 J/kg over much of
   the warm sector, and primarily from eastern VA southward. Although
   instability will be weaker farther north into PA and NJ, this will
   be in the area experiencing strong cooling aloft with the upper
   vorticity max. Overall, hodographs will favor cellular activity with
   storms ahead of the cold front. A broken line or perhaps fully
   linear storm mode may occur with time as the cold front surges. Hail
   will be favored during the day, and modest SRH values of 100-150
   m2/s2 and lack of a cap may support a few supercells. The severe
   risk is expected to wane as it approaches the coast due to
   stabilization.

[yoda]

LWX morning disco re the threat also looks nice

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
A deep mid/upper low will lift from the Great Lakes into
Ontario Saturday. A lead shortwave will take on a negative tilt
as it approaches and crosses the area during this time. Strong
upper-level divergence beneath a coupled jet structure and
strong PVA are expected to cross the area during peak heating.

In the low levels, a strong cold front will be moving across the
area. Strong and deep convergence will aid in lift, compensating
for a lack of stronger CAPE given modest moisture return. Still,
CAPE values of 300-800 J/kg are expected right along the front.
Strong surface-3km AGL shear of 35-50 kts is expected along the
front as well, along with some backed near-surface flow and SRH
of 100-250 m2/s2. A dry slot in the morning will lead to ample
surface heating near/east of I-81 and especially in the I-95
corridor (where dew points will also be a touch higher). A few
discrete cells (possible supercellular activity) may form during
the midday to early afternoon hours just ahead of the front
posing a risk of gusty winds, hail, or a couple brief tornadoes.
Then, as the strongly forced frontal system crosses, a squall
line will likely develop. This line may contain strong to
damaging wind gusts, with a continued conditional risk of spin-
ups given the strong shear. The intensity of convection may
further be aided by steep mid-level lapse rates of 7-8 C/km in
the 700-500 hPa layer along and ahead of the front.

A low-level jet of 40+ kts at 850 hPa will advect in higher
moisture content (i.e. PWs of 1-1.5") right along the front.
Flow may be briefly boundary-parallel, resulting in some
training and up to 2" of rain in a few localized areas. Should
this rainfall occur over urban centers, some minor flooding
issues could result. Otherwise, recent dry conditions should
prevent more widespread flooding concerns.

[CAPE]

Slight risk for much of the eastern half of our region.

SPC disco excerpt-

...Mid Atlantic/Northeast southward into the Carolinas... An extensive band of convection will likely be ongoing at the start of the period from the southern Appalachians into the lower Great Lakes region. Modest diurnal heating ahead of this band will result in some destabilization. MLCAPE of 1000-1500 J/kg is expected to develop from southeast VA into parts of the Carolinas, decreasing with northward extent to less than 500 J/kg across northern portions of the Mid Atlantic and Northeast. Meridional mid/upper-level flow will likely result in messy convective mode, with a mixture of clusters, bowing segments, and possibly a few embedded supercells possible. For the Delmarva area and northward, locally damaging gusts will likely be the primary threat, though backed surface winds and increasing low-level shear/SRH may support a tornado or two as well. From the Tidewater region into portions of the Carolinas, stronger instability will support a greater hail threat, in addition to a risk of locally damaging gusts and a couple of tornadoes. At least the southern portion of the Slight Risk area may also see multiple rounds of storms, with prefrontal convection through midday and robust redevelopment along the cold front possible by mid/late afternoon.

[CAPE]

Snippet from Mount Holly AFD-

The model forecast soundings indicate low instability, generally under 1000 J/kg, however there is near 40 knots of effective shear. This is looking like a mid/high shear and lower CAPE setup. The timing of the convective band would be when the instability is maximized though. The strong forcing for ascent that arrives early this evening with the cold front may compensate for the lower instability. As a result, there is some risk of a few strong to severe thunderstorms with locally strong/damaging wind gusts the main threat especially with a low-level jet of around 40 knots. Overnight guidance continues to hint at surface flow backing a bit as the line of storms approaches. This would increase the low- level helicity or spin. In addition to increased helicity, model soundings show low-level 0-1 km shear around 20-25 kt. This could result in a potential tornado or two developing as these storms move through. The greatest risk overall looks to be in Delmarva and SE PA, with slightly lower chances elsewhere. Given the instability forecast to be on the lower side, convection should tend to be lower topped with a linear mode given deep south to southwest flow.

[CAPE]

Pretty interesting sounding on the 3km NAM for the central eastern shore(around Denton) as the depicted line is approaching. A general clockwise curve on the hodograph in the lower/mid levels.. decent 0-3km SRH. Modest chance for a tornado? Dry air aloft/ respectable DCAPE suggests a chance for stronger winds to mix down. 

 

[batmanbrad]

My phone just gave me a notification of a severe thunderstorm watch being issues for much of the area...  this following the meso discussion issued about 1/2 hour ago.

[high risk]

Box coming shortly.    Instability won't be great this afternoon, but with the strong wind fields and ascent, I'm buying the idea of at least some damaging wind events.

[George BM]

Severe Thunderstorm Watch for the region now. NOAA weather radio.

[batmanbrad]

wow, rather substantial size for this watch box:

https://www.spc.noaa.gov/products/watch/ww0159.html

[vastateofmind]

On 4/6/2023 at 3:57 PM, mappy said:

Can you share the radio you use? I need a new one as well and looking for recommendations on brand/features 

Absolutely! This morning's STW reminded me that severe season is pretty much here...and I need to get off my arse and order a radio. I have several models saved on Amazon, but I'll let you know what I narrow the selection down to.

[Eskimo Joe]

Cell near Culpepper warned. Definitely looks like a little notch too.

[NorthArlington101]

Cell near Culpepper warned. Definitely looks like a little notch too.

Warned now. Definitely decent rotation

[SnowenOutThere]

Definitely some good rotation.

 

[mappy]

35 minutes ago, vastateofmind said:

Absolutely! This morning's STW reminded me that severe season is pretty much here...and I need to get off my arse and order a radio. I have several models saved on Amazon, but I'll let you know what I narrow the selection down to.

Thank you! 

[Kmlwx]

Actually looks decent on radar for the DC Metro area. Some lead activity has developed as well. Nasty looking bow structure coming up through VA. 

[yoda]

What is that near Gainesville/Haymarket area on radar?

[arlwx12]

The Haymarket storm just got warned.

[Kmlwx]

5 minutes ago, yoda said:

What is that near Gainesville/Haymarket area on radar?

Has looked like a bookend vortex kind of feature for a while. We seemingly see these frequently with this kind of storm trajectory. That's seemingly where the highest odds for a gustnado or short lived tornado exist IMO. 

[aldie 22]

Weak

[dailylurker]

This seems like a flood threat more then severe for the DC area. Looks like some training storm moving into my area in a few minutes. 

[Kmlwx]

Uptick in lightning showing up in the ENTLN data near Pleasant Valley/LWX radar - probably an indication of increasing intensity (at least for the moment) in that part of the line. That's likely an area to watch for anything severe now.