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2021 Mid-Atlantic Severe Weather - General Discussion


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Storms firing along a boundary up my way, everywhere but my backyard. Been rumbling for 30+ min from stuff the popped up to my north and have drifted around in S PA 

Hoping the stuff west hits

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58 minutes ago, mappy said:

Storms firing along a boundary up my way, everywhere but my backyard. Been rumbling for 30+ min from stuff the popped up to my north and have drifted around in S PA 

Hoping the stuff west hits

Good rumbling coming from those storms to our north.  Had the mute the squawker on the Boltek.

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 Mesoscale Discussion 1628
   NWS Storm Prediction Center Norman OK
   1205 PM CDT Sat Aug 28 2021

   Areas affected...South-Central Pennsylvania...Western
   Maryland...Eastern West Virginia...and Northern Virginia

   Concerning...Severe potential...Watch unlikely 

   Valid 281705Z - 281900Z

   Probability of Watch Issuance...5 percent

   SUMMARY...Isolated damaging wind gusts possible with the strongest
   storms this afternoon.

   DISCUSSION...Visible satellite shows strong insolation this morning
   has given way to scattered convective development over the northern
   part of region. Surface temperatures have warmed into the mid 80s F
   amid rich low-level moisture (dew point temperatures in the upper
   60s and low 70s F). This is yielding around 1000 J/kg of MLCAPE.
   With weak convective inhibition and continued
   heating/destabilization, additional pulse-like storms are expected
   to develop throughout the afternoon and gradually move southeastward
   with time. Weak flow throughout the atmosphere will limit storm
   organization, however, a few isolated damaging wind gusts will be
   possible with the strongest storms given at least marginal low-level
   lapse rates near 8 C/km that should develop, particularly over parts
   of northern Virginia and vicinity later this afternoon. Given the
   expectation for an isolated damaging wind threat, watch issuance is
   not expected.

   ..Karstens/Grams.. 08/28/2021


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Severe Thunderstorm Warning

Severe Thunderstorm Warning
National Weather Service Baltimore MD/Washington DC
718 PM EDT Sat Aug 28 2021

The National Weather Service in Sterling Virginia has issued a

* Severe Thunderstorm Warning for...
  Southwestern Montgomery County in central Maryland...
  Southeastern Loudoun County in northern Virginia...
  Northwestern Fairfax County in northern Virginia...

* Until 800 PM EDT.

* At 718 PM EDT, a severe thunderstorm was located over Poolesville,
  moving south at 20 mph.

  HAZARD...60 mph wind gusts and quarter size hail.

  SOURCE...Radar indicated.

  IMPACT...Damaging winds will cause some trees and large branches
           to fall. This could injure those outdoors, as well as
           damage homes and vehicles. Roadways may become blocked by
           downed trees. Localized power outages are possible.
           Unsecured light objects may become projectiles.

* Locations impacted include...
  Germantown, Reston, Herndon, Vienna, Broadlands, Lansdowne, Lowes
  Island, Brambleton, Poolesville, Dulles International Airport,
  Potomac, Ashburn, Oakton, Sterling, North Potomac, Tysons Corner,
  Wolf Trap, Great Falls, Countryside and Arcola.


For your protection move to an interior room on the lowest floor of a

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With a more NW track, looks like there may be a decent risk of severe for I-95 and points east. Mount Holly mentioning the possibility in their AM AFD.

Models are converging on the eventual track of the remnant low, with the 00z CMC making a noticeable shift northward, much more in line with the ECMWF/GFS. The consensus track would lead to the heaviest rainfall axis generally in the northern half of the CWA, with alarming QPF of 2-5+ inches in a broad region along and north of the track of the low. Meanwhile, the warm sector may sneak into the southern CWA, where a threat of strong to severe storms would exist (given sufficient instability and strong vertical shear). In short, the latest models suggest a multi-faceted and rather impactful event for the region. Continue to monitor the latest forecasts, as we continue to fine-tune the forecast axis of heaviest rainfall and the areas with the highest risk of severe weather.

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From Mount Holly morning AFD-

Meanwhile, the southern portions of the area will likely experience some period of time in the system`s warm sector. Though the main impacts of this system may occur after Wednesday`s peak heating, substantial warm/moist advection beneath very favorable large-scale ascent from a strong and intensifying anticyclonic jet streak in the Northeast will likely keep a modestly unstable thermodynamic profile through the overnight hours within this region. Shear profiles are also appearing favorable, with 0-6 km bulk shear 30-40 kt and low- level SRH exceeding 200 J/kg. Convection in this region will likely be organized and potentially rotating as the low moves through, with isolated strong/severe wind gusts and even a couple of tornadoes possible. The SPC has upgraded the southern half of the CWA to a slight risk for Wednesday night, which is quite reasonable given the evolving pattern.

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SPC AC 310554 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1254 AM CDT Tue Aug 31 2021 Valid 011200Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MID-ATLANTIC... ...SUMMARY...

A few tornadoes could occur across the Mid-Atlantic States as the remnants of Ida move through the region on Wednesday. Isolated severe thunderstorms are also possible across the northern Plains Wednesday afternoon through Wednesday evening. ...Mid-Atlantic... Tropical Depression Ida is forecast to be centered near the KY/TN/VA border intersection early Wednesday morning. Continued northeastward motion of the system is anticipated, taking it off the Mid-Atlantic Coast Wednesday night. Moist low-level southerly flow ahead of this system will likely bring mid 70s dewpoints into the Mid-Atlantic region, helping to increase instability. Additionally, a more banded storm structure is probable by this stage in its life cycle, result in the potential for modest diurnal heating between the bands. Current guidance suggest afternoon temperatures across much of NC and VA will be in the 80s, with dewpoints in the low to mid 70s. These conditions are expected to result in sufficient instability for deeper, more persistent updrafts. In addition to the favorable thermodynamics, strong low to mid-level flow will persist around the remnants of Ida. In fact, some guidance suggests the system may slightly deepen as it encounters increased baroclinicity and undergoes the transition to an extra-tropical system. All of these factors indicate a tornado threat will persist throughout the eastern quadrant of the system as it moves through the Mid-Atlantic. A few convectively augmented wind gusts are possible as well.

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LWX gung ho for Wednesday severe

Wednesday continues to have the potential to be a high impact
weather day for our area. In summary, northwestern portions of
our forecast area need to prepare for significant rainfall and
the threat for flash and river flooding. The southeastern half
may see less rain overall, but will have a greater risk of
tornadoes, likely during the afternoon and evening. River
impacts are discussed in the hydrology section below.

Some guidance is indicating the system comes in two pieces.
During the morning hours, the heaviest and most widespread
rainfall will likely continue to be west of the Blue Ridge in
the zone of isentropic ascent/tropical moisture flux. This could
serve to allow some additional heating to occur especially over
southeastern portions of the area, allowing greater instability
to build. The low center will cross our area during the late
afternoon and evening, potentially strengthening as it
encounters increasing baroclinicity along the stalled front.
While models continue to wobble some, and there is definitely
some spread in exact solutions, the main stories remain in tact.
Precipitable water values will exceed two inches during this
time with deep, tropical warm cloud layers. A sharp mid level
trough and jet streak to the north will provide additional
forcing. Therefore, very high rain rates are possible during
this time, which could be especially hazardous to our
northwestern counties which will have already had a healthy
soaking of rain. Widespread and significant flooding could occur
in these areas if the worst case rain totals verify. However,
anywhere these rain rates persist for any amount of time could
see flash flooding. Meanwhile, low level shear will increase
markedly, especially near the low track and frontal zone, but
shear will be large across the warm sector. Model forecasts of
instability, low level lapse rates, and the shear combine to
suggest tornadoes will be a threat in the warm sector. Initial
CAM depictions of broken/cellular convection also support this
idea. Given the strong winds aloft, storms could also cause
damaging wind gusts. At this time, am not sure we are able to
mix into the strong wind fields aloft enough to warrant wind
advisories, but in general gradient winds will also increase as
the low passes.

Precipitation will taper off from west to east late Wednesday
night into Thursday morning, and clearing should rapidly follow.
Timing of departure is still a little uncertain, but most areas
should be dry by afternoon. Gusty north winds will continue, and
temperatures will remain below normal even where the sun comes
out. Lower humidity levels and cold advection will allow for
temperatures to dip into the 50s and lower 60s Thursday night,
with some potential 40s in the mountains.
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9 minutes ago, nw baltimore wx said:

The thing that excites me the most about that discussion is where they say gusty north winds and below normal temperatures.

Just as I am leaving the country. I am sure it will be warm and humid again when I return.

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