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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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12 minutes ago, Kmlwx said:

I'm definitely a little more "pumped" than I was for our last tropical event. Seems we are in a better position for some activity. 

Euro went north with the rain this morning.  Storm cancel.  

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1 minute ago, H2O said:

Euro went north with the rain this morning.  Storm cancel.  

Eh - with the water "incidents" you and I have both had recently...thinking we can pass on the rain if it means having some exciting radar watching for spinnys. Even on the dry days our lawn has been like a saturated sponge when you walk on it. 

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Just now, Kmlwx said:

Eh - with the water "incidents" you and I have both had recently...thinking we can pass on the rain if it means having some exciting radar watching for spinnys. Even on the dry days our lawn has been like a saturated sponge when you walk on it. 

I don't need ark floating rain but a weak ass spin thing would be fun

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Just now, yoda said:

Thought you would be with LWX going pretty much all in in their morning AFD 

I've been burned twice this summer. Hopefully I'm wrong and we get slammed, it's been years since we've had a decent remnants system in Baltimore/DC proper. I will say that if I'm from US 15 west in Maryland, or the WV panhandle there could be some decent rainfall totals aided by terrain so someone out west of here could be in for a fun day tomorrow.

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DAY 1 SPC 1300Z OTLK 

   ...Northern VA to the Delmarva this afternoon/evening...
   Surface heating will be strongest the first half of the day, prior
   to the arrival of the thicker high clouds from the remnants of Ida. 
   At the surface, a weak front sagging southward from PA toward
   northern VA will provide a focus for thunderstorm development this
   afternoon into this evening.  Moderate buoyancy (MLCAPE of 1500-2000
   J/kg) is expected in the warm sector as surface temperatures warm
   into the 80s with dewpoints at or above 70 F.  Though midlevel lapse
   rates will be poor in the moisture plume aloft emanating from Ida,
   low-level lapse rates will be relatively steep with daytime heating,
   and there will be an increase in the 700-500 mb flow into the 40-50
   kt range this afternoon.  These factors will support a threat for
   damaging winds with the stronger cells/clusters this afternoon into
   this evening. 
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1 hour ago, yoda said:

Now if you can only get @Eskimo Joe to join in... pretty sure @high risk and @MN Transplant are in

         I'm in on SVR.     I'm not in on widespread flooding rains until you get further north and northwest, although there will be isolated local flooding where recent heavy rains have occurred.    

         Right now, guidance shows most of Wednesday being dry which will allow for some heating for sure.     We then get some bands of convection arrive later in the day, with perhaps some moderate instability and likely strengthening low-level wind fields.     If some of the more aggressive guidance is correct, these won't be little spin-ups in a big shield of rain;  these will be legitimate supercells embedded in intense convective bands.    This UH image from the 12z HRRR would warrant a potential ENH for tornadoes:

 

uh25_max.us_ma.thumb.png.c1f9c2f51b9f1305dc4436a20ccabeb5.png

  

       There are plenty of ways that this could fail, and we often fail here, but this setup has *potential* to be a big deal if we legitimately heat up tomorrow.    As for the rain, there could be some sneaky higher totals tonight, and those bands tomorrow evening will have torrential rainfall, but the heaviest rain will overall be too progressive, and the periods of intense rain will overall be relatively short-lived until you go further north.

 

 

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39 minutes ago, high risk said:

         I'm in on SVR.     I'm not in on widespread flooding rains until you get further north and northwest, although there will be isolated local flooding where recent heavy rains have occurred.    

         Right now, guidance shows most of Wednesday being dry which will allow for some heating for sure.     We then get some bands of convection arrive later in the day, with perhaps some moderate instability and likely strengthening low-level wind fields.     If some of the more aggressive guidance is correct, these won't be little spin-ups in a big shield of rain;  these will be legitimate supercells embedded in intense convective bands.    This UH image from the 12z HRRR would warrant a potential ENH for tornadoes:

 

uh25_max.us_ma.thumb.png.c1f9c2f51b9f1305dc4436a20ccabeb5.png

  

       There are plenty of ways that this could fail, and we often fail here, but this setup has *potential* to be a big deal if we legitimately heat up tomorrow.    As for the rain, there could be some sneaky higher totals tonight, and those bands tomorrow evening will have torrential rainfall, but the heaviest rain will overall be too progressive, and the periods of intense rain will overall be relatively short-lived until you go further north.

 

 

Hope not. Isaias was a little to close for comfort in my neck of the woods.

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LWX AFD from this morning... sounds like a fun afternoon and evening 

NEAR TERM /THROUGH TONIGHT/...
Latest surface analysis depicts a strong area of low pressure
over central Ontario with its attendant cold front draped across
the Great Lakes region down into Indiana/Ohio. The stationary
front that had been sitting along the MD/PA border has lifted
northward as a warm front this morning as high pressure moved
offshore. Water vapor satellite imagery depicts the large-
scale upper trough, whose axis runs from Ontario into Wisconsin.
Radar/IR satellite depict some ongoing convective activity out
ahead of the aforementioned cold front across the Ohio Valley,
which is starting to taper off.

With high pressure having shifted offshore and a warm front well
to our north, strong warm air advection is beginning to take
shape across the region. The first half of the day will be
rather uneventful, with only a little early morning fog in the
valleys in our far western zones perhaps. Cloud cover will
gradually increase throughout the morning as warm advection
increases.

This afternoon is where things start to get a little more
interesting. High temperatures are expected to rise into the
mid-upper 80s this afternoon, with dewpoints rising into the
mid-upper 60s and perhaps even some near 70. This will result in
a fairly wide swath of moderate CAPE values in the 1500-2000
J/kg range ahead of the approaching cold front (primarily east
of the Blue Ridge). Additionally, hi-res guidance hints at a
corridor of even higher CAPE amounts (closer to 2500 J/kg). A
subtle shortwave ahead of the main trough will move overhead
this afternoon. This combined with 10-15 kts of surface SSW flow
colliding with the bay breeze, should result in thunderstorm
development this afternoon ahead of the main line of storms,
which will come through during the evening. This afternoon round
could pose a threat for an isolated tornado or two as deep
layer shear begins to increase. The primary convective mode with
storms this afternoon will be supercellular. Tornado threat
with this round would stem from backed low level flow near the
bay breeze. Steep low- level lapse rates will yield the threat
for damaging winds as well. Additionally, while not the largest
threat, hail is still a threat with the fist round of storms.
Think it will be mostly on the smaller side given weak mid-level
lapse rates, but can`t rule out some larger hail should we get
a stronger supercell to form.

The second round of convection will come through during the
evening hours. This will be more of a linear structure
associated with the cold front. Primary threat with this round
will be damaging straight-line winds. An isolated tornado also
isn`t out of the question with round 2 either in any properly
oriented evening linear activity as a low level jet increases
ahead of the front. However, low-level winds may be more
southwesterly by that point (limiting SRH). Time of day and less
than ideal low level thermodynamics could be limiting factors.

In addition to the severe threat, as the front becomes more
parallel to the upper flow, forward propagation of linear
features will tend to slow down as well. This could limit
robust, forward- moving downdrafts. This fact may also lead to
some locally heavy rain totals, especially in eastern part of
the CWA, as clusters could train over areas for a time.
Hydrologically sensitive areas due to recent rainfall will be
most susceptible to any flooding, as precipitable water values
will not be excessively high.
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1300z OTLK from SPC 

 

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0749 AM CDT Wed Sep 08 2021

   Valid 081300Z - 091200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE MID-ATLANTIC REGION AND NORTHEAST...

   ...SUMMARY...
   A few tornadoes and scattered damaging thunderstorm winds are
   expected across portions of the Mid-Atlantic region and Northeast
   this afternoon and evening.

   ...Synopsis...
   A high-amplitude mid/upper-level pattern will prevail over the CONUS
   this period, featuring:
   1.  A strong anticyclone moving slowly east-southeastward over the
   Great Basin and Four Corners region, anchored by a 598-600-dm 500-mb
   high, and
   2.  A well defined trough extending south-southwestward from a
   cyclone now over northeastern ON.  As the cyclone moves
   northeastward to the QC Hudson Bay coastline, a series of shortwaves
   and vorticity maxima will traverse the amplifying trough over the
   Great Lakes, Ohio Valley and southern Appalachians.

   At the surface, 11Z analysis showed a cold front from southwestern
   ON across southwestern IN, southeastern MO, southern OK, northwest
   TX, and southeastern NM.  A dissipating, quasistationary to warm 
   frontal zone was drawn from the northern Chesapeake Bay region
   southwestward across middle/eastern TN to south-central TX.  By 00Z,
   the cold front should extend from VT/eastern NY southwestward across
   south-central PA, middle/eastern TN, northern MS, and central/west-
   central TX.  By the end of the period, the front should reach
   central/southern New England, southeastern VA, western SC,
   south-central AL, and portions of south-central/southwest TX.

   ...Northeastern CONUS to Mid-Atlantic/Carolinas...
   Scattered thunderstorms are forecast to develop during the midday
   through afternoon near the cold front, from northern NY across
   western PA, WV and eastern KY.  Additional activity should form in
   the warm sector over the Mid-Atlantic into the Carolinas.  The most
   intense, well-organized convection in both regimes (which may merge
   over the Susquehanna/Delaware Valley region by late afternoon)
   should be in a corridor of greatest shear and return-flow buoyancy
   from eastern NY and VT southwestward toward the DC vicinity, with
   damaging to severe gusts being common.  A few tornadoes will be
   possible as well, along with isolated large hail.  At least isolated
   severe-wind potential may persist eastward over central/southern New
   England and the southeast NY/Long Island region this evening. 
   Farther south into the Carolinas, activity will be less-organized,
   but still capable of isolated severe hail/wind.  Isolated damaging
   gusts also may occur with the frontal convection in higher terrain
   of the central/southern Appalachians, amidst weaker but still
   marginally supportive instability.

   Strong southwesterly flow and broad height falls will spread over
   the Mid-Atlantic and Northeast today along/ahead of the front and
   east of the slowly progressive upper trough, with largely front-
   parallel winds contributing to a dominant quasi-linear convective
   structure.  However, sufficient deep shear (35-45-kt effective-shear
   magnitudes as far south as MD/northern VA) and low-level SRH (150-
   250 J/kg effective values) will support early-stage discrete
   supercells, as well as line-embedded supercells, bows and
   mesovortices.  Pronounced weaknesses in the 2-4-km hodographs remain
   evident, which further indicate potential for messy storm
   structures.  A returning plume of mid/upper 60s F surface dew points
   is expected east of the Blue Ridge, and into southeastern
   NY/southern New England. This will act in tandem with diurnal
   heating to offset modest lapse rates aloft and yield MLCAPE in the
   500-1500 J/kg range, generally increasing southward.  MLCAPE values
   of 1500-2000 J/kg are possible over southeastern VA and the
   Carolinas, but amidst weaker midlevel winds and deep shear
   supporting multicells and marginal/transient supercells.
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i have this "farmer forecasting" theory that we don't usually do well with storms when we're having a breezy day leading up to it.  it'll probably fail with a cold front pushing through later, but curious how we do this afternoon.  hoping it does hold off because i want to get a trail ride in.

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4 minutes ago, 87storms said:

i have this "farmer forecasting" theory that we don't usually do well with storms when we're having a breezy day leading up to it.  it'll probably fail with a cold front pushing through later, but curious how we do this afternoon.  hoping it does hold off because i want to get a trail ride in.

Would think it's not just about wind speed - but more important wind direction. Consider a breezy south wind bringing in humid/unstable air with a warm front passage. That would be an indicator of potentially higher severe potential versus a stiff NE breeze bringing in a wedge in the cool season or spring/fall. 

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Just now, yoda said:

Would think there will be a MCD coming soon for the area

Radar is pretty empty other than the stuff approaching the Northern Neck. Seems the guidance had stuff kind of later than usual for us (0-2z). May be waiting for an MCD for a while. 

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5 minutes ago, Kmlwx said:

Would think it's not just about wind speed - but more important wind direction. Consider a breezy south wind bringing in humid/unstable air with a warm front passage. That would be an indicator of potentially higher severe potential versus a stiff NE breeze bringing in a wedge in the cool season or spring/fall. 

true, we certainly would expect severe during a tropical storm running under us, but something about having that stagnant air mass that we score in.  i'm mostly just basing it off experience without any science, which is why it'll probably fail lol.  definitely agree with your point for today's example.

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