2020 Mid-Atlantic Severe Weather - General Thread

[40westwx]

On 9/24/2020 at 1:03 PM, Eskimo Joe said:

There are several out there, what was the title?

Challenger: The Final Flight

[Kmlwx]

CIPS has backed way off - par for the course. 

[high risk]

yeah, the shear profiles for later Tuesday have so much potential, but over the years, I've seen a ton of great fall setups fail here due to terrible lapse rates and instability.   Any system at this time of year that is strong enough to have great accompanying wind fields usually generates a lot of cloud cover and showers well out ahead of the front.

[Kmlwx]

1 hour ago, high risk said:

yeah, the shear profiles for later Tuesday have so much potential, but over the years, I've seen a ton of great fall setups fail here due to terrible lapse rates and instability.   Any system at this time of year that is strong enough to have great accompanying wind fields usually generates a lot of cloud cover and showers well out ahead of the front.

I'm having a hard time remembering what the cloud cover/precip situation was just ahead of the Sept 2012 event. Based on the SPC events page, it looks like that might have been an event that started earlier in the day. We had mesoscale discussions by mid morning it seems. 

It seems the guidance wants to track the low nearby or even to the southeast. The low being SE of us is going to probably nix any severe potential. We'll need to see if that trends back north and west a bit. 

[Stormfly]

Anyone recall October 01, 1986?  I spent that day moving radio transmitter hardware from Severn MD to White Hall, it was near 90°F and could feel the change coming by dinner time.  Nice line of storms rolled through.  Power knocked out and tower for our 2M repeater in Phoenix took a hit.  Next day was cooler thank goodness.

Also, two years ago to this day we had nice storms roll through.  A close hit to an overhead across the street knocked out power momentarily and the thunder set off a howling wolf on our porch. 

 

[high risk]

22 hours ago, Kmlwx said:

I'm having a hard time remembering what the cloud cover/precip situation was just ahead of the Sept 2012 event. Based on the SPC events page, it looks like that might have been an event that started earlier in the day. We had mesoscale discussions by mid morning it seems. 

       I do remember that event - another classic low cape, high shear fall event here, although this one had dew points into the low 70s.      I don't think that there was much precip out ahead of the line, but it was definitely cloudy.   The reports map looks way better than the event was - I remember being very surprised by the upgrade to MDT and very unimpressed by the line.    Most of the reports in our area were of single trees being knocked down.

[George BM]

8 hours ago, high risk said:

       I do remember that event - another classic low cape, high shear fall event here, although this one had dew points into the low 70s.      I don't think that there was much precip out ahead of the line, but it was definitely cloudy.   The reports map looks way better than the event was - I remember being very surprised by the upgrade to MDT and very unimpressed by the line.    Most of the reports in our area were of single trees being knocked down.

I remember that day as well. I remember some heavy showers throughout the day w/ breezy conditions. I remember getting home from school in Herndon hust after 2:30pm and being surprised that the main line was already right on my doorstep. Looking back at that thread I remember lots on here being surprised at how early the main line arrived as well. There were brief torrential rains and wind gusts into the 30s (mph) here from the line. I noticed no thunder/lightning at all from it. I too was surprised to see looking back at SPC archives for that event a few years later that we had been placed under a MDT risk for wind (45% non-hatched). That would just be a high-end ENH risk the way that SPC works today. I remember the lack of tornado warnings as well despite being in a 10% non-hatched tor risk.

The September 8th, 2012 event ten days prior, on the other hand, was a lot more impressive in the region with a lot of minor wind damage. I got wind gusts of 50+ mph in my neighborhood from that event. The funny thing is that the line from that event seemed more impressive down here than it did up the urban corridor where there was an actual MDT risk in the place... save for the Long Island tornadoes that day. 

As a whole though, that September was definitely a bit more exciting than usual severe weather-wise. 

[Kmlwx]

SPC has been throwing out mention of the *chance* of severe potential towards next weekend in the D4-8 outlooks the last day or two. Too far out. 

[yoda]

8 hours ago, Kmlwx said:

SPC has been throwing out mention of the *chance* of severe potential towards next weekend in the D4-8 outlooks the last day or two. Too far out. 

LWX in their afternoon AFD talked about it too

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
For the extended period, high pressure will be present Wednesday
into most of Thursday. An upper-level trough will be migrating to
the east, dipping down into parts of the Midwest. This will be the
driver for our next chance of rain as a cold front out ahead of the
trough will starting pushing through Thursday into Friday. The
latest GFS run has it getting here quicker than the ECMWF by about
12 hours so confidence on timing is still a little low. QPF totals
could pose a threat depending on timing and intensity of the front.
As for now, confidence remains low on any potential hazards for the
event. Winds will increase ahead of the front by about 5-10 knots.

[A777]

Front needs to slow down by 12 hours

[WeatherShak]

1 hour ago, A777 said:

Front needs to slow down by 12 hours

Please no.  Getting married on Saturday in my backyard

[A777]

SPC mentioning the possibility of some low-CAPE severe fun on Wednesday

[yoda]

Last chance saloon on Wednesday for this years severe?  From this morning's AFD:

LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Troughing is expected to lift from the Midwest across the Great
Lakes Wednesday overtop of a persistent and unusually strong ridge
of high pressure just off the Carolina coast. Warm/moist advection
along a surface front ahead of the trough will likely result in rain
showers breaking out across the Middle Atlantic on Wednesday. Dew
points will be unusually high for this time of the year, which
combined with the increasing shear and jet dynamics raises the
question of potential severe weather. The extent of any
thunderstorms and severe threat will be dependent at least in part
on how much instability there is, which may be modest.

[A777]

Looks like another high shear nonexistent CAPE event that produces nothing for us... maybe a few rumbles of thunder south of I-64

[North Balti Zen]

Could be that "severe season" never really ends this year and just rolls into 2021.

[George BM]

5 minutes ago, North Balti Zen said:

Could be that "severe season" never really ends this year and just rolls into 2021.

Yeah. Just wait until February... and also, prior to that, mid/late December.

[Eskimo Joe]

After the surprise February tornado outbreak, it would be fitting to bookend 2020 with another surprise event.

[A777]

5% wind

Quote

...NC/VA... Water vapor imagery shows a subtle shortwave trough over middle TN/northern AL moving across the southern Appalachians. This feature will begin to affect parts of VA/NC later this afternoon with slightly strengthening low/mid level winds and vertical shear. Scattered thunderstorms are expected to affect this region through the day, with the increasing shear likely resulting in a few weakly rotating storms. Forecast hodographs are not particularly favorable for tornadoes, but one or two of the storms could become sufficiently organized to produce locally gusty/damaging winds.

 

 

[Stormfly]

Nothing for us but wet breezes.

[A777]

                                                  Another high-shear low cape event...  This is the 14z HRRR

[George BM]

We've been Slighted in much of the region east of the mountains.

..LOWER GREAT LAKES TO MID-ATLANTIC/NORTHEAST    

SCATTERED THUNDERSTORMS ARE ONGOING ACROSS SOUTHEAST LOWER MI INTO   WESTERN OH WITH A HISTORY OF WIDESPREAD STRONG TO ISOLATED SEVERE   WIND GUSTS. THIS INITIAL ACTIVITY MAY STRUGGLE TO FURTHER INTENSIFY   OWING TO BOUNDARY-LAYER DEW POINTS IN THE LOWER 50S WITHIN A NARROW   SPATIAL CORRIDOR AHEAD OF THIS CONVECTION. IT SHOULD EVENTUALLY   OUTPACE THIS NARROW WEDGE OF SURFACE-BASED INSTABILITY AS IT SPREADS   EAST/NORTH OF LAKE ERIE LATER THIS AFTERNOON.    

A MORE PRONOUNCED SQUALL LINE IS EXPECTED TO DEVELOP AROUND 21-23Z   FROM CENTRAL NY TO CENTRAL VA AND SWEEP EAST-NORTHEAST ACROSS THE   NORTHEAST AND NEW ENGLAND COAST THROUGH EARLY TONIGHT WITHIN AN   INTENSE SHEAR/MINIMALLY BUOYANT ENVIRONMENT. THIS SQUALL SHOULD   DEVELOP AS THE ROBUST COLD FRONT IMPINGES ON LOW-LEVEL MOISTURE   ADVECTING NORTH FROM THE CAROLINAS/SOUTH ATLANTIC COAST. BETWEEN   00-03Z, MID 50S BOUNDARY-LAYER DEW POINTS SHOULD REACH AS FAR NORTH   AS EASTERN PA INTO SOUTHERN NEW ENGLAND ALONG THE TRACK OF SECONDARY   CYCLOGENESIS. WHILE LOW-LEVEL LAPSE RATES WILL PROBABLY REMAIN   WEAKER RELATIVE TO THE LOWER GREAT LAKES REGION, THE COMPARATIVELY   RICHER LOW-LEVEL MOISTURE SHOULD COMPENSATE. IT IS PLAUSIBLE THAT   LIGHTNING GENERATION MAY BE CONFINED TO AREAS FARTHER NORTH AMID   SCANT ELEVATED BUOYANCY AND GREATER LARGE-SCALE ASCENT.   NEVERTHELESS, THE PRESENCE OF A LOW-TOPPED SQUALL LINE AMID 50-60 KT   925-MB WINDS SUGGEST STRONG TO SEVERE WIND GUSTS ARE POSSIBLE EVEN   IN THE ABSENCE OF LIGHTNING. AS SUCH, THIS REGION HAS BEEN UPGRADED   TO SLIGHT RISK.    

..GRAMS/DEAN.. 11/15/2020  

[high risk]

There is zero doubt that a convective line will move through the region later today.    I've been skeptical about the potential for winds to mix down, but given the reports coming out of Ohio, I guess I can't argue with the SLGT.

[A777]

Peeks of sun in Rockville 

[JakkelWx]

Power showers 

[CAPE]

25 minutes ago, JakkelWx said:

Power showers 

[CAPE]

Latest from Mount Holly-

A cold front is surging through the Ohio Valley, where a convective band has developed. With 50-70 kt low-level winds, the convection has easily mixed severe-caliber wind gusts to the surface in portions of Indiana and Ohio late this morning, and convection-allowing models (CAMs) indicate maintenance of this convective band all the way to the East Coast through the evening hours. Meanwhile, in advance of the front, strong southerly flow has developed, with diabatic heating sufficient to mix these winds to the surface. Widespread gusts of 25 to 40 mph should be expected during the afternoon across the area, with locally stronger gusts at the coast. Current wind advisory looks sufficient in accordance with this threat (and with the subsequent post-frontal winds during the late evening; see below). There should be a relative lull in wind gusts after 4 pm as diabatic heating wanes (and before the front arrives). Based on CAM guidance, the convective band should generally reach the area in the 22z to 03z time frame. Strong wind gusts are likely in association with downward momentum transfer via the precipitation-cooled downdrafts. With winds aloft in the 40-60 kt range, expect decent coverage of strong to damaging gusts. SPC has increased the Day-1 convective outlook to a slight risk, which appears quite reasonable. Given the impressive dynamics of the system, shear is off the charts (0-6 km bulk wind difference 80+ kt). Combined with strong lift along the front (in the virtual absence of ambient instability), convective organization is likely to be maintained through the CWA during the evening hours. Little or no lightning is expected with the convection given the unfavorable buoyancy profiles, but this most certainly will not limit the wind threat posed by the convection.

[MN Transplant]

They had to delay the Browns game due to lightning (I assume).  Looks like it is more robust to the north, but we’ll see.

[A777]

 

[CAPE]

6 minutes ago, losetoa6 said:

Squall line looks decent atm nearing HGR

Hrrr intensifies the line as it comes east 

It has the precip max over my yard ofc lol.

[CAPE]

2 minutes ago, losetoa6 said:

You're not winning this time kid 

I hope not. The wind has dried out the driveway quite nicely.