2020 Mid-Atlantic Severe Weather - General Thread

[George BM]

44 minutes ago, high risk said:

     FWIW, the NAM nest soundings look way better for Wednesday, both in terms of shear and instability, and the simulated radar isn't bad.    HRRR looks pretty good too, and all of the CAMs suggest storms scattered through the area late Wednesday.     If I wanted to go into weenie mode, I'd note some low-level curvature in the hodographs.....

     Thursday has a better shortwave.     For now, the Thursday soundings in the NAM nest lack instability, but deep-layer shear is there, and the event certainly has potential too.    But I'm intrigued by what I'm seeing for the first event and would suggest that we could get a day 2 SLGT for Wednesday in the early afternoon SPC update.

 

 I just got back from looking at some of the mesoscale guidance for tomorrow and thought: "Hmm... I bet @high risk made an appearance in the severe thread this morning."

Now we patiently await the day that we are actually put under your namesake AND it verifies. 

[high risk]

5 minutes ago, George BM said:

 I just got back from looking at some of the mesoscale guidance for tomorrow and thought: "Hmm... I bet @high risk made an appearance in the severe thread this morning."

Now we patiently await the day that we are actually put under your namesake AND it verifies. 

      Am I THAT predictable?         

      I can't even imagine what a synoptic setup would look like for an actual high risk here.     If it were to happen, my guess it would be for wind in a derecho event that has incredible predictability.       Derechos here haven't been particularly predictable in the past, but advances in NWP will eventually change that.

[yoda]

2 minutes ago, high risk said:

      Am I THAT predictable?         

      I can't even imagine what a synoptic setup would look like for an actual high risk here.     If it were to happen, my guess it would be for wind in a derecho event that has incredible predictability.       Derechos here haven't been particularly predictable in the past, but advances in NWP will eventually change that.

I don't think we will ever see a high risk here -- even the derecho in late June that was rampaging through the Ohio Valley the night of the infamous 00z LWX sounding (102/70 I think it was with nearly 6000 SBCAPE) only garnered a moderate risk on the 2000 SPC OTLK and the 0100 OTLK

[yoda]

Here's the sounding

[Kmlwx]

10 minutes ago, yoda said:

I don't think we will ever see a high risk here -- even the derecho in late June that was rampaging through the Ohio Valley the night of the infamous 00z LWX sounding (102/70 I think it was with nearly 6000 SBCAPE) only garnered a moderate risk on the 2000 SPC OTLK and the 0100 OTLK

I think the Northeast as a whole has seen one total high risk in history. I think it would be more likely for us to see a PDS Severe Thunderstorm Watch than a high risk. But - @high risk has a point. A lot of the outlook is based on predictability. If we have a CLEAR and OBVIOUS case of a massive severe outbreak days out ahead and it holds as we close, there could be a high risk at some point. And who knows what the future of the local climate will hold...

[high risk]

9 minutes ago, yoda said:

I don't think we will ever see a high risk here -- even the derecho in late June that was rampaging through the Ohio Valley the night of the infamous 00z LWX sounding (102/70 I think it was with nearly 6000 SBCAPE) only garnered a moderate risk on the 2000 SPC OTLK and the 0100 OTLK

        This would be an awesome discussion over a few beers at an AMS conference.     For the 2012 event, CAM guidance was really limited.    The NAM nest had little handle on this event, and the HRRR had some good runs but was still experimental.     There were real questions about whether the derecho would survive crossing the mountains, and even at 1z, SPC still wasn't totally sure how far east it would maintain strength.      I still envision getting to a point in such an event where there is agreement that an intense derecho will blast through the Ohio Valley and make it to the coast, and SPC will launch the HIGH.      It won't happen right away, but we'll get there.

[Kmlwx]

1 minute ago, high risk said:

        This would be an awesome discussion over a few beers at an AMS conference.     For the 2012 event, CAM guidance was really limited.    The NAM nest had little handle on this event, and the HRRR had some good runs but was still experimental.     There were real questions about whether the derecho would survive crossing the mountains, and even at 1z, SPC still wasn't totally sure how far east it would maintain strength.      I still envision getting to a point in such an event where there is agreement that an intense derecho will blast through the Ohio Valley and make it to the coast, and SPC will launch the HIGH.      It won't happen right away, but we'll get there.

It's truly hard to believe that 2012 was already almost a decade ago. 

I agree - I think that had we had a good handle that the complex would maintain intensity as it approached, we could have qualified for a high. The sheer number of reports backs that up. If there was the equivalent of "post season analysis" like they do for hurricanes, that could have been a high risk day IMO. 

I doubt we ever see a TOR based high risk in this area. Although...isn't it more about the number of reports than the intensity of individual events? Say we had a vigorous system (perhaps tropical in nature or hybrid) and it was clear that while there wouldn't be EF-5 stuff...we'd get a large amount of EF-0 to EF-2 and it was high confidence - would that be enough to trigger a high hypothetically? I doubt SPC would ever do that for a tropical system, though. 

[Kmlwx]

The other thing you have to remember - even with high confidence...the higher the outlook the higher the "egg on face" potential for SPC. There's already the old saying that meteorologists are always wrong...very few SPC forecasters would have the stomach to call a high risk for the nation's capital unless it was absolutely necessary. 

It's one thing to call a high where the local population understands what the risk categories mean and are familiar with severe weather. DC tends to have a "panic mode" inherently built into the population (just look at 495 with a half inch of snow). Can you imagine what a high risk would do to lay people around here? 

[yoda]

Just now, Kmlwx said:

The other thing you have to remember - even with high confidence...the higher the outlook the higher the "egg on face" potential for SPC. There's already the old saying that meteorologists are always wrong...very few SPC forecasters would have the stomach to call a high risk for the nation's capital unless it was absolutely necessary. 

It's one thing to call a high where the local population understands what the risk categories mean and are familiar with severe weather. DC tends to have a "panic mode" inherently built into the population (just look at 495 with a half inch of snow). Can you imagine what a high risk would do to lay people around here? 

True.  You could only go high risk here if the event was unfolding with as you say numerous tornadoes (EF2 or something) or a derecho coming in from the west.

The derecho in 2012 however, caught the region, including local TV mets off-guard per the NWS report though.

[mappy]

8 minutes ago, Kmlwx said:

It's truly hard to believe that 2012 was already almost a decade ago. 

I agree - I think that had we had a good handle that the complex would maintain intensity as it approached, we could have qualified for a high. The sheer number of reports backs that up. If there was the equivalent of "post season analysis" like they do for hurricanes, that could have been a high risk day IMO. 

I doubt we ever see a TOR based high risk in this area. Although...isn't it more about the number of reports than the intensity of individual events? Say we had a vigorous system (perhaps tropical in nature or hybrid) and it was clear that while there wouldn't be EF-5 stuff...we'd get a large amount of EF-0 to EF-2 and it was high confidence - would that be enough to trigger a high hypothetically? I doubt SPC would ever do that for a tropical system, though. 

you're telling me. I was preggo with mini-map at the time, and she starts second grade next week 

[Kmlwx]

6 minutes ago, mappy said:

you're telling me. I was preggo with mini-map at the time, and she starts second grade next week 

My mom just told me the other day that my 2nd cousins that I remember giving piggy back rides to are well into high school. Crazy. 

[high risk]

18 minutes ago, Kmlwx said:

I doubt we ever see a TOR based high risk in this area. Although...isn't it more about the number of reports than the intensity of individual events? Say we had a vigorous system (perhaps tropical in nature or hybrid) and it was clear that while there wouldn't be EF-5 stuff...we'd get a large amount of EF-0 to EF-2 and it was high confidence - would that be enough to trigger a high hypothetically? I doubt SPC would ever do that for a tropical system, though. 

    It would be a once-in-a-lifetime event, but if it can happen in upstate NY and in central NC.....      May 31, 1985 showed that outbreaks with high-end events CAN happen in the east.

   I envision a deepening 980 sfc low over NW PA during an afternoon, with intense wind fields at all levels and all CAMs showing discrete convection and strong, long-track UH signals over the Mid-Atlantic.   Of course, in an intense synoptic setup, we usually screw it up with either early morning crapvection.....

   A HIGH here would never happen for a TC remnant event.

[yoda]

MRGL remains for Day 2 on 1730 SPC OTLK... but talks of an upgrade

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1226 PM CDT Tue Sep 01 2020

   Valid 021200Z - 031200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE NORTHEAST/MID-ATLANTIC INTO THE OHIO VALLEY/MID-SOUTH...

   ...SUMMARY...
   Isolated strong to severe thunderstorms may occur Wednesday from
   parts of the Northeast/Mid-Atlantic into the Ohio Valley/Mid-South.

   ...Northeast into the Mid-Atlantic...
   An upper trough over Ontario/Quebec and the Great Lakes is forecast
   to develop across the Northeast and Quebec on Wednesday. The
   strongest mid-level flow should remain confined to parts of northern
   NY and New England, although modestly enhanced winds (around 30-35
   kt) at mid levels will likely extend as far south as the
   Mid-Atlantic. At the surface, a weak low initially over southern
   Ontario should develop northeastward through the day, with a
   trailing cold front moving southeastward across the Northeast and
   Mid-Atlantic. A warm front is also forecast to lift northward across
   parts of these regions through Wednesday evening.

   Poor mid-level lapse rates will be present across the warm sector,
   which should temper updraft strength to some degree through much of
   the day. Still, 500-1000 J/kg of MLCAPE should develop ahead of the
   cold front across parts of PA/NY into far western New England owing
   to diurnal heating of an increasingly moist low-level airmass.
   Greater instability (1500-2000 J/kg of MLCAPE) may be realized
   across parts of the Mid-Atlantic to the east of the Blue Ridge
   Mountains, where rich low-level moisture should be present and
   stronger diurnal heating will likely occur. Around 30-40 kt of
   effective bulk shear should act to organize storms as they form
   along/ahead of the cold front, and along a lee trough extending
   southward near/east of the Appalachians. A mix of multicells and
   marginal supercell structures will be possible.

   Isolated strong/gusty downdraft winds capable of producing some
   damage may occur as storms move eastward through early Wednesday
   evening given the enhanced mid-level flow. A tornado or two also
   appears possible with any of the more discrete storms, as low-level
   winds should be strong enough to support 100-150 m2/s2 of 0-1 km
   SRH. An upgrade to Slight Risk may be needed for parts of the
   Mid-Atlantic if current model trends continue, but confidence in
   overall storm coverage/intensity was not high enough to introduce
   greater severe probabilities just yet.

[Eskimo Joe]

1 hour ago, Kmlwx said:

The other thing you have to remember - even with high confidence...the higher the outlook the higher the "egg on face" potential for SPC. There's already the old saying that meteorologists are always wrong...very few SPC forecasters would have the stomach to call a high risk for the nation's capital unless it was absolutely necessary. 

It's one thing to call a high where the local population understands what the risk categories mean and are familiar with severe weather. DC tends to have a "panic mode" inherently built into the population (just look at 495 with a half inch of snow). Can you imagine what a high risk would do to lay people around here? 

 

1 hour ago, yoda said:

True.  You could only go high risk here if the event was unfolding with as you say numerous tornadoes (EF2 or something) or a derecho coming in from the west.

The derecho in 2012 however, caught the region, including local TV mets off-guard per the NWS report though.

All good points. Some could argue that Ivan in 2004 warranted a high risk for the area...there was something like 40 confirmed tornadoes from that event and it's highly unusual to have that number in this area. Heck, we get DY1 MOD Risk that "verifies" with like 7 EF-0 tornadoes. During Ivan, there was 29 F0/1, 10 F2, 1 F3.

[high risk]

36 minutes ago, yoda said:

MRGL remains for Day 2 on 1730 SPC OTLK... but talks of an upgrade

 

 

              Yeah, I really thought they should have pulled the trigger, but it's not a big deal if they wait.     SPC mentions questions about coverage/intensity; I thought that the most of the entire suite of 12z CAMs looked good with those aspects, but they clearly want to see if the trends in the guidance hold.

[Kmlwx]

3 hours ago, Eskimo Joe said:

 

All good points. Some could argue that Ivan in 2004 warranted a high risk for the area...there was something like 40 confirmed tornadoes from that event and it's highly unusual to have that number in this area. Heck, we get DY1 MOD Risk that "verifies" with like 7 EF-0 tornadoes. During Ivan, there was 29 F0/1, 10 F2, 1 F3.

I sort of alluded to that earlier. I feel like that would have been a no brainer high risk day if it had not been a tropical system. I don't think they go above slight if it is related to tropical or tropical remnants. That's definitely something that maybe should be discussed.

I get that the scale is supposed to denote the severity level - but the nature of categorical probs also is that COVERAGE and number of occurrences (regardless of intensity/magnitude) also go into the scale. 40 tornadoes should be a high even if they are all EF-0s...

We could get into the whole terminology debate too. I like that local mets have switched to saying "it's a 1 out of 5" on the scale for today. Rather than using the terms like "slight" - I've always been of the opinion that slight/mod/high is the wrong term set for the general public. 

[AdamHLG]

The "we are due" index is pretty high in several areas specifically:
1.) Derecho 
2.) Tropical system/remnants
3.) EF-2 or greater tornado
4.) Large scale river flooding event
 
Sooner or later the pendelum is going to swing back on us. 

Just curious. This was posted Jan 20. It’s now September 1. How did we do? Looks like we hit number 2 and number 3. Not number 1. Jury still out on 4? 2020 not done yet.


.

[yoda]

00z NAM soundings for both tomorrow and Thursday look pretty nice... Thursday looks a lil better IMO due to a bit stronger deep layer shear

[yoda]

SPC doesn't like today for us... but tomorrow... woah at the disco... here is the morning Day 2

   ...Central Appalachians into the Mid-Atlantic states...
   Model guidance continues to show a lower-latitude disturbance moving
   from the upper TN Valley east-northeastward into the Mid-Atlantic
   states by late afternoon.  With a very moist airmass located from
   KY/TN northeastward into PA/NJ south of the stalled front, showers
   and thunderstorms may be ongoing early Thursday morning across KY. 
   Cloud breaks ahead of this convection will lead to weak/moderate
   destabilization despite relatively warm 500 mb temperatures and
   modest mid-level lapse rates.  Scattered thunderstorm development
   will likely occur over the central Appalachians during the midday
   before spreading downstream towards the I-95 corridor during the
   afternoon/early evening.  In tandem with the diurnal storm
   development, flow fields within the 700-500 mb layer will strengthen
   during the day (30-40 kt at 700 mb increasing to 40-50 kt at 500 mb)
   and elongate hodographs.  A mixed mode of strong to severe
   clusters/linear segments plus supercells is likely.  Scattered
   damaging gusts and a few tornadoes are possible.  The tornado risk
   will continue to be re-evaluated at later outlooks but the potential
   for several supercells appears greatest in the MD/northern VA
   vicinity during the afternoon.  This activity will likely weaken
   during the evening as it moves towards the coast but some risk may
   continue well after dark.

[yoda]

LWX goes big for today and tomorrow in their morning AFD

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
406 AM EDT Wed Sep 2 2020

.SYNOPSIS...

A warm front will lift north of the area this afternoon. A
surface trough will linger across the area through Thursday,
before a strong cold front crosses the area Friday afternoon
with cooler and dry high pressure for the Labor Day weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...

Latest surface analysis shows our area is still wedged under high
pressure while a stationary front is stalled across North Carolina
and to our west. Tropical Storm Omar is sitting east of the Mid-
Atlantic region. East to southeasterly flow remains over our area. A
quasi zonal pattern remains across the Mid-Atlantic region aloft
with WSW flow along with pulses of shortwave energy.

Isolated to scattered rain showers continue to move across our CWA
from S to N this morning with low clouds. This is expected to
continue through this morning as the stationary boundary remains SW
of our area. This boundary will lift north as a warm front around
mid-day while SW flow develops and clouds begin to break. A surface
trough will develop east of the Blue Ridge and a cold front will be
approaching from the west. These along with shortwave energy aloft,
dew points in the mid 70s, and increasing instability, could result
in the development of scattered to numerous thunderstorms across our
area, especially between the late afternoon and evening. Shear will
be modest and there is the potential for damaging wind gusts with
any storms that develop. Tornadoes cannot be ruled out. There is
still a level of uncertainty with this forecast as the forcing is
just to our north and also how quick the cloud cover breaks behind
the warm front.

Tonight any break in the clouds could result in the development of
patchy fog, with low temperatures in the 60s and 70s. Drier
conditions, mainly after midnight. Cold front will be stalled just
north of our area.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...

On Thursday, weakening cold front will be lingering just to our
north while a secondary cold front quickly approaches from the NW.
Pulses of shortwave energy along with a wave of low pressure through
this front, SW flow, upper jet streak just to our north, modest
shear, and dew points in the mid 70s again will allow for the
development of showers and thunderstorms. Convection may remain
closed to the frontal position, so this will determine our local
impacts. The main threats are damaging wind gusts, while hail and
tornado threats remain more conditional.

[Kmlwx]

I know it's not a great product to use - but UH tracks for both today and tomorrow are very respectable for this area...

That's some nice language from SPC regarding tomorrow's outlook...especially because the TOR risk is already at 5%. September can be a good tor month around here...

[Kmlwx]

The ARW2 near the end of its run is VERY nice for the region. 

[Eskimo Joe]

2 hours ago, Kmlwx said:

The ARW2 near the end of its run is VERY nice for the region. 

Always Really Wet

[Kmlwx]

10 minutes ago, Eskimo Joe said:

Always Really Wet

I dunno - I know it had that rep before. This season it's been pretty gun shy on predicting big storms for us. ARW is actually less enthused than the ARW2. HRRR looks passable for this afternoon even. A tiny UH track over MoCo too  

It's REALLY dreary out right now, though. So we could fail on the instability side of things today. Pretty unusual for same areas to get it two times in two days. So I'm going to assume we either fail today or tomorrow. Tempted to put all my eggs in the tomorrow basket after reading the SPC disco and looking at the guidance. Even the GFS paints a decent amount of parameter space over the DC area tomorrow PM. 

[MN Transplant]

11 hours ago, AdamHLG said:

Just curious. This was posted Jan 20. It’s now September 1. How did we do? Looks like we hit number 2 and number 3. Not number 1. Jury still out on 4? 2020 not done yet.


.

In EJ's world, we only hit these if they are billion-dollar disasters.  So, still due

[Kmlwx]

6 minutes ago, MN Transplant said:

In EJ's world, we only hit these if they are billion-dollar disasters.  So, still due

Let's go for the biblical ice storm or the mass solar storm that sends us back to the 1800s. 

[high risk]

I completely get that SPC doesn't want to issue a huge SLGT on a day like today from TN to the northern NY border, but I would still argue for a SLGT in our area.   The CAMs still really like DC metro later today, and that's reflected in HREF probabilities.    Both the ops (left) and para (right) indicate high probabilities of updraft helicity exceeding 25.   (That's a low end threshold, but it still reflects that there is strong agreement in intense cells with at least weak rotation.   And the probabilities of higher UH thresholds are not terrible either....)

[Kmlwx]

9 minutes ago, high risk said:

I completely get that SPC doesn't want to issue a huge SLGT on a day like today from TN to the northern NY border, but I would still argue for a SLGT in our area.   The CAMs still really like DC metro later today, and that's reflected in HREF probabilities.    Both the ops (left) and para (right) indicate high probabilities of updraft helicity exceeding 25.   (That's a low end threshold, but it still reflects that there is strong agreement in intense cells with at least weak rotation.   And the probabilities of higher UH thresholds are not terrible either....)

And going back to the discussion we've all been having the last few days - a slight is so common around here there's little bust potential. Still pretty dreary here...so maybe that plays a role. 

[Kmlwx]

12z HRRR argues for a period of sunshine around DC for a little while at least. 

[Kmlwx]

Noteworthy parts of SPC

 Areas of precip and cloud cover will render a rather patchy or
   streaky planar buoyancy field today.  Still, with rich moisture over
   most of the warm sector, areas of sustained diurnal heating should
   offset modest mid/upper lapse rates enough for areas of 500-1500
   J/kg peak MLCAPE over higher terrain, and 2000-3000 J/kg over parts
   of the Mid-South and east of the Blue Ridge in VA.  Low-level and
   deep-layer shear generally should increase northward into areas of
   weaker overall instability, but may favor supercell potential as far
   south as central/southern VA.  Effective SRH of 150-300 J/kg may
   develop intermittently from there through northern NY, especially
   near and east of the prefrontal trough where surface flow is most
   backed.  Some part of that corridor may require an upgrade to
   unconditional probabilities once mesoscale  placement, coverage, and
   timing/forcing uncertainties are better resolved