2020 Mid-Atlantic Severe Weather - General Thread

[H2O]

4 hours ago, mappy said:

You mean Monday. Tomorrow’s action is down south 

Thanks for the correction. You are right. Should have said monday

[yoda]

3 hours ago, high risk said:

Two rounds of potential here on the NAM nest:  mid-morning and then mid-afternoon.    The morning has better wind fields but limited heating;  the afternoon will have better heating but weaker wind fields.    Regardless, both have healthy potential.

Regular 12z NAM soundings at 18z MON were not pretty looking at the soundings across the region... suxh as BWI/IAD/DCA/EZF... SBCAPE likely overdone, but even half of what it shows would be dangerous around here

[yoda]

LWX states severe threat is increasing in their afternoon AFD 

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
301 PM EDT Sat Apr 11 2020

.SYNOPSIS...

High pressure will shift offshore tonight through Sunday. Low
pressure will track to our west Sunday night into Monday,
ushering a strong cold front through the region Monday. The cold
front will stall out to the south for the middle portion of
next week, and waves of low pressure may track along the
boundary, bringing the potential for unsettled conditions.

&&

.NEAR TERM /THROUGH TONIGHT/...

The calm before the storm. Occasional mid-high level clouds
this evening, then clouds increase and thicken steadily from
southwest to northeast toward daybreak. Have a low chance of
showers for western areas after 06Z tonight.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...

Showers will continue to overspread the region from southwest to
northeast Sunday afternoon and become more widespread Sun
evening in response to strengthening low-level jet. Widespread
heavy rains expected late Sun night in zone of strong warm
advection pattern associated with a 60-kt 925mb/70-kt 850 mb
low-level jet. Chance of t-storms increases after 06Z.

Very active and hazardous weather is expected Monday morning
into early afternoon with the potential for QLCS to form ahead
of the front. Potential for damaging winds and embedded
tornadoes with this QLCS before mid-level dry slot moves in.
Latest 12z ECMWF simulated IR imagery now shows deep convection
forming within the dry slot region early Mon afternoon with
passage of secondary cold front and upper level system. Overall,
latest trends indicate severe wx threat is increasing.
Regardless of the severe wx threat, there will be very strong
post-frontal winds Mon afternoon with widespread high end wind
advisory event and potential for high wind warning in some areas
especially higher elevations and northern and central MD.
Anticipate that high wind watches will be issued for a large
portion of the fcst area next cycle.

[George BM]

A rare Day 3 update.

Day 3 Convective Outlook AMEND 1
   NWS Storm Prediction Center Norman OK
   0211 PM CDT Sat Apr 11 2020

...Virginia through central and eastern Pennsylvania and New
   Jersey...

   Have expanded the SLGT risk farther north into this region. Areas of
   rain and thunderstorms will likely be ongoing north of a warm front
   from PA and NJ into southern New England. This activity will shift
   northeast during the morning allowing modest destabilization to
   occur in the pre-frontal warm sector with MLCAPE from 400-800 J/kg.
   Storms are expected to redevelop along cold front and in association
   with deeper forcing accompanying the northeast-ejecting shortwave
   trough. Wind profiles with 50+ kt effective bulk shear along with
   large 0-1 km hodographs will promote a threat for organized storms
   including supercells capable of damaging wind and a couple of
   tornadoes.

[Kmlwx]

1 minute ago, George BM said:

A rare Day 3 update.

Day 3 Convective Outlook AMEND 1
   NWS Storm Prediction Center Norman OK
   0211 PM CDT Sat Apr 11 2020

...Virginia through central and eastern Pennsylvania and New
   Jersey...

   Have expanded the SLGT risk farther north into this region. Areas of
   rain and thunderstorms will likely be ongoing north of a warm front
   from PA and NJ into southern New England. This activity will shift
   northeast during the morning allowing modest destabilization to
   occur in the pre-frontal warm sector with MLCAPE from 400-800 J/kg.
   Storms are expected to redevelop along cold front and in association
   with deeper forcing accompanying the northeast-ejecting shortwave
   trough. Wind profiles with 50+ kt effective bulk shear along with
   large 0-1 km hodographs will promote a threat for organized storms
   including supercells capable of damaging wind and a couple of
   tornadoes.

Day 3 updates are extremely rare around these parts. Wow.

They must really want to communicate the potential threat. Otherwise - why not just wait for an official outlook update tonight for D2?

[Kmlwx]

30% D3 for the Carolinas also pretty robust. 

[yoda]

3 minutes ago, Kmlwx said:

Day 3 updates are extremely rare around these parts. Wow.

New day 3 map

[yoda]

3 minutes ago, Kmlwx said:

Day 3 updates are extremely rare around these parts. Wow.

They must really want to communicate the potential threat. Otherwise - why not just wait for an official outlook update tonight for D2?

Wouldn't be surprised to see ENH for us on Day 2 tonight and MOD down in the Carolinas... maybe into S VA

[Kmlwx]

7 minutes ago, yoda said:

Wouldn't be surprised to see ENH for us on Day 2 tonight and MOD down in the Carolinas... maybe into S VA

I could see mod for them. Not sure we'll be any higher than slight until uncertainty is less

[yoda]

1 minute ago, Kmlwx said:

I could see mod for them. Not sure we'll be any higher than slight until uncertainty is less

Well the afternoon AFD from LWX seems to be leaning that way IMO with its severe talk

[southmdwatcher]

I could possibly see outlook upgrades for DC/Baltimore area and southward through the Carolina's. However, don't expect any decisions until the early Monday morning SPC cycle.

[Eskimo Joe]

23 minutes ago, Kmlwx said:

Day 3 updates are extremely rare around these parts. Wow.

They must really want to communicate the potential threat. Otherwise - why not just wait for an official outlook update tonight for D2?

I'm getting kind of excited now.  These are all good trends up here.

[southmdwatcher]

We will also likely have a period of strong to damaging winds after the frontal passage.

[Kmlwx]

8 minutes ago, Eskimo Joe said:

I'm getting kind of excited now.  These are all good trends up here.

I don't like when SPC is upgrading so early. Recipe for a superstitious bust lol

[Kmlwx]

7 minutes ago, southmdwatcher said:

We will also likely have a period of strong to damaging winds after the frontal passage.

Yes LWX indicates high wind watches are likely coming. Especially for ridge tops and Northern Maryland

[Kmlwx]

Now we wait for the inevitable NAM run or HRRR run that socks us in and has like 3J/kg of CAPR

[southmdwatcher]

Just as an example......April 15, 2011 in MS/Alabama was a Moderate risk. That day had a messy storm mode for portions of those states, but could have verified High Risk in southern MS/AL. The system was a bit slower than forecasted. April 16th was a doozy of a day in SE VA and NC. A tamer version of that could be what we what we should look for and no High Risk for NC. Exceptional shear busted up the QLCS late morning in NC that day and allowed convection to become discrete south of the existing rain cooled boundary. Also we have the chance for supercells to form in the dry slot early afternoon.

[Kmlwx]

18z NAM (looking at the 12km right now) is a bit slower it seems. It's pushing the nose of instability through the area between like 17z and 21z. 

[Kmlwx]

There appears to have been a bit of a tendency to fatten up the CAPE a bit too on the soundings. Not a ton - but it had the "tall skinny" look a bit and it looks wider now. 

[southmdwatcher]

1 minute ago, Kmlwx said:

18z NAM (looking at the 12km right now) is a bit slower it seems. It's pushing the nose of instability through the area between like 17z and 21z. 

I hope that is not what pans out. That could be ugly for someone around here.

[Kmlwx]

50-55 knots of wind at 925mb still at 18z on Monday per the 12k NAM

75 knots at the 850mb level around DC at the same time. There's 90+kt 850 winds on the Eastern Shore at that time...

[southmdwatcher]

At 18z those wind fields with 800-1400  ML CAPE

[Kmlwx]

I'm guessing the GFS will (as always) spit out substantially lower CAPE values. Compromise in the middle would still be an active day. We seldom hit our "ceilings" on events - and I doubt we hit the ceiling on this one as well. But as CWG said...could be a turbulent morning/afternoon. 

[southmdwatcher]

Lapse rates were not great at 18z, but everything else looked primed. Maybe we get another great parameter day that just misses one ingredient. Two rounds of potentially severe storms are quite possible for central and eastern parts of our region.

[Kmlwx]

NAM nest sends a line through at 17-20z. That's about as good as we can get for this event. I'll be intrigued to see what the models show for synoptic wind after the front too. 

[Kmlwx]

NAM nest is pretty tame with winds behind the line it looks like. But even outside of sig storms AHEAD of the line, the model shows gusts over 50 knots in big parts of our area. That's HWW criteria. Going to be some power outages with that. 

[high risk]

5 minutes ago, Kmlwx said:

NAM nest sends a line through at 17-20z. That's about as good as we can get for this event. I'll be intrigued to see what the models show for synoptic wind after the front too. 

         The progged hodographs ahead of that line are remarkable.    If we get any heating to boost sfc-based cape, it will be a fascinating day around here.

[Eskimo Joe]

51 minutes ago, Kmlwx said:

I don't like when SPC is upgrading so early. Recipe for a superstitious bust lol

Shush.  If they go D2 MOD then I'll agree.  We can still fail on this in so many ways and I'm not going to be in 100% until 00z Monday but so far I'm liking what I'm seeing.

[Kmlwx]

15z SREF Tor Ingredients product has the 45 line kissing DC. That's an improvement from the prior run. 

@Eskimo Joe - I don't see s hitting moderate for this event. The closest I see a moderate getting is potentially to RIC. I see our ceiling in terms of the SPC scale at ENH. But that's not to say Mon won't be a fun day - it certainly could be. 

Although.....imagine if the models juice things up all the way to game time. I think I've just become way more conservative with weather since my debut on the forums in 2006.

[Eskimo Joe]

This is a great visualization of the expansive nature of the system as it moves up our way.