2019 Mid-Atlantic Severe Wx - General Discussion

[Kmlwx]

No real changes on the 1730z

[yoda]

3 minutes ago, Kmlwx said:

No real changes on the 1730z

I do like the talk of the cold pool though tbh

[H2O]

tomorrow will depend on the usual storm cloud blow off from today's midwest action.  Need full sun all morning

[mattie g]

31 minutes ago, H2O said:

tomorrow will depend on the usual storm cloud blow off from today's midwest action.  Need full sun all morning

It's all about the cold pool.

[high risk]

I'm definitely not ready to be in for this.      I do understand the SPC optimism based on the shear and the arrival of a well-timed vort.     But I don't like that multiple CAMs show an MCS coming out of OH later tonight and then falling apart as it approaches around midday tomorrow.     To be fair, the models that have that scenario do develop another round of convection later in the day, and it could certainly be severe, but we usually run into instability problems in those events due to the cloud shield or, in the worst case scenario, sfc outflow.

I still think we can score on either 1) the original midday/early afternoon line or  2)  new development later in the day , but I need to see the later CAM solutions look more favorable.

 

[yoda]

@high risk

How does the apparent lack of convection so far in the ENH day 1 affect us?

Also, seems that there is a lessening of the risk for a convective complex developing reading the latest AFD from Chicago NWS 

[high risk]

55 minutes ago, yoda said:

@high risk

How does the apparent lack of convection so far in the ENH day 1 affect us?

     terrific question.     While most of the CAMs had some cells erupting in IL before 00z, there was some consensus that the biggest contributor to an MCS approaching the Appalachians tomorrow morning would be storms that fired in central IL this evening.      And that development (while not SVR so far) appears to be underway, so it may still be on track.    That said, that morning MCS tomorrow could end up further south than expected, although I'd still be concerned about the cloud shield further north.

 

[AfewUniversesBelowNormal]

It's not going to rain tomorrow based around here lol maybe in your own reality.

[yoda]

Well then... looks like someone at CWG thinks tomorrow could be interesting severe weatherwise

 

[AfewUniversesBelowNormal]

A lot of convection moving through tonight, look at the storms in Illinois and Missouri, could be fun tomorrow. 

[jewell2188]

The enhanced risk has been cut back to basically 95 eastward. Which was to be excepted. I see another dud happening today. 

As I and others said yesterday, cloud cover will kill this threat. And it looks to hang strong for a while this morning.

[Kmlwx]

Looks lame unless you're south of DC.

[cyclogenesis]

August 13, 2019

this Tuesday morning

705 AM EDT

 

 

***  Severe storms a good chance over Eastern Virginia this afternoon & evening, Tues., 8/13  ***

 

***  Most likely form of severe is high wind gusts ***

 

*** Multi-cellular & line segment storms are indicated, in Eastern Virginia ***

 

***  A Tornado or Severe Storm Watch will be needed from early afternoon in to early nighttime, to include the Richmond, VA and Eastern VA region  ***

 

This writing applies to Richmond, VA & surrounding counties.

 

I.  Overview.

 

A wildly active day & night containing multiple rounds of showers & thunderstorms appear imminent starting this afternoon and carrying through the late evening hours, this Tuesday, August 13.

 

There are indications from a couple of the forecast models that winds aloft will increase by late afternoon around 4 PM to 6 PM, to accentuate a chance for severe storms containing high winds, from mid-afternoon onward to evening.  

 

Additionally, helicity forecasts, late in the day, finally rise to a level to which an isolated tornado is eligible to occur; although newest forecasts have toned down helicity from a couple days back, and thereby the attendant tornado threat.

 

II.  Timing of storms for Richmond, VA on Tues, Aug. 13

 

A.)  Richmond Timing for all showers & storms.

I believe the best timing for a scattering of showers & storms for Richmond to span between 1 PM to 11 PM this afternoon & early tonight.  Repeated periods of showers & thunderstorms should occur this afternoon & tonight.  I do expect a severe weather watch to be issued during this time frame to cover Eastern Virginia.

 

B.)  Richmond Timing for *SEVERE* storms.

The severe weather, for the Richmond metro, I think will be timed between 2 PM and 8 PM.

 

There is indication from several of the forecast models that a nighttime MCS, (large cluster of showers & storms), will re-develop 100-200 miles West-Southwest of Richmond over either Central or South-Central Virginia beyond 8 PM tonight, and propagate towards the East-Southeast.

 

There are divided differences in PLACEMENT of this nighttime MCS, with Nam and Wrf both showing Richmond to either be dry or miss it, after 8 PM tonight.

 

The other camp, from Gfs & UKMET, show a large area of showers & storms developing over Central VA and spreading Eastward between 8 PM and 2 AM tonight.    

 

Storm motions this afternoon will be a brisk pace, moving East-bound at 30-40 mph, and I do expect warned T-storm cells this afternoon & evening both North of Richmond and South of Richmond spreading Eastward in the evening hours.

 

III.  Tornado Target.

 

The surface low is mirky to make out with no model exactly agreeing in placement, timing, or even definition.  It's appearing a surface low will exist, transiently, for a brief period in the late afternoon, early evening hours over Northwest Virginia, and slowly pace Eastward during the early nighttime.  

 

I'm thinking the best helicity for a tornado will be lagging 2-3 hours behind the most robust cellular storms placement, occurring mostly to the West of storms today, and for this reason, I believe the highest severe threat is from high winds.   

 

My best preference for an identifiable tornado location is bounded between Fredericksburg, VA to Louisa, VA to Ashland, VA between 3 PM to 7 PM this afternoon.  Here, in this vicinity, it looks to have about 200 - 300 m2/s2 of 0-3 KM helicity.

 

Because the 850 mb forecast wind profiles are West-Southwesterly throughout the afternoon & evening, though, this will favor a more bonafide threat for high wind gusts, over the tornado.  

 

The tornado threat can't be excluded because there is some arcing in the hodographs between 2 PM and 8 PM, between 0 to 1 KM above; but after 1 KM, it's straight-lined.  So there may be just enough 0-1 KM helicity present to produce a few tornadoes. 

 

IV.  Rest of Severe Weather Details.

 

In other areas, the CAPE from a couple of forecasting models does point to between 1800 to 2200 J/kg, and an important key I look in to is the 850 mb wind strength, which is down from 2 days ago.  It's now appearing winds at this 850 mb level will be running West-Southwest about 20 kts.  This is borderline in what I seek for the MINIMUM threshold for summer-time severe given this Cape forecast.

 

A look at 6Z Nam, shows 20-25 kts for a good part of the day, so getting above that 20 kt threshold is GOOD for the production of severe storm wind gusts.  

 

I'll note that the WRF is pointing towards an acceleration of winds at this 850 mb level to 25-30 kts between 4PM to 5 PM.  Should this materialize, then I do expect a more widespread threat for damaging wind gusts by late afternoon.  Further to this, the 00Z Nam had indicated a 50kt 500 mb wind max spreading atop Richmond at 5 PM today.  

 

To me, for this time of year, in summer though, the 850 mb winds are more important to me in the severe weather bracket of for surface high wind gusts than at 500 mb.  But those higher speeds at 500 mb, with that wind max, can help promote better updraft speeds, and resultingly higher dbZ turnouts on radar reflectivity.  And I do believe we'll see just that, too! 

 

When inspecting the upper divergence at 250 Mb, the 00Z & 6Z Nam are suggestive at forcing for ascent to be prime between 11 AM and 5 PM, a bit sooner than other model timing for storms on this event.  Both the French & German models suggest showers & storms will be finished with Richmond by 8 PM.  

 

Storm integrity looks most solid West of I-95, wherein both lightning density & VILS look their best, and then when storms pass East of I-95, the integrity looks softer, although I still believe capable of producing high wind gusts.

 

Both Gfs & Nam forecast soundings suggest a peak wind gust to 53 kts in afternoon soundings based near Richmond, VA, along with lifted indices to -5 to -6 C.  It's interesting, though, that WRF-ARW does not indicate any surface wind speed gusts over 40 kts in its hourly grid domain from 00Z.  That's disappointing, considering the fiery convective portrayal this afternoon.

 

V.  Rainfall Amounts, Richmond.

 

While PW, precipitable water, is forecast to run between 2.10" to 2.40" from 8 AM this morning to 11 PM tonight, the rainfall projected totals aren't that much.  The reason is because of the anticipated fast forward progression from West to East of shower & T-storm movement, racing between 30 to 40 mph.  

 

Rainfall projected for Richmond, VA for this afternoon through early tonight:

 

00Z UKMET:  0.36"

00Z Gfs:  0.89"

00Z Nam:  0.24"

00Z C-Gem:  0.54"

00Z WRF:  0.05"

00Z HR-Rap:  0.88"

06Z HR-Rap:  0.98"

00Z ECMWF:  0.20"

00z Arpege:  0.20", before 8 PM

00Z Icon:  0.50", before 8 PM  

 

This yields a 10-model average of 0.48" for the Richmond, VA metro area bounded between this afternoon & tonight, 8/13.

 

--  cyclogenesis

[jewell2188]

1 hour ago, Kmlwx said:

Looks lame unless you're south of DC.

Yep. Nothing unusual lol

[CAPE]

Mount Holly's latest take.. Not sure this will pan out.  This looks like a graceful step down to what will be a lame event. Most of the action now looks like it will be well south in the Wakefield, VA forecast area.

Convection and an associated convectively enhanced shortwave trough is located across the Ohio Valley and moving eastward toward our region. Some showers have already moved into the region from the west. Will expect to see this activity continue through the morning hours with coverage and intensity increasing as the day progresses. This will lead to quite a bit more cloud cover than previously expected, especially across the northern half of the area. As a result, confidence has decreased for this area to see much in the way of destabilization this afternoon. This will preclude any severe weather or excessively heavy rainfall threat for the northern portion of the forecast area. Therefore, we have shrunk the size of the Flash Flood Watch and removed all northern NJ and Lehigh Valley counties. The heaviest rainfall is currently forecast to fall from northern Delmarva east across southern NJ where training of heavy thunderstorms appears more likely at this time. Farther south across Delmarva and far southern NJ, considerable destabilization still appears to be probable, especially if excessive cloud cover remains to the north. MLCAPE values of 1500- 2000 with 35-40 kts of deep layer shear are still forecast across the areas with the most destabilization. In this case, the severe weather threat remains in play with all hazards possible (damaging winds/isolated tornadoes/large hail), but damaging wind gusts will be the main threat. SPC has removed the enhanced risk from our area, but Delmarva and extreme southern NJ remain in the slight risk with the marginal risk still covering SE PA and central/southern NJ.

[JakkelWx]

Another lame event.. next. Gonna enjoy outdoor activities all day i guess. barely even under the slight now. Clouds messing everything up. Shouldn't even be an enhanced, there's cloud cover basically over the whole mid-atlantic.

[Eskimo Joe]

 

[yoda]

I see the sun lol

[Maestrobjwa]

4 hours ago, jewell2188 said:

The enhanced risk has been cut back to basically 95 eastward. Which was to be excepted. I see another dud happening today. 

As I and others said yesterday, cloud cover will kill this threat. And it looks to hang strong for a while this morning.

That's why I don't understand why they enhanced the risk knowing the clouds could reduce the chances!

[mappy]

3 hours ago, cyclogenesis said:

<snip>

thanks for this, can you next time make it smaller and easier on the eyes. 

[ErinInTheSky]

Whelp. Byebye enhanced.

[Eskimo Joe]

D2 ENH/MOD is the kiss of death in these parts.

[dailylurker]

Now I'm just hoping we at least get some showers to knock the dust down.

[jewell2188]

3 hours ago, yoda said:

I see the sun lol

I see rain and thick cloud cover lol

[H2O]

It will clear off at 2 pm and the sun will help fire up a small line that misses mattie g's crib

[H2O]

and never go against clouds.  Clouds are the strongest card you can get in Hearthstone.  And Pokemon.  And D&D.  And the Fog.  Clouds kill

[mattie g]

7 minutes ago, H2O said:

It will clear off at 2 pm and the sun will help fire up a small line that misses mattie g's crib

Bingo. And it'll heat up to 90 degrees and be a sauna all evening.

[yoda]

11 minutes ago, H2O said:

and never go against clouds.  Clouds are the strongest card you can get in Hearthstone.  And Pokemon.  And D&D.  And the Fog.  Clouds kill

I'm going to use a D20 for a saving roll for severe weather this afternoon

[H2O]

I was 45 min early.  Filtered sun now.  Its on like Donkey Kong

[JakkelWx]

 

Worst forecast bust ever. Pretty much went from ENH to MRGL in just 12 hours.