2020 Mid-Atlantic Severe Weather - General Thread

[Kmlwx]

The 06z run of the 3km NAM had a nice complex coming through the DC area tomorrow afternoon/evening. 

[George BM]

8 minutes ago, midatlanticweather said:

Potential is definitely starting to show some focus.  SPC highlighting Marginal next two days. HRRR going a bit crazy (notoriously).. We will see. Could be an interesting few days nonetheless. 

 

The "obviously overdone severe-weenie" 6z 3kNAM said we get a supercell through DC tomorrow afternoon.

[Kmlwx]

Just now, George BM said:

The "obviously overdone severe-weenie" 6z 3kNAM said we get a supercell through DC tomorrow afternoon.

LOL

[Eskimo Joe]

Can we all make a pact to not look at or share the HRR or NAM past 24 hours?  The MOD Risk bust in IL the other day should be a reinforcer to not trust meso models past HR 24.  

[southmdwatcher]

Well now that is quite a broad area of Slight Risk now for tomorrow. Salisbury to Baltimore to north of Pittsburgh and southwest are now included. 2 Tor 15 Wind 15 Hail for our whole region.

[high risk]

35 minutes ago, southmdwatcher said:

Well now that is quite a broad area of Slight Risk now for tomorrow. Salisbury to Baltimore to north of Pittsburgh and southwest are now included. 2 Tor 15 Wind 15 Hail for our whole region.

         Looking at the CAMs, it looks like round 1 develops as a weakening Ohio Valley MCS undergoes intensification in central VA early Tuesday afternoon and rolls southeast.    For the rest of us, our best chance appears to be in the evening hours, when storms that initiate in the late afternoon over eastern OH move southeast towards us.   (A few solutions have another batch of storms rolling through from the northwest in the early morning hours Wednesday).      Lapse rates look good, so I like our thunder chances - the potential for SVR will depend on how warm we get Tuesday afternoon and stay into the evening hours.     While I like our thunder chances with that event, I'm less excited about SVR potential, as I think they'll be elevated, although I suppose I can't rule out some hail.   

[yoda]

Hmmm... new Day 1 is 15 hail and 15 wind... all of LWX CWA is in SLGT... hatched hail is off in the Ohio Valley... but disco seems to imply it could get moved eastward some later today... also seems to imply a 1-2 punch for us - afternoon risk and then nocturnal threat

[yoda]

[yoda]

10 minutes ago, yoda said:

Hmmm... new Day 1 is 15 hail and 15 wind... all of LWX CWA is in SLGT... hatched hail is off in the Ohio Valley... but disco seems to imply it could get moved eastward some later today

Quote

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1250 AM CDT Tue Apr 07 2020

   Valid 071200Z - 081200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON INTO TONIGHT ACROSS SOUTHERN PORTIONS OF THE GREAT LAKES
   REGION AND OHIO VALLEY INTO PARTS OF THE MID ATLANTIC COAST
   REGION...

   ...SUMMARY...
   Severe thunderstorms are possible late this afternoon through
   tonight across southern portions of the Great Lakes region into the
   Ohio Valley and Mid Atlantic.  Strongest storms will pose a threat
   for very large and damaging hail, as well as potentially damaging
   wind gusts, and perhaps at least some risk for a tornado.

   ...Synopsis...
   Little change to the large-scale pattern is forecast through this
   period, with a higher latitude blocking ridge remaining prominent to
   the north of Hudson Bay.  As blocking also lingers across the
   mid-latitude and subtropical eastern Pacific, only slow movement of
   the closed mid-level low near the California coast is forecast, with
   a gradual digging just west of central through southern coastal
   areas.

   To the south of the higher latitude ridge, a deep mid-level closed
   low appears likely to remain quasi-stationary near the Canadian
   Maritimes, while a strong jet streak digging to the lee of the
   Canadian Rockies contributes to another evolving mid-level low
   near/east of the Canadian Prairies.  Smaller-scale perturbations
   progressing around the southern periphery of this feature will
   contribute to mid-level height falls and increasingly cyclonic flow
   across the northern Plains into the upper Mississippi Valley by late
   tonight.  

   One preceding short wave impulse is forecast to accelerate across
   the Great Lakes region through the southern New England/northern Mid
   Atlantic coast by the end of the period.  This is forecast to be
   accompanied by a developing surface low along an initially northward
   advancing warm front.  It is also expected to contribute to
   suppression of broader-scale ridging, initially present across much
   of the Ohio Valley into Mid Atlantic, by this evening.  

   ...Great Lakes/Ohio Valley into Mid Atlantic...
   Forcing for ascent and destabilization are already contributing to
   increasing thunderstorm development along the frontal zone across
   southern portions of the Great Lakes region, aided by a 30+ kt
   westerly 850 mb jet.  This activity appears likely to progress
   around the crest of the large-scale ridging, and may spread
   east-southeast of the Allegheny Mountains into portions of the Mid
   Atlantic region by this afternoon. Limited low-level moisture may
   only contribute to weak boundary-destabilization across this region,
   but deep boundary-layer mixing along and south of the warm front may
   contribute to potential for strong surface gusts across northern
   Virginia, aided by modest west-northwesterly mid-level flow.

   Meanwhile, in the wake of this activity, warm and capping elevated
   mixed-layer air is forecast to overspread much of the southern Great
   Lakes and Ohio Valley region.  This may suppress convective
   development through much of the day, but daytime heating and
   increasing low-level moisture (including surface dew point increases
   through the lower 60s), may contribute to "loaded-gun" type
   soundings with CAPE in excess of 1000 J/kg over a sizable area.

   Considerable spread exists among the various model output concerning
   the potential convective evolution within this environment, which
   will include strengthening deep-layer shear supportive of organized
   severe storm development with the approach of the upper impulse by
   this evening.  However, at least scattered discrete storm
   development appears possible across southern portions of the Great
   Lakes region by early evening.  Continued southward development of
   at least scattered discrete storms appears likely  across the Ohio
   Valley through this evening, ahead of a southward advancing cold
   front in the wake of the surface low.  

   Given the environment, strongest storms will be capable of producing
   very large hail, with at least some upscale convective growth
   through the evening contributing to potential for damaging surface
   gusts.  Tornadic potential remains more unclear, due to the forecast
   veered nature of the low-level wind fields, and resultant lack of
   more pronounced clockwise turning with height in the low-level
   hodographs.

   Eastward advection of the convectively unstable thermodynamic
   profiles, east of the Appalachians into northern Mid Atlantic
   coastal areas is forecast overnight.  This may occur above a
   residual stable layer near the surface, but it should contribute to
   increasing severe weather potential, at least in the form of
   thunderstorms capable of producing severe hail.

[Kmlwx]

6 hours ago, yoda said:

 

@yoda - I read that more as the storm potential will extend into our area - not necessarily that the hatching would come into our area. CAMs are a mixed bag it seems - I'm underenthused for today locally..for now. 

[mappy]

1 minute ago, Kmlwx said:

@yoda - I read that more as the storm potential will extend into our area - not necessarily that the hatching would come into our area. CAMs are a mixed bag it seems - I'm underenthused for today locally..for now. 

doesnt look super exciting up this way. 

[Kmlwx]

Just now, mappy said:

doesnt look super exciting up this way. 

Yeah...I think NoVa could get some activity. Certainly far west of our area looks much better. We'll find someway to bust on all three days. 

[mappy]

1 minute ago, Kmlwx said:

Yeah...I think NoVa could get some activity. Certainly far west of our area looks much better. We'll find someway to bust on all three days. 

I agree, if anyone sees a storm, or discrete non-severe cell, it will be that NOVA folks

[osfan24]

8 minutes ago, mappy said:

I agree, if anyone sees a storm, or discrete non-severe cell, it will be that NOVA folks

Agreed. Feel like the bulk of it dives southeast of most of us.

[high risk]

The late afternoon storm threat looks to be on the west side of DC, but I like the chances for a lot of us to hear thunder in the early evening.     The time period to watch, though, may be the 3-6 am period, when multiple cams show a line racing southeast across the area.    It will be elevated, but impressive lapse rates will be overspreading the area, leading to some severe hail potential.

[Kmlwx]

LOL. The 12z HRRR sends a big time cell right through Frederick County, Montgomery County and Howard County this evening. 

[high risk]

21 minutes ago, Kmlwx said:

LOL. The 12z HRRR sends a big time cell right through Frederick County, Montgomery County and Howard County this evening. 

     yeah, I feel good about convection in the area during the evening.    The soundings just don't look great, though, in terms of any severe potential.    

     but the soundings ahead of the late night line show lapse rates and most unstable cape values that are not common around here.    That's why I think that this is our best chance on the Maryland side for severe (hail).

 

[Eskimo Joe]

49 minutes ago, Kmlwx said:

LOL. The 12z HRRR sends a big time cell right through Frederick County, Montgomery County and Howard County this evening. 

Right after we opened COVID testing sites.  At least it's the HRRR so it'll probably end up verifying in the ocean or over Luray.

[high risk]

morning CAMs also seem to be locking in a cell or small complex developing this afternoon over north-central VA and rolling southeast on the west side of DC during the mid-late afternoon hours.     This is a bit further north and east than previously shown.    This activity has the best opportunity to be sfc-based, with some wind potential.  

[osfan24]

Cleared out quickly this morning, so that can't hurt.

[MN Transplant]

27 minutes ago, high risk said:

morning CAMs also seem to be locking in a cell or small complex developing this afternoon over north-central VA and rolling southeast on the west side of DC during the mid-late afternoon hours.     This is a bit further north and east than previously shown.    This activity has the best opportunity to be sfc-based, with some wind potential.  

It seems like the NAM/HRRR are hitting upon three different rounds.  Effectively, they are taking the "complex" near Pittsburgh and washing that out, but developing some early storms mostly south of DC.  The 2nd round is after sundown, and that appears to be our best shot for some thunder.  Then the front comes through in the early am hours.

The NAM is more keen on the first round, while the HRRR generally likes the 2nd round better (nice cell coming down the Potomac on the 14z).

[MN Transplant]

Lock it in.

[mappy]

1 hour ago, Eskimo Joe said:

Right after we opened COVID testing sites.  At least it's the HRRR so it'll probably end up verifying in the ocean or over Luray.

FWIW, Hogans people are aware of the weather threat today. 

[Eskimo Joe]

1 minute ago, mappy said:

FWIW, Hogans people are aware of the weather threat today. 

Yes.  Several jurisdictions have county-run operations and some hospitals have them as well so this it's a consideration for us as well. 

[high risk]

59 minutes ago, MN Transplant said:

It seems like the NAM/HRRR are hitting upon three different rounds.  Effectively, they are taking the "complex" near Pittsburgh and washing that out, but developing some early storms mostly south of DC.  The 2nd round is after sundown, and that appears to be our best shot for some thunder.  Then the front comes through in the early am hours.

The NAM is more keen on the first round, while the HRRR generally likes the 2nd round better (nice cell coming down the Potomac on the 14z).

     I'm still intrigued by the very late night stuff, although the morning CAMs definitely trended towards washing it out.      

    I'm also now looking closely at midday Thursday.    Nice line progged on the NAM nest with impressive wind fields.    Instability looks meager, which is for now tempering the severe threat.

[Rhino16]

Are we getting scammed again down here in Central VA? Need something to get these people inside...

[Eskimo Joe]

7 minutes ago, Rhino16 said:

Are we getting scammed again down here in Central VA? Need something to get these people inside...

Thick cloud cover and this crapvection rolling into the I-81 corridor has probably nixed the afternoon risk of storms north of I-66.  The 12z sounding out of IAD has a ConvT of 68° and the only place that really is exceeding that is from Warrenton south.  Everywhere else is struggling to heat.

[Roger Ramjet]

I'm at 80.

[Eskimo Joe]

Part of me was hoping for an 18z RAOB out of IAD or PITT given the setup for potentially large hailers, but that doesn't appear to be the case. 

[Eskimo Joe]

4 hours ago, high risk said:

morning CAMs also seem to be locking in a cell or small complex developing this afternoon over north-central VA and rolling southeast on the west side of DC during the mid-late afternoon hours.     This is a bit further north and east than previously shown.    This activity has the best opportunity to be sfc-based, with some wind potential.  

CAMS FTW...looks like that cluster near Haymarket may get warned here shortly.  Nice velocities on the 0.5° BV.