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2021 Mid-Atlantic Severe Weather - General Discussion


Kmlwx
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58 minutes ago, vastateofmind said:

Great reminder about Radarscope -- I'm going to pull the trigger on that today or tomorrow. Have been meaning to buy it for the past year or two for my phone, but always found other apps to waste money on.

I actually just got Radarscope yesterday for my phone. It's wonderful for tracking severe weather.

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My friends in the Birmingham area live near Helena, which is a small town to the south-southwest of BMX. They avoided the tornado hitting their new home getting built by 200 ft. Just some very minor shingle damage. Absolutely lucky as heck to avoid total destruction. Their future neighbors were not so lucky with their new home getting flattened :( . My friends are an EM for Jefferson county (Birmingham's county), and my other friend (her husband) is a met at BMX. This is the second time he's had to go survey damage within a football field from their home in the past 14 months

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   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0230 AM CDT Fri Mar 26 2021

   Valid 281200Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF
   THE SOUTHERN APPALACHIANS INTO THE CAROLINAS AND MIDDLE ATLANTIC...

   ...SUMMARY...
   Strong to severe storms are possible from the Carolinas into the
   Middle Atlantic region Sunday afternoon. A few strong to severe
   storms will also be possible from the central and southern
   Appalachian region into a portion of the Tennessee Valley and
   Southeast States.

   ...Mid Atlantic into the Carolinas...

   An intense low-level jet will shift from the southern and central
   Appalachians into the Carolinas and Mid Atlantic during the day in
   association with a progressive northern-stream shortwave trough. A
   warm front will move northward through the Mid Atlantic during the
   day prior to the arrival of a cold front. Upper 50s to low 60s F
   dewpoints will advect through the warm sector contributing to modest
   instability as the surface layer warms with up to 1000 J/kg MLCAPE
   possible. Thunderstorms are expected to develop along and just ahead
   of the cold front as it advances into this region during the late
   afternoon and early evening. This activity will be embedded within
   strong deep layer wind profiles that will support bowing structures
   as well as a few supercells. Damaging wind will be the main threats,
   but a few tornadoes and some hail will also be possible before the
   front moves offshore during the evening.
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From Mount Holly this morning-

By Sunday afternoon the precipitation field will likely take on a more convective appearance as elevated instability develops. The primary fcst question then becomes, can we warm enough near the surface to overcome the fairly stout low-lvl inversion that is progged to be in place? If we can... and thus generate sfc- based instability there would be an appreciable severe threat as kinematics will not be lacking with 850mb winds around 60-70kts and 925mb winds up to 50kts. However, at this time, the thermal evolution is not clear, particularly given the low-lvl cloud cover and overunning precipitation earlier in the day. This uncertainty is partially quantified by the fact that the NBM`s IQR for Sunday`s MaxTs is 7-9 degrees, which represents a higher than usual spread in its components. If storms remain elevated it should be a fairly mundane spring rainfall event, with current QPF in the 0.75-1 inch range (although with convection in play locally higher totals are possible).

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The 12z NAM (12km) is kind of insane for Sunday now. It looks like it tries to pop a little low right along the Mason-Dixon line which really ramps up the potential. Supercell composite is very high for Sunday PM for a decent chunk of the area. Remove that little meso-low feature and things maybe aren't as robust. Will be interesting to see what the 3km looks like (at range of course). 

For March...this has some higher end potential. 

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1 minute ago, George BM said:

The last time, from my memory anyway, that DC was in a hatched zone was on a Day 3 outlook for April 6, 2017.

The last time, from my memory anyway, that DC was in a hatched zone at gametime was on February 24, 2016.

I was kind of surprised to see the hatching for a D3 outlook. The outlook text reads less like a hatched day and more like a higher end SLGT day. Could just be because it's out in range for now. 

It looks like the NAM nest focuses the best parameters just to the west of the metro area, the 12k version had it in the immediate metro area and east. It looks like it still has that little meso-low type feature. 

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1 minute ago, Kmlwx said:

I was kind of surprised to see the hatching for a D3 outlook. The outlook text reads less like a hatched day and more like a higher end SLGT day. Could just be because it's out in range for now. 

It looks like the NAM nest focuses the best parameters just to the west of the metro area, the 12k version had it in the immediate metro area and east. It looks like it still has that little meso-low type feature. 

Yeah. March climo and the tendency for overnight storms to our west to sink south of modeled are really keeping my expectations in check for Sunday atm.

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1 hour ago, Kmlwx said:

The 12z NAM (12km) is kind of insane for Sunday now. It looks like it tries to pop a little low right along the Mason-Dixon line which really ramps up the potential. Supercell composite is very high for Sunday PM for a decent chunk of the area. Remove that little meso-low feature and things maybe aren't as robust. Will be interesting to see what the 3km looks like (at range of course). 

For March...this has some higher end potential. 

     I fully agree.     The shear on all guidance is incredibly impressive - I'm even seeing big, looping hodographs and PDS TOR on some forecast soundings.     Still some questions about instability:   the parent NAM by far looks the best.    GFS keeps showers and clouds around for much of the day, limiting heating.    NAM nest seems to mix out the low level moisture a bit during the afternoon, although even that model has an impressive QLCS approaching late in the day.

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46 minutes ago, high risk said:

     I fully agree.     The shear on all guidance is incredibly impressive - I'm even seeing big, looping hodographs and PDS TOR on some forecast soundings.     Still some questions about instability:   the parent NAM by far looks the best.    GFS keeps showers and clouds around for much of the day, limiting heating.    NAM nest seems to mix out the low level moisture a bit during the afternoon, although even that model has an impressive QLCS approaching late in the day.

Seems the model biases are always this way. NAM always tends to show bonkers soundings/parameters and GFS is more muted. Could be the first "true" threat of the year - will it also be the first bust? ;) 

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This sounds ominous. I will prepare to take shelter.

From Mount Holly AFD-

As the system`s cold front approaches from the west into the late afternoon and evening, MLCAPE values should be on the order of 500 to 1000 J/kg (possibly even higher across Delmarva and southern NJ) across much of the inland portions of the area. Meanwhile, deep layer shear will be quite strong (50-60+ kts) across the warm sector and low-level shear will also be very strong. Forecast effective SRH values will be on the order of 300-400 m2/s2 with large curved hodographs, so the kinematic profile will support organized storms and rotating updrafts of any deep convection that develops in the warm sector or along the cold front. It`s still a little too far out to determine the convective evolution, but this severe event needs to be monitored very closely. SPC has highlighted southern portions of the forecast area with a threat of significant severe weather, and damaging winds, large hail, and tornadoes are all possible Sunday afternoon and evening.

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8 minutes ago, andyhb said:

What in the crap are these soundings I'm pulling on Sunday off the NAM/NAM 3 km...

3000 J/kg CAPE in the Mid Atlantic in March (not to mention with a shear profile favorable for sig severe)?

People start paying attention when you pop in. 

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16 minutes ago, andyhb said:

What in the crap are these soundings I'm pulling on Sunday off the NAM/NAM 3 km...

3000 J/kg CAPE in the Mid Atlantic in March (not to mention with a shear profile favorable for sig severe)?

6 minutes ago, Kmlwx said:

People start paying attention when you pop in. 

For real, now I'm interested. Ellinwood was honking on Twitter a little bit earlier too.

I'd love to do some casual storm chasing in my neck of the woods. I've seen some local guys chase and get great photos around here. 

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Latest guidance seems to want to get the best activity to the south and east of the DC area. Not surprising - and certainly inline with the overall SPC outlook area. NAM and the nest don't look quite as impressive as they did for the immediate metro area as they did yesterday. 

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The GFS has pretty paltry CAPE values for most of the metro area. The NAM looks pretty meh as well - but the NAM nest does send a healthy line through. If it were me at the SPC desk (thank god it isn't) I'd probably trim the hatched area to remove DC proper. Severe weenies near Fredericksburg are seemingly better positioned. 

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Decent agreement on some sunrise surprise tomorrow morning. MUCAPE of ~1000-1500 and plenty of shear for morning TS. The big question I have is the evolution of overnight convection further west. If that decays slowly, then we may be left with a bunch of convective debris in the warm sector, and it's going to be tough for severe further north.

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9 hours ago, Kmlwx said:

The GFS has pretty paltry CAPE values for most of the metro area. The NAM looks pretty meh as well - but the NAM nest does send a healthy line through. If it were me at the SPC desk (thank god it isn't) I'd probably trim the hatched area to remove DC proper. Severe weenies near Fredericksburg are seemingly better positioned. 

Hatched wind remains for our area in new Day 1 morning update... along with 5% tor

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