2019 Mid-Atlantic Severe Wx - General Discussion

[Kmlwx]

12z NAM nest has almost nothing unless you're in extreme NE Maryland. Meh. 

[mappy]

Just now, high risk said:

        you're most welcome.    Tropical Tidbits has nice displays - it's listed in the mesoscale section as WRF-ARW2.      Pivotal Weather has it as HRW WRF-NSSL.

thank you! 

[high risk]

While its solution verbatim kinda screws some of this area, add the HRRR to the list of runs (all ARW, fwiw) which are much more widespread and further south with convection tomorrow than the NMMB runs.

[high risk]

12z Hi-Res Window runs are now in, and the NAM nest's uninspired forecasts for our area tomorrow are looking like an outlier.

[yoda]

1730 SPC OTLK moves the SLGT and ENH risk south some compared to earlier Day 2

[mappy]

8 minutes ago, yoda said:

1730 SPC OTLK moves the SLGT and ENH risk south some compared to earlier Day 2

includes Baltimore and Frederick now

[Kmlwx]

20 minutes ago, yoda said:

1730 SPC OTLK moves the SLGT and ENH risk south some compared to earlier Day 2

Let's recklessly go chasing up US15. 

[Kmlwx]

11 minutes ago, mappy said:

includes Baltimore and Frederick now

Can I come watch a wedge pass by from Mappyville?

[mappy]

6 minutes ago, Kmlwx said:

Can I come watch a wedge pass by from Mappyville?

Sure can! Ill be home  

[Kmlwx]

Just now, mappy said:

Sure can! Ill be home  

Unfortunately my presence would guarantee no storms within 25 miles.

[yoda]

SPC Disco from the 1730 OTLK

Quote

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1220 PM CDT Wed May 22 2019

   Valid 231200Z - 241200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE OH
   VALLEY/MIDDLE ATLANTIC AND SOUTHERN/CENTRAL PLAINS...

   ...SUMMARY...
   Severe storms with large hail, damaging wind and tornadoes will be
   possible over a part of the central and southern Plains Thursday.
   Other severe storms with a threat for mainly damaging wind and large
   hail are expected from a portion of the Ohio Valley into the
   northern Middle Atlantic.

   ...Upper OH Valley/Northern Middle Atlantic...

   Central US short-wave trough is forecast to eject northeast across
   the Great Lakes and flatten the eastern ridge as 80kt 500mb speed
   max translates across Lake Erie. This feature is expected to aid
   early-morning convection across the OH Valley which will propagate
   into eastern OH/western PA by 18z. Depending on the evolution of
   this convection it appears environmental shear will become favorable
   for sustaining fast-moving organized updrafts. Latest model guidance
   suggests upward-evolving thunderstorms by early afternoon within
   strengthening westerly flow regime. Boundary-layer heating is
   expected to be maximized from south-central PA, south along the lee
   of the central Appalachians. If a cold pool develops early, severe
   thunderstorms should initiate along the
   eastern-southern-southwestern flank of this activity then
   spread/develop east-southeast toward the Delmarva. Several CAMs
   solutions support this scenario and will extend higher severe probs
   into northern MD to account for the more southeast propagational
   component. Damaging winds, and some hail, are expected with
   convection as it spreads across eastern OH/PA toward northern MD by
   late afternoon.

[yoda]

LWX's afternoon AFD re tomorrow from 2:30PM

The warm front will pass through the area Thursday morning. A
couple showers and perhaps even an isolated thunderstorm may
accompany the frontal passage, but again coverage will be
isolated to widely scattered.

A west to southwest flow behind the boundary will usher in
noticeably warmer and more humid conditions. Max temps will top
off well into the 80s for most areas, and a few locations may
even approach 90 degrees. Dewpoints should rise into the 60s for
most areas, making it feel more uncomfortable as well.

Still keeping a close eye on the potential for severe
thunderstorms Thursday afternoon and evening. The warmer and
more humid conditions will lead to an unstable atmosphere. The
12z HREF forecasts mean SBCAPE to be about 1-2KJ/KG across most
of the area with locally higher amounts east of the Blue Ridge
Mountains (where dewpoints will be a bit higher east of a
pressure trough). Deep layer shear will most likely be around 40
to 50 knots, which is plenty to support the threat of severe
thunderstorms. Latest guidance has come into better agreement
that an MCS will track across the Midwest tonight and then
toward our area Thursday morning. The system will likely pass
through our area Thursday afternoon and evening, and with the
moderate instability and shear in place...the threat for severe
thunderstorms is elevated with damaging winds being the
primary threat along with large hail. Confidence is still low on
exactly how this will play out because it will be highly
dependent on the strength of the MCS, which has not developed
yet. If the MCS holds together and tracks through our area, then
the threat for severe thunderstorms will be enhanced. However,
if the MCS dissipates before reaching our area, then popup
thunderstorms will still pose a threat for severe weather but it
will be more isolated. Latest thinking is that the best chance
for more enhanced severe weather will be across our northern and
perhaps even central areas...where height falls are more
noticeable and there will be less of an impact from downsloping
low-level westerly flow.

The actual cold front will drop into our area from the north
Thursday night. Convection will dissipate overnight with the
loss of daytime heating and a downslope west to northwest flow.

[Kmlwx]

Parameters continue to look pretty impressive. But sim radar is pretty weak sauce for us on most models (even the better ones @high risk ) mentioned. Still think it could go either way. I want to get excited but that's always a losing strategy around here. On the plus side - it does look pretty certain that we'll see a good bit of sun tomorrow...that's one of the factors we sometimes don't have (often). 

[yoda]

21 minutes ago, Kmlwx said:

Parameters continue to look pretty impressive. But sim radar is pretty weak sauce for us on most models (even the better ones @high risk ) mentioned. Still think it could go either way. I want to get excited but that's always a losing strategy around here. On the plus side - it does look pretty certain that we'll see a good bit of sun tomorrow...that's one of the factors we sometimes don't have (often). 

I think it will continue to look that way on sim radar until the MCS that LWX mentioned in the afternoon AFD develops 

[yoda]

18z NAM soundings at 21z THUR and 00z FRI are pretty impressive across the region

[CAPE]

Interesting read from Mount Holly on the severe potential, and limiting factors:

Although showers, and possibly a thunderstorm or two, will continue to be possible in the warm sector through the morning, the main round of storms we are concerned about are storms that are expected to develop along and ahead of the pre-frontal trough late Thursday afternoon into Thursday evening. Some of these storms could be severe. Most models depict ML CAPE values near or above 1000 J/kg in the 21 to 00Z time frame along with 0-6km bulk shear values of 40 to 50 kt. Not only is this a significant amount of shear, but model soundings depict plenty of veering with height (especially within the first 3 km). This further enhances the risk that updrafts could be persistent. There are a few potential caveats. First, low/mid level clouds may not erode through the morning. This will limit diurnal heating (in anticipation that this may be the case, have gone with the cooler guidance for highs on Thursday), which would limit instability/CAPE values. Secondly, related to the first caveat, the NAM depicts a low level inversion (around 900 mb) which never fully erodes through the day (unlike the GFS which depicts this eroding between 21 and 00Z). Even if we are cooler and the inversion stays in place, I think we will continue to have at least some severe threat as lift along the trough could be enough to lift elevated parcels above the inversion. The final caveat is that remarkably, model soundings are depicting several dry (and one very dry) layers through the afternoon and evening. This means the LCL will be higher than normal, and will have an impact on the risk for wind, tornado, and heavy rain. Speaking of hazards: Damaging wind: This looks to be the primary hazard thanks to a low and mid level jet, and plenty of shear. The low level inversion mentioned above may limit how efficient the mixing is down to the surface, but the dry levels will help to increase the risk of downbursts thanks to an increased risk of dry air entrainment. Hail: Severe hail (1" in diameter or greater) is certainly possible, especially if we warm up as much as what the GFS is depicting and are able to realize the higher CAPE values. The highest threat for hail looks to be over Delmarva and far SE PA where the highest CAPE values are possible. Tornado: The veering wind profiles increase the risk for rotating updrafts. However, as mentioned above the LCL will be higher than normal which could limit the threat for tornadoes.

 

[yoda]

Ok... those are some disturbing soundings the 00z NAM is tossing out at 00z and 03z FRI at KIAD... 03z FRI at KBWI and KDCA...  Yes, just a sounding, but you don't see those types of soundings around here very often

Yes, doesn't guarantee we see severe.  But still... wow @Kmlwx @high risk

[yoda]

00z NAM sim radar brings some nastiness for the evening commute from BWI to DCA to near EZF at 21z

[yoda]

Oh hai... sounding around DCA at 03z FRI per the 00z NAM

[yoda]

5 minutes ago, yoda said:

00z NAM sim radar brings some nastiness for the evening commute from BWI to DCA to near EZF at 21z

00z NAM NEST decides to drive through some what would appear to be supercells around 20z to 21z... then brings a pretty decent line south from PA as a finale around 03z but its fragmenting around DC at that time

[yoda]

Another view of the sounding at DCA at 03z FRI per pivotalweather

[yoda]

00z HRRR and 02z HRRR bring a line through of cells around 20z

[Kmlwx]

I am still not in yet. 

[yoda]

That's a large 5 percent tornado area from SPC on the new Day 1 OTLK 

[yoda]

ENH is just north of DC... includes just about all of MD (except S MD) and S PA

[NorthArlington101]

ENH is just north of DC... includes just about all of MD (except S MD) and S PA

[yoda]

I forget where @mappy gets those zoomed in outlook SPC maps

[Treckasec]

3 hours ago, yoda said:

I forget where @mappy gets those zoomed in outlook SPC maps

https://www.spc.noaa.gov/public/state/images/

 

[jewell2188]

Tired of slight risk!! When was the last enhanced or mod risk we had ??

[southmdwatcher]

6z 3kNAM shows scattered severe storms rolling through our region between 18z and 21z. 9z HRRR run shows similar scenario with more storms. 10z HRRR run was much more quiet. The MCS is in western Ohio and southern Indiana, We should see some decent storms later today.