2019 Mid-Atlantic Severe Wx - General Discussion

[yoda]

Updated morning LWX AFD:

.NEAR TERM /THROUGH TONIGHT/...
While some heavier activity and thunderstorms evolve over
southeastern parts of Pennsylvania near a weak boundary, much of
our region remains dry and mostly cloudy. There could be a
couple of sprinkles over western Maryland, eastern West Virginia
Panhandle, and far northern Virginia over the next two to three
hours. Temperatures are pushing 80 degrees across much of our
region with dewpoint temperatures in the lower to middle 70s.
This rich surface moisture will help to feed developing showers
and strong to severe thunderstorms later this afternoon and this
evening. There is a Slight Risk for severe thunderstorms in
central and northeast Maryland this afternoon and evening.
Thunderstorms will be capable of producing damaging winds, large
hail and very heavy rainfall. 1500 J/kg surface based CAPE or
1000 J/kg mixed layer CAPE is concentrated over northeast
Maryland at this time. There is also about 20 to 30 knots of
wind shear over this same area. A few of the convective models
and NAM deterministic model indicate some strong to severe
thunderstorms that could develop over northeast Virginia and the
D.C. metropolitan area between 4pm and 7pm, and then some
damaging thunderstorms developing over northeast Maryland and
southern Maryland between 7pm and 10pm. Timing and location is
low to middle confidence. Nonetheless, there is a threat for
some damaging thunderstorms. A Flash Flood Watch remains in
effect for central, northeast and southern Maryland, the
metropolitan areas and eastern portions of Virginia. Rain rates
of an inch per hour is likely with the heaviest activity.

Later this evening and overnight, upper level energy will
continue crossing the region, so showers and storms could linger
for some time, perhaps most of the night, though intensity
should wane as the night progresses. Lows in the 60s and 70s.

[Eskimo Joe]

LWX's AFD is a bit curious...the visible satellite shows the region is socked in with mid level clouds.  Not sure how we manage to get north of ~1,000 CAPE without better sunshine.

[jewell2188]

2 minutes ago, yoda said:

Updated morning LWX AFD:

 

 

All seems very iffy again. Lots of clouds all morning here in newington. Still waiting on the region wide severe/flood event 

[yoda]

2 minutes ago, Eskimo Joe said:

LWX's AFD is a bit curious...the visible satellite shows the region is socked in with mid level clouds.  Not sure how we manage to get north of ~1,000 CAPE without better sunshine.

12z KIAD RAOB has FCST SURFACE of just below 2000

[yoda]

2 minutes ago, Eskimo Joe said:

LWX's AFD is a bit curious...the visible satellite shows the region is socked in with mid level clouds.  Not sure how we manage to get north of ~1,000 CAPE without better sunshine.

Um, there already is 1500 SBCAPE in NE MD

[Eskimo Joe]

Just now, yoda said:

12z KIAD RAOB has FCST SURFACE of just below 2000

Also have a convective temp of 87° which is dubious to reach.

[Eskimo Joe]

Just now, yoda said:

Um, there already is 1500 SBCAPE in NE MD

That's centered over KMTN which has a high surface Td compared to the rest of the stations nearby.  KGED also does that sometimes on the eastern shore and it gives a bad impression.

[adelphi_sky]

I see sun and blue sky in Adelphi. 82.2F. Dewpoint is 74. I'd imagine that's enough to get some storms going. 87 shouldn't be too hard to reach in a few hours if it stays partly cloudy. 

[mappy]

5 minutes ago, Eskimo Joe said:

LWX's AFD is a bit curious...the visible satellite shows the region is socked in with mid level clouds.  Not sure how we manage to get north of ~1,000 CAPE without better sunshine.

spc mesoanalysis suggests a larger area of 1000 to 2000 already present west of the bay. 

[yoda]

1 minute ago, Eskimo Joe said:

That's centered over KMTN which has a high surface Td compared to the rest of the stations nearby.  KGED also does that sometimes on the eastern shore and it gives a bad impression.

Well LWX mentions it in their AFD, so they must either accept it on the SPC mesoanalysis page or have other stations to look at that support it

[yoda]

4 minutes ago, Eskimo Joe said:

Also have a convective temp of 87° which is dubious to reach.

LWX in their updated zones as of 10:37 AM has DCA reaching upper 80s for highs which would likely breach ConvT

[Eskimo Joe]

5 minutes ago, yoda said:

LWX in their updated zones as of 10:37 AM has DCA reaching upper 80s for highs which would likely breach ConvT

I just hope DCA can hit 90° again.

[high risk]

     Even if we came up a degree or two short of the convective temp, most of the CAMs show a modest shortwave approaching later this afternoon, which (assuming it's real) will certainly get the initiation job done.     Without full surface heating, the about of instability probably won't be sufficient for widespread severe (although I won't rule out a few wet microbursts), but heavy rainers seem pretty likely with the high PWs

[CAPE]

This might be a dumb question, but why would reaching the convective temp be critical when the synoptic setup provides mechanism(s) for lift? We have a front, with upper level perturbations moving through. Seems reaching the convective temp would be much more important when there is little to no forcing available, as with typical summer air mass storms.

[CAPE]

LOL.

Question answered!

[adelphi_sky]

6 minutes ago, high risk said:

     Even if we came up a degree or two short of the convective temp, most of the CAMs show a modest shortwave approaching later this afternoon, which (assuming it's real) will certainly get the initiation job done.     Without full surface heating, the about of instability probably won't be sufficient for widespread severe (although I won't rule out a few wet microbursts), but heavy rainers seem pretty likely with the high PWs

I'm already up to 84.7F THe sun disappeared on me. But I would think that would be just fine for today's threat. 

[mappy]

latest mesoanalysis shows a 3000 CAPE contour around DC

[mappy]

11 minutes ago, losetoa6 said:

And another 3000 bubble just north of your yard along with the best lift atm 

I see that! here's hoping things work out in my favor later. 

[Eskimo Joe]

So, I guess we're getting a watch?

https://www.spc.noaa.gov/products/md/2019/md1115.html

[yoda]

12 minutes ago, Eskimo Joe said:

So, I guess we're getting a watch?

https://www.spc.noaa.gov/products/md/2019/md1115.html

60% today... yesterday was 40%... so I would believe so

Would also probably mean that the SLGT risk at 1630 will be drawn more SWward -- when it decides to come out... its 10 mins late

[H2O]

I poo poo'd yesterday and got some rain.  I'm doing it again due to clouds despite it being muggy af out there.

[Kmlwx]

Wow - look at the severe analogs from CIPS from the GEFS (last night's 0z) - this is for THURSDAY

[Eskimo Joe]

^i'm in Maine that day...bank on a big event.  Even possible legit MOD risk day.

[mattie g]

1 hour ago, mappy said:

latest mesoanalysis shows a 3000 CAPE contour around DC

I find this suspect. Not sure how we'll get even 1/3 of that CAPE.

[Eskimo Joe]

1 minute ago, mattie g said:

I find this suspect. Not sure how we'll get even 1/3 of that CAPE.

The high SB CAPE on the SPC meso page is probably being shown due to a few stations with anomalously high Td, namely KMTN (Martin St Airport),  KNHK (NAS Patuxent) and KNAK (Naval Academy).  Their proximity to the water may be representative of the local conditions near the observation site but it's similar to how DCA can torch if the winds flip to the SW or back to the SE off the water.  The ML CAPE values are more realistic, and even then might be a ~100 j/kg too high because they are incorporating the above stations.

[Kmlwx]

11 minutes ago, Eskimo Joe said:

^i'm in Maine that day...bank on a big event.  Even possible legit MOD risk day.

Ehhh I dunno if we'll be able to pull a mod risk this year. Thursday does continue to bear watching. SPC discussion on it didn't sound super tasty though. 

[Eskimo Joe]

Blue Box until 02:00 UTC

[yoda]

LWX expanded the FFW

Flood Watch
National Weather Service Baltimore MD/Washington DC
152 PM EDT Tue Jun 18 2019


MDZ017-018-VAZ036>040-050-051-056-057-507-508-190200-
/O.EXA.KLWX.FF.A.0005.190618T1800Z-190619T0300Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
St. Marys-Calvert-Nelson-Albemarle-Greene-Madison-Rappahannock-
Orange-Culpeper-Spotsylvania-King George-
Northern Virginia Blue Ridge-Central Virginia Blue Ridge-
Including the cities of Lexington Park, California,
Chesapeake Beach, Huntingtown, Dunkirk, North Beach, Lusby,
Prince Frederick, Lovingston, Charlottesville, Stanardsville,
Madison, Washington, Orange, Gordonsville, Culpeper,
Fredericksburg, Dahlgren, Big Meadows, and Wintergreen
152 PM EDT Tue Jun 18 2019

...FLASH FLOOD WATCH IN EFFECT UNTIL 11 PM EDT THIS EVENING...

The National Weather Service in Sterling Virginia has expanded
the

* Flash Flood Watch to include portions of southern Maryland and
  Virginia, including the following areas, in southern Maryland,
  Calvert and St. Marys. In Virginia, Albemarle, Central
  Virginia Blue Ridge, Culpeper, Greene, King George, Madison,
  Nelson, Northern Virginia Blue Ridge, Orange, Rappahannock,
  and Spotsylvania.

* Until 11 PM EDT this evening.

* Thunderstorms with heavy rainfall are expected to develop across
  the watch area this afternoon and linger into the evening.
  Localized rainfall totals of several inches are possible. This
  could lead to flash flooding, especially in the urban areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Flash Flood Watch means that conditions may develop that lead
to flash flooding. Flash flooding is a very dangerous situation.

You should monitor later forecasts and be prepared to take action
should Flash Flood Warnings be issued.

[JakkelWx]

Not a big fan of this cloud debris.

[wawarriors4]

https://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=0448&yr=2019