high risk

1 hour ago, WxUSAF said:

We’re really socked in east of the BR. Not sure that mid October sun can burn that off

     I would think that warm advection might be enough, even without a lot of sun....

5 hours ago, Kmlwx said:

I'm ready for my pencil thin line of gusty showers! (hoping for more!) 

           The minimum is probably a line of heavy showers with gusts to 30-40 or so.   The higher end is widespread gusts to 50 and some localized 60, with maybe a brief spinup or two.   Probably at least a few scattered lightning strikes if we can get some heating.

Let's fire up the severe thread for one last hurrah!   SLGT for parts of the region tomorrow; MRGL for just about everyone else.   Strong front approaches Friday evening with a good signal for a line of forced convection just ahead of it.   Shear will be very strong, and some forecast soundings have a little bit of instability.   The threat of a few damaging gusts seems legit.  (I'm ignoring the 2% TOR for now.)

2 hours ago, SnowenOutThere said:

First mention of winter wx in the morning AFD!

Behind the frontal system, surface high pressure builds over the
central CONUS beginning on Friday before shifting eastward. A tight
pressure gradient between the surface high and the departing low
pressure system leads to breezy conditions across the forecast area
Friday night into Saturday. Northwest winds gust 20 to 30 knots,
with higher elevations gusting up to 40 knots. Wind headlines may be
needed across the higher elevations but we will continue to monitor.
It`s also worth mentioning that with gusty northwest winds, upslope
snow showers are possible along the Alleghenies on Saturday with
high temperatures staying in the 30s across the ridges. Little to no
accumulation is expected although the first flakes of the season are
possible.

            LWX mentions the possibility of wind headlines over the higher elevations, but recent guidance suggests that wind advisories will be needed for most of the area Friday afternoon and Friday night.

Cams consistent with late evening heavy convection. Forecast soundings show elevated instability and support the possibility of thunder.  

Pretty certain that the morning soaker will wrap up by midday or early afternoon.   Then we go into scattered shower mode, and there is a clear convective threat around dinner time into the early evening.   The low level shear will support rotation, but will any of the storms be surface-based?  It still looks like the best chance at some modest instability will be over central and southern VA and possible the lower Eastern Shore.   I'll be happy with some thunder and lightning.

My initial reaction was that tornado potential would be confined to southeast VA and the Eastern Shore, because widespread rain over the DC metro area would limit instability.   Looking at CAMs, however, suggests that rain will likely end by early or mid afternoon for areas south and southeast of the warm front, and some decently high theta-e air will be available.    With the intense shear forecasted, it won't take much instability to make things very interesting.   The question, though, the track of the surface low.  My money is still on a track that keeps the warm sector south and east of DC, but there are solutions that track the low further to the northwest which would put our area into the game later Sunday.

2 hours ago, WxUSAF said:

GGEM way southwest at 12z. Measurable rain to the Potomac. 

  12Z Euro and our rapidly-aging uncle the NAM Nest definitely give credence to the idea that at least a chunk of our weekend will be messy.

Euro really wants to retrograde the coastal low and ruin the second part of the upcoming weekend.

1 hour ago, WxUSAF said:

GFS blipped but so far all the other 12z runs, meso and global, look pretty solid.

     Yeah, it's pretty clear that it won't be the 3-5 day event that guidance had been showing, but most of us should still get a nice soaking between now and Wednesday morning.  (And there could even be a backdoor sneak attack from the coastal on Saturday if you want to buy into the ECMWF.)

3 hours ago, WxUSAF said:

WPC kept the slight risk for heavy rainfall right through the 95 corridor. Still seems like the metro corridor could be a relative minimum based on much of the guidance and the eastern shore would get more? 

Remarkably, the slower NAM timing yesterday seems like it’s going to be correct, and that hurts the setup here. 

36 minutes ago, WxUSAF said:

*NAM nest not included lol 

   Besides the overall NAM Nest struggles this summer that you've documented, this looks to be a classic case of the NAM being too slow with the system, causing it to arrive at a very unfavorable time.    Its timing is a clear outlier for now.

Morning CAMs suggest a heavy rainfall threat Saturday evening (timing unsurprisingly still somewhat in doubt).   Good signal for convection spreading east ahead of a shortwave into an axis of very high PWs and some instability.

24 minutes ago, WxUSAF said:

WPC just issued a meso for heavy rain for central and NE MD with a nearly clean sweep on radar?

          I was really surprised when this popped up on my Radarscope.    The HRRR hates this event, and while WPC talked up the 850 mb confluence, it seems kind of subtle to me.  That said, the RRFS likes it to some extent, as did some of the cams earlier today, and storms are indeed firing across central PA.   I'll be surprised if anything makes it southwest of Baltimore, but it's worth monitoring for a while this evening.

1 hour ago, TSSN+ said:

Well if get anything later tonight it’s that complex developing over Michigan. 

It’s actually more likely the storms firing out ahead over northeast Ohio.  That would be better, because we want these storms to arrive as early as possible. 

The front is slower than had been shown, so the updated Day2 has expanded the SLGT back to the north.  Still tons of CAM disagreement (of course).  

34 minutes ago, TSSN+ said:

Best threat over SE Pa or NW? That area is under the enhanced risk. 

Sorry.  Bad wording on my part.  The southeast PA reference was regarding where the complex heads as it moves out of western PA. 

There seems to be growing consensus that an intense MCS will form over northeast OH and western PA late this afternoon and move southeast.   While it (shocker) appears that the best threat will be over southeast PA, at least some of the complex should make it into northern MD and potentially into the Baltimore-Washington corridor later this evening or overnight.     

1 minute ago, WxUSAF said:

Going to need to expand the STW into MD quickly…

Certainly sounds like SPC is going to issue a new box over us soon. 

10 minutes ago, yoda said:

Severe Thunderstorm Watch up for Central and Southern PA until 2pm

   Hard not to think that this cluster will persist south of the M-D line, although instability isn't what it could have been, given that the eastern half of the area has easterly winds behind that weak backdoor front.

24 minutes ago, yoda said:

What about the MPAS?

      I personally don't look at it very often, as it's still being tweaked.   That said, it's the future, so as it matures, I'll definitely be looking more often.   

1 hour ago, The Dude said:

Dumb question:  When folks are referencing the CAMs here, which models are you looking at.  I assume the HRRR, NAM Nest, RRFS.  Any others?  FV3, WRF-ARW? 

        Correct.   HRRR, NAM Nest, RRFS, and the three Hires Windows (FV3, ARW, ARW2).

1 hour ago, Kmlwx said:

The CAMs are really all over the place (seems to be a common theme this year). I could technically see chunks of the area getting skunked through the whole week...The game of weather lottery! 

 Even this evening has a lot of questions.  While there is general agreement that a cluster of storms drops south through NJ/DE, some of the CAMs have storms building back to the west and catching much of central MD.

One complication for tomorrow is that some of the guidance pushes a front from the northeast through the area later tonight.  If that pushes well to our southwest like shown in the NAM Nest, we'll be cooler and more stable, at least on the Maryland side.  Less aggressive guidance puts the boundary somewhere between DC and Baltimore and has it retreat later in the day.   This would in theory be a focus for afternoon convection.

39 minutes ago, vortex95 said:

And, of course, the derecho on June 29, 2012.  I think an EML present is important for high-end derechos.
 

         I'd say that there isn't much doubt about it, especially in the East.    We've had several derechos over the year die an ugly death over the mountains to our west when no EML was in place downstream.   One event in 2000 led SPC to issue a rare PDS severe thunderstorm watch here due to an intense bow echo over southeast Ohio blasting east.    Our environment did not have an EML, and the Appalachians shredded the system - we ended up with line of showers featuring gusts to 30 kt.