2017 Severe Thread

[mappy]

..Mid-Atlantic...
   To the east of the aforementioned low and attendant surface front,
   strong southerly low-level flow will transport surface dew points in
   the low/mid 60s northward across coastal NC and into southeastern
   Virginia. With what remains of a remnant EML plume pushing over the
   region, this uptick in low-level moisture (as well as northward
   warm-air advection) should give rise to approximately 1000-2000 J/kg
   of MLCAPE by morning. While considerable uncertainty exists with
   ongoing convection expected across the region at the beginning of
   the period, the crossover of ample effective shear and favorable
   buoyancy over this area should contribute to an organized severe
   threat within a mixture of storm modes. Ahead of the composite cold
   front/outflow boundary, an initial opportunity exists for
   semi-discrete convection organizing along confluent boundaries
   within the warm sector. Strong low-level shear and a moist boundary
   layer suggest tornadoes will be possible with any of these cells.
   The ongoing enhanced risk was expanded southward to the NC coast to
   account for this potential. Through the morning, however, increasing
   forcing for ascent and a veer-back-veer wind profile with height may
   force more linear modes, favorable for damaging wind gusts and
   perhaps a few embedded circulations. Considering the strength of
   surface-to-850mb flow, a few swaths of damaging wind gusts may be
   possible with these developing linear segments.

   No significant changes are made to the ongoing northern extent of
   the severe risk categories. Some uncertainty remains with regards to
   the depth of the stable layer (and resultant ability of stronger
   downdrafts to reach the surface with sufficient momentum) along the
   northern fringes of the slight/marginal risks across the Delmarva
   and coastal New Jersey. However, considering the strong kinematic
   fields and potential for sufficient warming of the near-surface
   stable layer, the strong wind threat appears considerable enough to
   maintain the ongoing categories.

[Bob Chill]

Someone correct me if I'm wrong but we seem to rarely get severe level winds with storms coming up from the south like this. Most of our downbursts and severe straight line winds seem to come from storms moving from W-E. OTOH- in the back of my mind I'm remembering that quick hitting spinney things are more common with strong coming up from the south. 

[Treckasec]

1 minute ago, Bob Chill said:

Someone correct me if I'm wrong but we seem to rarely get severe level winds with storms coming up from the south like this. Most of our downbursts and severe straight line winds seem to come from storms moving from W-E. OTOH- in the back of my mind I'm remembering that quick hitting spinney things are more common with strong coming up from the south. 

I believe that the reason why it seems that more tornadoes produce in storms coming from the south are because a lot of those situations in the Mid-Atlantic are caused by tropical cyclones traveling up the coast and not necessarily because of the storm motion itself ...

 

regardless, there probably will be 'nados somewhere.

[nw baltimore wx]

4 hours ago, Ellinwood said:

Myself, Ian, and James (wxmeddler) will be out chasing this year. Planning on being on the road May 20-June 4, which gives us the possible chase days of May 21-June 3.

Awesome.  I can't wait to read the updates and see the photos.  I know you guys will be without anyone saying it, but be safe!

[Bob Chill]

Euro is basically identical to 0z. We're close to chips fall mode. The broad brush view is that active weather will be moving through the entire region between 8am and 2pm. Places south in VA have the best chance at severe. 

Tomorrow will be an interesting test for those who get headaches from low pressure (I suffer from this sometimes). A 987 SLP just a few miles north of us in PA is pretty close by. Euro surface panels have almost all of us sub 990 late morning/early afternoon. 

[MN Transplant]

I have a couple of non-consecutive meetings in CO in May and I'm staying out there in between for a few days.  Have a road trip planned that would knock off states #46 (NM) and #47 (UT).  However, I will be keeping my eye on the weather and could possibly waste a day in KS.

 

The HRRR is flipping around on what exactly it is doing with the Ohio Valley line of storms overnight.  Latest has it kind of washing out and then setting us up for the possible severe line in the late morning.

[MN Transplant]

LWX afternoon AFD is a bit light on details, but they make one good point:

Warm fronts often have a difficult time to push
very far to the north during the night hours, but the winds in
the lower levels are going to be quite strong so that may not be
a concern. 

We'd be bemoaning this pattern in the winter as the warm air busts through

[09-10 analogy]

1 hour ago, Bob Chill said:

Someone correct me if I'm wrong but we seem to rarely get severe level winds with storms coming up from the south like this. Most of our downbursts and severe straight line winds seem to come from storms moving from W-E. OTOH- in the back of my mind I'm remembering that quick hitting spinney things are more common with strong coming up from the south. 

The Superoutbreak of 2011 did produce several tornadoes the next day in our general vicinity. A couple EF2s among them. Then again, that wasn't just any old system.

[mappy]

I love having this data on hand for random moments like these

confirmed tornadoes from April 27/28th 2011

[WxReese]

FWIW, the 0Z run of HRW-NMMB  (4-5-17) is doing a heck of a job with this system so far. Forecast radar image for around 3 PM vs actual radar: 

 

 

Here's what that same model shows Thursday morning around here... So.. Yeah. Definitely something to watch. 

[eurojosh]

18z 3k NAM looks weird... Dry...  A continuation of the SNAFU on the GFS identified above?

 

Edit - NVM, I jumped the gun.  Just holds back the main line.

[yoda]

18z NAM soundings really pounding the 12z to 18z time period across the region... maybe until 19z... Def decent SRH and 0-3km MLCAPE for a tornado threat

[WinterWxLuvr]

3 hours ago, mappy said:

I love having this data on hand for random moments like these

confirmed tornadoes from April 27/28th 2011

The F2 on this map to my southwest was on the ground for 33 miles if I'm not mistaken.  Pretty incredible for my area.

[yoda]

38 minutes ago, WinterWxLuvr said:

The F2 on this map to my southwest was on the ground for 33 miles if I'm not mistaken.  Pretty incredible for my area.

The biggest tornado in our area moved through portions of the Shenandoah Valley in Rockingham and Shenandoah counties from Fulks Run to St. Luke. It traveled 33.2 miles and the path was 400 yards wide! Winds approached upward of 130 mph during its duration from 2:12 a.m. until 2:41 a.m. It was classified as an EF2 by the local weather service office after the damage was surveyed. Two people suffered minor injuries — the only injuries reported during the two-day spat of tornadoes.

http://wtop.com/weather/2015/04/twisted-april-the-tornadoes-of-2011/

[Huriken]

Most people calling bust for the SVR threat down south. Not sure how this translates for the potential SVR overnight.

[WinterWxLuvr]

23 minutes ago, yoda said:

 

 

http://wtop.com/weather/2015/04/twisted-april-the-tornadoes-of-2011/

Thanks for sharing Yoda

[yoda]

A little concerned that both the 18z GFS/18z NAM and HRRR runs are getting DPs into the 58-62 range in the DC metro around 15z-18z

[Scraff]

3 minutes ago, yoda said:

A little concerned that both the 18z GFS/18z NAM and HRRR runs are getting DPs into the 58-62 range in the DC metro around 15z-18z

Only be concerned if you don't have storm cellar. Though if a wedge hit 1600 Penn Ave, would anyone care? You know. Kinda like a tree falls in the woods scenario...

[yoda]

The 0100z SPC OTLK is running late...

[yoda]

^  

Well done

[yoda]

Pretty decent disco from 0100 SPC OTLK... suggests new storm development in both Western and Central VA with all severe hazards possible overnight due to strengthening deep layer and low level shear

[Huriken]

6 minutes ago, yoda said:

Pretty decent disco from 0100 SPC OTLK... suggests new storm development in both Western and Central VA with all severe hazards possible overnight due to strengthening deep layer and low level shear

I'll take it. Things could get interesting in the overnight hours.

[yoda]

9 minutes ago, HuriKane F0RC3 said:

I'll take it. Things could get interesting in the overnight hours.

For the LWX CWA, I would assume anything interesting would probably be after 2am or so

[yoda]

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
951 PM EDT Wed Apr 5 2017

.SYNOPSIS...
Low pressure in southern Indiana will track to the northeast
tonight. Its associated cold front will cross the region
Thursday. High pressure then builds over the area through early
next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
Latest surface analysis puts the surface low in southern Indiana
with a complex warm front extending northeast across the Ohio
Valley, then southeast acorss the Appalachians and Mid-Atlantic,
ending up near Norfolk, VA. Slightly more stable air is actually
advecting into the region on a southeast wind at present, at
least across the DC and Baltimore metros. The greatest
instability right now across our CWA is in the far southwest,
down near Highland County, which is on the warm side of the warm
front.

Chances for showers will continue to expand north and east
across the region tonight. Low pressure is expected to track
into OH by late tonight, with a nearly stationary warm front
remaining across our CWA. Warm fronts often have a difficult
time to push very far to the north during the night hours, and
at present surface winds are almost parallel to the front, but
the winds in the lower levels are going to be quite strong and
shift more southerly, so that may not be a concern. Latest
guidance is a bit slower with the progression, with the cold
front entering the CWA towards 12Z but not clearing us
completely until after 18Z.

Those 6 hours (probably a little longer) could be quite action
packed for this CWA, although not as much as what is going on
further to our south at the moment. The morning-midday timing
in early April is not prime for severe weather, given that CAPE
will be limited, but there will be a period of strong low level
turning of the winds in the pre-dawn-through-early-afternoon
hours.

What does this mean for Mid Atlantic? Heavy showers with
scattered thunder. The best chance for severe looks to be in
the I-95 corridor south of DC. Given the low level spin
tornadoes cannot be ruled out, again south of DC would be the
prime area. The exact final northward extent of the warm front
will be critical to extent of severe weather. Latest guidance
brings it into central MD, north of DC, but perhaps not quite
to Baltimore.

 

[olafminesaw]

The rest is worth a read, but strong wording from Wakefield:

High confidence for significant severe weather threat early
Thursday morning through midday. Widespread damaging winds,
large hail, and tornadoes are all possible.

[yoda]

[southmdwatcher]

Did that sounding say zero CIN and 317 j/kg CAPE 0-3KM

[yoda]

1 minute ago, southmdwatcher said:

Did that sounding say zero CIN and 317 j/kg CAPE 0-3KM

0 CIN and 317.4 CAPE at 3km

[southmdwatcher]

I have seen significant severe weather here in central Charles County with storms coming due south to north, that is not normal to the rest of our region( I suppose) but I had significant tree damage from an event with that scenario. Tomorrow is eerie, but the ceiling is limited since the timing for the event is early afternoon at best.

[yoda]

8 minutes ago, yoda said:

0 CIN and 317.4 CAPE at 3km

Interesting quick read about what large values of 0-3km CAPE means --- http://theweatherprediction.com/habyhints2/632/