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severe weather

Severe weather possible in the Mid-Atlantic tonight/tomorrow

The synoptic setup is somewhat favorable for damaging winds and perhaps an isolated tornado or two tonight into early tomorrow in the southern Mid-Atlantic as storms ahead of a cold front push through the region. Poor lapse rates will likely prevent severe weather from occurring in DC, Baltimore and points north and west.

The storm system will be what we typically see for severe weather setups in the Mid-Atlantic during the winter and early spring… low CAPE/high shear. This system was looking fairly marginal for the region up to this morning due to the poor mid-level lapse rates, but it appears that the previously under-forecast dynamics will help introduce better lapse rates to the southern Mid-Atlantic. It is still fairly borderline, but with a strengthening low-level jet producing 50-60 kt. winds at 925mb it wouldn’t take much to bring those damaging winds to the surface.

925mb winds at 4am:

Forecast sounding for Richmond at 4am:

The sounding shows that there is enough directional shear for the anticipated storms to produce a tornado or two in the southern Mid-Atlantic tonight into tomorrow morning.

SPC’s outlooks for tonight into tomorrow morning:

I am mostly in agreement with them, but I would tone it down to a SEE TEXT instead of a Slight Risk north of the NC/VA border as the storms don’t look to be terribly organized, which is something you want to see for a Mid-Atlantic low CAPE/high shear system (at least for the damaging wind potential).

Severe weather outbreak likely in the Southeast/Midwest

The SPC has released their first Moderate Risk for severe weather of the season for today:

The biggest risk will be for damaging winds along a squall line that is expected to form during the late evening to early morning hours just west and along the Mississippi River from southern Illinois southward into central Mississippi. 50-55 kt. winds in the 925-950mb level could mix down to the surface as the squall line pushes through. This is also a fairly good low CAPE/high shear setup for tornadoes, which could develop along the squall line.

The one thing to keep an eye on is the somewhat stable layer of air between the surface and 950mb, which will inhibit the potential severity for most of the storms except maybe in the southernmost areas.

I think the SPC prediction for today is fairly reasonable, but I will say that the northern extent of the Slight Risk and Moderate Risk could be cut back as the low-level air is forecast to be too stable north and east of southern Illinois. If the warm front associated with this system can get advected further north than forecast, then the SPC’s risk area could be justified. I could see that happening to a degree as the models often underforecast the northern extent of the warm sector in dynamically-strong cases such as this one, but I don’t think it will be as significant as the SPC appears to think it will be.

Widespread rain event over the next 5-7 days… some severe

An upper-level low is forecast to move into the Midwest tomorrow before cutting off from the main flow, which will allow it to linger over the Midwest and Tennessee Valley regions through around Monday or Tuesday before it lifts out of the eastern U.S. This has a couple of different implications for the region…

The most pronounced threat with the cut-off low is the potential rainfall, with widespread totals of 1-3 inches or more in the Mid-Atlantic and Northeast. Normally 1-3 inches isn’t that critical, but when you add it to the recent record-breaking rainfall in these regions any larger rainfall potential becomes a significant event.

Here’s a look at the total rainfall and the percent of normal rainfall for the period starting August 1st and ending yesterday, September 19th:

With some areas with over 20 inches of rain in the last 45-50 days, anything over a couple of inches will cause some of the rain-soaked areas to flood once again. Right now it looks like the coastal areas are more at risk for heavy rain compared to the inland/mountain areas in the Mid-Atlantic.

In terms of severe weather, strong to severe storms will be possible Thursday through next Monday or Tuesday, depending on the position of the cut-off low. This complex cut-off will have a few pieces of energy floating around it (at least initially… some guidance suggests one of the pieces breaks away before it completely stalls):

Having 2-3 pieces of energy in this cut-off low will make the forecast very difficult as models struggle to resolve the complex mesoscale interactions between the different pieces of energy and what they’ll do in turn at the surface.

Also associated with this energy will be an upper-level jet streak out ahead of the trough, which will help enhance lift. The problems, at least initially, will be the fact that the energy is just a bit too far to the west to have that great of an impact on the Mid-Atlantic, and clouds and rain could inhibit heating and worsen the lapse rates. My main focus for severe is when the trough does finally push eastward over the region… hopefully the timing will be good and it could trigger some afternoon/evening storms over the Mid-Atlantic. Once it progresses into the region, the energy involved with it will cause greater lift and the lapse rates should improve.

Not getting my hopes up on severe yet, but at least it’s something to watch over the next several days.

MD/DC/VA bake in record heat as severe storms form up north

DCA has already gotten to 102 twice today… shattering the daily record of 99 set back in 1993. One more degree would make it DCA’s hottest day of 2011, with three 102 highs already on the board.

IAD is up to 101, breaking its daily record of 97 (also set in 1993) and BWI is at 100, beating the old record high of 99 that was set back in 1954.

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Further north, severe weather is the main concern of the day. A Severe Thunderstorm Watch is up for the eastern two-thirds of PA, most of NJ and southern NY. Wind damage will be the main threat, with an isolated tornado or two also possible.

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UPDATE:

DC region official highs: DCA 104, IAD 103, BWI 101.

Also, multiple tornado warnings have been issued with two cells… one in NE PA near the PA/NY border and one in SE NY heading towards NYC and Long Island.

Chasing a Possible Tornado Outbreak in NC today

Jason and I will be heading out to North Carolina around 8:00 this morning, and our target area that was picked 2-3 days ago is in the heart of the Moderate Risk area today, which includes a strong risk for tornadoes. A full chase log will be posted later today or tomorrow. It’s potentially going to be pretty epic.

Putting things into perspective, as of now there has been 6 deaths and 23 injuries from the tornado outbreak that occurred yesterday in the Southeast, and the threat for severe weather will be almost/just as significant today from central Virginia through Georgia. For those living in the risk area, please pay very close attention to the weather today, as these storms could form quickly and with very little warning, so do your best to avoid becoming another statistic in today’s severe weather.

 

Severe storms firing in WV, VA

Hail and damaging winds have been reported with several severe storms that are moving through West Virginia and are forming and moving into Virginia. Some of these storms have shown signs of rotation, so in addition to large hail and damaging winds is the concern for isolated tornadoes. There is currently no weather watch out for the over half-a-dozen severe-warned cells, but there was a Mesoscale Discussion out earlier (whole lot of good that does for the general public).

Beware of these storms, as they could be a bit more powerful than expected.