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mid-atlantic discussion

First severe threat of 2013 in the Mid-Atlantic

While the severe weather outbreak will be more focused on the southern states, I did this write-up just for folks in the Mid-Atlantic.

A widespread strong to severe wind event appears to be unfolding over the eastern half of the U.S. Tuesday into Wednesday, with isolated tornadoes also a threat, which is mostly across parts of the Southeast. The Mid-Atlantic has some opportunity for both on Wednesday, with the main threat obviously being a line of strong to severe winds.

We will be battling marginal lapse rates and pre-frontal clouds/rain, as we normally do in these early year setups. Very strong winds aloft (50-60 kt jet at 925mb!) suggests any sort of convection will bring down strong to severe level winds. With the strong forcing associated with the cold front, I don’t see much of a problem getting those winds to the surface. The only issue would be if a stable layer at the surface can linger ahead of the front, but that appears to be just a minor problem as the lift from the front should overcome the stable layer (if there is indeed a stable layer).

With dewpoints climbing into the lower 60s ahead of the front, we should be able to see a fairly strong frontal passage with widespread strong to severe winds. The main thing I’m watching now is the potential of a secondary low formation, which the NAM has (though that can’t be relied upon at this point). The Euro also develops a secondary low, but it comes later and further north than the NAM. If this secondary low develops before the front comes through, and if it’s far enough south, it will be able to back the winds more at the surface and would provide a greater risk for tornadoes in the Mid-Atlantic.

Mid-Atlantic Discussion – Feb 24, 2012

I can’t believe I haven’t done one of these since August… been too long.

The first real chance for severe weather in the Mid-Atlantic this year has arrived! Tomorrow’s looking increasingly promising for at least some severe wind threat in addition to an isolated tornado or two and maybe some hail. Strong post-frontal winds and brush fires are also risks with this system.

The latest models have been pushing out CAPE values of 500-1000 J/kg in parts of the Mid-Atlantic from DC down to eastern NC tomorrow afternoon, which isn’t much, but for February it’s not too shabby. The low-level jet will also be roaring in southern VA and eastern NC, which strong thunderstorms could mix down to the surface. There is enough directional shear in the low-levels for a tornado threat in southeast VA and eastern NC, which is where I plan to storm chase.

Behind the front, dropping dewpoints and strong winds gusting to 50-60+ mph will bring a risk for brush fires to the region as well, especially in the areas that were north of the recent snowfall from last Sunday.

All of this will be going on during the afternoon and evening hours tomorrow, though winds will remain somewhat gusty going into Saturday.

Here’s the latest forecast from the SPC (click the image for their discussion):

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.

Mid-Atlantic Discussion – Aug 21, 2011

It seems like I jinx our severe weather every time I make a post about it. We’ve been faring a lot better with the pulse-type storms than with any sort of organized system this summer, but unfortunately you can’t really chase pulsers since they almost always weaken before you can get to them… not to mention the fact that they almost never produce tornadoes.

Anyway, getting to tomorrow’s threat, we see a cold front and upper-level trough moving through the region, with the best dynamics to our north in PA/NJ/NY up through parts of New England. I’m not particularly thrilled with the setup locally, though it does raise an eyebrow. Most of the concern comes with how the mesoscale features pan out, which the models have had a hard time dealing with since the upper-level energy isn’t that organized. The complicated and convoluted upper-levels, along with weak low-level winds, has been our biggest downfall this summer. Stronger, more highly concentrated features would help improve not only lift but the mid-level lapse rates as well, which is another key to getting well-organized and sustained storms (at least in our region).

Tomorrow looks a bit better than previous setups this summer (mostly due to the better looking lapse rates and possibility of a low-level “jet”) as a cold front and upper-level jet streak move into the region. Lapse rates are good up to 650mb, but the 650mb-300mb lapse rates are fairly poor. A low-level jet could develop tomorrow across the eastern parts of the region, which would help boost storm formation and organization. Another issue is timing, with the storms expected to form before peak heating in most of the region. Pre-frontal rain/clouds are also a concern, thought not so much as they have been in previous setups.

Chase-wise, I would pick eastern PA/NJ or even the Delmarva Peninsula as possible targets unless good storms can get going early in MD/NoVA/central PA. I may have to sit this one out as I am working the overnight tonight, and sleep will weigh into the decision.

SPC’s thoughts:

…NEW ENGLAND/ERN NY/MID-ATLANTIC/CNTRL APPALACHIANS…
A LARGE UPPER-LEVEL TROUGH WILL MOVE EWD ACROSS THE GREAT LAKES AND
OH VALLEY SUNDAY AS A 60 TO 75 KT MID-LEVEL JET ROUNDS THE BASE OF
THE TROUGH. AHEAD OF THE UPPER-LEVEL TROUGH….MODEL FORECASTS
INITIATE NUMEROUS THUNDERSTORMS ALONG AN AXIS OF MODERATE
INSTABILITY FROM WRN NEW ENGLAND SSWWD INTO THE MID-ATLANTIC BY
EARLY SUNDAY AFTERNOON. FORECAST SOUNDINGS ALONG THIS CORRIDOR AT
21Z SHOW MLCAPE VALUES IN THE 1200 TO 2000 J/KG RANGE WITH MODERATE
DEEP LAYER SHEAR AND SOME DIRECTIONAL SHEAR IN THE LOW-LEVELS. AS
THE NOSE OF THE MID-LEVEL JET MOVES INTO THE NERN STATES SUNDAY
AFTERNOON…DEEP LAYER SHEAR WILL INCREASE MAKING CONDITIONS
FAVORABLE FOR SEVERE STORMS ALONG THE INSTABILITY AXIS. IN
ADDITION…MODEL FORECASTS INTENSIFY A LOW-LEVEL JET ACROSS THE
SLIGHT RISK AREA IN THE LATE AFTERNOON SUGGESTING WIND DAMAGE COULD
BE THE GREATEST THREAT. CONSIDERING 500 MB TEMPS SHOULD BE IN THE
-10 C TO -12 C RANGE…HAIL WILL ALSO BE POSSIBLE IN AREAS WHERE
INSTABILITY AND SHEAR ARE MAXIMIZED. ALTHOUGH MORE CONDITIONAL…AN
ISOLATED TORNADO THREAT COULD ALSO DEVELOP NEAR THE CENTER OF THE
LOW-LEVEL JET IN THE MID-ATLANTIC WHERE THE STRONGEST INSTABILITY IS
FORECAST AND SFC DEWPOINTS SHOULD BE IN THE MID TO UPPER 60S F.

Mid-Atlantic Discussion – Aug 14, 2011

Clouds and weak LL winds will hurt severe chances today, but okay lapse rates, decent UL support and dewpoints in the lower 70s should help make things a little interesting this afternoon. Secondary low development in NC/S VA certainly won’t help our poor LL wind situation as the SFC winds weaken and become more variable.

RUC shows a much better setup for severe weather in the DC/MD region (which would warrant the slight risk), but it has been overzealous with the wind field and dewpoints in recent events.

SPC was rather bullish this morning… we’ll see what their thoughts are in future updates, as they have been too bullish with the last two systems that have passed through the region.

Mid-Atlantic Discussion – Aug 9, 2011

Aha! Another chance for storms! But what’s THIS?!? Latest models say best dynamics will be to the north in eastern PA and NJ?

If enough instability can get going up that way, that’s where I’ll be chasing tomorrow. Pretty nice wind field coupled with modest CAPE, with one of the stronger vort. maxes we’ve seen in the region lately and left-exit region goodness from the 300mb jet… things are shaping up nicely per the latest models.

For the Mid-Atlantic states south of the Mason-Dixon, there will still be a severe threat as this shortwave trough moves through the region. The secondary low and its associated cold front will pass through the region tomorrow, providing the risk for severe winds and possibly severe hail. There is a very, VERY minor chance of tornadoes along and just ahead of the front, as some low-level veering is possible but will likely be dominated by the very deep column of unidirectional shear.

Of course, all of this stuff is changing on a run-by-run basis and we could be looking at something completely different tomorrow… it will all depend on what the next 18 hours does in terms of rain, clouds and timing and placement of the developing secondary low.

Mid-Atlantic Discussion – Aug 3, 2011

So… here we are a month after the last Mid-Atlantic write-up (the event failed, BTW) with a new threat and different variables as we look at tomorrow’s severe weather.

Gonna just list the pros and cons and go from there:

PROS:
– Good low-level speed and directional shear.
– Excellent low-level lapse rates.
– Upper-level support via 500mb vort. max and some influence from the jet.
– Winds are veering throughout the column.

CONS:
– Possible cloud cover from storms to the northwest could inhibit heating.
– Lackluster mid-level lapse rates (could change for the better if dynamics are stronger).
– Upper-level jet is perhaps too far away to have a significant impact and we are not in the ideal (upper-level divergence) part of the jet.
– Main line of storms could come in just a bit too early for optimal destablization.
– High LCLs.

With everything put together, it looks like a pretty mixed bag between meh and awesome. I’m going to put tomorrow’s chasing chances at 50%… some nowcasting is definitely for tomorrow’s storms, so there’s no reason to decide on anything now. No idea where I’m going to go yet, either (should I end up going). Primary threat is wind… could see a tornado or two out of it if the instability is good enough.

SPC’s thoughts:

…MID ATLANTIC REGION…
A RATHER STRONG SHORTWAVE TROUGH NOW OVER THE DAKOTAS WILL TRACK
ACROSS THE GREAT LAKES AND INTO THE MID ATLANTIC STATES ON
WEDNESDAY. SEVERAL CLUSTERS OF THUNDERSTORMS ARE ONGOING TODAY WITH
THIS FEATURE…AND WILL LIKELY PERSIST INTO TOMORROW. MODEL
GUIDANCE SUGGESTS THESE CONVECTIVE CLUSTERS WILL BE OVER PARTS OF
LOWER MI/NY/PA/OH AT 12Z. THERE IS CONSIDERABLE UNCERTAINTY
REGARDING THE EXTENT OF CLOUD COVER AHEAD OF THE STORMS…WHICH WILL
IMPACT THE DEGREE OF AFTERNOON DESTABILIZATION OVER THE MID ATLANTIC
REGION. HOWEVER…RATHER STRONG LOW AND MID LEVEL WIND FIELDS
ASSOCIATED WITH THE UPPER TROUGH POSE SUFFICIENT CONCERN TO INCLUDE
THIS REGION IN A SLIGHT RISK FOR SEVERE STORMS. THE MOST LIKELY
THREAT WOULD BE AN ORGANIZED MCS TRACKING THROUGH THE AREA DURING
THE AFTERNOON PRODUCING LOCALLY DAMAGING WIND GUSTS.