Word on the SVR threat in the Mid Atlantic Tomorrow.

[USAwx1]

Earlier WV loops suggest the 12z GFS initialized 500H trough over the UPR MS valley better than the ETA, which is in relative agreement w/ the earlier 06z ENSEMBLE means as well as the trend in the GGEM and UKMET. The ETA had the most amplified look to the 500H pattern and was also the fastest.

The GFS however was the quickest w/ the eastward progression of the SFC cold front, at least initially (which is probably the result of grid-scale/convective feedback problems), before, for a short time coming in line w/ the ETA and GGEM solutions, until that is of course, SLP develops along the front tomorrow off the mid Atlantic coast tomorrow, when it becomes the slower solution. This once again is likely b/c of convective feedback. Although, at any rate, the GGEM appears to be the mid ground between the ETA and GFS solutions for tomorrow afternoon WRT to the SLP development.

Synoptically, we notice four key features aloft:

1. LARGE 500H low in the 50-50 low position near New Foundland/SE CAN.
2. 500H trough across the Northern Plains
3. Shortwave Ridging in-between the large low over SE CAN and the trough over the upper plains.
4. 60-65 KT mid level jet streak pulling out of North central TX/S central OK.

18z Surface analysis showed 992mb low over ERN SD/WRN Minnesota, w/ associated occluded boundary draped across south central MN, and into central IA, where the triple point is located. Cold front extended South from the triple point through MO/OK/TX, w/ warm front extending EWD over IL/IN/KY.

During the day tomorrow, 500H trof will build an increasingly negative tilt as it becomes elongated eastward through the southern lakes. Associated 500H jet streak will undercut the shortwave ridge between the large low across SE CAN and the aforementioned through, causing block to form along the western shore of Hudson Bay bay by later in the day, meanwhile triple point associated w/ occluded SLP over the upper Midwest will push into the lower lakes, as cold frontal boundary extends southwestward from it through the OH VLY back into NE parts of TX during the morning hours. Warm front will likely be running from the lower lakes to the Delmarva. The northern portion of the front will move FASTER than the southern part as SLP becomes elongated from MN through the central lakes into WRN NY.

Instability wise --- cloud debris from old convection or blow-off from still ongoing thunderstorms may limit instability in the warm sector (E of the cold front and S of the warm front extending outward/away from the triple point). However, latest 18z MesoETA suggests lowest 100mb Mean layer CAPE values increasing to 1000 J/kg over portions of the Mid Atlantic by late in the day...within the warm sector. This given favorable deep layer shear in the lowest 6 KM AGL of generally 40-50 KT, increasing upper level divergence, and forced ascent along the front as it progresses eastward through the day, should lead to the development of a squall line along the cold front, that will traverse the mid Atlantic before moving out to sea during the late evening hours.

The areas included would be much of Central and SRN MD/ all of VA/ central and SRN DE (Delmarva region in general) and perhaps EXTREME SRN NJ. Primary threat will be isolated wind damage and perhaps some marginally severe hail given weak mid level lapse rates. BEST potential for tornadoes (which is already limited given lackluster instability, and poor lapse rates), would up along the warm front, into N MD, N DE, S/SE PA, S NJ, where 18z ETA forecasts best low level shear, w/ lowest 3 KM SR-helicity values above 200 m^/s^2, and low LCL heights. Also, INVOF the warm front is where the best backing of winds from SE at the surface to South at 850H and eventually West at 500H.

Furthermore, going against the tornadic threat would be the relatively stable boundary layer, implying that convection would likely be elevated.

Overall......the severe threat is much LOWER tomorrow than it has been these past two days, w/ the primary severe threat across the region given anticipated convective mode being ISOLATED ---- marginally severe hail and wind damage.

[Skywatch_NC]

What about the Carolinas for tomorrow?

Eric

[Guest]

Good discussion USAwx1. And i pretty much agree. This seems very fitting for the kind of year it has been around these parts. Good for all those that live in these areas however bad for us chasers again. Timming is gonna be very big as well as like you said cloud cover going into the afternoon. I do think IF we can get (Doubtfull but not impossible) everything to come together and at the right time it could be a very active day from VA north.

[USAwx1]

What about the Carolinas for tomorrow?

Eric

pretty much the same thing, although the southern end of the cold front will drag its heels somewhat. Surface-based instability will be somewhat better also w/ LI's of -2 or -3 and SB CAPE 1000-2000 J/kg by later in the day. MID LEVEL lapse rates are still < 6.00 DEG C/km which doesn't help any either when it comes to enhancing CI (Convective Instability).

Although deep layer vertical shear in the lowest 6 KM is between 30-35 KT at 21z (per the 18z MesoETA) which is borderline, 0-3 KM AGL helicity is over 150 m2/s2 suggesting favorable low level shear --- that in combination with marginal instability should contribute to at least somewhat of a SVR threat. Especially as the cold front approaches from the west.

[Skywatch_NC]

Good discussion USAwx1. And i pretty much agree. This seems very fitting for the kind of year it has been around these parts. Good for all those that live in these areas however bad for us chasers again. Timming is gonna be very big as well as like you said cloud cover going into the afternoon. I do think IF we can get (Doubtfull but not impossible) everything to come together and at the right time it could be a very active day from VA north.

As well as extreme northern NC and western NC...

http://www.spc.noaa.gov/products/outloo ... 30_any.gif

[USAwx1]

Good discussion USAwx1. And i pretty much agree. This seems very fitting for the kind of year it has been around these parts. Good for all those that live in these areas however bad for us chasers again. Timming is gonna be very big as well as like you said cloud cover going into the afternoon. I do think IF we can get (Doubtfull but not impossible) everything to come together and at the right time it could be a very active day from VA north.

Thanks...IF we were NOT dealing with all the cloud debris from ongoing or decaying convection from today, instability would be much stronger, which in concert with the more favorable deep layer vertical shear over the northern mid atlantic region would make for a more widespread SVR situation, but instability (as it it has been so many times in the past) will be the MAIN limiting factor.

[USAwx1]

May also be another round for the Northeast on WED afternoon/EVE as positively tilted 500H trough over the great lakes region (the axis of which running appx. right through central Michigan) develops closed low between 18z WED and 0z THU, and associated mid level jet streak rounding the base of the trough approach the region.





the eta also shows two pootential shortwaves of interest, the first, the lead s/w across PA at 18z and another upstream following it over the ohio river VLY.

Instability and mid level lapse rates are also more impresive, w/ SB CAPE of 1000-1500 J/kg at 18z, underneath 500-700mb lapse rates of 6.0-6.5 DEG C/km, and lowest 6 KM vetical shear > 35 KT.

We'll let the rest of the details wait for later, but things COULD get interesting on WED over E PA/ Central and ERN NY/DE/MD/NE VA during the afternoon and EVE on WED.

[Colin]

Sounds good..I'm ready and waiting here in East-Central PA!

[Stephanie]

Thanks USAwx!

Right now it's cloudy and cool - only 66 degrees. We're getting a little rain shower now. The rest of the current conditions are;

Humidity: 73%
Wind Speed: SE 9 MPH
Barometer: 29.75 in.
Dewpoint: 57°F


If we do get a few breaks of sun, we'd have some problems, but the showers are moving in from the west, so it doesn't look like we'll see any sun today.

[Guest]

Well I think the threat here is pretty much done for. Lots of clouds and rain here which should limit the instability. Another typical lack luster day here.

[Stephanie]

I'm sure that we'll be seeing our share of storms soon KOW!

[Skywatch_NC]

Well I think the threat here is pretty much done for. Lots of clouds and rain here which should limit the instability. Another typical lack luster day here.

Harry, when did you move to DE? Do you miss OH?

I lived in sw OH for 20 yrs. and still get homesick every now and then for that area.

[USAwx1]

Well I think the threat here is pretty much done for. Lots of clouds and rain here which should limit the instability. Another typical lack luster day here.

I would not count it out yet, lowest 300mb MU CAPE values are already in some cases above 2000J across VA in the warm sector.

[Guest]

Well I think the threat here is pretty much done for. Lots of clouds and rain here which should limit the instability. Another typical lack luster day here.

Harry, when did you move to DE? Do you miss OH?

I lived in sw OH for 20 yrs. and still get homesick every now and then for that area.

I moved back here 2 weeks ago. This is where i am from btw.. Right now all i am missing there is the weather.

[USAwx1]

for the WED THREAT.....

12z ETA had a more meridional look to the trough over the great lakes region, as compared to yesterday, given instability (w/ 21z WED sounding at PHL showng LI's down to -4.6, and SB CAPE between 1500-2000 J/kg, underneath increasing mid level lapse rares) and approiaching 500H s/w kicking out of the OV region at 18z, it could be a very interesting situation.

Still some questions though as to how the pattern will evolve at the Surface, however those should be worked out in the next few runs.

[USAwx1]