Expect another batch of severe weather on Tuesday as a cold front and surface low move through the region.
The cold front developed from a strong Canadian low and has been rolling eastward for a couple days, producing strong storms in the Great Lakes region along the way. Meanwhile, the low pressure system developed down near the Gulf and has been swinging northeastward. The two look to converge right over PA. The question is… where in PA?
Recent 4KM WSI RPM models (my favorite) show the front and low combining forces over central/eastern PA, looking to be just east of State College. When the two merge, a squall line will develop (just east of State College) and rumble eastward, picking up in intensity as it heads toward Philly and NYC and dissipating over western New England.
The timing of the merge between these two systems will ultimately determine the location of the development of the squall line. This is definitely something to watch for. This squall line will be associated with the most widespread severe weather of the day, with the primary threat being damaging winds.
There is also a slight chance for tornados forming within supercells ahead of the squall line. Currently, little CAPE is forecasted for the mid-Atlantic region due to weak mid-level lapse rates. This could change, though, in places where the clouds break tomorrow morning, which would allow for more surface heating. Dewpoints will be sufficient to support strong updraft development, with forecasted dewpoints currently pushing 70 for tomorrow afternoon. Given the right combinations (i.e. already present low-level moisture and possible surface heating), tornadic supercells may form in southeastern PA, northeastern MD, northern DE, and western NJ.
So, overall, expect lots of rain and isolated, strong storms developing throughout the day ahead of the cold front in central PA. Given the timing of the combination of the front and low, we might see the squall line's effects here in Centre County, or the line might develop just east of us.
Either way, expect lots of rain and strong storms tomorrow afternoon and evening.
Stay safe tomorrow, folks!
Matthew Flournoy
Meteorology Major | The Pennsylvania State University
Schreyer Honor Scholar | Class of 2015
Schreyer Honor Scholar | Class of 2015
Good job, Matt: Low instability over PA and the location of the merging systems will be major factors that could prevent severe storms here despite all other ingredients here. A comparable event in early June had lifting w/o instability and was a bust.
ReplyDeleteI must point out that the mid-Atlantic region (1) is south of PA and technically does not include the state and (2) there's more likely to be instability in that region but there's less shear down there.
EHI (Energy-Helicity Index = CAPE * SRH) will be the parameter to use today. Where EHI is 0.75 to 1.5 [(m/s)^3], severe storms possible; >1.5: severe storms likely.
Jaron Breen
- CWS 4cst Shift Manager
- Class of 2013 (Dec.)
EHI is actually CAPE * SRH / 160,000.
ReplyDelete