Chubbs Posted March 7 Report Share Posted March 7 Slight risk today - our typical cool season threat - limited instability/strong shear/winds ...Southern Appalachians through northern Mid Atlantic coast... Modest pre-frontal low-level moistening and, perhaps more notably, relatively warm layers aloft are generally forecast to limit warm sector boundary-layer destabilization today through tonight. However, given at least weak conditional instability, mid-level forcing for ascent along/ahead of the eastward advancing cold front will probably be sufficient to maintain or support new developing lines of fairly vigorous convection, particularly across the Cumberland Plateau and Allegheny Mountains vicinity into the northern Mid Atlantic coast by this evening. Coinciding with one belt of 50-70+ kt south-southwesterly flow in the 850-700 mb layer propagating to the west of the Allegheny Mountains, and another developing to the lee of the Blue Ridge into the northern Mid Atlantic coast by this evening, this convection will contribute to the downward transfer of this momentum toward the surface. It seems probable that this will contribute to at least scattered, if not more widespread, damaging wind gusts. 1 Quote Link to comment Share on other sites More sharing options...
Bananashadow Posted March 7 Report Share Posted March 7 1 hour ago, Chubbs said: Slight risk today - our typical cool season threat - limited instability/strong shear/winds ...Southern Appalachians through northern Mid Atlantic coast... Modest pre-frontal low-level moistening and, perhaps more notably, relatively warm layers aloft are generally forecast to limit warm sector boundary-layer destabilization today through tonight. However, given at least weak conditional instability, mid-level forcing for ascent along/ahead of the eastward advancing cold front will probably be sufficient to maintain or support new developing lines of fairly vigorous convection, particularly across the Cumberland Plateau and Allegheny Mountains vicinity into the northern Mid Atlantic coast by this evening. Coinciding with one belt of 50-70+ kt south-southwesterly flow in the 850-700 mb layer propagating to the west of the Allegheny Mountains, and another developing to the lee of the Blue Ridge into the northern Mid Atlantic coast by this evening, this convection will contribute to the downward transfer of this momentum toward the surface. It seems probable that this will contribute to at least scattered, if not more widespread, damaging wind gusts. Yeah the 850/500 total totals looked rather yawnable yesterday. No denying the winds. Quote Link to comment Share on other sites More sharing options...
ACwx Posted March 7 Report Share Posted March 7 Funny that last year's general thunderstorm thread was started on almost exactly the same day, March 6th. Nothing like highs near 80 and evening thunderstorms to make it feel like spring (and for figs to start growing) Quote Link to comment Share on other sites More sharing options...
Chubbs Posted March 18 Author Report Share Posted March 18 Day 2 SPC outlook - tstm/marginal/slight. Spot checking NAM3k, severe parameter's tomorrow are in the ballpark of a typical local event in parts of area. 2 Quote Link to comment Share on other sites More sharing options...
mshaffer526 Posted March 18 Report Share Posted March 18 Look at that "snow hole" in southeast PA 🤣 Quote Link to comment Share on other sites More sharing options...
JimCaruso Posted March 18 Report Share Posted March 18 Can’t imagine this year could be anything like last year… 2021 taught me not to be so cynical as to keep underestimating the potential around here… Yet at the same time, laws of probability say this year can’t possibly repeat last year… (Well, that’s not technically true, statistically each year’s probability is independent, but we revert to the mean which is VERY low probability…) Anyway, love that first crack of spring thunder but never expect much around here… Right now looking forward to my annual Plains storm chasing trip - been doing it since 1996, only missed three years - for the first time with my son this year, which makes it extra special… Then when that’s over, I’ll be more dependent upon Philadelphia area table scraps… 1 Quote Link to comment Share on other sites More sharing options...
Chubbs Posted March 19 Author Report Share Posted March 19 Snippet from SPC - supercells with tornadoes/hail possible. The most favorable environment for severe thunderstorms is forecast to develop across eastern Pennsylvania and northwest New Jersey late this afternoon. Forecast soundings at 23Z from north of Philadelphia to near Trenton have supercell wind profiles, with 0-6 km shear near 80 knots and gradually veering winds with height below 850 mb. As a result, 0-3 km storm relative helicity is forecast to be near 300 m2/s2. This should be favorable for tornadoes with supercells that interact with the western edge of the low-level jet late this afternoon and early this evening. Although supercells will be relatively low-topped, the strong deep-layer shear combined with steep lapse rates in the mid-levels should also be favorable for isolated large hail. Wind damage will also be possible with the stronger cells. 5 Quote Link to comment Share on other sites More sharing options...
cbelke Posted March 19 Report Share Posted March 19 1 hour ago, Chubbs said: Snippet from SPC - supercells with tornadoes/hail possible. The most favorable environment for severe thunderstorms is forecast to develop across eastern Pennsylvania and northwest New Jersey late this afternoon. Forecast soundings at 23Z from north of Philadelphia to near Trenton have supercell wind profiles, with 0-6 km shear near 80 knots and gradually veering winds with height below 850 mb. As a result, 0-3 km storm relative helicity is forecast to be near 300 m2/s2. This should be favorable for tornadoes with supercells that interact with the western edge of the low-level jet late this afternoon and early this evening. Although supercells will be relatively low-topped, the strong deep-layer shear combined with steep lapse rates in the mid-levels should also be favorable for isolated large hail. Wind damage will also be possible with the stronger cells. I thought today was going to be a washout, but now spotty showers and increase in severe t-storms by night fall. How things change overnight. 🙄 1 Quote Link to comment Share on other sites More sharing options...
mshaffer526 Posted March 19 Report Share Posted March 19 Always nice waking up to a better forecast than expected. Especially on a Saturday. 2 Quote Link to comment Share on other sites More sharing options...
Bananashadow Posted March 19 Report Share Posted March 19 More and more common. May thermal profiles with March winds. 1 Quote Link to comment Share on other sites More sharing options...
JimCaruso Posted March 19 Report Share Posted March 19 5 hours ago, Chubbs said: Snippet from SPC - supercells with tornadoes/hail possible. The most favorable environment for severe thunderstorms is forecast to develop across eastern Pennsylvania and northwest New Jersey late this afternoon. Forecast soundings at 23Z from north of Philadelphia to near Trenton have supercell wind profiles, with 0-6 km shear near 80 knots and gradually veering winds with height below 850 mb. As a result, 0-3 km storm relative helicity is forecast to be near 300 m2/s2. This should be favorable for tornadoes with supercells that interact with the western edge of the low-level jet late this afternoon and early this evening. Although supercells will be relatively low-topped, the strong deep-layer shear combined with steep lapse rates in the mid-levels should also be favorable for isolated large hail. Wind damage will also be possible with the stronger cells. Haven’t actually looked at any data (and probably won’t, no time today and rarely worth the effort around here, last year’s two big days notwithstanding), but the 13Z outlook language no longer seems quite as bullish. Quote Link to comment Share on other sites More sharing options...
Chubbs Posted March 27 Author Report Share Posted March 27 Day 5 slight for Thursday Quote Link to comment Share on other sites More sharing options...
snowlurker Posted March 29 Report Share Posted March 29 Still there Quote Link to comment Share on other sites More sharing options...
eastonwx Posted March 30 Report Share Posted March 30 Slight risk expanded a bit to include most of eastern half of PA Quote Link to comment Share on other sites More sharing options...
snowlurker Posted March 30 Report Share Posted March 30 Slight risk area shifted back 2 Quote Link to comment Share on other sites More sharing options...
irishbri74 Posted March 30 Report Share Posted March 30 For EPA/SEPA, timing looking closer to 8-midnight, which I think limits the threat. Still, could be a decent squall line with good upper level support. 2 Quote Link to comment Share on other sites More sharing options...
greg ralls Posted March 30 Report Share Posted March 30 Wonder if enough shear will be around to increase the tornado threat even if after or close to sunset? Last year’s tornadoes certainly got my attention! Quote Link to comment Share on other sites More sharing options...
Allsnow Posted March 31 Report Share Posted March 31 Best time of the year! Tomorrow looks interesting 1 Quote Link to comment Share on other sites More sharing options...
Chubbs Posted March 31 Author Report Share Posted March 31 ...North Carolina into the Lower Hudson Valley... A mid-level impulse will eject into the Hudson Valley during the afternoon and overspread the core of the low-level jet, promoting an intense tropospheric vertical wind profile and associated strong deep-layer shear. Enlarged hodographs from the Carolina Piedmont northward suggest storm organization with any convection that can intensify and become surface-based. The primary factor limiting the introduction of higher probabilities this outlook is scant buoyancy. 5.5-6.5 C/km low- and mid-level lapse rates atop 55-60F surface dewpoints may promote SBCAPE up to 750 J/kg across North Carolina, to 250-500 J/kg into the Hudson Valley. Damaging gusts and a brief tornado may accompany any sustained, robust updrafts, hence the maintenance of a Category 2/Slight risk. Given 50-60 kt flow at/just below 500 meters AGL and the enlarged hodographs, higher wind/tornado probabilities may be needed in subsequent outlooks if it becomes evident that greater surface-based instability will be realized. 1 Quote Link to comment Share on other sites More sharing options...
Chubbs Posted March 31 Author Report Share Posted March 31 HRRR is concerning. Instability (shading) and low level winds this evening plotted below (lines show speed with height above ground). Enough instability for forced convection with very strong low-level winds. Outer scale ring below is 40 knots 2 Quote Link to comment Share on other sites More sharing options...
tombo82685 Posted March 31 Report Share Posted March 31 Parameters look solid, but I wonder with timing around 10pm for the city diminishes this a bit? 1 Quote Link to comment Share on other sites More sharing options...
Bananashadow Posted March 31 Report Share Posted March 31 5 minutes ago, tombo82685 said: Parameters look solid, but I wonder with timing around 10pm for the city diminishes this a bit? Back in the day, I'd say yeah that seems a very likely outcome. Now it just seems it does not hold all of the time. 1 Quote Link to comment Share on other sites More sharing options...
Chubbs Posted March 31 Author Report Share Posted March 31 41 minutes ago, DebShadow23.0 said: Back in the day, I'd say yeah that seems a very likely outcome. Now it just seems it does not hold all of the time. Sun isn't going to do much today. Low 60s dew point will be pretty uniform across region so there isn't an obvious weakening zone before coast. Quote Link to comment Share on other sites More sharing options...
greg ralls Posted March 31 Report Share Posted March 31 Definitely a good day to go back and re-read that 7/29/2021 tornadogenesis thread to compare & contrast today’s parameters 2 Quote Link to comment Share on other sites More sharing options...
cbelke Posted March 31 Report Share Posted March 31 Lights winds at the ground level, but beginning to hear the occasional roar overhead. Could get some interesting straight line winds later. Quote Link to comment Share on other sites More sharing options...
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