Author: Miguel Pierre

Possible Tornado in Southern NJ… More Flooding and Severe T-Storms Likely Today

Miguel Pierre Severe Wx

Yesterday t-storms produce mostly heavy rains with only some widely scattered reports of damage or strong winds. However, radar detected strong rotation and winds with thunderstorm over near Permberton,NJ last night around 8:30pm. A storm chaser on twitter took this picture of a possible tornado that hit near that town. A weak low forming yesterday over Southern NJ, enhanced low-level directional shear that may of produced tornado. The National Weather Service will likely go out and survey the area today. I may have another  post about it, when the survey is completed. Update: NWS confirms straight-line winds. No tornado.

Base velocity radar loop show strong rotation with winds 75kts aloft near Perbermton, NJ (courtesy of Weather Underground)
Base velocity radar loop show strong rotation with winds 75kts aloft near Perbermton, NJ (courtesy of Weather Underground)

Meanwhile, the Storm Prediction Center has slight risk for the entire tri-state area again today. In my last post I discussed, that the severe weather threat may be reduced today with more showers and thunderstorms through the day, keeping instability lower. However, models still show moderate instability with SBCAPE values 1500 J/kg to 2500 J/kg and liifted Index values between -3 and -6, by this afternoon. 0-6km bulk shear is also 30kt to 40kts this afternoon.  Those parameters support organized severe thunderstorms, in some locations. Especially over NYC, New Jersey, the Lower Hudson Valley . A southerly wind off the water, will likely keep parts of LI and South CT less unstable. Damaging winds from thunderstorms are still biggest severe weather threat. However, cold upper-level low a little closer to area to today,  the threat for large hail is little higher than yesterday. Model soundings also indicate a backing of low-level flow this afternoon. So an isolated weak tornado cannot be ruled out.

Today's 6z run of the GFS, showing SBCAPE values between over 1500 J/kg - 2500 j/kg over the tri-state area. (image courtesy of College of Dupage)
Today’s 6z run of the GFS, showing SBCAPE values between over 1500 J/kg – 2500 j/kg over much of the NYC Tri-state area (image courtesy of College of Dupage)

The National Weather Service has also issued a flash flood watch for the entire area. Flooding still appears to be bigger threat than severe weather, as only marginal instability is needed for t-storms with heavy rainfall this afternoon and evening. With precipitable water values near 2.00″ any storm produce between 1″ – 3″ of rainfall in short period of time, resulting in flooding of poor drainage areas or small rivers and streams. Showers and thunderstorms will likely continue overnight and into Wednesday morning, as the cold front with system, slowly moves through the area. With the of loss diurnal heating, instability will diminish. So the threat for more severe thunderstorms will be over. But threat for heavy rainfall will continue. After the cold front passes, clouds will likely break for sunshine tomorrow afternoon. Sunshine, low humidity and seasonable temperatures are expected for Thursday and Friday.

Severe Weather & Flooding Threats Monday & Tuesday 7/14- 7/15

Miguel Pierre Severe Wx

An anomalous cold closed upper-level low swinging over the Great Lakes, will cause another period of stormy weather early this week, in Northeast and Mid-Atlantic. A deep southwesterly  flow ahead of this system, will provide moisture feed out the Gulf of Mexico and Atlantic. The Storm Prediction Center has again issued a slight risk for the local tri-state area on Monday. That means they are anticipating some organized severe thunderstorms. But not widespread in coverage and violent in intensity.

SPC 1730 UTC outlook with 15% risk of severe thunderstorms on Monday
Today’s SPC 1730 UTC outlook with 15% risk of severe thunderstorms on Monday.

 

The main threat, from any of these storms Monday will be flash flooding, damaging winds Large hail is possible. But poor mid-level lapse rates and high freezing levels shown on model forecast soundings, will keep this threat lower. A warm frontal boundary will develop over the local region on Monday. This will cause winds the low-level winds to back from south-southeast at the surface to southwest aloft. For areas near the coast, including NYC, there will be more of marine influence that may keep thunderstorms under severe levels. But areas further inland, may heightened risk for isolated weak tornado. Especially over the Lower Hudson Valley.

Hodograph on the 12z NAM model with strong directional shear and significant CAPE over Newburgh, NY
Hodograph on the 12z NAM model with strong directional shear and significant CAPE over Newburgh, NY Monday evening

On Tuesday, as the upper-level low moves further east, shear and lifting will increase. Without much capping in the atmosphere, showers and thunderstorms could be more widespread and frequent through the area. But this may also act to keep instability lower across the area for thunderstorms to become severe. Flash flooding is likely to be a bigger threat.  Very high precipitable water values and some unidirectional shear will causes thunderstorms to train and produce torrential downpours in parts of the area. Stay tuned for another update tomorrow for this threat.

 

 

Potential for Severe Thunderstorms Late Today

Miguel Pierre Uncategorized , ,

The Storm Prediction Center has issued a slight risk of severe thunderstorms for far western parts of the area today. The rest of the area including the Northeast NJ, NYC and Long Island area are in a lower 5% risk for thunderstorms producing damaging wind gusts and large hail. An upper-level trough and cold front approaching from the west, will trigger showers and thunderstorms, late this afternoon and this evening. With a humid airmass in place and temperatures rising into lower to middle 90s today away from the shore, the atmosphere will become very unstable some of those thunderstorms to possibly become strong or severe.

Storm Prediction Center outlook for 13z Wednesday, shows slight risk for parts Upstate NY, Pennsylvania, and Extreme Western Nj
Storm Prediction Center outlook for 13z Tuesday, shows slight risk for parts Upstate NY, Pennsylvania, and Extreme Western Nj

The severe threat is greatest over Upstate New York, Pennsylvania and extreme Northwest New Jersey. Where they will be closer to an embedded 500mb shortwave trough and a 40-60kt southwesterly low-level jet streak late this afternoon and early evening. Both features will enhance shear and lift for more organized severe thunderstorms that can produce damaging winds, large hail and isolated tornadoes.  For areas closer to to I-95 corridor, with less shear and lifting later today, the threat for severe thunderstorms with damaging winds and large hail is more isolated.

12z NAM showing 40-60kt 850mb jet
Today 12z run of the NAM showing 40-60kt 850mb jet over Upstate New York  and Pennsylvania (image courtesy of College of DuPage)

The cold front will move through area tonight and tomorrow, with more showers and thunderstorms with heavy downpours. Shear and lifting will be more sufficient. But a slightly cooler and drier airmass behind front, will mean less instability for severe thunderstorms. For more organized, widespread severe thunderstorms, sufficient lifting, shear, instability, and moisture need to all come together. But forecasting how all these ingredients will come together for severe, is hardly ever simple in Northeast US, even on the same day of threat.  For this reason, I will continue to monitor this potential here today and tomorrow.