Evening Zones Update: Showers/T-Storms Late, then Variable Weather

Good evening, everyone! We hope you all enjoyed this lovely Friday. Mid and high-level cirrus clouds have increased from the west due to a weakening complex of showers and thunderstorms in the Ohio Valley and Western PA. While they are not that strong right now, they should strengthen as they head towards our area. This is because a warm front will be moving into the area during the overnight and it will be accompanied by a very strong vorticity maximum embedded within a weak shortwave trough.

With strong elevated instability from an EML (elevated mixed layer), precipitable water values approaching 1.8″, and strong winds aloft (look at the 850mb and 500mb winds), combined with the aforementioned vorticity maximum and warm front, these showers and thunderstorms could be somewhat strong with heavy, tropical downpours and loud thunder and bright lightning. However, the surface will have a very strong nocturnal inversion, so these strong winds will not mix down to the surface, and this should limit the overall potential of the severe weather. Also, the vorticity maximum is somewhat small and there may be some 500mb height rises after 5:00am, so this means that a good chunk of the area may miss out on these storms.

After these storms move through, the HRRR model shows another small cluster of showers moving in at around 9 or 10am, but this is unlikely due to continued height rises. Thus, we generally expect skies to gradually clear with more subsidence, and the airmass will be very warm and humid behind the front. We thus expect temperatures to rise well into the 80s as downsloping westerly winds really help the warm temperatures aloft translate to the surface. This westerly flow may even be strong enough to keep the sea-breezes at bay — look how the westerly streamlines blow right through Long Island — and thus even coastal areas should rise into the low to mid 80s. But also notice the 15-20 knot winds that are showing up — this downsloping will lead to a lot of deep mixing with the strong winds aloft, so winds may gust between 30-40mph at times.

Later Saturday night, a backdoor cold front will move through the area, leading to much cooler temperatures. Additionally, an area of high pressure will be sliding offshore, leading to onshore flow. Thus, temperatures have may have a hard time even reaching the low 60s for highs on Sunday.

But on Sunday night, a warm front will be moving through the area out ahead of a strong storm system in the Plains. This warm front may lead to low clouds, patchy fog, and light rain — but the atmosphere will be too unstable for anything more than that.

Behind this warm front, Monday will warm back up again into the 70s to perhaps low 80s, depending on cloud-cover. But the airmass will again become very moist with precipitable water values between 1.6 and 1.8″. When combined with a very dynamic storm system to the west with a potent jet streak, strong moisture convergence,  and strong mid-level winds, heavy tropical downpours with rumbles of thunder are possible, and they may train over themselves to generate flash flooding, with wind flow relatively parallel to the cold front. However, the actual mid and upper-level trough is almost somewhat too widely-rounded, which makes vorticity maximums and jet streaks relatively broad instead of tight and consolidated. This may act to mitigate this heavy rain threat, so we will be watching this closely.

After pleasant weather on Tuesday and Wednesday, attention will turn to a significant blocking pattern which will act to force a large and strong storm system to develop to our south and potentially turn into a vigorous, wound-up coastal system with multiple periods of heavy rain in the Thursday through Saturday morning period. More details can be found in our premium article and video from very early this morning.

But just to briefly illustrate the potential, look at the above image. We have a beautiful full-latitude trough that is extremely sharp and amplified, sending incredible dynamics up the coast. There will also be a full Gulf of Mexico and Caribbean moisture feed that gets sent up the Atlantic and plenty of warm-air advection up the coast as well. Thus thus leads to a very large and expansive area of synoptic and convective rains in the Northeast. A secondary low pressure would then develop at the base of the trough and head up the coast, bringing even more heavy rain on Friday evening into Saturday morning. Even though the lead time is large, we are more confident than usual in this storm occurring due to the blocking pattern that will be in-place. But that doesn’t mean that things can’t change. We will be sure to keep you updated on this storm.

Have a great weekend!