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Afternoon Update: Enhanced risk of severe weather in PA, NJ

July 9, 2015/by John Homenuk

Strong to severe thunderstorms remain a distinct possibility this afternoon and evening across much of Eastern Pennsylvania and New Jersey. As a low pressure system moves quickly through New York State today, southerly and southeasterly winds will draw in warmer, more moist and unstable air. The incoming atmospheric disturbance will act to touch off thunderstorms, and these storms will form in an environment featuring instability and favorable shear. Accordingly, they may organize to strong and severe levels. The main threat with these storms will be damaging wind gusts, but an isolated tornado cannot be ruled out given the aforementioned atmospheric shear.

The threat for storms is much less as one travels farther east. Marine air near the coast will make New York City the dividing line for strong storms and weak storms — with thunderstorm complexes expected to weaken as they approach New York City and move toward Long Island. Still, thunder/lightning and heavy rain are likely over these areas. Highlights from today are included below:

The Storm Prediction Center has placed Western NJ and Eastern PA in an “Enhanced Risk” for severe storms this afternoon. An Enhanced Risk is issued when organized thunderstorms are possible, with the potential to produce locally damaging winds, hail, or isolated tornadoes. The Enhanced Risk is meant to signify the area where more concentrated severe weather may occur relative to its surroundings.
The risk for severe weather decreases as you head farther east. More stable air will be in place near the coast, thanks to south/southeasterly winds off the water. Still, some thunderstorms and a period of heavy rain is expected in New York City later tonight.
The weather will dramatically improve Friday into the weekend. As this storm system slides off the coast, a high pressure will build in. Temperatures will remain warm, with lots of sun, and very little chance for any precipitation.

*This post will update throughout the afternoon with details and information on thunderstorms.

Morning Overview: Strong storms possible this evening

July 9, 2015/by John Homenuk

An approaching mid level disturbance will aid in the development of a low pressure system today, which will track from Pennsylvania to Southeast New York during the afternoon hours. Southeasterly winds at the surface will help to advect in warmer, more moist and unstable air during the afternoon hours. Near the coast, this low level wind flow will bring in a marine layer that will keep the air more stable. So, naturally, as the disturbance approaches the best chance for severe weather will be away from the coast and west of New York City. In those areas, from Pennsylvania to New Jersey, strong to severe thunderstorms will be possible. We’ve included some details and information below, but stay tuned for an updated article later today if any watches or warnings are issued:

A Slight Risk of severe weather today from the Storm Prediction Center for much of Pennsylvania, Western New Jersey and the Mid Atlantic States. A risk of strong winds and isolated tornadoes exists in those areas.
Hot and humid once again today. Highs approach the upper 80’s after a cloudy start. Southerly winds will draw in a more moist and humid airmass, with more clouds along the coast and near the area beaches and local waters.
A disturbance approaching the area will bring the potential for strong to severe thunderstorms, mainly west of New York City. These storms will be capable of producing strong winds, lightning, flooding rains and possibly an isolated tornado.
A period of heavy rain is likely during the evening hours, even in New York City and near the coast. As the storms weaken and spread east, localized flooding will be possible with heavy rains.
Much nicer conditions are expected for Friday and into the weekend, as high pressure settles in. Temperatures will remain warm with plenty of sun and a very minimal chance of any precipitation.

Severe thunderstorms possible this afternoon and evening

June 23, 2015/by John Homenuk

12:30pm: This morning, we initially had a strong area of showers and rumbles of thunder in Pennsylvania that was moving toward our area. if it hit us, the atmosphere would have stabilized and the severe threat for thunderstorms would have significantly gone down.

Current SPC Mesoanalysis as of noon shows an area of mid-level lapse rates in excess of 7C/KM in our area. This is very significant, as it leads to plenty of instability in the middle of the atmosphere, as well as providing a capping inversion below it that weakens any weak convection and keeps us sunny and unstable.

However, the EML we discussed yesterday was able to work its way into the region and provide a capping area that completely disintegrated this area of showers. This means that clouds will quickly be disintegrating, and we will quickly be able to destabilize the atmosphere, making it very ripe for severe weather.

Current Mesoanalysis from the SPC shows already building values of surface-based CAPE.

In fact, surface-based CAPE values are already in excess of 3,000 J/KG in many areas, which is actually ahead of schedule. When this is combined with the strong mid-level lapse rates and strong wind shear, severe weather is expected to hit a decent chunk of our area later this afternoon. The primary threat will be damaging wind gusts and vivid lightning, but large hail is also a threat, and a tornado threat is non-zero.

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An energetic mid level disturbance, impressive wind shear, and moderate to significant atmospheric instability will combine to create an enhanced threat for organized severe thunderstorms in the Northeast US on Tuesday. While some uncertainties still exist in regards to exactly how the event will unfold, confidence is rising in the heightened threat for severe thunderstorms — even in the NJ and NYC Metro Area. While not everyone will experience a severe storm, the threat for organized thunderstorms is much higher than normal today.

Thunderstorms are forecast to develop over Northern Pennsylvania and New York State, and begin progressing southeastward throughout the day. Meanwhile, atmospheric destabilization will occur over much of New England, the NYC Metro, New Jersey, and the Mid Atlantic. Instability parameters are expected to be quite high, especially by Northeast US standards. With more than adequate wind shear for thunderstorm organization, these storms are expected to spread southeast toward the coast during the late afternoon and evening.

This post will serve as a Live Blog throughout the day for updates and information on the latest analysis as well as a relay point for Watches and Warnings from the Storm Prediction Center and Local NWS offices. A de-brief on the threat is below:

Remnants of TS Bill will impact weekend forecast

June 17, 2015/by John Homenuk

While Tropical Storm Bill is making headlines today impacting parts of Texas, with rains expected in the Plains this week, we aren’t out of the woods here in the Northeast. A Tropical Storm thousands of miles away will eventually become engulfed in the mid and upper level atmospheric flow, bringing tropical moisture northeastward into the Ohio Valley and eventually the Northeast. For our area, this will have a major impact on the weekend forecast.

Forecast models are struggling with the exact intensity of TS Bill as it moves inland, as well as the timing of it’s absorption into the mid and upper level atmospheric flow. These two factors are very important for our areas forecast, as they will dictate the timing of a surge of tropical moisture into the Northeast US. Showers, thunderstorms, and even areas of heavy flooding rains are possible near where the center of the remnant low pressure tracks.

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