July 29, 2011 Storm Updates

Below, short term updates will be posted on the severe storms that will affect the area this afternoon and evening.

**Forecast graphics will be posted with each update. Click on the images to view them in a larger size.**

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7:45 PM: Most of the storms have ended across the area, but there is still some activity east of NYC. There is a strong storm near Bronx moving SE, towards northern Nassau. Another severe storm producing heavy rain and strong wind gusts is near central Nassau moving east, towards western Suffolk, and there is a strong thunderstorm with heavy rain affecting JFK airport.

This is the last storm update for tonight. Due to the storm updates, no discussion on the upcoming weather will be posted tonight. Instead, the typical evening update will be posted tomorrow morning, with updates to the 5-Day Forecast, Tropics page, Long Range Outlooks, and the Storm Summary pages during the rest of the day tomorrow.

7:20 PM: Warning: A severe thunderstorm capable of producing small hail and strong wind gusts up to 60 mph is currently over Union city, and will enter central/southern Manhattan (34th street and further south) within the next 10 minutes. This storm will then enter Queens within the next 15 minutes.

6:50 PM: **Tornado Warning is still in effect for Westchester county.**

The severe storm capable of producing a tornado is currently near Port Chester, NY, and is moving southeast. Some weakening of this cell is expected as it moves through the Long Island sound into a more stable air mass, but rotation may still persist once it crosses the sound. Places that will be affected by this cell within the next 1/2 hour are NE Nassau and NW Suffulk counties. Towns/cities in these areas include Bayville, Oyster Bay, Syosset, and Huntington.

Looking across the rest of the area, there is a heavy thunderstorm in central Bergen county moving east, towards southern Westchester. Another strong storm in eastern Morris county is moving ESE, towards Clifton and Fort Lee, later on moving into northern Manhattan. There is another strong storm near northwestern Passaic moving ESE, towards northern Bergen county. The last storm recently formed in eastern Union county, and is moving towards Staten Island and Brooklyn.

6:15 PM: **Tornado Warning is in effect for Westchester county.**

Widespread severe storms are currently affecting the area, with some of them producing rotation. The most intense storm is near Ossining, NY, and is moving SE. Places directly in the path of this possible tornado include White Plains and Port Chester.

Another severe storm with weak rotation is near the border of Sussex/Orange counties and is moving ESE, right along the border. This storm will affect places along the NY/NJ border over the next 1/2 hour. A severe storm in southern Sussex county capable of producing gusty winds and small hail is moving ESE as well, and will affect northern Morris, East Passaic, and southern Bergen counties.

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4:00 PM: Storms Starting To Fire Up

Since this morning, the western half of the area began to destabilize with some clearing in the cloud cover. Most places west of NYC are seeing partly to mostly cloudy skies, with mostly cloudy skies in NYC and cloudy skies in Long Island/S CT, where temperatures are much colder, in the lower to mid 70s in southern Connecticut and the mid 70s to lower 80s in Long Island. While Long Island/S CT are under a stable air mass, places from NYC and further west are seeing more instability, with lift index values between -4 and -7, CAPE between 1000-2500, and bulk shear between 40-50 knots. Lower lift index values support a higher severe weather risk, and higher CAPE/bulk shear support a better severe weather risk.

The parameters above support at least a 30% risk of severe weather, where severe storms would be capable of producing strong to damaging wind gusts, hail, heavy rainfall, and an isolated tornado or two. As we have seen many times, however, the parameters alone don’t determine if we see severe weather or not, as it is possible that severe storms just north or south of the area prevent storms from developing/persisting over the area.

Possible Storm Scenarios: As of now, we are seeing a severe storm in northeastern Pennsylvania moving ESE, which would take it into Orage and Rockland counties, and an area of strong thunderstorms in east central PA, moving towards places directly west and south of NYC. Every short range model showed this storm where it is now, then forming a line of severe storms extending further south, resulting in a widespread area of severe thunderstorms moving through most of northern NJ, SE NY and NYC between 6-10 PM tonight, producing heavy rainfall, strong wind gusts, smaill hail, and an isolated tornado.

The scenario mentioned above is a reasonable solution. It is possible, however, that storms fail to form south of the NE PA cell, and northern New Jersey/NYC would stay dry, missing today’s storms. At this time, looking at the latest radar, there is no indication of additional storms forming in between the isolated cells near Allentown and the severe cell in northern PA, and that area will be monitored over the next 1-2 hours as it will determine whether NYC/N NJ see severe storms or only isolated storm activity.

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11:00 AM: Severe Storms This Evening

The area is currenly seeing mainly cloudy skies after a round of showers and thunderstorms moved through northern NJ/NYC last night, bringing rainfall amounts up to 1/4 inch. This is just the first round of today’s storms, as more widespread severe weather will affect the region, including the area, this evening. With the last widespread rain event, on July 25, the warm front was stuck to the west of the area, keeping us stuck with cloudy skies and non-severe rain and thunder. Today’s scenario is different, however, as the warm front has already passed NYC, and is currently near central New England. As a result, today will bring more instability and a bigger risk of severe weather.

This Afternoon: While the area is currently under mainly cloudy skies, clearing in the cloud cover is expected around 12-2 PM, with mostly to partly sunny skies from NYC and further west. With the warm front still stuck in the eastern parts of the area, however, most of Long Island and southern Connecticut will see mostly cloudy to cloudy skies. With the break in the cloud cover, temperatures west of NYC will quickly warm up into the upper 80s to lower 90s, and a few mid 90s may be possible in NE NJ. Combined with the humidity, as dew points will be in the lower 70s, the heat index will reach the 96-100 degree range in NYC later this afternoon.

Evening / Overnight: The cold front will then approach the area overnight, bringing more widespread storms. The most widespread storms should stay in New York, where heavy rain and thunderstorms are expected, but as there will be instability in the area, there is a better risk of severe storms. Thunderstorms should start to form in SE NY/NE Pennsylvania late this afternoon, and move into the area in the evening hours, between 6 PM and 11 PM. These storms will be capable of producing strong wind gusts, small hail, and heavy rainfall with localized flash flooding possible. Stay tuned for storm updates this afternoon and evening.

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