July 8, 2014 - New York Metro Weather

Hazy, hot and humid air has settled into the region this afternoon as southerly winds pump in the warmth thanks to mid level ridging. Back to our west-northwest, an energetic disturbance is ejecting northeastward through the Ohio Valley. Increased lift and forcing is helping to force the development of thunderstorms within an unstable environment, leading to the threat of widespread severe weather over Pennsylvania and New York State. The Storm Prediction Center has issued a Moderate Risk for severe weather in those areas through this evening.

Why is this threat developing?

There are many pieces at play, but the main culprits are most definitely the Western Atlantic Ridge (actually centered near Bermuda at this point) and the incoming energetic trough. The combination of the two is leading to increased instability, strong forcing for thunderstorms, and sufficient wind shear for storm organization. Figure 1 (below) shows a four panel model image from this afternoons 12z NAM model. On the top left, the model is producing precipitation along elongated height falls from the system to our northwest. On the top right, very warm air at 850mb has advanced into the region with temperatures over 18 C. Finally, the bottom two panels show the energetic pattern at 500 and 300 mb.

Figure 1. (NYMetroWeather models)

A warm and muggy airmass has its grip on our area, and combined with a slowly approaching cold front and a disturbance aloft, some showers and thunderstorms will be triggered. For most of the day today, the cold front will still be a bit far to our west, which will generally lead to mostly sunny skies, hot temperatures, and a delay in any thunderstorm activity.

NAM model valid for 2:00pm shows temperatures in the low-to-mid 90s in our area, with 80s along the shores.

850mb temperatures of 18C with sunshine support high temperatures in the low-to-mid 90s, which will generally be commonplace throughout the area. The one exception will be for most of Long Island and the immediate Jersey Shore beaches, where temperatures will stay in the 80s, due southerly winds from the ocean bringing in slightly cooler temperatures.

Initially, the highest 500mb vorticity and core of the trough are still to our west, as evidenced in the image below. The cold front is associated with the low pressure system well to our northwest, and we have a warm, southwesterly flow out ahead of it. However, there is a weak surface pressure trough in the Mid Atlantic — which combined with a weak 500mb vorticity maximum — may act to try and force some convection during the evening.

NAM model showing a weak surface trough and weak area of vorticity, which may help to trigger some thunderstorms. The core of the trough will remain to the west for most of the day, which will delay the thunderstorms somewhat. Additionally, 18C 850mb temperatures will lead to quite the hot afternoon.

As far as the type of thunderstorms that can be expected, some may produce some some strong winds and very heavy rain, due to sufficient wind shear, moderate instability, and very high precipitable water values. Read more

Strong, severe storms possible this afternoon west of NYC

Heat with afternoon thunderstorms today and Wednesday

Archive for date: July 8th, 2014