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John Homenuk

Severe weather, heavy rain likely Monday

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As an expansive, powerful upper level low will shift eastward from the Great Lakes toward parts of the Ohio Valley late this weekend into early next week. Immediately, the southerly flow ahead of it — and the nature of the upper level low shifting so far south this time of year — caught forecasters eye for severe weather potential in the Northeast US.  The combination of warm, southerly flow ahead of the approaching upper level low will at least support the potential for heavy rain, while the severe weather setup has become more complicated.

Sunday evening, the first “threat” for thunderstorms will develop over Pennsylvania and Western New York state, where lift for thunderstorm development and instability will support severe storm potential. These storms will move eastward toward parts of our area later tonight, but are expected to weaken over time as they lose support for organization. On Monday, however, things will change — as southerly flow strengthens in our area, shear aloft increases, and lift develops during the afternoon to aid in the development of thunderstorms. Figure 1 shows the approaching upper level system.

Figure 1 - NAM model showing the upper level system shifting toward the area on Monday.

Figure 1 – NAM model showing the upper level system shifting toward the area on Monday.

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John Homenuk

Heat builds, severe thunderstorm risk increases

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As a mid level ridge builds throughout the eastern half of the nation today, temperatures in the mid and low levels of the atmosphere will increase. South of a warm front, which is organizing and becoming more well defined to our north, west-southwesterly winds will begin to usher in the warmer airmass. Mid level temperatures (at 850mb) will warm over 17 C, and with sunshine expected during the afternoon hours on Tuesday, temperatures will warm into the upper 80’s to lower 90’s. When coupled with increasing humidity, it will feel hot and quite muggy.

Back to our west-northwest, a mid level disturbance will be riding along the northern periphery of the building ridge axis. As it does so, it will help to trigger the development of thunderstorms — some of which could be strong to severe. These storms will initially form well to our north and west, but are expected to slide east-southeastward through the Northeast States as the disturbance shifts accordingly. Subsequently, the Storm Prediction Center has placed much of the area in a Slight Risk for severe thunderstorms.

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John Homenuk

Strong to severe thunderstorms possible this afternoon

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1:00pm Update: The NWS Storm Prediction Center has issued a Severe Thunderstorm Watch for Northern New Jersey and Southeast New York until 8:00pm tonight. Thunderstorms are expected to develop over the next few hours and shift southeastward through New Jersey and New York. The combination of developing instability, a nearby frontal zone, and a disturbance aloft will aid in organization of storms. Thunderstorms will be capable of producing frequent lightning, hail, and strong winds.

Severe Thunderstorm Watch graphic from the Storm Prediction Center. Blue highlighted counties are included in the watch.

Severe Thunderstorm Watch graphic from the Storm Prediction Center. Blue highlighted counties are included in the watch.

The Storm Prediction Center has placed much of the area in a Slight Risk for severe weather on Thursday, including much nearly all of New Jersey. The Slight Risk area runs to about New York City and Western Long Island northward through Southeast New York and near the Connecticut border. A Slight Risk is issued by the Storm Prediction Center when organized severe thunderstorms are possible, in this case there is a 15 percent chance of gusty winds or hail within 25 miles of any point within the Slight Risk area.

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John Homenuk

Thunderstorms with gusty winds, downpours Thursday

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Update: The Storm Prediction Center has placed our area in a Slight Risk for severe thunderstorms today (Thursday). Stay tuned for further updates and information including a live blog post.

As a mid level disturbance moves toward the area on Thursday, a frontal boundary and convergence zone will shift near the area during the late morning to afternoon hours. The combination of the two, when juxtaposed with daytime heating and some instability, will lead to sufficient lift to develop thunderstorms during the afternoon hours. Accordingly, the Storm Prediction Center has placed parts of the area in a “Slight Risk” for severe thunderstorms.

The threat for strong to severe thunderstorms is likely to be focused west of the area beaches and shores, but heavy downpours and thunderstorms are still possible there. Farther west, over the interior parts of New Jersey and New York, more focused instability and southerly winds are more likely to work with marginally favorable wind fields to help develop thunderstorms. These storms will be capable of producing very heavy rain, frequent lightning and possibly even some small hail and gusty winds.

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