Monday 9 a.m.
Very humid air is in place throughout the Northeast today, and a series of disturbances will move through the area from west to east during the next few days. Each of these can cause some showers and thunderstorms. A cold front approaching Wednesday may be strong enough to cause locally severe thunderstorms from the Ohio Valley to New York state and New England.
Once the front goes by, it is likely to become comfortable with low humidity across the Great Lakes and perhaps as far east as the Appalachians. Closer to the coast (and including the I95 corridor), the front could stall. This would increase the chance of more frequent rainfall, though the increased cloudiness would also hold temperatures down. This video has more:
This satellite picture with a radar overlay shows the most concentrated area of showers and thunderstorms this morning was over the western Great Lakes region.
Now, drier air has arrived, and most of the Northeast will have abundant sunshine today and tomorrow.
A front that will usher in slightly less humid air for the Northeast tomorrow will trigger locally strong thunderstorms today.
Thunderstorms will continue to erupt near the northern edge of the heatwave, enhanced by a series of disturbances rippling along in the upper air flow. This is the NWS Storm Prediction Center's severe thunderstorm outlook for today
... the main upper air steering current moves eastward across the northern Plains, then dives southeastward toward the Middle Atlantic states. The core of this current defines the rim of the hottest weather and serves as a conduit for clusters of thunderstorms.
3. Hot air will be moving east from the Plains, reaching the major East Coast cities Friday and Saturday. This map shows the upper-air flow that will make this happen.
This map shows lightning strikes from 8 a.m. EDT yesterday until 7:20 a.m. EDT today. A concentration of thunderstorms can be seen in the Midwest ahead of the cold front.