Friday 8:15 a.m.
Temperatures will stay in the 60s and 70s across New Jersey and Pennsylvania today, the coolest day so far this summer. Many areas from Chicago to New York City have had significant rain. Does this mean the over dry spell is over? Does this mean the heat has had it? No. Looking at the GFS ensemble forecast for the next 16 days in Philadelphia, today and tomorrow are the coolest days between now and Aug. 4. However, last night's run did not show temperatures returning to this week's extreme.
In terms of the drought vis a vis (as that really a term?) recent rain in parts of the drought-stricken area, I have these thoughts. 1. Where places got more than about a half inch of rain it was helpful for the short term for grasses and flower beds. Where rain was much heavier, a good part may have run off, but in the short term was helpful. 2. The key now is whether the rain is a one and one thing or the start of some new pattern that will cause more frequent rainfall in the future. If that turns out to be the case, the recent rain will be seen as the turning point. If new rain fails to materialize, then those areas will revert back to the same conditions that have worsened all summer.
This video looks at the weekend and early next week.
This pressure analysis shows the boundary between hot air to the south and cooler air to the north. You can see a few low pressure areas along the front, each increasing the rainfall as it approaches, then introducing some drying upon departure.
For the almost 24 hours between 10 a.m. ET Tuesday and 9:20 a.m. ET today, here is a the lightning recap. The dry pattern from the Midwest will now advance across New York and New England.
Cooling aloft and heating moist air closer to the ground should trigger strong thunderstorms from eastern New York and much of New England southwest through parts of the Middle Atlantic states.
The front will move into a region with high humidity as it approaches the I95 corridor tomorrow. This is the basis for SPC's forecast of thunderstorms approaching severe limits tomorrow.
Tropical Storm Colin is caught in the southern stream while the northern stream is helping to send unseasonably cool air out of central Canada.
Then, as the cold front arrives, there may be violent thunderstorms. This map shows the early morning SPC assessment of the severe weather risk on Sunday:
Farther east on Sunday, rain is likely to be more extensive, and there is a severe thunderstorm threat from the Middle Atlantic region on south.