Currently: Summary of hazards in effect from our 3 WFO's. Severe thunderstorm warnings are in effect for many counties around the state. An advisory for flooding is in effect for the extreme SW. A Flash Flood Watch is in effect through tonight for the SW half of the state. A Severe Thunderstorm Watch is in effect for the entire state through the first half of tonight. An Excessive Heat Watch is in effect for the SW half of the state for the weekend.
Tonight: Ongoing severe and flash flood threat continues tonight, mostly for the first half of the night, but I wouldn't rule out activity (mainly isolated) for the rest of the night, especially in the southern half of the state. Instability will remain high, and the air mass will remain very soupy in that part of the state. As far as temperatures, guidance is in excellent agreement. However, I'll slash a degree or two off in most places, due to the fact the air will likely be rain-cooled. Even so, that only yields low temperatures a couple degrees above 70 across the state.
Tomorrow: Tomorrow's forecast is very tricky, especially temperatures. A back door cold front will probably move through some of the state, but where it stops, nobody knows. In the coldest sector behind the front, temperatures may be in the 60s with low clouds, light rain and the like. In the warmest sector, temperatures will be in the 90s with sun. The relatively "easier" thing to predict is precipitation. It will likely rain measurably tomorrow at some point, throughout the state- whether it's "stratiform" rain with cool temperatures, or convective precipitation, with warmer temperatures. The GFS has been fairly consistent, and the NAM has trended towards the GFS, which is to bring the front a little further north. O have to say this makes more meteorological sense, given the strength of the Western Atlantic Ridge and the lack of any high pressure to the north. With this all said, and keep in mind, there is high bust potential with this forecast, but the best I can come up with right now is to call for high temperatures generally in the upper 70s. This is closest to, but not all the way to , the warmest temperature guidance. As far as precipitation, there may in fact be two rounds of precipitaiton, one in the morning and one later in the day. Then, of course, if there is any clearing, temperatures would be higher than what I am currently forecasting. With the frontal system nearby, there is also a chance of a shower at any time during the day, in between the "main action".
Long Term (Friday and beyond): The main issues in the long term are heat the first three days of the period, then potential for strong to severe thunderstorms either later Sunday or Monday, depending on the timing of the frontal passage. First, I'll address the heat, and how high I think temperatures are going, and then we'll get to the frontal passage. So, for temperatures, Friday has been trending warmer on guidance, and I agree with it. Meteorologically, if I start with the front further north, it has less distance to go to clear the area, so we'll have a higher "launching point". Therefore, I went a touch above guidance to try and beat the trend. So highs should approach 90 across the state.
For the rest of the long term, here are the temperatures and reasoning:
Saturday and Sunday- mid 90s
Monday- mid 80s
Tuesday- near 80
Wednesday- near or just above 80.
The GFS has trended even warmer for Saturday and Sunday, and it could very well be right, given the fact that it led the way with this heat wave and it has been verifying much better of late. However, it's tough to go "all in" this far out, since things would have to be perfect for that to pan out. So I went just a touch cooler than the GFS guidance. I went a bit cooler than guidance for Monday, since I think there will be more clouds than what the GFS-based guidance suggests. I also went a touch below GFS guidance in subsequent days, especially Tuesday, since the high pressure system moving in from the north looks strong.
Speaking of thunderstorm chances for Sunday into Monday, throwing all models away and using basic meteorology suggests a good potential for at least scattered strong to severe thunderstorms. Of course, a lot can go wrong with this kind of a presumption at this juncture. Timing has to be right for one thing. And timing has varied drastically from one model cycle to the next. GIven the strength of the aforementioned Western Atlantic Ridge, meteorology favors a slower frontal passage, so I'll bring it through Monday afternoon.
Finally, looking into the long range, and for obvious reasons, I did not spend too much time on it, we ma enjoy the benefits of a little ripple in the pattern, giving us a break from the heat for 7-10 days. However, models are beginning to show a return of the pattern we are in right now. So that would mean more of this type of heat around the end of the month.
Now, let's take a look at some of the systems slated to affect the region during this period. Since tonight's event is already ongoing, I'll focus on tomorrow and Monday. This map, valid midday tomorrow, shows precipitation just beginning in the western half of the state, with a lot more coming from New Jersey and Pennsylvania.