Currently: High pressure over the area is keeping the area high and dry for now. However, the impetus for our potential heavy rain event, a warm front, stretched from Saint Louis to near Huntington, West Virginia. This will propogate NEward towards the region tomorrow.
Tonight: Temperatures depend on cloud cover. Since cloud cover will be mostly high-based, we should be able to radiate fairly well. With a mostly onshore flow persisting, temperatures near the south coast will reflect those of the Long Island Sound. Low temperatures tonight should be in the 60s.
Tomorrow: Clouds steadily increase during the day, but I will keep the day dry, as any showers that do develop should be south and west of the state. For high temperatures, I'll shave a couple degrees off guidance, due to increasing clouds and an onshore flow and go with generally mid 70s statewide.
Tomorrow Night/Friday: The warm front approaches and so do heavy rains. The western and southern portions of the state stand the best chances for heavy rain, but the entire state should get a good, quick soaking. Precipitation should develop between midnight and 3 AM tomorrow night and last until somewhere between 9 AM and noon, from SW to NE, on Friday. I'll keep the rest of the day Friday dry. Any instability tstorms that develop Friday afternoon should remain to the South and West of the state. Guidance is highly divergent on Friday, and a lot depends on when the rain ends and skies clear. The NAM guidance looks like a good compromise, so for now high temperatures of 75 to 80 for Friday look good.
As for rainfall totals, west of I 91, look for widespread 1-3" rainfall amounts, with locally higher amounts, especially in the SW. East of I 91, look for 0.5"-1.5", with locally higher amounts.
Longer Term: The weekend and beyond: Saturday a cold front approaches. Now this cold front does not have a lot of moisture to work with, but does have some instability. There is a chance that this cold front could trigger an afternoon thunderstorm. The best chances are north of the Merritt Parkway, since there will be more stable air along the south coast. The NE CT I 84 corridor may actually have the best chance of storms. The 12Z GFS looks a touch too warm with high temperatures, so I'll go a touch cooler than that. High temperatures should range from the upper 70s to mid 80s, with some upper 80s possible along the I 91 corridor.
Fair and dry weather is expected for Sunday and Monday, with Sunday being the cooler of the two days. However, with a downslope flow and plenty of sun, guidance could be a touch too cool both days. So I expect high temperatures in the low 80s Sunday and mid 80s Monday.
The next cold front could trigger a round of showers and thunderstorms on Tuesday. There is some model disagreement (which is typical at that range) regarding whether or not the showers and storms linger into Wednesday with the front stalling out. For now, I'll just say that the best chance for storms is Tuesday, with a slight chance they linger into Wednesday. For now, as far out as we are, a smooth 80-85 for temps seems to look pretty good.
The longer range looks to pretty much continue the theme of this summer so far of having frontal boundaries pretty close to the state through the period. For our region, this would mean frequent shower and thunderstorm chances, like we have seen during this summer season so far. There is also some ensemble and pattern agreement for a heat wave somewhere around the 20th. But, as has been the case this summer, it could be a fairly intense, but transient (brief) heat wave.
Now, let's take a look at systems to affect our state this upcoming week in graphical format. First, let's take a look at tomorrow night's warm front. You can see the wave of low pressure near Washington, D.C. and you can also trace the heavy rain axis from just W of NYC all the way to Pittsburgh. Extrapolating that shows a nice depiction of the heaviest rain hitting the Southern portions, and especially SW portions of the state.