Modeling Note: I planned to do this discussion a bit late today to view all the models for the weekend's forecast to add clarity. Unfortunately, after reviewing all the data, there isn't much more clarity than there was 12 hrs ago. I will be using a blend of GFS/GGEM/ENS for this fcst and very little input from the ECMWF, which I'll explain blo.
Tonight: First ongoing issue is convection that has made it to the S coast. Models have not handled this convection very well, w/nearly all of the globals not showing any measurable. Yet, in reality, about half an inch of rain has fallen across much of the S coast. Models are showing something of a resurgence in convection tonight, likely from what's ongoing across S/C NJ right now, but keep it S of the area. However, given what has happened today, I am inclined to introduce a chance of showers and t-storms along the S coast only, probably most likely around midnight. As for temps, because we are starting 5-10 degrees below model consensus, I'll go a couple degrees lower than guidance for lows tonight. So xpct lows in the mid to upper 60s.
Tomorrow: I hate showing this much lack of confidence in a day 1 forecast, but it is what it is. NBM guidance is showing low POPs, but at the same time has decently-high QPF nearly all the way up to the S coast. You don't normally see this on day 1, and it is indicative that the majority of the members have nothing, but a select few have very heavy precip. As for a source for possible precip, one is not hard to find, between the stalled frontal boundary and a coastal low to our SE. So yes, I can see where precip would come from. The global models are generally dry, but the ECMWF does have a little precip on the S coast. Globals were a fair bit too far S today. Putting all of this into perspective, I'll go close to a consensus and keep the day largely dry, with just a slight chance for some rain along the S coast. I'll also go close to guidance on temps, but this could be too warm if it indeed turns rainier than fcst, ala what happened today. Highs shud genly be in the mid 80s. It is not impossible for someone near KBDL in the valley to get a few deg warmer than that, but only in the Nrn 1/2 of the state, where there will likely be less cloud cover.
Tomorrow Night/Sat: This is, by far, the easiest part of the forecast. No matter what happens with the two coastal lows, Sat should be a nice day in between systems. The GFS tries to get some moisture in here ahead of the next coastal low by day's end, but since it tends to run 6 hrs too fast, we'll keep Sat dry. Due to a gusty onshore breeze and increasing clouds, I'll go a few degs cooler than guidance. Highs shud be close to 80, maybe staying in the 70s in Srn Middlesex/Srn New London Counties.
Long Term (Sun and beyond): The biggest concern in the long term is in the beginning of the long term period- on Sun. The GFS and GGEM models indicate a coastal low coming far enough N to at least graze the S coast with steady light rain. The ECMWF is about 20 hrs slower and about 500 miles SE of consensus. The ECMWF was also much slower with Isaias. W/Isaias it did get the track right, but that was a pretty steady pattern, where a little change in speed probably would not chg the track too much. Sun's pattern is not steady. Therefore, the ECMWF being much slower allows the high to build in ery and push the storm well S & E. This is a known bias of the ECMWF, being too slow, lately that they are addressing acrs the pond in Greenwich (England, NOT CT!). Then we have the NBM guidance, which actually agrees w/the ECMWF on timing, but has 0.5-1" QPF across the entire state, w/the highest down on the S coast! Therefore, w/all the issues and moving parts going on, I think the best way to attack this right now, is to go somewhere between the GFS and NBM on speed, and a bit N of global mdls (WAY N of ECMWF) on QPF and pcpn placement. What this means for us is, showers or rain likely Sun aftn to Mon aftn S of I 84 and chc of rain or showers N of there. I'll also go 3-5 deg blo guidance on temps both of those days, which makes sense given xpctd cloud cover, wind dir, and pcpn. This yields highs only in the low 70s Sun and near 80 Mon. If pcpn lingers longer Mon, temps could turn out even lower, esp in Srn Middlesex/Srn New London Counties, but I don't want to stray that much from gdnc yet, given lwr than avg confidence.
Tue and Wed should feature nice weather for the time of year. GFS has dew points in the 40s all the way down to SNJ! So we're looking at highs of 80 to 85 Tue and maybe a degree or two cooler than that Wed. Guidance is accepted w/no changes at all. No reason to quibble over a degree or two!
The Bermuda heat ridge may begin to flex its muscles as we head deeper into the long term. Humidity increases on Thu. I will keep Thu dry for now, but pcpn is knocking on the door by then, so we may need to add pcpn into the fcst at some point, esp for SW CT. But for now, I took the exec decision to leave it out, since everything has trended slower this summer when the Bermuda Ridge has flexed its muscles.
Looking into the long range, the Bermuda Ridge looks to return with more heat, humidity, and unsettled weather beginning Thu. This probably lasts abt 4-7 days, thereafter, cooler Canadian High pressure may infiltrate the area again. We're getting later in Aug now, this is when you usually start to see Canadian highs strengthen and the Bermuda high weaken. Also, I wouldn't pay too much attn to Josephine right now, as it looks to be both vry weak and out to sea. Hwvr, the tropics overall shud get more active by the end of the month, and as long as a Bermuda ridge is still in place, they could be guided up the coast. Just something to keep an eye on!
Now, let's take a look graphically at the two systems slated to influence our weather this weekend. The first is tmrw's coastal low. I xpct that one to largely remain S of the region, and maybe produce a vry brief rain shower along the S coast.