Currently: A cold frontal system extends from W PA and WNY, up through Northern New England. A weak tropical impulse was near the Delmarva. The combo of these two features, in addition to a warm, humid air mass in place, has left us unsettled today.
Tonight: Areas of showers and thunderstorms will be ongoing the rest of today into tonight. The general trend will be diminishing after midnight. E of I 91, a few showers may linger into early morn. I will not carry that into tmrw's fcst, because there's really no need. If it does go beyond dawn, it would be less than an hr. I'll go a couple degrees above guidance for tonight's low temperatures. It is going to be a very muggy and sticky night. Low temps should only be around 70.
Tomorrow: Skies clear and we dry out. This will probably be another one of those days where we start out a bit humid in the morn, but are dry by the end of the day. I will generally go with guidance temperatures. It could turn out a degree warmer in spots, due to high launching pads, but I am not going to go all crazy over one degree. Staying close to guidance yields hi temps in the mid 70s, except some upper 70s along the I 91 corridor.
Tomorrow night/ Saturday: This will be the nicest part of the weekend and the air will have a fall like feel to it! Again I have no real reason to differ from the guidance which the NBM is presenting, so I'll ride it. Expect hi temps generally in the low 70s.
Long Term (Sunday and beyond): The only real weather concern in this time frame is on Sunday, so we'll start off with that. A frontal system approaches the region. Abt 90% of the gdnc has the warm sector staying to the S (in fact well to the S) of the area, so we'll use that as the basis for the fcst. Now that we're getting toward fall, it starts becoming harder for warm fronts to just blast thru the area. We shud also be in a deep onshore flow regime, which would make it that much harder for any warm front to go thru.
Therefore, I will expect the main precipitation mode to be stratiform vs convective, but it wouldn't shock me if we had an imbedded flash or rumble. The GFS is shockingly low on QPF (less than 0,25"), but all other guidance is much higher. The NBM avg is abt an inch. So xpct a good amt of rain and I will ignore the GFS for now. As for temperatures, assuming that the forecast basis is correct, I'll go 3-5 degrees cooler than NBM guidance, to compensate for clouds, precipitation, and onshore flow. Therefore, high temps should only be near 70 degrees! As for timing, noon to midnight west of I 91. As the system slows, it could be much later East of I 91, as in 10 PM to 10 AM Mon morning. For now, I have not xtndd the event into Mon, but it's worth noting that we may need to add a Mon Morn pd E of I 91 to cover lingering rain.
Looking beyond that, there really are no systems of note in the rest of the long term period. So I'll broadbrush everything and just cover temps, which also look very pleasant. The general temp theme is pretty typical for September: A cold front will go through dry on Monday, then by Thursday, return flow sets up and we get a bit warmer. Nothing should be too extreme on either side.
As far as temperatures and reasoning, I went a bit below guidance on Monday, because even though the cold front should pass through with no precipitation, I do anticipate more cloudiness than the models advertise, perhaps a fairly solid mid-level cloud deck, as soundings are moist above 5,000 feet. I went a couple degrees below guidance on Tuesday, with strong cold air advection, which models often underestimate. There are also low convective temps, which suggest cumulus cloud formation, which would also put a lid on temps. I went a couple deg abv gdnc for Wed, and several degs abv gdnc for Thu. Wed shud downslope and warm us up nicely. Thu shud see good return flo, which shud aid in warming the atmos a lot more than mdls show at the lwr lvls.
What does all this mean in terms of actual temperatures? Expect hi temps in the mid to upper 70s on Mon, only near 70 on Tues (possibly staying in the mid to upper 60s in the NW hills!), low to mid 70s on Wed, and upper 70s on Thurs.
It is very possible that there are widespread 40s for lows north of the Merritt Parkway both Tuesday and Wednesday mornings.
Into the long range, there are some signs from deterministic and ensemble model guidance that there could be some sort of an East Coast tropical threat in the 9/23-25 time frame. It is, of course, WAY too early to say anything else on that matter, other than that time period does look like a threat at this point.
Not much to cover graphically today. Quiet week in progress and there is really too much uncertainty w/the event on Sun to really post what I would want to post anyway. Take care and stay safe! See you next week!