PM All Zones Update: Even Warmer Tuesday; Showers Wednesday

Good evening, everyone! We hope you enjoyed this beautiful Monday! Plenty of warmth was had in areas from NYC and west, with Newark tying a record high of 82 set in 1955. JFK, Long Island, and the Jersey Shore were much cooler due to the sea-breeze, but it was still a lovely day with plenty of sunshine and highs in the 60s. The rest of this evening looks quite pleasant and also milder than yesterday evening, as some moisture advection will prevent truly ideal radiational cooling conditions. Thus, low temperatures will generally hold around 50 or in the 50s for most of the region, with temperatures near 60 in urban areas. This will give us a nice head start for Tuesday’s warmth.

As we mentioned in yesterday’s PM article, the warmth is due to increased southwest flow in the atmosphere as the upper-level low from last week finally truly departs. This southwest flow will actually accelerate further on Tuesday, as a disturbance will be moving into SE Canada, which will increase the height gradient and thus accelerate the SW winds aloft, which will advect even warmer temperatures.

Today's NAM model valid for Tuesday afternoon shows very strong SW flow in the atmosphere, leading to plenty of warmth.

Today’s NAM model valid for Tuesday afternoon shows very strong SW flow in the atmosphere, leading to plenty of warmth.

Notice in the bottom left panel how there is a pretty strong shortwave moving into the Great Lakes, which has low heights — in a pattern where we are already under ridging with 500mb heights at almost 580dam, this serves to increase SW flow in an already warm airmass — notice how tight the height gradient is and thus how fast the 500mb winds are blowing. This disturbance is actually associated with some severe thunderstorms in the Midwest, and given the dynamics above and the warm airmass ahead of it, we can see why. This increased SW flow leads to 850mb temperatures easily between 12 and 15C across the region, and with more SW flow, this leads to more mixing in the atmosphere than on Monday and thus even warmer temperatures.

An animated gif of the NAM sounding for NYC on 2pm Monday and 2pm Tuesday shows more SW flow aloft on Tuesday, and thus warmer temperatures.

An animated gif of the NAM sounding for NYC on 2pm Monday and 2pm Tuesday shows more SW flow aloft on Tuesday, and thus warmer temperatures.

An illustration of this increased warmth can be seen in the above gif. This is a forecast sounding for NYC valid at 2pm Monday (first image) and 2pm Tuesday (second image). Notice how on the image valid for Tuesday, the flow is much more uniformly southwest, rather than west, from 700mb to 500mb in particular. This leads to more mixing in the atmosphere at those levels and also a general warmer trend in that layer as well. This can thus translate to more warmth at the surface. As a result, high temperatures may be widespread in the low to mid 80s from NYC and west on Tuesday, with perhaps even an 86-87F max somewhere in NE NJ. And despite that disturbance to the west, enough ridging still exists to mostly keep clouds at bay, though clouds will increase a bit in the afternoon as storms fire in W NY and W PA. Of course, though, this time of year, the sea-breeze will again play another large role, so coastal areas will mostly hold in the 60s or perhaps be able to eek out an early-afternoon high in the low 70s before quickly falling in the mid-afternoon as the sea-breeze accelerates. The increased mixing will also lead to 20-25mph wind gusts across the entire region.

Clouds will increase on Tuesday night as the aforementioned disturbance moves eastward and triggers some thunderstorms that will move in our vicinity. The best forcing with this disturbance will remain to our north and west, so the storms will be outrunning the best forcing, and they will also be running into our ridging and will thus weaken as they make their approach.

Today's GFS model valid for Wednesday morning shows weakening forcing for lift as you head towards NYC.

Today’s GFS model valid for Wednesday morning shows weakening forcing for lift as you head towards NYC.

We will again use our new Q-Vector Analysis plots to dissect this further. This approximates synoptic forcing in the 400mb to 700mb layer of the atmospere — the above plot is valid for 8:00am Wednesday morning. It shows some forcing for lift in our region, but it also shows that by far the best forcing will remain to our north and west, and thus nothing looks too terribly impressive for our area. The storms will be running ahead of the best Q-Vector convergence, but there is still just enough Q-Vector convergence there combined with the warm airmass to produce some showers with perhaps a quick moderate burst of rain and a rumble of thunder. The timing of the storms being in the morning also doesn’t help too much with instability. High temperatures will be held around 70F due to the initial clouds and showers as well as the front coming through — though we expect the afternoon to be mainly dry; we may pull off enough afternoon sunshine to sneak back into the low to mid 70s.

In New England, showers and thunderstorms could be a bit more widespread as the front will move towards them a tad later in the day after they warm up a bit (better timing with diurnal heating), and they will also be located in areas with better Q-Vector convergence.

Once this front comes through, notice all the Q-Vector divergence behind it — evidence of quickly clearing skies on Wednesday evening and Thursday, though temperatures will be much cooler with highs only in the low 60s on Thursday.

Today's GFS model valid for Sunday afternoon shows enough SBCAPE for strong thunderstorms.

Today’s GFS model valid for Sunday afternoon shows enough SBCAPE for strong thunderstorms on Easter Sunday.

We think it will stay dry on Friday and Saturday. However, the flow will be pretty fast to the north and also zonal, but more ridgy/slow to the south. This will lead to an active train of disturbances passing to our north, but they may not be able to dig far enough south for major impacts to our area. However, there may be just enough high-latitude blocking to get one of these disturbances just far enough south to create decent forcing for lift, yet stay far enough north to keep us somewhat in a warm and moist sector via SW flow from the gradient with the ridging to the south and the disturbances to the north. This may lead to a couple of days in this period where showers and thunderstorms develop, with some heavy rain being possible.

Interestingly, the above map is the GFS forecasting sufficient CAPE for strong to severe thunderstorms on Easter Sunday — so this will have to be watched. With synoptic forcing staying well north in that zonal regime, the lifting mechanisms will have to be more convective — harder to forecast and less reliable for precipitation, but can have a high ceiling for thunderstorms. Of course, this time of year would still favor a sea-breeze creating a marine layer to weaken storms from NYC and east.