Premium Weekly Outlook 5/23 – 5/29: 80+ Degree Temperatures by Wednesday…More T-Storm Chances?

Some unsettled weather will start off this week with a cut-off low tracking in the region. But much warmer and drier conditions will finally arrive with temperatures soaring well into the 80s away from the shore by Wednesday and Thursday. The main question remains: will this warming trend to continue into the Memorial Day weekend, or is more cooler/ unsettled weather with showers and thunderstorms in store? We discuss more technical details and thoughts with the upcoming weather this weekly period.

So far — Monday began with plenty of sunshine as weak high pressure temporarily built into the region.  Despite a northeast flow, deep mixing will help temperatures today to rise in the middle to upper 70s.  This brings our temperatures to slightly above average for late May. Closer to the south-facing shores,  temperatures will be cooler with sea-breezes developing and pushing inland later this afternoon.

However, this sunshine and warmer temperatures will lead to the atmosphere becoming increasingly unstable, owing to steepening low-level lapse rates underneath a mid-level cold pool associated with the cut-off low south of our region. There could be enough lift, instability and moisture to trigger some widely scattered showers and thunderstorms today, especially northwest of New York City. Near the coast, a stable marine layer may cause convection to weaken. This will be especially true over Long Island and Coastal Connecticut, although sea-breeze boundaries could be also be a focal point for some shower and thunderstorms development today as well.

Showers may become more a little widespread later tonight and Tuesday with the cut-off low moving northward closer to the region. We will have positive vorticity advection from the cut-off low and it will produce a strong jet streak offshore — putting us in the left-exit region. Additionally, we will have upper-level diffluence. These are all good factors for lift and precipitation, giving us some moderate and localized heavy rain at times tonight.

Model guidance has been consistent in tracking the surface low south of the region — over the Western Atlantic. Some more clouds and showers are likely to keep eastern sections cooler on Tuesday, especially over Long Island and Connecticut. Further west over New York City, New Jersey and the Lower Hudson Valley, more instability again could help trigger showers and thunderstorms. High temperatures will likely reach the lower to middle 70’s west of the Hudson River.

However, by Wednesday this cut-off will be lifting out of the Northeast US. An upper-level ridge with 500mb heights over 588dm will start to build over region. A west to southwest flow around a high pressure to our south will pump much warmer temperatures in the mid and lower levels toward our area. 850mb temperatures of 12°C to 14°C with deep mixing will cause temperatures to rise well into 80s. Afternoon sea-breezes may keep temperatures slightly cooler near the shore.

The warmth continues on Thursday with the upper-level ridge over the region. Temperatures will likely reach at least lower to middle 80s, away from the coast with some sunshine and southerly winds. A upper-level disturbance approaching from the west may bring more clouds with showers and thunderstorm by Thursday night.

Then weather conditions become more uncertain as we head into the big Memorial Day holiday weekend. More upper-level disturbances moving on top of the aforementioned ridge may touch off more showers and thunderstorm overs the Northeast. The GFS model has suggested some type of remnant EML (elevated mixed-layer) will be present over Northeast and Mid-Atlantic region. If correct, this would result in much more instability for stronger convection and potentially severe thunderstorms. However, the strong ridge aloft could keep the area more capped and also push more favorable kinematic support (shear and forcing) north of our local area. Models will likely have various solutions over next few days. The potential for any severe weather is highly uncertain at this time.

Another factor with these disturbances is the potential for a larger trough over Newfoundland to the Northeast of New England. The end result would be a backdoor cold front over New England that might push southwest through the region sometime during sometime between Friday and Sunday. This will cause a marine airmass to enter the region with onshore winds and perhaps more cloud cover. The marine airmass behind backdoor is mainly in lowest-levels and shallow. High temperatures could go back to being closer to average for this of year.

Model guidance has had various solution timing of this backdoor cold front pushing through our area. Some model solutions have also showing high pressure rebuilding to south, with more southwest flow and keep this backdoor cold front further north. If that’s correct, warmer than average temperatures will likely continue through the weekend. Underneath a 588dm ridge temperatures could warm actually  into upper 80s or lower 90s in parts of the region.

Stay tuned for more forecast updates throughout the week, as we will likely be fine tuning the forecast as we get closer to Memorial Day weekend.