Premium weekly outlook: Very warm start, cooler air to follow

The anomalous warmth we spoke about last week? It’s finally here! Sunshine will mix with clouds occasionally this afternoon, but by and large, high pressure will remain in control of the weather throughout the Northeast United States. Forecast model guidance suggests that 850mb temperatures of 12-14+ C will surge northward toward the Mid Atlantic states, with southwest winds drawing in warmer air at the surface. Temperatures will rise in the upper 70’s to near 80 this afternoon, with the possibility of some clouds later this afternoon and evening as a weak disturbance passes by. Otherwise, clearing is expected later tonight underneath high pressure and light winds. The interior valleys will drop into the 50’s, but this will be much warmer than the past several nights. Radiational cooling and warm air advecting in the mid levels could cause moisture to be trapped in the low levels — leading to low clouds and patchy fog in spots through Tuesday morning.

A stronger, deep-layered ridge will move into the Northeast on Tuesday and Wednesday with 500mb heights rising to between 582dm and 588dm, by Wednesday. Subsidence from this ridge will keep skies more clear of cloud cover and will also act to keep a cold front to the northwest of the NYC region on Wednesday. So plenty of sunshine is expected each day. Model soundings are showing temperatures around 18°C to 19°C on top of an elevated mixed-layer somewhere between 850-925mb.  This will support temperatures to reach into the lower or middle 80s over much of the Mid Atlantic on Tuesday and Wednesday. More typical during the summer, a thermal gradient over inland areas may cause seabreezes to form during the afternoon hours. This will keep temperatures a little cooler near the shore, especially on Tuesday with winds likely to have more southerly component during the morning hours.

By the middle of the week the pattern will begin to undergo fairly significant changes. A large mid-latitude trough moving in from the Mississippi River Valley will start to cause the ridge, which caused anomalous heat during the early part of the week, to break down, with some lowering heights. This will allow the cold front over New England to a little further southeast Wednesday night. Showers are likely to become more numerous throughout New England, but remain mostly north of the NYC Area. This same front will gradually drop southward toward the Northern Mid Atlantic as time goes on this week, with chances for clouds and shower increasing each day and night. Southern parts of our area, particularly Southern New Jersey, will remain warmer during this time frame with less clouds and showers.

By Friday and Saturday, a trough associated with an upper level system will be digging into the Southeast US and then amplifying, until it takes at least a modest negative tilt. Some energy at the base of thistrough may also break away from the trough and form a cut-off upper-level low over over Southeast US..  This will result in a broad area of surface low pressure forming along the Mid-Atlantic or Southeast coast with moisture from Atlantic surging northward up the coast. Strong forcing from jet streak and shortwave energy with this areas, suggests the potential for periods of rain on Friday and into Saturday. How widespread and heavy rainfall becomes, will depend alot on how quickly this low pressure area organizes and consolidates, before moving northward up the coast. This low will also bring more onshore winds and a martime airmass over the region Depending on cloud cover, temperatures could wind in up in the 60s or 70s — which, while cooler than early this week, is still above average for this time of year in the Northern Mid Atlantic.

Further complicating this setup will be the potential for a tropical or sub-tropical low to form near the Bahamas late this week. How the trough interacts with this feature has varied on model solutions on each day. The faster the tropical or sub-tropical system phases or merges along the East Coast, the greater the chance for more heavy rainfall in our region. This would significantly aid in the moderate to severe drought conditions in our region. At this time, the National Hurricane Center is pinning a 50% for this system to develop over the next 5 days.

However, much of the latest guidance continues to suggest more separation between both features and more disjointed storm system along the East coast. A strong ridge forming over Kara Sea region by this weekend might help to support more East Coast amplification, but the overall pattern remains progressive with a fast pacific jet and very little high latitude blocking. If this system remains more unphased, subsidence possibly between each trough could keep some portions of the area drier than others. These timing or wave spacing issues, between the trough and tropical/sub-tropical disturbances,  are somewhat similar to the struggles we had with any impacts or rainfall from Hurricane Matthew over the region. At this time, owing to the progressive pattern, we are leaning toward minor impacts in our area from this system.

There is still some uncertainty on quickly this all moves out the weekend and early next week.  At this time, we anticipate temperatures to be near or cooler than normal and some unsettled weather to continue, with energy associated with the trough lagging behind. However, we don’t think the weekend is looking like a washout at this time. If the progressive trend continues, we could see the weather conditions improve more rapidly.

Stay tuned for more forecast updates and thoughts during week on our main dashboard and member zones. The going forecast will be fine tuned later this week as we gain confidence moving forward.