Premium AM Update: More Heat & Humidity Today…PM T-Storms Possible Wednesday

Good morning! More typical summer-time heat and humidity is in store for next few days. For today, weak high pressure and upper-level ridging will be over Northeast and Mid-Atlantic region,. This will result in mostly sunny skies for much of the day. Latest models show 850mb temperatures between around 15° C to 17° C with very light westerly winds later today. This will support high temperatures in the upper 80s to around 90 over much of the local region today. A weak flow will allow for some sea-breezes to develop again this afternoon and keep temperatures from rising out lower to middle 80s right along the shores.

There isn’t much of a trigger for convection today. But a surface trough will develop again over  the Interior. The NAM model forecasts instability to build with MLCAPE 500 -1000 joules. So few isolated showers and thunderstorms could develop this afternoon over Interior parts of NY, PA, New England and over Northwest NJ. The main threat from thunderstorms with a very weak shear and poor mid-level lapse rates, with be locally heavy rainfall, as any thunderstorms will likely be slow-moving. Therefore these showers or thunderstorms are not likely make it down to more coastal areas, before diminishing closer to sunset.

Partly cloudy skies and muggy conditions are expected overall for tonight, with some mid-level warm-air advection. Also some low-level moisture trapped underneath inversion and light winds will support some areas of patchy fog to develop again late tonight. Cloud cover and higher dewpoints will keep temperatures warmer than past night over Interior, with lows mostly in mid-upper 60s. Over urban and coastal areas low temperatures will be low to mid 70s.

Another very warm and humid day is expected for Wednesday. After some low clouds and patchy fog early in the morning, more sunshine is expected for rest of the day. High temperatures will be likely in mid-upper 80s again. However, weak shortwave trough with a cold pool aloft will be approaching the region during the afternoon. The atmosphere will be less capped and more unstable across the region with steeper mid-level lapse rates and higher CAPE values. So there is potential for more showers and thunderstorms to pop up across the region. Some thunderstorms could be strong with small hail and gusty winds. However, shear will be very weak with very high precipitable water values. This will result in showers and thunderstorms that will be slow-moving and pulsing up and down in intensity. So the main threat again will be from locally heavy rainfall with some flash flooding also possible.

NAM model forecast for Wednesday afternoon

NAM model forecast for Wednesday afternoon

 

Any shower and thunderstorms will come to an end later tomorrow evening as instability diminishes and shortwave energy exits the region. Skies will remain partly cloudy later Wednesday night, with low temperatures again in mid-upper 60s over Interior valleys and lower to middle 70s over more urban and coastal areas. Some areas of patchy fog may also develop late.

On Thursday a cold front and shortwave trough from the Great Lakes will be begin approaching the Northeast and Mid-Atlantic region. So more isolated or widely scattered showers and thunderstorms are possible during the afternoon and evening hours, especially over the interior again. But much of the day will just warm and humid, strong Western Atlantic ridging keep best forcing dynamics to the west. High temperatures will be in the mid-upper 80s, with some spots hitting 90 again. Except more southerly winds and sea-breezes will keep temperatures some what along the shore.

Warm and humid conditions will continue into Friday and Saturday. But some unsettled weather is possible, as the cold front and shortwave trough moves slowly across the Northeast and Mid-Atlantic regions. Stronger forcing and lower heights will support more numerous showers and thunderstorms, at some point during this period. There is still some model differences with the timing of this system moving through. So forecast details, more locally will be fined tuned as we move closer.

GFS model forecast for Friday afternoon

GFS model forecast for Friday afternoon

But instability overall is still appears likely to reduced somewhat by more cloud cover or convective debris. So more organized severe weather is not anticipated. However,  asoutherly plume of sub-tropical moisture with very high precipitable water values, will support potential for more heavy rainfall and localized flooding. High temperatures both days will depend on amount of cloud cover.

The frontal boundary and shortwave trough will move offshore on Sunday. A cooler, drier airmass will come into Northeast on Sunday. More sunshine and high temperatures lower to middle 80s are expected. However, this pleasant weather may not last long as another system may be approaching from Great Lakes with showers and thunderstorms by Monday. So stay tuned for more premium updates this week, on forecast over next 7 days!

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