July 7, 2013: Temps Cool, But Storms Continue

Forecast Highlights:

The Bermuda high pressure remained in place over the region today leading to another very hot and humid day, although the high shifted further southeast with isolated storms reaching the western half of the area. As the high continues to retreat offshore, additional scattered storms are expected on Monday, with another front expected to stall nearby for the late week resulting in another round of rain and storms.

---

Tonight - Tuesday: More Scattered Storms

Earlier this afternoon, a line of severe thunderstorms tracked ENE through Pennsylvania, producing heavy rainfall and gusty winds. The line has been gradually weakening for the last few hours, and as of 9 PM only two scattered heavy storms remain near Morris county, NJ, tracking to the northeast. These storms are expected to affect the rest of NE NJ and SE NY before weakening later on as well with continued loss of daytime heating and instability.

The Bermuda ridge that was in place near the region over the last few days producing a 3-4 day heat wave is weakening and shifting southeast, allowing for the upper level low that has been stuck in the Ohio Valley region to track NE, with the shortwave trough weakening while moving through the region on Monday afternoon/evening. This shortwave will trigger scattered thunderstorms in the afternoon hours in the northern Mid Atlantic/southern Northeast region, especially north/west of NYC, which will be capable of producing locally heavy rain, gusty winds or small hail within the stronger cells, although several factors, such as less instability and more cloud cover compared to today, the higher wind shear displaced south of the area, and marginal mid level lapse rates are likely to prevent a more significant risk of severe thunderstorms. Due to the cloud cover and the ridge shifting southeast, cooler temperatures are expected, peaking in the mid 80s to near 90 degrees across the area, with somewhat lower humidity as well. The shortwave will quickly clear the area late on Monday with drying conditions overnight; more sunshine and slightly warmer temperatures are expected for Thursday, although with a frontal boundary over central-northern New England and weak warm air advection, isolated storms are possible again in the late afternoon/evening hours especially for interior areas.


Wednesday - Next Week: Stormy, Then Humid Again

By Tuesday night into Wednesday, a low pressure will form over the Midwest region, tracking northeast into Canada as a trough dives southeast into the eastern half of the US and amplifies, with a cold front extending southwest of the low pressure approaching the region but slowing down as it approaches the nearly stationary ridging in the western Atlantic Ocean. Widespread showers and thunderstorms are expected as a result on Wednesday, with the most significant storm activity likely north/west of the area but with occasional storms reaching the area as well. With sufficient instability and somewhat steep lapse rates, some of the storms could be strong or severe, although with the highest shear north/west of the area, the focus of severe storms is likely to stay north/west as well. Regardless of the severe weather potential, with high precipitable water values near 2 inches, storms will be capable of producing heavy rainfall. Slightly warmer temperatures and higher humidity are expected, with highs in the mid to upper 80s inland and upper 80s to low 90s for the rest of the area. The front is then likely to stall nearby on Thursday with continued scattered storms, possibly strong especially inland, along with cooler temperatures likely around the mid 80s.

With the western Atlantic ridging nearly stationary, the front will stall over the region into Friday as well, bringing a temporary relief from the heat and humidity. Temperatures are expected to remain in the lower half of the 80s with lower humidity and continued scattered thunderstorms, which may be strong and capable of producing locally heavy rainfall. By the weekend into early next week, the trough is expected to become cut off with the upper level low drifting SW into the southern US, allowing the western Atlantic ridging to retrogreade back west into the region, bringing a humid air mass back into the region. While there are model differences regarding the setup, with the ECM now keeping the ridging further east and the GFS/CMC more aggressive in bringing the ridging and heat/humidity into the region, the overall expectation is for temperatures to stay in the 80s through the weekend into early next week with gradually increasing humidity and the frontal system either remaining nearby or shifting further west. Stay tuned for more information on the longer range outlook.

Another aspect of the forecast to make note of is Invest 95L, currently in the Atlantic Ocean ESE of the Lesser Antilles. This tropical disturbance will continue to move WNW into the northern Caribbean through the next week. While additional development is likely into a tropical depression or storm, which would be named Chantal, it should be noted that most model guidance shows little or no development of the invest, and at this time it is unlikely to become a hurricane. Should the invest reach the Florida region by the late week as currently expected, it will likely be blocked from tracking NE up the coast especially if the western Atlantic ridging spreads west, although it may add more tropical moisture to the frontal system over the East.