Forecast Highlights:
Tonight - Friday: Storms Continue
As the radar image above shows, most of today's storm activity has dissipated, including a strong MCS that affected Ohio and western Pennsylvania this afternoon and evening with severe thunderstorms. According to the latest Weather Prediction Center (WPC) surface analysis, the cold front is currently located near central-eastern Ohio and is gradually moving to the east. The front is expected to reach central Pennsylvaia by Thursday morning, with partly to mostly cloudy skies expected for the NYC area in the morning with highs peaking in the low to mid 80s. With the proximity of the frontal boundary to the area, along with marginal instability, scattered thunderstorms are expected to develop in the early afternoon, persisting through the evening and early overnight hours. Marginal mid level lapse rates, widespread cloud cover and a lack of bulk shear are likely to limit the severe weather risk, although with precipitable water values near 2 inches, storms will be capable of producing heavy rain and localized flash flooding, with gusty winds a risk with the stronger storms.
As the trough aloft reaches the nearly stationary ridging in the western Atlantic, it is expected to stall overhead while splitting into a closed upper level low. Meanwhile, the surface cold front will cross NYC around Thursday evening and is expected to stall just to the east overnight, with a wave of low pressure developing along the front overnight into Friday. This is expected to keep mostly cloudy skies and scattered storms into Friday as well, but with the front to the east, a noticeable drop in temperatures and humidity is expected, with highs only peaking in the mid 70s to near 80 degrees.
Occasional storm updates will be posted on Thursday afternoon, both on the blog and on Twitter.
Saturday - Next Week: Heat, Humidity Gradually Return
Even though the weekend is only a few days away, the model guidance remains inconsistent with the handling of the upper level low and the western Atlantic ridging. Some of the model runs such as the 12z GFS keep the ULL over the region through most of next week as well, preventing ridging from building in and keeping temperatures in the 80s with a risk of isolated storms each day. Meanwhile, other runs such as the 18z GFS and 12z ECM, expand ridging into the region while forcing the upper level low southwest into the central US, with drier conditions as heat and humidity return with temperatures back into the upper 80s to mid 90s, not unlike the recent heat wave that affected the area. Earlier discussions noted Tropical Storm Chantal as a potential player in the long range setup in the East Coast; over the last day, however, Chantal quickly became disorganized and collapsed back into a tropical wave while failing to make the anticipated northwest turn, with its weaker intensity and fast speed likely to take the remnants into the Gulf of Mexico, where they will have to be watched for redevelopment.
At this time, I am siding closer to the ECM, with temperatures over the weekend staying in the lower half of the 80s with partly cloudy skies and a risk of isolated thunderstorms. By early-mid next week, the upper level low is forecast to gradually shift west and weaken as ridging slowly builds in, with an increase in heat and humidity with highs forecast to reach the upper 80s to low 90s, possibly higher should the ridging extend more west than currently forecast. The next potential chance of storms appears to be late next week when the next possibility for a cold front exists. The outlook is still subject to some changes, however, and more information will be posted over the next few days.
Thank you for your thorough blog posts. I have a climate history question, which may or may not be of interest. First, why does the region almost always experience warm weather with a dose of high humidity - dew points >65 degrees, and as we've seen this July much higher than that, with dew points in the low 70s? Historically, has there ever been a warm summer or perhaps a heat wave where such high dew points were absent?
ReplyDeleteThank you,
Ben
Hi Ben,
DeleteThe humidity with each heat wave depends on the source of the air mass. Humid air masses originate from the Atlantic or Gulf of Mexico, while drier air masses originate from the desert regions in the Southwest. For example, the heat wave last week brought a warm, moist air mass north from the western Atlantic Ocean into the region, bringing dew points into the low 70s.
There have been some dry heat waves; the air mass leading to the July 4-7, 2010 heat wave originated in the West and started out with low dew points, in the 50s to low 60s with highs in the low 100s, until humidity increased towards the end of the heat wave.