Aug 1, 2013: Heavy Rain This Afternoon, Evening

Forecast Highlights:

1438A wave of low pressure will move through the region today, producing widespread showers and thunderstorms across the region capable of heavy rainfall and localized flash flooding. Seasonable conditions will return for Friday and Saturday as another weak cold front moves through, followed by a strong trough pattern settling over the region with below average temperatures continuing through the first two weeks of August.




Wednesday, July 31 Observations:

7.31.13 - CopyAn upper level low continued to lift out of the region with a cool air mass slowly moving out, resulting in slightly warmer temperatures than Tuesday, although cloud cover was increased as well. High temperatures generally reached the upper 70s to low 80s inland and the low to mid 80s for the rest of the area. The highest temperature observed in the area was 84 degrees in Teterboro, NJ, and the coolest high was 79 degrees, tied across several locations.




Short Term Outlook: Heavy Storms Expected Today

1438As the latest radar image shows to the left, widespread showers and areas of thunderstorms are currently moving through New Jersey, tracking northeast. This area of rain is forecast to expand and intensify while moving through the area through the area; moderate to locally heavy rain and thunder is expected to spread into Long Island and CT over the next few hours while continuing over northern NJ, SE NY and NYC; west of NYC, rain may lighten up after 1-4 PM as the warm front slowly approaches from the south, while continuing to the east. High temperatures are expected to reach the mid to upper 70s across the area early in the day. In Long Island and CT, where temperatures are in the mid-upper 70s as of 10 AM, additional slight warming is expected until the rain spreads in and temperatures cool down.

Additional scattered thunderstorms are likely to develop in eastern PA and western NJ later this afternoon and evening, which will be capable of producing heavy rainfall and gusty winds; these storms are likely to gradually weaken as they track into and east of NYC, with rain ending early tonight west of NYC and later into the mid overnight hours to the east. Rain totals of at least 1/2 to 1 inch are expected across the area, locally higher up to 2 inches especially west of NYC.

Storm updates will occasionally be posted this afternoon and evening both in the blog and on Twitter.

Friday – Monday: Briefly Seasonable, Then Cool Again

A cold front will move through the area tonight as the wave of low pressure departs, but with a westerly flow setting up, temperatures will fail to cool down behind the front, warming up into the upper 70s to low 80s inland and the low to mid 80s for the rest of the area with partly sunny skies. Another weak cold front will move through late on Saturday, with partly to mostly cloudy skies and scattered showers and thunderstorms expected, although instability should be limited preventing a significant severe weather risk. Highs are expected again to reach the upper 70s to low 80s inland and the low to mid 80s for the rest of the area.

The front should clear the area overnight, with a trough in place for Sunday and Monday, which will result in a cooler air mass over the region, while also sweeping the remnants of tropical storm Dorian, currently near the Bahamas, out to sea as well. 850mb temperatures are expected to be near or slightly below 10C, supporting slightly cooler than average temperatures with highs reaching the mid to upper 70s inland and upper 70s to low 80s for the rest of the area. A weak shortwave will move through on Sunday resulting partial cloud cover but with little, if any rain expected; a high pressure will build in overnight into Monday, resulting in clearing skies and with chilly overnight lows, falling on Sunday night into the low to mid 50s inland and mid 50s to near 60 degrees in the rest of the area, except for NYC and the immediate coast, in the low 60s.

Tuesday – Next Weekend: Some Rain; Cooler Pattern Continues

f120The pattern through the medium range, represented to the left with the 6z GEFS 500mb height anomalies (image credit: PSU e-Wall) is expected to remain fairly stable, with high latitude blocking near central-northern Canada and Greenland keeping a strong upper level low stationed near southern-central Canada, with the mean trough positioned over the eastern half of the US resulting in widespread cooler than average temperatures, primarily from the Midwest and Plains extending into the Northeast US. Through the first two weeks of August, occasional brief surges of above average temperatures are likely, but with otherwise near-below average temperatures.

A wave of low pressure is forecast to approach the region on Tuesday and Wednesday with increasing cloud cover and scattered showers likely; as the area will be in the northern end of the frontal boundary, this setup is likely to favor slightly cooler high temperatures, potentially in the lower half of the 70s if the latest modeled setup verifies. With such a setup, it is difficult to narrow down the smaller scale details several days out, such as the exact timing of the clouds/rain and the coverage area, and the forecast is subject to some changes. A cold front is likely to move through late in the week as another, potentially stronger cool air mass pushes south into the region, resulting in temperatures likely cooling back down into the mid-upper 70s for highs and lows in the 50s away from NYC and the coast. In the cooler case scenario, interior locations may reach and even slightly drop below 50 degrees. Going into the longer range, this pattern is likely to persist through the first two weeks of August; based on the latest longer range model guidance, it appears the strongest heat of the summer may already be behind, although at least some periods of heat and/or humidity are not done yet, especially towards the second half of the month. Stay tuned for more information on the longer range outlook.


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