July 25, 2013: More Showers Today, Sunday

Forecast Highlights:

StormSetup - CopyA coastal low pressure will develop east of the region today, tracking north into New England on Friday while producing scattered showers and unseasonably cool temperatures east of NYC. More seasonable conditions will return into the area for Friday and especially on Saturday; a slow moving cold front will produce additional showers and thunderstorms on Sunday followed by a return to seasonable conditions for the first half of next week.



Wednesday, July 24 Observations:

7.24.13 - CopyA cold front moved through the area throughout the day, bringing in a much cooler air mass from the west. Partly sunny skies were generally observed with little to no precipitation accompanying the frontal passage. Temperatures were cooler west of NYC, peaking in the upper 70s to low 80s in northern NJ and SE NY, with the warmest temperatures in NYC and Long Island, peaking in the mid to upper 80s. Southern Connecticut reached the low to mid 80s for highs. The highest temperature was 88 degrees at JFK airport.


Today – Saturday: Coastal Low Stays East

A frontal boundary is currently stalled off the coast, with areas of showers and thunderstorms offshore. Mostly cloudy skies and scattered showers are expected along and west of this frontal boundary, extending into Long Island/CT and eastern New England with up to 1/4 inch expected, locally higher, and a few isolated showers are possible in the immediate NYC area as well. A cooler air mass is in place, which combined with the cloud cover and rain will result in unseasonably cool high temperatures, peaking in the low to mid 70s north and west of NYC and the upper 60s to low 70s for the rest of the area.

StormSetupA wave of low pressure will develop along this frontal boundary east of the area later tonight, tracking north into New England on Friday while producing heavy rain in coastal Massachusetts and Maine. This coastal low will stay east of the area, with highs reaching the low to mid 80s from NYC and further north/west and the mid 70s to near 80 degrees east of NYC. Showers are expected to clear the area overnight, with partly sunny skies on Friday but with isolated showers still possible in LI/CT, especially early in the day. A warmer air mass will briefly return on Saturday, with partly sunny skies and highs rising into the mid 80s for most of the area and the upper 70s to low 80s for the coast. Overnight lows, which will be chilly through Friday night with lows in the mid 50s to low 60s away from the coast, will be warmer as well, only falling into the mid 60s to low 70s on Saturday night as cloud cover increases.

Sunday – Next Week: Some Storms, Then Seasonable

A weak cold front will slowly approach the region on Sunday as an upper level low approaches the Great Lakes, then slowly tracks north into Canada. Widespread showers and thunderstorms are expected, especially from central Pennsylvania and northern NJ into the rest of New York State and New England, although a widespread severe weather outbreak is unlikely with marginal instability, as CAPE reaches 1000 J/kg, and unfavorable mid level lapse rates, under 6 C/km. Some storms may still be capable of producing locally heavy rain, however, with isolated strong storms capable of producing gusty winds/small hail especially north of NYC. Due to the cloud cover and storms, highs are expected to slightly cool down, reaching the upper 70s to low 80s inland and near the coast, and the low to mid 80s for the rest of the area. The cold front will slowly move through late overnight into Monday morning; overnight lows are again likely to struggle falling below the mid 60s inland to low 70s in NYC. With the trough lifting north, however, the air mass behind the front will not be much cooler than the one preceding it, with highs still expected to reach the low to mid 80s across most of the area on Monday with drier conditions and a risk of isolated storms in eastern parts of the area.

Since the heat wave ended a few days ago, the large scale pattern has changed, with ridging centered in the central Atlantic, preventing cold fronts from progressing far offshore while keeping the mean trough over the eastern US. The upper level low will gradually lift out of the region in the mid week, but with ridging failing to build back west into the region, keeping temperatures seasonable, peaking in the low to mid 80s for highs and the low to upper 60s for overnight lows. Continuing the current pattern theme, the next potential cold front appears to be towards late next week or next weekend.

Tropics: Tropical Storm Dorian Forms

Yesterday morning, tropical storm Dorian formed in the eastern Atlantic Ocean, this year’s first Cape Verde-type storm. Dorian is currently a 60 mph tropical storm with a minimum pressure of 999 millibars, and is moving to the WNW at 17 mph. Sea surface temperatures are currently relatively cool and are forecast to gradually increase, but with a gradual increase in wind shear likely as well. At this time, significant strengthening is unlikely through the medium range, with Dorian forecast to continue tracking WNW around the strong central Atlantic ridging, reaching the Bahamas region towards the middle of next week. Beyond that point, it’s too early to speculate what, if any, impact Dorian might have on the East Coast as there is a lot of uncertainty regarding both Dorian and the exact US pattern; more information will be posted on Dorian as details on the longer range become clearer.

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