Oct 7, 2013: Heavy Rain, Storms, Wind Today

Forecast Highlights:

northeastA strong cold front will move through the region today, producing widespread moderate to heavy rain and strong wind gusts up to 40-60 mph, in what will be the first widespread rain event in half a month. Cooler temperatures will return this week, with temperatures in the 60s to low 70s, but with a slow moving coastal low affecting the Mid Atlantic and possibly spreading into the area with rain for the late week into the weekend and next week.



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Sunday, October 6 Observations:

10.6.13The back door cold front on Saturday moved through the area, settling not far to the south which separated southern parts of New Jersey with more sunshine and warmer temperatures from the NYC area with cloudy skies, areas of fog, drizzle and chilly temperatures relative to the recent unseasonable warmth, despite remaining above average. The stalled frontal boundary was predicted to remain near NYC with warmer temperatures and more sunshine, but remained further south, with temperatures cooler than expected, peaking in the upper 60s to low 70s across the area. The highest temperature was 74 degrees in Teterboro, NJ, and the coolest high temperature was 63 degrees in Meriden, CT.



Today’s Outlook: Heavy Rain, Wind, Thunder

Storm Setup: As the latest radar image shows to the left, a strong cold front is currently located near western Pennsylvania, and is steadily moving to the east. Ahead of the cold front, widespread heavy rain and thunderstorms are falling across western parts of the region, and will continue to gradually shift east today. The strong upper level low that slowly drifted east in the Midwest is being picked up by a Canadian trough, and as a result is becoming negatively tilted while quickly moving through the region. Along with a tightening pressure gradient near the surface and a strong low level jet with 925 millibar winds up to 40-50 knots, windy conditions are expected across the region today, with sustained winds from the south of 15 to 30 mph and non-storm wind gusts up to 40-45 mph. These winds will bring a warmer air mass into the region, with temperatures reaching the mid to upper 70s from NYC and further west in the early afternoon; a sharp drop in temperatures is expected with the frontal passage, quickly falling from the 70s to upper 50s-low 60s within 1-2 hours of the onset of rain.

Widespread cloud cover will limit instability somewhat, with CAPE generally below 1000 J/kg, although given the strong low level jet and surface-500 millibar bulk shear, strong wind gusts will be the biggest risk with this afternoon’s storms, with some of the stronger winds aloft mixing down towards the surface with the heavier storms resulting in wind gusts locally up to 60 mph possible. With the strong low level shear, the possibility of an isolated tornado can’t be ruled out towards northwest NJ, NE PA and southeast NY. Heavy rain is also expected across the region as precipitable water values approach 2 inches with moisture feed from the Gulf of Mexico and the western Atlantic, despite the remnants of Karen staying well to the south, with totals locally over 1 inch expected. As the storms encounter a more stable air mass east of NYC and the strong shortwave lifts north into Canada, weakening is expected as the line shifts east of NYC into Long Island and eastern New England.

Forecast for NYC Area: Mostly cloudy skies are expected today with a strong south wind of 15-30 mph, gusting up to 35-45 mph at times, with highs rising into the low to mid 70s east of NYC and the mid to upper 70s from NYC and further west. Currently there is widespread isolated shower activity ahead of the front, and this is expected to continue with isolated storms possible in the area through the early afternoon. The onset of heavy rain and thunderstorms is expected around 2-4 PM in northern NJ and SE NY, 4 PM in NYC, and 5-7 PM in Long Island and southern CT. With the onset of storms, a sharp drop in temperatures into the upper 50s-low 60s is expected, along with strong wind gusts locally up to 50-60 mph with the heaviest storms. The heaviest rain is expected north and west of NYC, with the storms gradually weakening as they shift east of NYC. The rain will be quick moving, with most locations near and west of NYC dry by 7-8 PM and east of NYC by 10 PM-12 AM. Rain totals are expected to end up around 1/4 to 3/4 inch east of NYC, and 1/2 to 1 inch from NYC and north/west, with locally higher totals expected.

Storm updates will be posted a bit late today, starting around 5 PM.


Mid-Late Week And Beyond: Cooler; Coastal Low Possible

As the cold front moves to the east, a strong high pressure will build into the region with a chilly air mass, resulting in the coolest temperatures since the late September time frame with mostly sunny skies, widespread high temperatures in the mid to upper 60s, and lows in the upper 30s-low 40s inland, low-mid 50s in NYC, and mid 40s-low 50s elsewhere. No widespread warm up is expected, however; amplifying ridging is expected towards the central and eastern US ahead of a strong western US trough, but with the remnants of Karen remaining off the southeast coast along with energy that split from the current trough, the ridging will be displaced too far north, towards southeastern Canada, keeping a northeast flow over the region with temperatures generally remaining in the mid 60s to low 70s. This ridging will keep the southern energy trapped underneath the ridging, allowing it to slowly expand north towards the region and linger for at least a few days as the jet stream stays well to the north and west.

Moderate to heavy rain is expected over the Mid Atlantic south of PA/NJ from Wednesday into Friday, although there is quite a bit of uncertainty regarding how far north the rain shifts, with scenarios ranging from the rain staying entirely to the south, to rain briefly spreading in around Thursday and Friday before retreating south as a back door cold front approaches, to the rain shifting north and settling in from Thursday/Friday into the weekend and possibly early next week as well. The 7-day forecast will be updated later tonight, and based on current thinking is likely to reflect a chance of rain in the area for Thursday into Saturday, with increasing probabilities south of NYC. Otherwise, generally seasonable temperatures, or slightly cooler than average should the rain settle over the area, are currently likely to continue into early next week as well. Stay tuned for more information on the late week outlook over the next few days.

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