Oct 16, 2011: Heavy Rain On Wednesday

As a cold air mass remained stuck over southern Canada and the northern Northeast, average temperatures were observed across the area once again today. Temperatures today were slightly warmer than those of yesterday, reaching the mid 60s inland and the mid to upper 60s across the rest of the area, though Newark reached a peak high temperature of 70 degrees. Windy conditions were observed again today but the gusts were not as strong as yesterday’s, and wind gusts reached 20-30 mph across the area.

Monday and Tuesday will bring temperatures similar to those of today, but the break from the rainy conditions won’t last, as a strong low pressure moves up the East Coast on Wednesday, bringing heavy rain and thunderstorms into the area with the potential for 1-2 inches of rain and strong wind gusts. Behind the storm, a colder air mass will move in, bringing the coldest temperatures so far this fall across most of the area, and while this cold will not stick around over the region with the progressive pattern in place, it will be a start towards what will likely be a colder ending to October and early November.

Tomorrow’s Outlook:

A weak cold front will move through the area tonight, bringing scattered showers and mostly cloudy skies. As this front moves through, 850 mb temperatures will quickly warm up from 5 to 10 degrees celsius, and behind the front, 850 mb temperatures will cool back down to 4-5 degrees celsius again, which combined with partly to mostly cloudy skies and a WSW/SW wind, will bring high temperatures similar to those of today. High temperatures are expected to peak in the mid to potentially upper 60s inland, upper 60s in the immediate NYC area, and the mid to upper 60s in Long Island and southern Connecticut. Parts of NE NJ may reach the lower 70s again.

Tuesday – Wednesday: Heavy Rain, Strong Winds Expected

A weak low pressure over the southern Ohio Valley on Tuesday will move towards the region, approaching southern Ohio, which will push the warm front towards the area. As a result, south/SSW winds are expected with mostly cloudy skies. High temperatures will reach the mid to upper 60s across the area as a result.

By Tuesday night, however, steadier rain will approach the region. A tropical disturbance currently near the Yucatan Peninsula, which may potentially develop into a weak tropical cyclone, will move into Florida and up the coast, bringing a surge of tropical moisture. This low pressure will then interact with the primary low pressure near the eastern Ohio Valley while intensifying, causing the storm to move due north into eastern/central Pennsylvania on Wednesday. The storm is then expected to nearly stall for a short period of time near western NY before starting to move northeast and out of the region. This is a set up supporting widespread heavy rain, gusty winds, and some convection across the region.

Since last night’s update, the models have adjusted further west, and most of the models now follow a track similar to the one I drew in my scenario map last night, taking the storm through eastern Pennsylvania. As a result, there is increased confidence for Wednesday’s forecast. With the tropical moisture moving north, rain is expected to develop across the area between 4-6 AM, with moderate to heavy rain expected for Wednesday late morning into the afternoon. The area is then expected to briefly enter the warm sector of the storm, which combined with slightly negative lift index values and strong bulk shear, may result in convection for the evening hours, with thunderstorms producing heavy rain and gusty winds. The rain is expected become lighter by the early overnight hours, ending by at least 12-2 AM. By the time that the storm ends, at least 1 to 2 inches of rain are expected, with the potential for slightly higher amounts. More information on Wednesday’s storm, including a rain map, will be posted with tomorrow’s update.

Thursday – Saturday: Colder Temperatures Return, Windy Again

Behind Wednesday’s storm, a colder air mass will move in. When the storm will be over the region, a moderately strong but widespread cold air mass will drop into the central US, with sub-freezing 850 mb temperatures near the Gulf coast producing widespread low temperatures in the 30s and 40s. The cold air mass will weaken by the time that it reaches the region, but it will still produce at least slightly below average temperatures. Temperatures on Thursday will cool down into the upper 50s to mid 60s across the area, with overnight low temperatures reaching the lower 40s to lower 50s across the area.

The coldest temperatures are expected for Friday and Friday night. At this time, the models are showing cold temperatures with high temperatures in the upper 40s to mid 50s across the area, but the same temperatures were modeled for the previous cold spell but turned out to be too cold. Considering the models’ cold bias, I am expecting high temperatures to end up slightly below average, reaching the mid 50s inland and the mid to upper 50s across the rest of the area, with a few lower 60s possible in the immediate NYC area. Friday night will bring temperatures into the 30s in the interior parts of the area, and if there are mostly clear skies, frost may be possible across a more widespread parts of the area, with temperatures dropping below the 40 degree mark as far as the immediate north/west suburbs of NYC. As the trough weakens on Saturday, temperatures will slightly warm up, into the upper 50s to lower 60s across most of the area. Stay tuned for more information on this cold spell potential.

Longer Range: Colder Pattern To Gradually Develop

The current pattern we are seeing is a mostly transient one, meaning that the cold and warm air masses aren’t stuck over the region, and mostly affect the region around for short periods of time before moving out. Currently, we are seeing a Polar Vortex (PV) over southern Canada, which is keeping the cold air trapped in that region, but Wednesday’s storm will exit the region without stalling, which will allow the late week cold air mass to move out of the region without sticking around for a longer period of time. While the pattern does not support any strong warm surge returning into the region, it does not appear that a solid, persistent cold pattern will develop over the region yet. Even though a persistent cold pattern isn’t expected to develop, there are signs that a cold surge may affect the region during the end of October into early November, and along with the cold potential, the possibility is there for a storm to affect the region around October 27-29. More information on the longer range will be posted as this time frame approaches.

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