April 30, 2011: Chilly And Rainy Start To May

Note: The 5-Day Forecast will be updated on Sunday morning, as well as the Short Range Severe Weather section.
As an upper level low exited the region, today brought mostly to partly sunny skies to the area along with comfortable temperatures, reaching the lower to mid 60s inland, upper 60s to lower 70s in the immediate NYC area, and in the lower to mid 60s as well for Long Island and southern Connecticut.

Tomorrow will bring dry conditions to the area again, however cloud cover will increase late in the day as a cold front slowly approaches from the west, bringing a low risk of severe weather to parts of the South which will stay away from the hardest hit areas from Wednesday’s outbreak. This cold front, however, will bring an end to the brief break from the active pattern, as a wave from this front will become a cut off low by mid week sitting over the Northeast, which combined with a -NAO and a trough over the NE US, will likely bring a chilly and wet pattern into the region.

Tomorrow’s Outlook:

Mostly sunny skies are expected again tomorrow, but cloud cover will increase towards the evening. High temperatures will be in the upper 50s to lower 60s east of NYC, and in the mid to upper 60s from NYC and further west.

Monday – Tuesday: Cold Front Slowly Approaches

The cold front previously mentioned will slowly move east towards the region. On Monday, rain associated with the front will enter the western parts of the region, such as Pennsylvania and western NY, however as the cold front slows down, rain will have difficulty getting east of the Interstate 95 corridor, and as a result, mainly cloudy skies are expected across the area with the best chane for showers from NYC and further west. With the warm sector staying south of the area, no thunderstorms are expected, and with an onshore SSE wind expected as well, high temperatures will be in the mid to upper 50s east of NYC, and in the upper 50s to mid 60s from NYC and further west.

The front will significantly slow down on Monday night, and is expected to stall from NYC and further southwest on Tuesday. The NAM model is currently the westernmost and strongest outlier, keeping the low pressure well west of the area with the warm sector getting as far west as Kentucky. The NAM is likely going too strong with the storm, and its 18z late afternoon run did shift slightly east and weaker, therefore I went with the further east models, such as the GFS and GGEM. The GFS is showing signs of potential severe weather in the southern Mid Atlantic on Tuesday, and while no significant severe weather outbreak will take place, any severe weather potential will be watched.

Wednesday And Beyond: Cut Off Low Brings Rain, Clouds

As the cold front stalls near the area, a wave of low pressure will develop in the Southeast US and move northeast, just west of the coast. The heaviest rain will stay west of the area, though moderate rain is expected as well across the area with the heaviest rain west of NYC, and overnight temperatures will be steady in the 50s. On Wednesday, the storm is likely to stall near eastern New England, with rain expected to weaken in the area. Both the 18z GFS and 12z GGEM are currently the outliers out of today’s models, with the 18z GFS stalling the storm over the area and the 12z GGEM quickly moving the storm out of the region, however as there is uncertainty, the location where the storm stalls, if it does so, may vary over the next few days. Stay tuned for more information on this storm.
Regardless of whether the storm stalls or not, Thursday and Friday will be mostly dry, though the temperatures and cloud cover depends on the storm. Going by the likely scenario, should the storm stall, mostly cloudy skies will stay in place on both days, with temperatures slowly warming up, reaching the mid to potentially upper 60s at most on Friday. Should the storm keep moving away from the area, mostly clear skies will be in place for Thursday and Friday with temperatures rising into the mid 60s to lower 70s from NYC and further west.
By Saturday, uncertainty increases with the smaller details, however another disturbance is expected to move towards the region from the Great Lakes with the trough still stuck over the region, and there is another chance of rain over the weekend. Beyond next weekend, the smaller details cannot be nailed down yet, but with the -NAO and the trough in place, a much warmer pattern isn’t likely to quickly return. More information will be posted as details become clearer.

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