Oct 21, 2013: Cooling Down This Week

Forecast Highlights:

Warmer than average temgfs_namer_084_500_vort_htperatures continue again today and tomorrow before a dry cold front moves through on Tuesday, with a gradual cool down beginning around then, with scattered showers mainly east of NYC on Wednesday followed by the peak of the cooler temperatures on Friday and Saturday with temperatures a few degrees below average. A brief moderation in temperatures is expected by the weekend, but with uncertainty regarding whether below average temperatures return afterwards.

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Sunday, October 20 Observations:

10.20.13As another frontal system exited the region, yet again keeping most of the rain east and west of the area, temperatures slightly cooled down as a weak cool air mass struggled to enter the region, but was quickly removed. Partly sunny skies were observed with highs in the low to mid 60s across the area. The highest temperature was 65 degrees in Newark, NJ, and the coolest high temperature was 60 degrees in Danbury, CT and Yorktown Heights, NY.




Today – Thursday: Slowly Cooling Down

Today is expected to be the warmest day of the week; following strong radiational cooling last night, with Sussex, NJ falling to 32 degrees and Westhampton Beach in Long Island to 30 degrees, more sunshine will return today with a southwest wind and a warmer air mass advecting into the region, bringing widespread highs in the mid 60s again. This time, however, the warmer air mass won’t settle over the region, as a cold front will move through on Tuesday night, producing little to rain but with temperatures cooling down. Highs on Tuesday are expected to reach the mid-upper 50s inland and low-mid 60s further east, with lows overnight in the mid to upper 30s inland.

A shortwave trough will move through the region on Wednesday, producing areas of light rain mainly east of NYC in the morning hours, with otherwise mostly cloudy skies and highs reaching the mid 50s for most of the area. Rain totals are generally expected to stay under 1/4 inch, perhaps locally up to 1/2 inch in Long Island; this would make it the second most significant rain event of this month. Skies will clear overnight with temperatures cooling down into the 30s away from NYC and the coast. Despite the shortwave trough moving through, however, the trough will struggle to fully expand into the region throughout this time frame, and 850mb temperatures look to cool down less than previously modeled, failing to reach -4C except for a brief 24-hour window on Friday night with -4 to -5C 850mb temps, which is not unusual for this time of the year. With the slower entrance of the trough, the forecast temperatures for Thursday have been adjusted upwards, with highs in the low 50s inland and the mid to locally upper 50s for the rest of the area, which is several degrees below average but also several degrees warmer than what the model guidance showed over the last few days.


Friday – Next Week: Peak Of Cool Down, Then Moderating Temps

The peak of the cooler temperatures is expected on Friday and Friday night, during a brief window when 850mb temperatures fall near or below -4C along with the high pressure approaching the region. Highs on Friday are expected to reach the upper 40s to low 50s inland and low to mid 50s for the rest of the area, and overnight lows are likely to fall into the upper 20s inland, low to mid 30s in the north/west suburbs, southern CT and interior Long Island, and the upper 30s to low 40s near NYC and the immediate coast. The first frost of the fall outside of interior areas and eastern Long Island is possible in this time frame.

A weak, moisture starved low pressure will track through the region on Saturday night through Sunday, bringing a slightly warmer air mass into the area with highs likely returning into the 55-60 degree range. Light rain showers are mostly expected to stay north of the area; I included a slight risk of showers at this time, although currently it appears little to no rain should fall in the area, and any rain that does fall should likely stay north of NYC.

Temperatures will slightly cool down on Monday behind this system, but with uncertainty regarding the next part of the setup. As the pattern outlook from Saturday mentioned, additional amplification of the northeast Pacific ridging is expected next weekend, with a colder air mass being pulled south from northern latitudes towards the middle of next week. The uncertainty is where the air mass ends up, and the latest trends have been away from the East Coast and more towards a cutoff low in the western US. If the air mass reaches the region, temperatures would cool down, perhaps significantly, by the end of the month into the start of November. This is still over a week away and subject to change over the next few days, but should the former scenario verify, temperatures would rebound to above average levels with the coldest temperatures staying well to the west. Stay tuned for more information on the longer range.

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