Oct 22, 2013: Few Showers, Then Colder Temps

Forecast Highlights:

northeastA cold front is moving through the area today, bringing with it a cooler air mass that slowly enters the region, with the last day of widespread 60s today until next week. Temperatures will cool down into the 50s for highs and 30s for lows, perhaps even the 20s for interior areas. The coldest temperatures will be relatively short lasting, however, with another warm up early-mid next week ahead of a possible late week cool down, and rain mostly stays out of the forecast until the very end of the month or early November.


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Monday, October 21 Observations:

10.21.13After the weak trough exited on Sunday, and cool morning temperatures due to radiational cooling, falling as low as 32 in Sussex, NJ and 30 in Westhampton Beach, NY, a warmer air mass returned into the region with a southwest flow ahead of the next trough entering the Midwest. As a result, temperatures warmed up, staying warmer than average with sunshine and highs in the mid to upper 60s. The highest temperature was 69 degrees in Newark, NJ, and the coolest high temperature was 64 degrees in Danbury, CT and New London, CT.



Today – Wednesday: Cooling Down, Scattered Showers Possible

As the latest radar image shows, posted above, a line of showers is currently over Pennsylvania and New York states, moving east. This line, however, is weakening and will continue to dry out before reaching the area, as has become typical under this fall’s pattern, with partly cloudy skies and dry conditions today. A shortwave trough will move through the area on Wednesday with a developing low pressure offshore; some of the model guidance still shows a moderate rain event with up to or over 1/2 inch, although given the progressive flow limiting the duration and intensity of the storm, as well as recent trends, the 7-day forecast remains unchanged with scattered showers, mainly east of NYC before Wednesday afternoon, with totals under 1/4 inch, generally staying below 0.1 inch. This would still be the second most significant rain event of the month; if no significant rain event occurs at the end of the month, this month will end up as one of, if not the driest Octobers on record. High temperatures are generally expected to reach the low to mid 50s east of NYC and mid 50s west of NYC, making it the coldest day since late May with temperatures several degrees below average.


Thursday – Saturday: Peak Of Cool Down, Frost Likely

As the developing coastal low stays east, a colder air mass will enter the region; while the core will stay to the west, with 850mb temperatures mostly in the -2C to -4C range, it will still be enough to bring the coolest temperatures so far this fall, with the first widespread frost possible for locations that have not yet had frost. Partly sunny skies are expected on Thursday with a breezy west wind and highs in the low 50s inland and the mid 50s for the rest of the area. The coolest temperatures are expected on Friday and Saturday, with temperatures on Thursday and Friday nights falling into the upper 20s to low 30s for lows inland, low to mid 30s in the north/west suburbs of NYC, southern CT and interior Long Island, upper 30s in NYC, and upper 30s-low 40s in the immediate coast. The coolest lows are especially expected on Friday night, with widespread temperatures in the low 30s likely in the suburbs of NYC and southern CT. Friday will be the coolest day with highs in the upper 40s to low 50s inland and the low-mid 50s elsewhere, with a slight moderation on Saturday into the low 50s inland and mid 50s elsewhere.


Sunday – Next Week: Warming Up; Possible Late Week Rain And/Or Cool Down

A weak low pressure will move through New England on Saturday night, producing light rain and snow showers staying well to the north. A few isolated showers may be possible north of NYC, but with the area otherwise staying dry. This will bring warmer temperatures on Sunday, reaching the mid 50s inland and upper 50s to possibly low 60s for the rest of the area. Chilly temperatures are expected overnight again as a cooler air mass briefly enters the region behind the low pressure, with highs on Monday similar to those of Sunday.

With typhoons Francisco and Lakima in the western Pacific recurving by the weekend, additional amplification of the northeast Pacific ridging is expected, with the possibility of 500 millibar heights reaching 594 decameters, which is anomalous for this time of the year. As a result of this amplification, a strong trough will dig south across Canada, with colder temperatures than the current trough as there will be a more widespread cold air supply available than there was last week. Given the orientation of the ridging, an exiting upper level low south of the ridging, and a strong polar vortex entering Canada, however, this cold air mass appears to be targeted more towards the central and western US as opposed to the east coast, which would bring the coldest temperatures further west, where a low pressure would organize and gradually track north and east, resulting in ridging amplifying to its east and a warmer air mass advecting into the region with highs returning into the 60s, before a late week potential cold front brings the colder air mass in but in a moderated form. There is still uncertainty towards this time frame, however, and the possibility is still there that the trough focuses on the eastern half of the US, in which case much colder temperatures would be observed for a period of several days with lows in the 20s and highs in the 40s.

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