Aug 15, 2013: Gradual Warming Trend Begins

Forecast Highlights:

8.15_6zA strong cool air mass for this time of the year remains in place over the region, with temperatures remaining cooler than average across the region. A gradual warming trend will continue slowly through the weekend with highs returning back into the low 80s, which will become more noticeable next week as a warmer and more humid air mass returns into the region with 90s likely to make a comeback for some after a month-long absence.




[notice]Starting on Friday, August 16, the blog updating schedule will be returned to the morning hours, and observations will be posted for the previous day; today’s observations will be posted with tomorrow’s update.[/notice]


Tonight – Weekend: Slowly Warming Up

A cold air mass gradually dropped southeast through Canada, and was advected into the region with a westerly flow aloft behind a strong shortwave trough on Tuesday night. The air mass entered the region in a moderated form, with temperatures aloft at the 850 millibar level originally as low as 0-2 degrees Celsius in Canada, warming up to 6-8C as the air mass entered the region, although this is still cooler than average for August, which resulted in colder than average temperatures in the surface as well. With a high pressure overhead, clear skies and relatively light winds were observed last night, allowing for temperatures to quickly fall with unseasonably cool overnight lows in the 50s for most and the 40s inland. Central Park had a low of 59 degrees, which is 9 degrees below average and 5 degrees warmer than the record low of 54 set in 1964. Temperatures fell as low as 46 degrees in Sussex, NJ.

Winds aloft will switch towards the southwest as a weak trough digs into the central US, slowly bringing a slightly warmer air mass into the region, which along with ridging in the Atlantic Ocean slowly expanding west into the region will result in the cool air mass weakening, although this will be a gradual process with a slow warming trend over the next few days. After high temperatures reached the mid to upper 70s across the area today, mostly clear skies are expected again tonight with lows falling into the upper 40s inland, low to mid 50s in the north/west suburbs, southern CT and eastern-central Long Island, and the upper 50s to low 60s in NYC and the immediate coast.

The high pressure will remain over the region through Friday and the weekend, keeping mostly sunny skies for Friday and Saturday with highs slowly warming into the upper 70s to low 80s on Friday and the low to mid 80s on Saturday. A frontal boundary will slowly crawl to the north in the Mid Atlantic states, but will remain suppressed south of the area due to the high pressure; some increase in cloud cover, however, is expected, with partly to mostly cloudy skies and highs in the upper 70s to low 80s, with cooler temperatures in the mid 70s towards eastern and coastal Long Island where a breezy SE wind is expected.


Next Week: Above Average Temperatures Return

The slow warming trend will continue on Monday and Tuesday, with highs likely back near average in the mid 80s in the immediate NYC area. An increase in cloud cover is expected as the central US trough lifts north and moves through the region, producing scattered showers and thunderstorms, but with no widespread rain expected at this time. Afterwards, a warmer and more humid air mass will return into the region as ridging in the western US flattens out, with a west flow carrying the warmer air mass east into the central and eastern US by mid-late next week, bringing 90s back into parts of the region for the first time in a month.

The core of the hot temperatures is expected to remain west of the region, in the central US, although temperatures in the area are likely to warm back up into the mid 80s to low 90s range. Meanwhile, a SW flow at the surface will bring a more humid air mass into the region as well, with dew points climbing back into the 60s, which is likely to bring overnight lows into the upper 60s in NYC. This warmer time frame is likely to last through late next week but with increasing uncertainty afterwards, as some models indicate the possibility of a back door cold front to bring down temperatures especially in New England. The large scale pattern, however, is likely to end up warmer than the first half of August, with these warmer temperatures likely persisting through the rest of August and possibly into the beginning of September. Stay tuned for more information on the longer range.

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