Aug 27, 2013: Warmth Ends On Monday

Forecast Highlights:

northeast4Following last night’s heavy rainfall, partly cloudy skies return through Thursday with temperatures in the low-mid 80s for highs, although isolated thunderstorm activity is still possible. These conditions are likely to continue through the weekend with temperatures slowly warming up again until Monday, when a cold front likely moves through the region with additional showers and thunderstorms, followed by cooler temperatures for the middle of next week.



Today – Weekend: Slightly Warmer Than Average, Isolated Storms

Behind yesterday’s thunderstorms, which produced heavy rain north of NYC, wind direction will switch to the north at 5-15 mph today, but with a warm air mass still in place with 850mb temperatures near 16C, high temperatures will remain slightly warmer than average, peaking in the low to mid 80s in eastern CT/Long Island and the mid to upper 80s for the rest of the area. While high temperatures in this current pattern are generally not far from average, the overnight lows have a greater positive departure from average, with lows ranging from the mid 60s inland to the low 70s in NYC. Conditions today will generally remain dry other than isolated evening thunderstorms, mostly north and west of NYC.

The previous forecast discussion noted that another low pressure is forecast to track into the region on Wednesday. Since then, however, the model guidance has changed towards a much weaker and further south low pressure than originally modeled, with the MCS on Tuesday night diving southeast into West Virginia and Virginia, keeping Pennsylvania-New Jersey and further north mostly dry on Wednesday with partly sunny skies. The NAM and GFS were the southernmost models but still depicted rain and storms over the area, while the ECM and CMC were way too far north, tracking the low pressure near northern NY state and southern Canada, keeping most of the storms to the north of NYC. The latest forecast for Wednesday is for partly cloudy skies and scattered afternoon thunderstorms, some which could be locally heavy, but with the heavy thunderstorms staying south and west of the area. High temperatures are forecast to reach the low to mid 80s with a light SE wind.

Behind Wednesday’s storms, mostly to partly sunny skies are expected for Thursday and Friday with drier conditions and highs generally in the low to mid 80s, possibly the upper 80s in northeast NJ on Thursday. There is some uncertainty with the weekend outlook as earlier models indicated a mostly sunny and dry weekend, although the latest ECM and GFS runs depict mainly cloudy skies and scattered showers and thunderstorms. At this time, I am siding towards partly cloudy skies and mostly dry conditions on Saturday with highs in the low to mid 80s, with similar temperatures on Sunday but with increased cloud cover and isolated showers/thunderstorms as a warm front approaches.


Next Week: Stormy Start, Cooler Midweek

Up until this point, the uncertainty in the pattern has been regarding whether the central US ridge will shift west or east in the long range, with an east shift resulting in a more significant heat surge and a west shift resulting in a stronger and longer lasting trough. As this time frame is entering the more reliable 7-day range, the model guidance is narrowing down on a consensus for the ridge to shift west, which results in a brief warm air mass surging into the region on Monday, followed by a frontal passage with showers and thunderstorms and cooler than average temperatures returning for the middle of next week.

At this time, the cold front is likely to move through the area around Monday, although the timing is subject to some changes. The model guidance varies with the intensity of the incoming trough and thus the strength of the cold front, with the ECM and GFS depicting a stronger cold front and the CMC showing a weaker cold front. Some of the latest runs show a strong trough coming into the region, although some of these runs are likely overdoing the intensity of the trough, such as yesterday’s 12z ECMWF which was most likely too exaggerated with much cooler than average temperatures and 850mb temperatures falling to near zero as south as the Hudson Valley, which typically does not occur until late September-mid October. At this time, a frontal passage is likely on Monday with showers/thunderstorms, and least a temporary cool down is likely for the middle of next week with temperatures cooling down to near-below average, although it is too far out to narrow down the specific details such as the exact temperatures and how much rain falls on Monday. More information will be posted on next week’s outlook as details become clearer.

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Sunday, August 25 Observations:

8.25.13The strong high pressure that entered the region on Saturday continued to sink southeast throughout the day, with mostly sunny skies continuing on Sunday. Temperatures were slightly warmer than those of Saturday, ending up generally close to average with highs reaching the upper 70s to low 80s across the area with temperatures near the mid 80s in northeast NJ. The highest temperature was 84 degrees in Teterboro and Newark, NJ, and the coolest high temperature was 78 degrees in Sussex, NJ and New London, CT.

Monday, August 26 Observations:

8.26.13As a northwest flow set up aloft, several vort maxes dived southeast along the mid level flow into the region, resulting in increased cloud cover and several rounds of thunderstorms entering the region. A decaying MCS produced scattered showers in parts of the area in the late morning, with otherwise partly to mostly cloudy skies until the evening hours, when a weakening MCS moved into the area producing rain, locally heavy, with some thunder observed, although the storms were not severe due to a lack of instability. The highest rain totals fell in SE NY and southern CT, with at least 1/2 to 1 inch, with totals in northern NJ, NYC and most of Long Island near to under 1/4 inch. High temperatures were again in the upper 70s to mid 80s range across the area, with the highest temperature 86 degrees in Newark, NJ, and the coolest high temperature 75 degrees in Yorktown Heights, NY.


4 thoughts on “Aug 27, 2013: Warmth Ends On Monday

  1. Anonymous Reply

    Any pop-up thunderstorms expected for later today on NYC and Long Island?

    • NYC Area Weather Post authorReply

      A few pop up storms are possible in Long Island later this evening, although storm coverage today, if any, should remain isolated at most.

  2. Anonymous Reply

    Do you know at what time are the first thunderstorms expected to pop up on Long Island?

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