Oct 18, 2013: Colder Weather Returns Next Week

Outlook was slightly revised on Saturday morning, 10/19.

Forecast Highlights:

gfs_namer_144_850_temp_mslp_precipA cold front moved through the area last night, but produced little rain as the much drier than average pattern continues. Temperatures have generally been much warmer than average in the first half of the month; the current warmer than average pattern will slowly moderate until a stronger cold front moves through on Tuesday, bringing the most significant cool down of the fall so far across the region by the late week, with the first widespread frost of the fall likely by this time period.

<< October 16 | October 17 | October 18 >>

Thursday, October 17 Observations:

10.17.13A cold front slowly approached the area with a developing wave of low pressure tracking into New York and Pennsylvania. A few isolated showers developed, but the heavy rain again stayed north and west of the area, continuing this fall’s well below average precipitation. Temperatures slightly warmed up ahead of the cold front, peaking in the low to mid 70s across the area in general. The highest temperature was 75 degrees in multiple locations, and the coolest high temperature was 69 degrees in Montauk, NY and New London, CT.

Observations Note: Due to recent unreliable observations, Teterboro, NJ (KTEB) has been temporarily removed from the stations used for daily observations.



This Weekend – Tuesday – Temperatures Stay Above Average

Pattern Analysis: Over the last few days, a significant pattern change took place over the northern Pacific ocean and North America in response to super typhoon Wipha, which affected Japan and is currently a strong extratropical cyclone approaching Alaska. Anomalous strong ridging developed over the northeastern Pacific Ocean, which is leading to a slower and more amplified pattern, as a strong trough dived into the central US, while blocking continues near southwest Greenland. Despite this pattern setup already in place, however, the colder temperatures have not reached the area yet, and the stronger cold air mass won’t reach the area until the middle of next week. As the trough axis is focused over the central US region, along with a strong southwest flow over the region in the mid and upper levels, the strong shortwave trough that moved through last night quickly tracked northeast into Canada, with a continued southwest flow.

Another strong shortwave will move through on Saturday night producing isolated showers, again mostly northwest of the area, but with a colder air mass already present over the Great Lakes region, having gradually entered behind last night’s front, this cold front will be able to bring slightly colder temperatures for Sunday, falling closer to average. Despite 850mb temperatures near 0C, however, temperatures will fail to significantly cool down with a persistent southwest flow. This cool air mass will not quite mark the onset of the more sustained colder temperatures, however, as a stronger upper level low will dig from Canada into the Midwest and the Great Lakes region, bringing a stronger but not anomalously cold air mass with 850mb temperatures near -5 to -10C. The entering trough will lead to rising heights aloft over the region, with a southwest flow continuing and temperatures warming up again into the mid to upper 60s range ahead of the trough.

Forecast for NYC Area: Mostly sunny skies are expected to start the day on Saturday with highs in the mid 60s, but with increasing cloud cover ahead of the next cold front. Isolated showers are expected on Saturday night, generally below 0.10 inch but with locations inland and towards eastern Long Island possibly ending up with higher totals, locally up to 1/4 inch. Due to the clouds and rain, overnight lows will stay in the 50s. The cooler air mass will reach the area on Sunday, but will fail to bring any remarkable cool down as a southwest flow continues; highs will reach the upper 50s-low 60s inland and low-mid 60s elsewhere on Sunday with mostly sunny skies and a breezy west wind at 10-20 mph. Partly sunny skies are expected for Monday and Tuesday with highs warming into the mid to upper 60s for both days, possibly approaching 70 degrees near NYC on Tuesday.


Wednesday – Next Week: Cool Down Arrives

As previously mentioned, a stronger trough will enter the Midwest in the early week, forcing warmer temperatures to return into the region. This trough will then move east, with the surface cold front moving through around Tuesday night. While there is some uncertainty regarding exact rain totals, this is likely to be a mostly dry frontal passage, continuing the trend for a lack of significant rainfall events this fall. Behind this front, a stronger cold air mass will be able to enter the region, marking the actual onset of more sustained below average temperatures. This marks a typical example of the model guidance bias to speed up pattern changes, as last week’s models generally agreed on the sustained colder temperatures starting late this week. The colder temperatures will be initially slow to spread into the area, with highs on Wednesday expected to reach the mid to upper 50s with partly sunny skies; average high temperatures are generally in the low 60s.

Colder temperatures are possible on Thursday as the trough amplifies and shifts east towards the region with more widespread cloud cover as a wave of low pressure develops offshore, in which case temperatures would generally reach the mid 50s. There have been recurring signs for a potentially stronger low pressure closer to the coast, which if happens would produce widespread rain and colder high temperatures; due to low confidence, a chance of rain will be introduced in today’s 7-day outlook, although this possibility will be watched over the next few days, and it is possible rain probability may need to be raised. As a high pressure slowly builds in towards Friday and the weekend, temperatures will continue to gradually cool down, with more sunshine, widespread lows in the 30s, and high temperatures in the low to mid 50s likely, subject to slight changes depending on the intensity of the cold air mass as it reaches the area. By next weekend, the possibility is there for the first widespread frost of the season affecting the area for locations that have not seen frost in September.

More information on the longer range outlook beyond next weekend will be posted with tonight’s 2-week pattern outlook, although indications are that this trough will not remain persistent over the area, with a period of moderation in temperatures possible again ahead of another potential trough by the end of the month. The pattern outlook will also address the recent dry pattern in more details, as parts of the area have been classified by the Drought Monitor as D0, or abnormally dry, conditions, with precipitation running several inches below average this fall.

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