Oct 6, 2012: Frost Possible Next Weekend

Forecast Highlights:

– Showers on Sunday afternoon through night hours
– Cool down in early week followed by mid-week warm up, showers
– Stronger cold likely next weekend; frost possible
– Long Range Pattern Outlook #1 Issued Tonight

 

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Blog Announcement:

Starting with tonight’s update, a discussion on the long range pattern outlook will be posted once or twice a week, typically on weekends, covering the current pattern, the expected pattern going at least 1-2 weeks out, and occasionally including some thoughts on the longer range, such as the upcoming winter.

As these pattern outlooks are issued weekly, minor revisions may occasionally be made.

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Tonight – Monday: Showers, Then Cold

Cooler temperatures returned to the area behind a cold front earlier in the day that pushed out the warm air mass, with temperatures in Sussex falling nearly 9 degrees in an hour this afternoon. Temperatures will continue to slowly drop tonight in the area, reaching the low 40s inland and the mid to upper 40s for the rest of the area with slightly warmer temperatures in NYC, in the low 50s.

A weak low pressure will develop and affect the region with light rain and chilly temperatures on Sunday. Highs will peak towards noon in the mid 50s inland, mid to upper 50s in the immediate NYC area, and the upper 50s to low 60s in Long Island and southern CT. Showers will develop in the afternoon hours, mainly after 12-4 PM, with dropping temperatures. The showers should last through the mid overnight hours, towards at least 12-2 AM, with clearing skies afterwards and lows dropping into the mid to upper 30s inland and the low to mid 40s for the rest of the area, except for Long Island, NYC and parts of SE CT in the mid to upper 40s. At least 1/4 to 1/2 inch of rain is expected, slightly lower for some areas especially further north/west. Partly sunny skies are expected on Monday with highs in the upper 50s to low 60s across the area.

Tuesday – Saturday: Warmer, Some Showers, Then Cold

Temperatures on Monday night will be slightly warmer than those of Sunday night, with partly sunny skies likely again on Tuesday. The NAM develops a low pressure offshore with widespread clouds and showers on Tuesday into Wednesday, although it is an outlier solution compared to the rest of the model guidance; I slightly increased cloud cover and temperatures with tonight’s 5-Day Forecast, but not to the extent of the NAM, especially given its typically lower performance approaching its hour 84 range. Partly cloudy skies are likely again on Tuesday with highs generally in the upper 50s to low 60s inland and the low to possibly mid 60s across the rest of the area. More cloud cover is likely especially for eastern areas, with a risk of isolated showers.

A cold front will move through the area on Wednesday night as a strong shortwave moves through the region. Some showers are expected with the cold front, especially north and west of NYC, with highs reaching the mid to upper 60s across most of the area. Temperatures overnight behind the cold front will drop into the 40s for most of the area with upper 30s to low 40s inland and low 50s in NYC and parts of Long Island. A cooler air mass will briefly move in but will once again lift out quickly ahead of another shortwave approaching the region, with Thursday’s temperatures reaching the upper 50s to low 60s across the area. The next shortwave will move through on Friday, although the frontal passage is expected to be dry with partly cloudy skies on Friday and highs similar to those of Thursday, perhaps slightly warmer.

A stronger cold air mass will enter the region behind Friday’s shortwave, with the coldest temperatures of the fall so far expected. With a high pressure moving overhead, clear skies, and 850mb temperatures near or slightly below 0 degrees Celsius, widespread lows in the 30s are likely away from NYC, with low 30s possible for interior parts of the area. The exact temperature outlook may be subject to slight changes although there is an increasing probability that the first widespread frost event of the fall may take place on Saturday morning. Highs for Saturday are expected to be in the 50s.


Pattern Outlook Archive

<< No previous outlook
Pattern Outlook #1 – October 6, 2012
>> Pattern Outlook #2 – October 16, 2012


Long Range Pattern Outlook

Slightly revised 10/7/12

Tonight’s long range pattern outlook will focus on the collapse of the strong block off the western North American coast and the implications it will have on the US pattern in the medium range.

To the left, I posted the GEFS initialized 500mb pattern from the Pennsylvania State University e-Wall (link to GEFS page). The highlight of this week’s pattern is the strong blocking feature off the western North American coast, with 500mb heights near 588-591dm, which is much higher than average as indicated by the dark red under the block. With the block barely moving, a persistent trough is present over Canada, dropping into the central US, with colder than average temperatures in the central and eastern US.

By the late week, changes will be taking place in the pattern. The block will collapse as lower heights return to Alaska and a less amplified pattern develops in North America, accompanied by a spike in the EPO from strongly negative to moderately positive. With the more zonal Canadian flow, the trough over the region will lift out, shifting into eastern Canada, with a ridge building in. Meanwhile, with the collapsing block, the upper level low trapped to its south will gradually move east into the western US, then through the rest of the country, approaching the region. While at this time, it does not appear that there will be a persistent polar vortex over Alaska with a very progressive pattern across North America as we have seen last year, this change in the pattern is still less favorable for persistent chilly conditions in the eastern half of the US.

[slightly revised 10/9] As a result of the changes, temperatures will warm up in the region on Sunday into early next week, returning into the 60s. With the low pressure tracking through the central US towards the region, the area is expected to be near or within the warm sector of this low pressure, with a rain event expected between late Sunday into Monday, perhaps Tuesday if the low ends up slower. The latest model guidance also suggests this low may result in a potential for severe weather in the central US. While the pattern will not be a colder than average one one, it does not have the makings of a significantly warmer pattern either at least for the first half of next week, with the early week low pressure which is expected to be followed by at least slightly cooler temperatures for the middle of next week, keeping the region under near to above average temperatures while delaying any significant warm up slightly. Behind the early week storm and cool air, however, there may be a higher probability for a period of warmer temperatures going into the beginning of the last third of the month. Going further into the long range, the EPO is modeled to trend towards neutral after peaking next week; a lot can still change from now until then, although the possibility may be there for a cooler ending to October. At this time, October is still likely to end up with near average temperatures, slightly on the positive side, although the full extent of the slightly warmer pattern and the late October outlook are still uncertain, and leave a possibility, although not a high one at this time, that October may end up cooler than average. More will be posted on that with the next long range update.

The next long range pattern discussion will be posted next weekend, with an update on the pattern outlook for next week and some thoughts going forward into November and the winter.

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