[notice]The 7-day forecast has been updated today. Updates to this page are currently scheduled to continue on a daily basis.[/notice]
The trough and cool air mass that was present during the late week modified as a southwest flow returned, with highs through Monday returning to near average. A brief cool down is expected on Tuesday, but with a mild, windy and wet ending to the week as the first significant rain event in nearly a month affects the region on Friday, ahead of another transient cool down for next weekend.
Tonight – Tuesday: Near-Below Average Temps Continue
The current synoptic pattern consists of a departing trough over the northeastern US, while a strong upper level low is digging south over the West Coast in response to anomalous ridging in the northeast Pacific, caused in part by the recurving of the remnants of typhoons Lekima and Francisco. A strong surface high pressure is expanding south, bringing much colder temperatures aloft with it, but instead of surging south into the US, it will flatten instead with a relatively zonal flow aloft over the eastern half of the US, and the persistent upper level low stuck in the west where a low pressure is expected to organize, producing rain and severe weather in the central US region. The high pressure will shift east into the northeast US, and will be located over the area on Tuesday, providing the region with mostly sunny skies through Tuesday. Despite the cold air mass not digging nearly as far south nor as widespread as the recent trough, temperatures will be similar to those of late last week as the high pressure stays to the north, with the wind direction mostly out of the north/NW as opposed to the west/SW. More widespread cold temperatures will stay north of the area, with widespread lows in the 20s expected in the Northeast.
In between the departing trough and the approaching cold air mass, the southwest flow will continue on Monday with temperatures warming up again, with partly sunny skies, a SW wind becoming west at 5-12 mph, and highs in the mid-upper 50s inland and the upper 50s-low 60s elsewhere. With the high pressure moving into the Northeast overnight, winds will decrease and shift to the north, with clearing skies and lows falling into the upper 20s to low 30s in interior SE NY and Connecticut, low to mid 30s in NW NJ, coastal CT and interior Long Island, mid to upper 30s in the north/west suburbs of NYC, and upper 30s to low 40s in NYC and the coast. Mostly sunny skies are expected on Tuesday with light winds and highs in the low to mid 50s, with increasing cloud cover overnight as temperatures struggle to fall below the low 40s.
Wednesday – Friday: Cold Front Produces Rain, Wind, Warmth
As the previous forecast discussion mentioned, the main uncertainty in the late week outlook was regarding the setup of the upper level low, whether it will quickly move out of the West with a frontal boundary stalled nearby, keeping temperatures near average with widespread rain on 10/31-11/1, or if it would take more time to exit, in which case a more significant warm up would occur with rain sometime in the first few days of November. The original ECM outlooks were likely too slow with the ULL, as the previous update noted, although the rest of the model guidance has since trended to support the slower scenario, where the early week high pressure is able to shift east of the region, allowing for a widespread southwesterly flow and ridging aloft to build into the region, resulting in a brief yet significant warm up in the late week ahead of the cold front moving through on Friday, 11/1, producing widespread rain as the low pressure stays well to the north and west.
As the previous forecast discussion sided with this scenario, there are not many changes with today’s outlook regarding the overall setup; the main uncertainty is now focused on the more specific details, such as the timing and amount of rain, and how warm temperatures end up. A weak shortwave is expected to move through on Wednesday, producing mostly cloudy skies and isolated showers with temperatures slightly warmer than those of Tuesday. The frontal boundary will slide to the south on Wednesday night with temperatures in the 30s in the interior again, and will retreat north on Thursday in time for Halloween with mostly cloudy skies and scattered showers expected. Temperatures will depend on the timing of the warm front; the GFS is currently more progressive, with highs in the mid 60s, while the ECM is slower with highs in the mid 50s-low 60s. Given recent trends and previous outcomes with similar setups, I am siding towards the slower passage of the warm front with temperatures in the mid 50s inland and upper 50s to low 60s for the rest of the area, subject to minor revisions. Rainfall on Thursday is likely to be generally light, with under 1/4 inch expected.
The low pressure will intensify overnight as the mid level shortwave trough amplifies, with a strengthening low level jet expected overnight as 925mb winds rise to near 50-60 knots, advecting a warmer air mass in the lower levels while leading to increasingly windy conditions. Temperatures will fail to drop much overnight, if at all, holding steady initially in the upper 50s to low 60s before gradually rising. At this time, the frontal passage is likely on Friday afternoon, but with the timing subject to some changes. Given the current forecast scenario, rain and wind will develop on Thursday night, with moderate rain expected to peak on Friday morning into the early afternoon, along with a strong south wind along with the strong low level jet, likely around 15-30 mph sustained with gusts up to/over 40 mph likely, especially in Long Island and coastal CT. Temperatures will be warmer as well, peaking in the mid to upper 60s across most of the area. Drier conditions are then likely towards the evening hours as the cold front moves to the east. The exact timing is still uncertain, however, and the peak of the wind and rain is subject to some revisions. Regarding rain totals, overall thinking at this time is generally 1/4 to 1/2 inch for most of the area, locally lower south/east of NYC and locally higher north/west of NYC, with the highest totals north and west of the area. While these totals will be the most significant in nearly a month, since October 7, they will not be enough to significantly reduce the below average precipitation anomalies, about 4-8 inches below average over the last 60 days (2 months), and should most of the rain fall on Friday as currently expected, October will be on track to end up in the top 5 driest Octobers and top 10 driest months on record in Central Park.
Next Weekend – Week: Another Transient Cool Down
With the anomalous northeast Pacific ridging having broken down by this time period, a generally progressive flow is expected by the medium range, with another trough entering the region by next weekend. The cold air mass will be slow to enter initially, however, with temperatures near/above 60 degrees possible again on Saturday as a wave of low pressure develops off the coast. Cooler temperatures are expected to return for Sunday and Monday, similar to those that were recently observed late this week. Given the progressive flow, however, another trough is likely to enter the NW US by early next week, with temperatures expected to warm up for the early-mid week over the region until the next cold front approaches late next week; while temperatures may not be as warm as those as late this week, low 60s are not out of the question.
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Saturday, October 26 Observations:
The trough began to slightly weaken on Saturday as another cold front approached, which resulted in slightly warmer temperatures across the area as a west-SW wind continued. High temperature reached the low to mid 50s inland and the mid to upper 50s for the rest of the area. The highest temperature was 57 degrees in Newark, NJ, and the coolest high temperature was 53 degrees in multiple locations.