Oct 25, 2011: Cold Rain For Thursday

Behind last night’s weak cold front, which brought isolated showers across the region, today brought mostly sunny skies across the area with high temperatures reaching the lower 60s inland and the lower to mid 60s across the rest of the area. Cold temperatures are expected again tonight, dropping into the upper 30s in the interior parts of the area with 40s across the rest of the area.

A weak wave of low pressure moving into the southern Great Lakes will bring increased cloud cover for tomorrow with the risk of isolated showers. Cold air will slowly drop into the Northeast, and combined with a wave of low pressure moving into the region on Thursday, a chilly moderate rain is expected across the area with high temperatures struggling to reach the lower 50s, and parts of New England, New York and Pennsylvania are even expected to see accumulating snow with several inches possible. A strong high pressure will build in behind the storm to bring colder temperatures and the first freeze potential for the area, but even though the potential for a storm this weekend has become less clear, the possibility is still there.

Tomorrow’s Outlook:

With the wave of low pressure previously mentioned moving towards the region, increased cloud cover is expected with SW winds expected. Combined with mostly cloudy skies and 850 mb temperatures near 9-11 degrees celsius, high temperatures will reach the lower 60s inland and the lower to mid 60s across the rest of the area. In the warmer case scenario, places near and southwest of NYC may pass the 65 degree mark.

Thursday – Friday: Rain, Then Cold

The low pressure near the Great Lakes will fail to move into the region, and instead, a stronger wave of low pressure will develop near the southern Ohio Valley and move towards New Jersey on Thursday. This wave of low pressure will have a colder air mass to its north, as a dropping trough behind this storm will bring below freezing 850 mb temperatures in the Northeast while the precipitation falls. This set up is supportive of an early season snow event in the Northeast and a chilly rain for the NYC area. Rain is expected to develop in the area late tomorrow night, with a steady light to moderate rain falling throughout the day on Thursday. High temperatures will be unusually chilly, reaching the mid to upper 40s inland, upper 40s to lower 50s in the immediate NYC area, and the lower to mid 50s east of NYC. The rain will continue until at least 12-2 AM before ending, with a storm total between 1/2 and 1 inch of rain expected.

This storm will also bring the first widespread snow event of this fall into the Northeast. The combination of cold air and a high pressure to the NW of the storm will result in a widespread rain/snow mix falling in central New England, most of New York state, and parts of northern Pennsylvania. The higher elevations will likely change over to plain snow, with 2 to 4 inches of wet snow possible. As the storm exits the region, any rain will likely change over to a mix of rain and snow across New England except for the immediate coast, and if the changeover happens fast enough, parts of Sussex and Orange counties may see some flakes on Thursday night. Behind the storm, colder air will move into the region, and low temperatures will drop into the lower 30s inland, mid to upper 30s in NE NJ and southern CT and upper 30s to mid 40s in Long Island/NYC. Stay tuned for more information on this storm, including a regional snow map, with tomorrow’s update.

Weekend: Storm Or No Storm?

The outlook for this weekend is more uncertain, however, as the latest models continue to go back and forth with the storm. Two days ago, no hints of a storm were shown on the models. Yesterday, over half of the model guidance trended to show a significant coastal storm with snow in parts of the region, even down to the coast. Today’s models, however, quickly went back, with the GFS, CMC and UKMET models back to showing a weak coastal low staying well offshore. The ECMWF is the only model staying consistent with a significant coastal storm idea, bringing accumulating snowfall into the immediate north/west suburbs of NYC which seem to be reasonable given the set up that it shows, but the ECMWF ensemble mean is well to the east of the operational run. The latest models showed only slight hints of a west trend, however, as the 18z GFS showed a slightly further west and stronger storm with more individual ensemble members showing a stronger storm idea.

With Hurricane Rina in the western Caribbean moving towards the Gulf of Mexico at the same time that the shortwave responsible for this potential storm will be near the southern US, Rina appears to be a part of the equation for this storm as well. The 12z GFS, which kept the storm well offshore, is an outlier as it brings Rina into Florida while the model consensus keeps Rina near Cuba, but there are signs showing that the ECM is an outlier with how it handles Rina, as it quickly dissipates the hurricane within the next two days. Considering that Rina is an intensifying category 2 hurricane, the ECM is clearly having issues with handling Rina, while most of the other models, which happen to be the same ones keeping the coastal storm offshore, do not weaken Rina and take it into Cuba. While Rina is not the only part of determining whether we see an offshore storm or a strong nor’easter, as the intensity and timing of the shortwave in the southern US also need to be considered, it appears at this time that a more likely scenario may be a coastal low staying offshore, with partly cloudy skies near the coast. At this time, I went slightly to the west of the model consensus, putting a risk of showers in the forecast, but there is still uncertainty, and it is possible that I may remove the rain chances from the forecast, or if the models trend back west, increase rain chances and add a mention of snow for the interior parts of the area. Stay tuned for more information on the weekend potential storm.

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