Jan 24, 2012: Rain Returns Thursday Night

Throughout the day yesterday (Monday), temperatures slowly warmed up across the area. The cold air stayed in interior areas longer than expected, leading to chilly daytime temperatures inland, although by the late afternoon temperatures quickly warmed up near the coast, with the warmth spreading inland by the early overnight hours as expected, and temperatures ended up reaching the expected highs, peaking in the mid to upper 40s inland and the lower 50s across the rest of the area. Today (Tuesday) had drier conditions again with warmer temperatures melting most of the remaining snow cover from the weekend snowstorm across most of the area, with temperatures reaching the upper 40s to lower 50s inland and the lower to mid 50s across the rest of the area.

With only a slightly cooler air mass coming in, the pattern consisting of above average temperatures and very little, if any snow has returned, with temperatures staying above average through the rest of this week and into the weekend. Stormy weather will return by Thursday night, with widespread rain and mild temperatures, and while uncertainty increases by Sunday, a weak storm could be possible for parts of the region, followed by a transient cold air mass to start next week.
Tomorrow’s Outlook:

With a slightly cooler air mass moving in, temperatures tomorrow will cool down, although remain at least 5 degrees warmer than average across the area. Temperatures will peak in the upper 30s to lower 40s inland and the lower to mid 40s across the rest of the area. Mostly sunny skies are expected along with a light NW wind.
Thursday – Friday: First Storm Potential

With Sunday’s update, I mentioned that there are two storm potentials, one on Thursday and another on Saturday. The timing depended on a cutoff low pressure in the southern US, which could either phase on Thursday or on Saturday. The model guidance corrected itself yesterday to show a scenario where the cutoff phases on Thursday, resulting in a larger storm for the region on Thursday night into early Friday, while no storm takes place on Saturday. Some models have attempted to bring up a storm for Saturday, including the 12z GFS, however with the latest trends, there is little support for such a scenario, and the 12z GFS run is considered as an outlier run.
Storm Set Up: The differences with the models for Thursday night have once again narrowed down to the usual differences between the foreign and the American models. The foreign models, consisting of the CMC, UKMET and ECMWF, show a more phased storm further north/west, wetter and warmer, with the CMC bringing temperatures up to 60 degrees for NYC on Friday. The American models, the NAM and GFS, show a much weaker and further southeast storm; although temperatures still get mild on Friday morning on these models, they only do so briefly before cooling down again. The CMC and UKMET are most likely too strong and too warm with the storm, with the CMC even bringing what appears to be a squall line with potential thunderstorms through the area, while the ECM is going with a scenario in between the CMC and the GFS, with locally heavy rain on Thursday night into Friday morning with temperatures rising into the mid 50s across the area. The GFS and the NAM may be a little too weak with the storm, and are slowly trending towards a more phased scenario. As a result, I am leaning towards the foreign models for the scenario on Thursday, which as will be discussed later on, will also affect the outcome for the weekend. I am currently going with a scenario slightly cooler than the ECM to balance out the extreme solutions on either side, although the storm could end up slightly warmer or colder than currently expected.
Forecast: Rain is expected to develop on Thursday evening, lasting through the overnight hours and into the first half of Friday. Going with the scenario mentioned above, temperatures would remain steady on Thursday evening before slowly rising overnight, reaching the 40s across the entire area by Friday morning and the upper 40s to lower 50s in parts of the immediate NYC area and Long Island. Temperatures may slightly warm up on Friday in the late morning into the early afternoon, although skies will clear later on in the day with dropping temperatures.
This scenario is still not final, as there are still going to be some changes with the models. A possible change is for slightly cooler temperatures with rain ending by early Friday morning, not by late Friday morning. Should the CMC/UKMET verify, temperatures would be warmer with heavier rain, although this is a less likely scenario. Stay tuned for more information on this storm.
Saturday – Sunday: Second Storm Potential

With the cutoff low phasing partially on Thursday, the Saturday potential mentioned on Sunday most likely will not verify, with the leftover energy from the cutoff low drifting offshore on Saturday with slightly cooler temperatures. Even if a storm was to come up the coast on Saturday, it would more likely be rain as there is still no strong cold air coming down. By Sunday, however, a stronger trough drops from the north central US with more ridging in the western US. This more amplified scenario will bring a risk of scattered snow showers in parts of the region, potentially including the area. Some models develop a larger storm on Sunday, with the CMC keeping a coastal low pressure slightly offshore while the UKMET has a much stronger storm for the region. The UKMET solution is most likely too extreme, and while any bigger snowstorm is unlikely in this time frame, the potential for light precipitation is there.
Tomorrow’s update will discuss the storm potential for Sunday in more details, including the colder temperatures that will follow behind the cold front bringing a colder start to next week.

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