Mar 1, 2013: Chilly Pattern; Storm Possible Next Week

Forecast Highlights:

Following the mid week storm, drier but partly to mostly cloudy conditions took place over the last two days, and are expected to continue through this weekend into early next week as temperatures slightly cool down. The next potential for a storm is expected towards the middle of next week, with the latest models still not having reached an agreement but pointing towards a potentially significant storm for parts of the region.

February Summary: Slightly Colder Than Average

Following a change to a colder pattern in late January, a tough was persistent over the region with colder than average temperatures much more frequent than the last few months, especially in the early and mid month time frames. With a lack of frequent warmth surges this month to undo the cold anomalies established during the beginning of the month, February ended up 1.4 degree colder than average in Central Park. This makes February 2013 the first colder than average month since November, and only the 3rd month in the last 23 months to feature colder than average temperatures; before November, the last months with colder than average temperatures were June 2012 and March 2011.

Tonight – Tuesday: Slightly Cooler Than Average

Over the next few days, one of the most amplified setup of the year is taking place, with a strong deep trough over the eastern half of the US and a strong ridge towards the western US. Despite the amplified trough, no major storm develops out of it, with dry and partly to mostly cloudy conditions expected to persist through the rest of the weekend into early next week. Temperatures will remain slightly below average during this time frame, as due to the significant southward extent of the trough, the greatest negative temperature departures remain over the southern US. During early next week, significant blocking currently in the northern Atlantic will also extend westwards into the Davis Strait and eastern Canada with 500mb heights up to 552dm, making it the 2nd significant block of the winter over North America; the other notable block of the winter took place in late December with a relatively strong, albeit transient, block over Canada. This will set up the pattern for the next storm, which will be discussed in more detail in the next section.

During the weekend and into early next week, highs are generally expected to peak in the upper 30s to low 40s inland and low to mid 40s for the rest of the area. Overnight lows will be in the 20s across the area except for NYC, with the coldest lows likely on Sunday night near 20 degrees inland. WNW to NW winds are expected during this time frame, peaking on Monday with breezy conditions likely.

Wednesday – Friday: Storm Possible

The next storm to affect the region is expected to take place towards next Wednesday and Thursday. The model guidance remains inconsistent with the handling of the storm, with solutions ranging from the UKMET and 18z GFS which completely kept the storm south of the area, to the ECMWF and 12z GFS which showed a major snow, rain and wind event across the region including the area. This storm is still at least 5-6 days away, however, and especially considering the model performance so far this year, additional changes will continue to take place with the models over the last few days, and no forecast is final yet. The most recent example of this is last weekend, when despite a model agreement of a significant storm affecting the region several days out, even as close as 2-3 days away, a sudden last minute shift took place in the models, with the end result only a minor rain event for the area.

The main highlight of this setup is the blocking over southeastern Canada, which weakens following this event. The blocking will prevent the storm from tracking too far north to result in mostly rain across the region, although the main uncertainty with the storm track is whether it is far north enough to affect the area or remains suppressed. The shortwave responsible for this storm is still over the Pacific Ocean, and is set to move into the United States with better sampling on Sunday morning. There is also uncertainty with the model handling of the upper level low over northern New England and another shortwave over southern Canada and their interaction with the southern shortwave, which will continue to change over the next few days. If the storm ends up close enough to affect the region with significant impact, the next question is the temperatures, as this setup is associated with a stale cool air mass, especially with a lack of initial strong cold air at the surface and no new source of cold air coming in behind the storm, as the remains of the cold air mass are expected to weaken once the low occludes with warmer temperatures possible for the longer range. This lack of cold air is likely to result in precipitation type issues for coastal areas, although how much impact this has further inland will be determined better once the track of the storm becomes settled.

At this time, it is too early to know for sure whether the storm will affect the area with significant impacts or not, although at least some impacts from this storm are becoming more likely. At the very least, should the weaker and further south solutions verify, temperatures would remain seasonable in the 40s with increased cloud cover and some showers. The possibility is there for a stronger and further north storm, however, in which case significant impacts would take place across the region with strong winds, significant rain for the coast and a wet snowstorm inland. Stay tuned for more information over the next few days as details become clearer.