Saturday, February 12, 2022 - 10:02 A.M.
A big factor in the type of Winter we are experiencing in the northeastern United States this year, and every year, is a teleconnection pattern known as the North Atlantic Oscillation (NAO). A teleconnection pattern, as defined by the Climate Prediction Center, is “a recurring and persistent, large-scale pattern of pressure and circulation anomalies that spans vast geographical areas.” The manner in which the NAO configures itself determines where the jet stream is located, and as a result, the prevailing type of weather that affects the northeastern part of the country (and many other places). In general, when the NAO is in a negative phase the jet stream is usually positioned south of New England, resulting in colder weather and snowier (vs. rainy) precipitation. When the NAO is “positive”, our weather tends to be milder with less snow and a jet stream located farther to the north. Anomalies can occur though, so a snowstorm or Arctic air outbreak can still occur during a positive NAO and rain and/or milder temperatures can occur for short periods during a negative NAO in the northeast, however those tend to be deviations from the prevailing pattern.
The NAO is basically calculated by measuring the difference in atmospheric pressure between a low center that tends to establish itself near Iceland (the sub-polar low) and a high pressure center that gravitates toward the Azores (sub-tropical high). The graph below shows the recent and forecast phase of the NAO from the Climate Prediction Center.
The solid, black line in the above graphs indicates the observed level of the NAO, while the red “spaghetti” lines on the top graph and the thin, blue line on the bottom 3 graphs indicate the forecasted phase of the NAO per an ensemble of forecast solutions. Notice that the forecasts only go out about 2 weeks into the future. Unfortunately, the NAO phase is difficult or impossible to forecast accurately and consistently beyond this period of time. Also notice that the NAO has been in a positive phase recently (above the dashed, horizontal line labeled 0 in the center of each graph) and is forecast to remain positive through the end of February.
This is a big part of the reason that the weather in the northeast is milder now and likely to be generally milder most of this month. Of course, that doesn’t mean that the occasional batch of Arctic air or snow won’t pay a visit, but these types of events will tend to counter the prevailing pattern of milder air and less snow, as long as the NAO remains positive.
Temperatures today are likely tie or break record highs in parts of the northeast. Here are some current record highs for February 12th as of this morning:
Hartford, CT (BDL): 54 (1999)
Boston: 58 (1999)
Providence: 61 (1999)
Worcester, MA: 56 (1999)
Bridgeport, CT: 54 (2018)
NY City: 62 (2018)
Here is the HRRR temperature forecast for this afternoon:
The fun will end rapidly this evening and tonight as temperatures tumble behind a cold front. As the front slows down and an area of moisture rides up along it. it looks like there will also be some light snow moving through the region Sunday. Valentine’s Day will be cold, however temperatures will moderate again during the 2nd half of next week, likely reaching the 50’s again by Thursday in many parts of the region.
Speaking of Sunday and above normal temperatures, tomorrow’s Superbowl in Los Angeles may be one of the warmest ever played! Los Angeles has been under a Heat Advisory since Wednesday that continues through Sunday. Here is the temperature forecast for that region tomorrow afternoon: