The weather pattern this winter and specifically this February, has been unusual to say the least. Apart from the roller-coaster temperature swings and the over-all mild weather temperatures, the ‘predictability’ of the weather systems this season has been above average.
Indeed, the ‘spread’ of the probability-based ensemble models seems to have been below average in recent weeks indicating higher confidence and lower expected variations in the longer term forecasts.
This is something I haven’t seen much. Put another way, in past winters, I would check the GFS in the morning and again later in the day and the model forecast had a fairly high chance of having changed in the interim, often dramatically. Not so in the past few weeks.
For the most part, the remaining two weeks of February look to be similar to recent weeks— Rain, followed by a couple of days of cold weather. then a return to over average temps and more rain as another front moves in.
A cold front moves through tonight (Tuesday) with light rain and cold air and high pressure build in for a two or three day period of cold temps. Temps moderate by Sunday.
As discussed last week there just haven’t been large/dense cold air masses to sink straight south into the continental US, nor have there been similar masses to set up in the North Atlantic, giving us a ‘blocked’ pattern.
The current pattern looks to continue until near the end of February. No snow expected.
There have been signs that a pattern change is possibly occurring the very end of February or the first week of March. The EKDMOS temp stats show very large “spreads” developing in the long range.
While there are always larger spreads in the longer range, the latest GFS extended range model forecast is suggesting something is changing. We’ll see.
A cold front moves through on Thursday and cold high pressure moves over us for Friday and Saturday. The National Blend of Models (NBM) is showing highs of 33° for both Friday and Saturday although some statistical models (ensemble models) show highs to be a bit colder. Skies will be sunny both Saturday and Sunday.
The pattern is fast moving and progressive; temperatures rebound into the mid 40s on Sunday as winds shift to southerly with the departure of the high.
The Extended Range GFS model attempts forecasts 384 hours (16 days) into the future. No potential snow storms are currently predicted, except a possibility the last day in February. Don’t change your plans.
This winter has been characterized by a lack of large, dense, cold air masses sinking straight south in the middle of the country.
There is a common misunderstanding, perpetuated by TV weather entertainers, that the jet stream determines where the air masses go. Actually, it’s really the other way around— the size, shape and temperature-density of the cold air masses in winter determine the position, shape and configuration of the jet stream. The ‘valley’ between the polar air mass and the tropical air mass is where the jet stream is positioned and where major low pressure systems develop and track.
The current pattern has been with us for almost three months. Like bull stock markets, weather patterns don’t last indefinitely. Weather patterns tend to change as the seasons change.
Updated Thurs 11 PM —Tonight’s models are showing very high winds starting 9-10 AM Friday morning, especially from Philadelphia and east into NJ.
The fairly uneventful winter weather season continues here for the weekend.
Deep low pressure will be departing our area on Friday, and high pressure will build in for Saturday morning, giving us sunny skies but seasonably cold. High 42.
Fast moving weather flow will be evident as clouds build in during Saturday afternoon ahead of a series of weak disturbances that will approach our area.
These weak disturbances have been handled differently by several models; the latest GFS suggests the chance of light snow flurries early Sunday morning as a result of one of these disturbances. This feature has been inconsistent, with several models having shown this earlier in the week, then backing off.
Either way, Sunday’s morning clouds should break for sunshine by the afternoon. High 46.
Another front approaches Monday with more clouds and showers.
Saturday night’s model runs briefly showed the possibility of snow, however subsequent model runs have all moved to predicting mostly rain for our area Thursday into Friday.
A slow moving cold front in the Midwest will have waves of low pressure move up along the front, bringing rain, possibly heavy for Thursday into Friday. The precipitation starts late Wednesday evening or Thursday after midnight. Some areas to the northwest of Philadelphia will have a period of freezing rain or sleet before daybreak, before changing to all rain.