Sunday, January 13, 2013

Perspective On Incoming Colder Pattern

This isn't the first time this winter where cold patterns have been hyped. You might remember back in late December the potential for a cold start to the year...and it was cold...for a couple of days but not very long and certainly not as long as modeling was indicating a week to ten days prior to reality.

Cold "shots" in December and January have been fleeting, weak-kneed, and wimpier than model hype so far.  However, the pattern over the past six weeks wasn't generally supportive of winter holding much substance for the East or Mid Atlantic.  We were glanced and grazed with colder weather, enough to get a couple of minor snowfalls around the region, but warm eventually, ultimately nudged back into the picture.

This upcoming colder pattern will have more substance as the pattern overall becomes more supportive for cold in eastern North America.  The Arctic block is flexing its muscle and with a more favorable look in the North Atlantic gradually taking over, we will see a transition towards more typical temperatures in January.

Putting this in perspective though, the pattern will have some yo-yo to it over the next week as we go from mild today and early tomorrow to seasonal to cold for a day before trending back seasonal this weekend.   The first cold front is bringing us back to reality tomorrow, setting up that slight chance for some conversational light snow or sleet on early Tuesday and early Wednesday near the city (enough to perhaps coat your lawn) as a couple of waves of energy push along the front.

We take a bigger step into colder weather on Thursday night with a cold front pushing through, with a seasonally cold morning setting up on Friday and again Saturday for the region.  Lows, while not harsh, will be around where they should be.

That means that this week will feature reality...not unseasonally cold...not harsh nor Arctic or even Arctic-like.  In fact, Tuesday through Saturday still might average out above normal when all is said and done.  The core of cold in wave #1 this week stays in the Northern Plains and even there the cold will not be terribly bad in duration.

Back to what I said on the yo-yo...we will likely see our coldest temperatures so far this winter not this week but next week.  Before that hits, we could see a brief bounce milder ahead of that cold shot next week.  The Euro has hinted a couple of model runs of 50+ on Sunday in Philadelphia.  This may change as we trend in...and the GFS doesn't completely agree with the level of mildness but it does support a milder end of next weekend.

If the modeled hype of a significant cold shot next week does take hold, we probably will see our coldest temperatures of the winter take hold in the Tuesday-Thursday timeframe.  Lows in the teens, highs near 30 in the city.  It's cold, not the coldest in years cold for us, but cold nonetheless.  This looks to be a setup where coldest to normal may be likely to dive into the Plains and Midwest while we don't get as cold compared to normal.  If you were to believe the Euro model for ten days from now, temperatures would be in the 20's for daytime highs next Tuesday.

Whether that level of cold that's modeled is what reality serves up is still to be debated but even if it's not, the pattern is what's important and that pattern is one that's supportive of colder weather for us in Philadelphia overall, with the pattern probably holding serve into early February.  It won't be cold day after day, locked and loaded, but the general pattern that's setting up will support a three week (perhaps longer) run of more typical January and early February weather.

Whether it snows or not is another story -- those specifics can be nailed down as we move along through the pattern.  The key is that colder reality will set in and those 50's we're "baking" in now will be a rarity of sorts in the coming days.