Getting A Pumped Up Ridge

Channel your inner Hans and Frans -- Mother Nature is about to pump *clap* up the atmosphere with a ridge of high pressure in the mid atmosphere, resulting in a stretch of rather hot weather late next week or next weekend locally, with a run at 100 degrees not out of the question locally.

Mercifully, we will not see the worst of the heat and humidity.  That honor belongs to the Midwest, where this ridge will set up shop and temperatures could reach or breech 100 degrees in Minneapolis, Chicago, St. Louis, and other cities for a few days next week, with Chicago potentially seeing several days of upper 90's and near 100 degree temperatures.   This heat wave has the look of 1995's long duration heat wave to it...thankfully, it should not last as long but it could be just as nasty for Chicago and for the Midwest and it would not surprise me if there were fatalities in a number of the big cities from the heat.

 The question regarding "how hot we get" comes down to position of the upper ridge over us for Thursday-Saturday.   The GFS in the afternoon runs on Friday centered the ridge over the Appalachians, a pretty good spot for us to get some hot weather as upper levels are rather warm nearby.   The core of the heat ridge is near us and temperatures could approach 100 in such a scenario.  The Euro is a bit farther west with the heat core, over the Ohio Valley on Friday evening, which results in mid 90's for highs...still hot but not "prime heat."    The models have flipped and flopped over which scenario they prefer but in either scenario we're talking mid 90's, at least, for Thursday through Saturday.

If the "cooler" solution were to verify we could see some thunderstorm complexes track closer to the region around the periphery of the heat ridge.   The "ring of fire" of thunderstorm activity around the upper ridge is certainly possible...if the ridge isn't quite as strong or is centered a bit farther west we could see some thunderstorms in/close to the region during the heat event.

Factoring in humidity, heat index values could reach 105 during this time frame.   It will be oppressive but not as bad as in the Midwest, which could see heat index values around 120 on Monday or Tuesday in some locations.   The heat is back on...and this is likely the prime heat event for the year across the country.

Fire & Flood

The news has been rather active of late with stories of wildfires in Southwest, floods in the Mississippi, Ohio, and Missouri River Valleys, not to mention the wild tornado season we experienced in April and May -- much of which can be blamed on the weakening La Nina that wreaked havoc across the US with record snows and rains in the North and Ohio Valley, while leaving little if any rain to spare for Texas and the Southwest.   Over the last couple of months or so, the most waterlogged parts of the country compared to "typical" have been in the High Plains of Montana and in a belt from the Ozarks through the Northeast.  Notice our region had been just slightly below average over that timeframe...and if you throw out the three inch soaker that pelted our region on April 16th we had been running between 50 and 75 percent of normal in the rainfall department through late last week and before our much needed rains that we picked up late last week and again last Sunday.

Taking that 60 day trend and extending it out to six months, you can see the excessive rains (and snows) to average across the High Plains, an area that had seen excessive snow and rain all winter (going back to November), with the conveyor belt of moisture in the Ohio Valley not as excessive (rains started in earnest there in February).   The dryness, however, of the South and Southwest has been persistent -- particularly in Texas as they have been drought stricken and suffering from exceptional drought conditions that have been going on since October.    La Nina is a major consideration in the precipitation patterns of the past winter as storm systems will gravitate towards a northern track and subtropical moisture from the Pacific is less of a factor, meaning that the South stays dry while the North generally is not...the reverse would be true with an El Nino (the South is wet, North is typically not).

Uncertainty For The Weekend...Except A Chance of Rain

Arguably the best stretch of weather we've had this year so far has given us consistent temperatures in the 70's day after day since Friday...and you can thank the blocking pattern in the Atlantic that has been giving us this wonderful run of weather that will continue through the end of the work week. The bad news is that the weekend will not be as nice as we have thunder chances returning on Saturday as an upper level storm system and surface low meander through the Southeast, coupled as well with a frontal boundary drifting south from Canada.

There are questions over how widespread thunderstorm activity will be -- the Euro computer model is painting thunder chances for both Saturday and Sunday, with Sunday's chances more widespread for the region although scattered storms could be the rule both days this weekend.   The GFS is less robust in thunder chances -- that could be due to the placement of the upper level low over the Great Lakes on the GFS and the frontal boundary from Canada being much slower in its approach than on the Euro.   If the GFS is correct, it would yield more isolated thunderstorms and showers around town and less widespread activity.

The other thing we will have to watch this weekend is winds coming in off of the Atlantic ahead of the low.  If the Euro is right, winds could be more east than south, which is what the GFS is suggesting.  That could yield forecasting havoc on temperatures for the weekend as the Euro's solution suggests 60's while the GFS is saying 70's in today's run for the coming weekend.    Like we said a few days ago, hope you enjoy the coming days of weather!

The First of Two Chilled Rains Next Week

After flirting with or hitting 80 degrees yesterday, the wilds of March have to turn the other cheek. Mother Nature can't let us enjoy May-like warmth for too long, can she? Colder air will be on the advance starting today as temperatures drop to more typical levels for March -- daytime highs in the upper 50's. While still nice, it's not quite yesterday nice. The cooler trend will become increasingly established over the next few days as a couple of systems scoot through from west to east, generally across our region, with chances of chilly rain here in the city. Farther north, some snow is certainly possible as these systems work through colder air than what we have here.

Monday brings the first system -- this generally passes through during the morning hours and may start up just before daybreak west and northwest of the city. With some residual cool air lingering around the region and temperatures aloft starting off cool, some snow and/or sleet could fall at the onset north of I-78 before transitioning to rain. South of I-78, some sleet could mix in with a chilly rain on the front end of the system before temperatures warm above freezing aloft and we all see a cool rain.

With temperatures generally in the 30's (blue) and near freezing (pink line) to the north, some frozen precipitation can't be ruled out over the northern parts of the area.  I tend to think the best chances will be Scranton, the Poconos, Northwest Jersey but the timing (morning) and intensity (light) means any accumulating frozen precipitation may be confined only to grassy surfaces and not to roadways up north.

A second system is poised to impact the region on Wednesday night and Thursday.  There is a chance some frozen precipitation could work closer to the city but computer guidance has been trying to keep the frozen precipitation to a minimum in recent runs.   Both of these systems will help to establish a -NAO over the East for the next week or so, with temperatures cooling off quite a bit by the end of next week....where highs could be in the lower and middle 40's as a large trough pivots through the East for the end of March.

Hope you enjoyed the Spring Fling yesterday, folks.  Old Man Winter still has a little more spark in his step yet.

A Cool Battle Ahead

In the wake of last night's fluffy snow and the upcoming couple of days of cold that await, the transition to a more zonal pattern will take hold by this weekend if computer guidance is correct. This means we'll see some interesting battles between spring-like warmth in the Southeast and some winter chill in the northern tier of the country, which puts us in the firing line and "stuck in the middle" between the two camps. An active pattern seems to be shaping up for the next week to ten days, which means we'll have a few shots of precipitation before the end of next week and perhaps some frozen precipitation to deal with on at least one of those events.

Typically, true zonal patterns result in fairer weather across the country and milder temperatures in the East.  However, this isn't a pure "zonal" look in the sense of having mild weather and limited moisture.  With a stronger polar low over Central Canada, cold air will lurk nearby and occasionally seep farther south.   The Pacific will be a bit more active and provide additional moisture and storminess to the mix, with the Gulf open for business as the Southeast ridge will be shunted eastward into the Western Atlantic.   This pretty much means a family of storm systems -- some stronger than others -- will take a general track from Missouri to Ohio to New England over the next ten days.   The first of these will hit us on Friday, a stronger system that should pull warmth northward and bring a lot of rain to the region.  We could have some stream rises/localized flooding from this first storm as the snow that fell last night will be all gone by Friday but we're also looking at a potential for an inch to two inches of rain from this event.   Today's GFS run is a bit of a burp from past runs in that it suppresses the track of the storm to our south -- generally from Arkansas to Southern Virginia to the Delmarva -- and brings snow from Philly on north and rain south of the city...the Euro is farther north and milder.

Keep in mind that about this same timeframe out from this past storm the GFS was putting 60's into the Philadelphia region on Monday...didn't work out too well, did it?   It doesn't mean the GFS is wrong...but it is an its own and colder of the guidance.  The NAM, which is now seeing the storm, is a milder model.   We'll keep an eye on the other guidance and how this system evolves in the coming day in the US West.   Stay tuned...but with a skeptical eye.

Two, perhaps three more storm systems will follow after Friday's first event.   Storm #2 of this parade will be weaker and will track quickly in, impacting Saturday night into Sunday.   With cooler air lurking around from the wake of storm one, we could see some frozen precipitation with the second system, especially north of Philadelphia, before temperatures warm and precipitation possibly transitions to rain (GFS suggests a transition, Euro does not with system #2 as Euro keeps this system far weaker).    After that, another system lurks for midweek next week...this one looks a bit stronger and with that general track in place looks like rain at this point.

Breaking Records?

Ready for some records?   Well, it's POSSIBLE we break a couple of these records on Friday with the upcoming warm surge.  The most likely location for any record to get knocked out is Atlantic City (record of 69).   Some of the other records -- Trenton, Wilmington (both 72), Allentown (66), Reading (70) and Mount Pocono (63).   The first two locations have the highest records, the latter three have significant snow cover still in place.    That leaves Philly and AC.   Philly could also knock out the record warm low (48) that was set back in 1890...that one might be tougher than the record high and both are tough ones to knock out.   I'm forecasting 68 for Friday, which is warmer than guidance and is accounting for a mild breeze that's forthcoming from the west and southwest.

The early tease of Spring is only two days in duration -- tomorrow with 60ish degree weather for most locations from Philly on south and then on Friday with a general splashing of 60's regionwide and isolated pockmarks of 70 degree weather.   The last time we hit 70 in Philadelphia during February was on February 1st, 2002 and our last 70, regardless of date, was back on October 28th (77 degrees).

Enjoy the tease of spring -- car roofs open or convertible tops down, windows open, bad music up in your car as you sit in traffic.   Come Saturday night, we'll be back into the thrill of typical February chill.

In A Zone

Surface high pressure over the Southeast, without strong high latitude blocking in the Arctic, usually means mild weather around here and we're about to trot into such a pattern over the next week, perhaps a touch longer.   The jet stream, which is current shoving Canadian chill our way, is poised to shift to a more zonal pattern as high pressure at the surface waxes and wanes.  In its stronger times, the high will bring us temperatures that will approach 50 degrees, perhaps as early as Sunday in Philadelphia.   In a zonal pattern, however, quick moving fronts try to push through and we'll probably have such a front on Monday that will try to knock temperatures down a couple of degrees.

However, the surface high pressure will wax stronger towards midweek next week -- this combined with a slight nudging of the zonal jet to react to a stronger dip in the jet over the Pacific will result in a west-southwest flow at the surface and aloft.   IF this takes place, we could hit 60 at some point next week.   We're forecasting 55 for next Thursday but it's based on "playing it safe" at this point because what is modeled seven days out and reality sometimes are two different things -- see the "paper storm" computer guidance was spitting out a bit more than a week ago.  However, little in the way of flies in the ointment are popping up at this point as modeling and pattern analysis are in pretty strong agreement about some sort of warm up taking place.   How warm we ultimately get is still to be determined -- 60 is definitely do-able in this warm-up...and for many around here, it will feel quite nice.

A cold front will slash into that warm up for President's Day Weekend, with temperatures that may bounce back down towards normal.    It does look like, for the foreseeable future anyways, that the cold we're dealing with now may be it for a while...and perhaps the uber cold (daytime high temperatures in the 20's or low 30's) may almost be a thing of the past.

Thursday Event Not Likely, Tonight's Event Modest At Best

With the latest surge of chill pushing south, combined with a fast moving flow in the upper atmosphere, and the threat for the Thursday storm that was "on paper" a few days ago is trending away from us and is getting squashed by a broad based trough that will set up in the East.  The storm is "there" on guidance but the broad trough will prevent it from lifting north up the East Coast.

The upcoming pattern after tonight's rain/snow event suggests cold weather through Friday, with daytime highs in the lower 30's on Wednesday, near 30 on Thursday, and in the mid 30's on Friday.   Several degrees below normal and the last blast of cold before the pattern eases starting this weekend.

Speaking of tonight's rain/snow event, computer guidance suggests the brunt of tonight's event will come after midnight.  Rain is falling as close as York at 6 PM but most of the returns on radar, at this point, aren't reaching the ground in Eastern PA.  That should change later tonight as the cold front works east and interacts with the coastal system that will miss us wide right.   As the front works east, precipitation will work through -- initially as rain and then transitioning to snow in the Lehigh Valley and Poconos.  The Poconos could pick up a couple of inches of snow overnight, with coating accumulations possible as close as Reading and Quakertown.   Rain showers could end briefly as snow in Philly tomorrow morning but accumulations in the city are not likely.   Most of the precipitation should be out of the region by 9 AM although a few lingering snow showers could move through during Tuesday afternoon.