January 5th-6th Potential Winter Event

[ChescoWx]

Latest Wxsim with 6z GFS and NAM data show problems for NW Chester County come Sunday. As precipitation begins temps will be just above freezing during the early PM. Mainly a mix of IP and Snow quickly transitioning to rain and by 430pm ZR as temps fall back below freezing. Temps will remain below freezing through around 10pm with 0.21" falling as frozen before going over to rain after 10pm. Precipitation will continue with temps in the mid-30's and before falling back during the early PM on Monday and mixing with and changing to snow before ending. Total event precipitation is 0.52"

[eastonwx]

Thanks for starting Paul. May not be a big deal Philly proper, but some frozen stuff looks possible n&w

[eastonwx]

A snippet from today's AFD from Mt. Holly:

 

THE LATEST GFS SUGGEST A WINTRY MIX POSSIBLE WHEN PRECIPITATION BEGINS LATE SUNDAY
AFTERNOON, WITH A CHANGEOVER TO RAIN FROM SOUTH TO NORTH AS WARMER
AIR MOVE IN, WITH LIGHT SNOW POSSIBLE NEAR THE END OF THE EVENT AS
COLDER AIR MOVES IN BEHIND A COLD FRONT THAT SWEEPS THROUGH EARLY
MONDAY MORNING.

THIS CHANGEOVER TO RAIN NORTH AND WEST OF
PHILADELPHIA SEEMS A LITTLE OPTIMISTIC GIVEN THE EXISTING SNOW COVER
AND THE RECENT BUILDUP OF COLD TEMPERATURES THROUGHOUT THE
ENVIRONMENT.

WE`LL OBVIOUSLY MONITOR THIS SYSTEM AS IT GETS CLOSER.

[tcutter]

there is also potential for end of next week too?

[NJ_Ken]

I have nothing scientific to add so take this all with a very large grain of salt.  It is just hard to comprehend that we could go from the kind of bone-chilling cold we will see today and tonight along with 6" to 10" of snowcover and still have temps above freezing by Sunday morning (even though we've seen it happen before).  I am not saying that the Sunday event won't eventually turn to rain for most/all of us.  I just think temperatures will trend lower for the start and give many even in the immediate Philly area something frozen before the changeover, and I think N&W of the city, this could get much uglier than current forecasts are implying.  In any case, the snow is now on the ground and temperatures have begun to plummet so, if there is going to be a trend toward a colder solution on Sunday, we should start seeing it immediately in the models.       

 

EDIT:  After I posted this, I saw the snippet above from the PHI AFD.  They made the same point I did, but, obviously, did it a lot better and did it with some science to back them up.  Maybe I am not so crazy... or maybe I am the blind squirrel who finally stumbled upon the proverbial acorn.   

[NortheastPAWx]

This one will be very interesting to follow with an arctic front. We're forecast to have a high of 39 Monday but tanking to a low of -10...

[NJ_Ken]

This one will be very interesting to follow with an arctic front. We're forecast to have a high of 39 Monday but tanking to a low of -10...

 

Yeah, the forecast for Cherry Hill, NJ calls for a high of 48 F on Monday (presumably early in the day) followed by a low Monday night of 4 F and a high on Tuesday of 13 F.  On the heels of today's weather, that will most definitely fit the definition of a roller coaster ride. 

 

EDIT:  Over at EasternUSWX, I would periodically comment on the fact that, regardless of what average temperatures tell us, there has seemed to be a dearth of really frigid days in the winter in recent years.  Prior to, say, 1990, it seemed like most winters (not every one, but most of them) would have at least one cold snap where we would have a day (or two or three) where high temperatures at PHL stayed in the teens and lows were in the single digits (with even the occasional below 0 F reading).  It seems like in the last 20+ years, those kinds of extreme cold outbreaks were becoming an increasing rarity.  Well, in the next 5 days, it looks like there is going to be two days at PHL where the high does not get out of the 10s F and the low gets down to the single digits or below.... and somehow in between those two days, we are going to get rain!     

[Sophisticated Skeptic]

Expect the models to trend colder.   12z NAM is even hinting at a weak secondary offshore.  

 

If that trends just slightly more colder, most of NJ (away from the coast) could have an interesting sleet / freezing rain event.   The 10m temperature line could only try so hard to be perfect in such a brutal airmass this storm will be running up against. 

[Redmorninglight]

High amplification givith and high amplification taketh away.

[famartin]

I have nothing scientific to add so take this all with a very large grain of salt.  It is just hard to comprehend that we could go from the kind of bone-chilling cold we will see today and tonight along with 6" to 10" of snowcover and still have temps above freezing by Sunday morning (even though we've seen it happen before).  I am not saying that the Sunday event won't eventually turn to rain for most/all of us.  I just think temperatures will trend lower for the start and give many even in the immediate Philly area something frozen before the changeover, and I think N&W of the city, this could get much uglier than current forecasts are implying.  In any case, the snow is now on the ground and temperatures have begun to plummet so, if there is going to be a trend toward a colder solution on Sunday, we should start seeing it immediately in the models.       

 

EDIT:  After I posted this, I saw the snippet above from the PHI AFD.  They made the same point I did, but, obviously, did it a lot better and did it with some science to back them up.  Maybe I am not so crazy... or maybe I am the blind squirrel who finally stumbled upon the proverbial acorn.   

 

Certainly the models may be warming up the low levels a bit too much.  But... we've certainly seen huge turn-arounds before.  At TTN a low of 1 on 1/27/1994 turned around to a high of 56 on 1/28/1994.  It wasn't that extreme at PHL, 11 to 58.  However, ABE was even more impressive, going from a low of -5 on 1/27 to a high of 55 on 1/28.

[NJ_Ken]

Certainly the models may be warming up the low levels a bit too much.  But... we've certainly seen huge turn-arounds before.  At TTN a low of 1 on 1/27/1994 turned around to a high of 56 on 1/28/1994.  It wasn't that extreme at PHL, 11 to 58.  However, ABE was even more impressive, going from a low of -5 on 1/27 to a high of 55 on 1/28.

 

Totally agree.  It still seems crazy to me... even though I've seen it happen with my own eyes.  

[famartin]

Totally agree.  It still seems crazy to me... even though I've seen it happen with my own eyes.  

Come out here and you can see ranges like that in a single 12 hour period   And not due to a front either

[NJ_Ken]

Come out here and you can see ranges like that in a single 12 hour period   And not due to a front either

 

LOL.  I recently moved to Oklahoma, and, while we don't get the same kind of insane diurnal temperature variations that you see, it does get pretty crazy here at times... at least when compared to what I thought was normal in New Jersey.    

[famartin]

LOL.  I recently moved to Oklahoma, and, while we don't get the same kind of insane diurnal temperature variations that you see, it does get pretty crazy here at times... at least when compared to what I thought was normal in New Jersey.    

There was a day two summers ago where it was 45 at 630 AM... and 95 at 1230 PM.

[eastonwx]

Certainly the models may be warming up the low levels a bit too much.  But... we've certainly seen huge turn-arounds before.  At TTN a low of 1 on 1/27/1994 turned around to a high of 56 on 1/28/1994.  It wasn't that extreme at PHL, 11 to 58.  However, ABE was even more impressive, going from a low of -5 on 1/27 to a high of 55 on 1/28.

Ray, I vaguely remember that...was there some flooding involved with rapidly melting snowpack?

[KamuSnow]

Certainly the models may be warming up the low levels a bit too much.  But... we've certainly seen huge turn-arounds before.  At TTN a low of 1 on 1/27/1994 turned around to a high of 56 on 1/28/1994.  It wasn't that extreme at PHL, 11 to 58.  However, ABE was even more impressive, going from a low of -5 on 1/27 to a high of 55 on 1/28.

 

I don't recall, but was that warmup associated with any precip? It would seem so...

[NortheastPAWx]

Not as impressive here; but KAVP went from 3 on 27 January 1994 to 51 the next day.

[ChescoWx]

Latest Wxsim with 12z data has indeed trended both colder and wetter here is the breakdown for NW Chesco

Light Sleet arrives around 11am temp 31.4

becoming ZR during the early PM with temps rising to 32.4 by 3pm before falling again

ZR between 3pm and 1130pm with the temp falling back to 28.7 before slowly rising after 8pm

Temps go back above freezing at 1130pm and stay there till Monday at around 11am when it goes back to snow and accumulates between 0.5 to 1.0"

[famartin]

Ray, I vaguely remember that...was there some flooding involved with rapidly melting snowpack?

There was.  ABE went from a snow depth of 16" to 9" from that storm, with 1.55" precip (mainly rain, but some snow/sleet early, just a half inch). 

[famartin]

I don't recall, but was that warmup associated with any precip? It would seem so...

Widespread 1-2" rainfall, yes.

[White_Mtn_Wx]

Latest Wxsim with 12z data has indeed trended both colder and wetter here is the breakdown for NW Chesco

Light Sleet arrives around 11am temp 31.4

becoming ZR during the early PM with temps rising to 32.4 by 3pm before falling again

ZR between 3pm and 1130pm with the temp falling back to 28.7 before slowly rising after 8pm

Temps go back above freezing at 1130pm and stay there till Monday at around 11am when it goes back to snow and accumulates between 0.5 to 1.0"

Glacier time!

[famartin]

FWIW, perhaps not much, the EC has temps rising into the low 50s along I-95 by early Monday morning.

[Lady Di]

At any rate, still interesting to see a 40 degree swing.  NWS has 43 high for Monday with a low of 0. 

[NJ_Ken]

Ray, I vaguely remember that...was there some flooding involved with rapidly melting snowpack?

 

You might be thinking of the aftermath of the Blizzard of '96.  About two weeks after that storm, there was fairly heavy rain coupled with a similar ridiculous warmup (it hit 62 F at PHL and I believe that Pittsburgh also reached the 60s) that quickly melted snowcover.  There was horrendous flooding across Pennsylvania (and elsewhere).  If memory serves, that flood partially inundated the old Three Rivers Stadium in Pittsburgh and resulted in crests in western, central and northeast PA that came close to (and in some cases exceeded) the previous floods of record.     

[NortheastPAWx]

You might be thinking of the aftermath of the Blizzard of '96.  About two weeks after that storm, there was fairly heavy rain coupled with a similar ridiculous warmup (it hit 62 F at PHL and I believe that Pittsburgh also reached the 60s) that quickly melted snowcover.  There was horrendous flooding across Pennsylvania (and elsewhere).  If memory serves, that flood partially inundated the old Three Rivers Stadium in Pittsburgh and resulted in crests in western, central and northeast PA that came close to (and in some cases exceeded) the previous floods of record.     

That flood event, as I recall, brought President Clinton to the area.

[eastonwx]

There was.  ABE went from a snow depth of 16" to 9" from that storm, with 1.55" precip (mainly rain, but some snow/sleet early, just a half inch). 

 

 

You might be thinking of the aftermath of the Blizzard of '96.  About two weeks after that storm, there was fairly heavy rain coupled with a similar ridiculous warmup (it hit 62 F at PHL and I believe that Pittsburgh also reached the 60s) that quickly melted snowcover.  There was horrendous flooding across Pennsylvania (and elsewhere).  If memory serves, that flood partially inundated the old Three Rivers Stadium in Pittsburgh and resulted in crests in western, central and northeast PA that came close to (and in some cases exceeded) the previous floods of record.     

My apologies to Ray. Ken, I believe that's the one I was thinking about. Snowpack went down to virtually nothing, and there was some pretty bad flooding as a relsult. I only remember because my basement flooded!

[bricktamland]

.LONG TERM /SATURDAY THROUGH THURSDAY/...
THE EXTENDED PORTION OF THE FORECAST STARTS OUT WITH BENIGN WEATHER
COURTESY OF A SURFACE HIGH PRESSURE SYSTEM CENTERED OVER THE
MID-ATLANTIC SEABOARD AND IT`S ASSOCIATED SOUTHWESTERLY FLOW OF
MILDER AIR. HIGHS ON SATURDAY ARE EXPECTED TO BE 5 TO 10 DEGREES
HIGHER THAN FRIDAY/S BITTER COLD TEMPERATURES BUT STILL 5 TO 10
DEGREES BELOW NORMAL. SUNDAY/S HIGH TEMPERATURES WILL ACTUALLY BE
NEAR NORMAL FOR THIS TIME OF YEAR. THEN THE WEATHER GOES DOWNHILL AS
A DEEPENING LOW PRESSURE SYSTEM FROM THE MISSISSIPPI AND TENNESSEE
RIVER VALLEYS MOVES NORTHEAST THROUGH WESTERN PENNSYLVANIA AND
WESTERN NEW YORK STATE LATE SUNDAY AND EARLY MONDAY. THE LATEST GFS
SUGGEST A WINTRY MIX POSSIBLE WHEN PRECIPITATION BEGINS LATE SUNDAY
AFTERNOON, WITH A CHANGEOVER TO RAIN FROM SOUTH TO NORTH AS WARMER
AIR MOVE IN, WITH LIGHT SNOW POSSIBLE NEAR THE END OF THE EVENT AS
COLDER AIR MOVES IN BEHIND A COLD FRONT THAT SWEEPS THROUGH EARLY
MONDAY MORNING. THIS CHANGEOVER TO RAIN NORTH AND WEST OF
PHILADELPHIA SEEMS A LITTLE OPTIMISTIC GIVEN THE EXISTING SNOW COVER
AND THE RECENT BUILDUP OF COLD TEMPERATURES THROUGHOUT THE
ENVIRONMENT. WE`LL OBVIOUSLY MONITOR THIS SYSTEM AS IT GETS CLOSER.
AT ANY RATE, ARCTIC AIR WITH VERY COLD TEMPERATURES WILL ONCE AGAIN
INVADE OUR REGION MONDAY NIGHT INTO WEDNESDAY AS HIGH PRESSURE BUILD
IN FROM THE WEST. STRONG NORTHWEST WINDS WILL ALSO RETURN FOR BOTH
MONDAY AND TUESDAY, BRINGING WIND CHILL VALUES DOWN TO NEGATIVE
TERRITORY. LESS HARSH WEATHER IS EXPECTED LATE WEDNESDAY INTO
THURSDAY BEFORE A WEAKER LOW PRESSURE SYSTEM DEVELOPS NEAR OUR AREA
AND INTENSIFIES OFF THE COAST AS IT MOVES AWAY.

 

Mount Holly seems to think this might stay all frozen north and west of the city

[Itstrainingtime]

My apologies to Ray. Ken, I believe that's the one I was thinking about. Snowpack went down to virtually nothing, and there was some pretty

bad flooding as a relsult. I only remember because my basement flooded!

Jumping in from the CPA thread...back in '96 I went to bed on the 17th of January with a 30" snowcover. The next morning it was gone. That resulted in part of the Walnut Street bridge in Harrisburg getting ripped apart and slamming into the Market Street bridge downstream. I could not believe that much snow could disappear that quickly...but it did.

[Kevin Reilly]

Record low at the Airport tonight is 2... I think we are breaking or at least coming very close.  Fresh snow cover light winds think -2 to 1 is attainable in most areas around the 5 county areas especially away from the city

[NJ_Ken]

Jumping in from the CPA thread...back in '96 I went to bed on the 17th of January with a 30" snowcover. The next morning it was gone. That resulted in part of the Walnut Street bridge in Harrisburg getting ripped apart and slamming into the Market Street bridge downstream. I could not believe that much snow could disappear that quickly...but it did.

 

...to make matters worse (if it is even possible in such a situation), I believe that a number of the floods in 96 were made even worse by ice dams forming and/or breaking up.  Much of that January (and much of the previous December) was cold in the east so many of the major rivers in Pennsylvania (from the Delaware to the Susquehanna to the Monongahela and everything in between) were frozen prior to the late January flood so the ice on the rivers broke up and began rushing downstream as quickly as the snow on the ground disappeared.  I forget if that is what happened at the Walnut Street bridge, but I believe in quite a few other places in PA, ice dams forming against bridges and adding to the pressure against them caused a number of bridge failures.  Luckily, nothing like that is going to happen this time around, no matter how warm it gets on Monday.