ChescoWx

JB excited this AM with pattern change....while I see the change coming....reversing winter warmth thus far?? I am not biting at this point "Since Christmas, our forecast team has been touting the pattern from the 20th on getting cold ( transition the 16-20. The turn around may rival the winter of 65-66 CFSV2 500 MB/temps 30 days starting Jan 20. If correct would erase the warmth of the winter thus far!"

63.7 currently which is the high temp - also represents a elevation record high for the day - eclipsing the old mark of 59.6 in 2014. The all-time Chester County mark of 67 set back in 1975 appears to remain safe

Agreed 100% - great idea!!

East Nantmeal Township - Chester County PA 8pm Obs Light Snow and 32.5 but appears accumulation is over. Total accumulation was 1.5" (ties for our largest snow of the season!) back on December 11th. With our 1.5" of snow today and the 1st for the new year we are at 69% of normal snow for January through today (2.2"). Seasonal Snow now stands at 3.5" which is only 42% of our normal seasonal snow of 8.4" through the 7th.

Heaviest snow as back edge approaches starting to cover paved surfaces temp at 32.9 - will measure when finished but had 0.5" at 5PM maybe approach the 1" mark - 2nd biggest snow of the season!!

East Nantmeal Township Chester County PA 5pm obs Light snow temp 33.7

Snow coming down at a near moderate clip with temp down to 37.6 - non paved quickly getting covered

Very Light Snow has begun in East Nantmeal with a temp at 41.0 DP 21.8

Latest WXSIM with 6z data holds serve with Snow arriving by 330pm. Snow gets heavy between 6 and 7pm before ending by 11pm. Total snow accumulation of 3.8" to 4.5". I still expect this to trend lower with the 12z runs... this will be a highly elevation dependent event with the only chance at approaching the above levels being above 650 ft - as Steve noted above lower spots I would be surprised if lower elevations see any more than 2" of snow at most.

WXSIM for NW Chester County with 0z data ticks up a bit again now showing 4" to 4.5" of snow by 11pm....

Nice FGEN forcing at about 8 to 9pm tomorrow....

WXSIM with 18z data has snow arriving by 4pm with some heavy snow around 7pm and ending by 10pm - total snow now up to 2" to 3"...it will change with 0z runs

Latest WXSIM for NW Chester County PA continues to have snow developing by 330pm and all over by 7pm with between 0.8" to 1.3" of snow

Latest WXSIM with 12z NAM/6z GFS has snow developing on Tuesday PM ending by 7pm with around 2 inches of snow for Western Chester County PA - more snow to the south on the latest NAM....something to potentially watch during our remaining 2 weeks before winter's potential return....

Steve - exactly a KU - no way - a snow event...possibly

I have been recording my own daily data from East Nantmeal Twp since 12/1/03. On another forum I was challenged on the validity of the data between multiple sites (albeit at the same elevation) So, to attempt to validate my data I started by first comparing 4 years of my daily data from 12/1/03 through 12/31/07 vs. the Final NWS COOP Observer at Coatesville 2W same relative elevation - I came up with an average difference of an incredible 0.001 degrees 52.672 vs. 52.673 over 49 months of daily data (surprised myself how close!). I then took the daily readings from the KMQS Airport AWOS (see below) and compared to my observations for the 11 years from 2008-2018 - again almost the same. Finally I ran a statistical significance test with both data sets with the hypothesis they are the same - the result a p-value of less than >.005. So the data sets are statistically significantly the same data for the period of record. The things we do to prove a point!

I would imagine so - I do not have any other long term data sites in the County with higher elevation. But I would expect it to be so - keeping in mind the biggest accumulation differences happen in those marginal events regarding boundary layer temps where even a couple hundred feet can make a difference. So likely most often in November and March/April events etc. Hope this helps!

So in analyzing completed decade data in the Chester County PA data set we see the following highlighted Trends. The Decade of 2010-19 was the 4th straight decade with increasing temperatures - which followed 4 straight decades of decreasing temperatures. Sounds kind of cyclical! This decade was the warmest decade in the data set with the current decade outpacing the previous warm decade (1910-19) by an average of 0.22 degrees or an increase of 0.4% This was also the snowiest decade on record besting the previous all-time snowiest decade with an average of 45.5" of snow per year. This eclipses the previous snowiest decade of 1900-1909 by 0.4 inches or 0.8% increase from the previous snowiest decade. Interesting to note that the coldest decade 1970-79 recorded the least average snowfall while the warmest decade 2010-19 saw the most snow. What will the future changing climate bring us?

Happy New Year to all! Another year in the books - let's see how we did climate wise The average temperature for 2019 was 53.6 degrees which was 2.7 degrees above normal - this was the 9th warmest year since 1983 and the 23rd warmest in Chester County history back to 1894. The warmest temperature was the 92.5 degree high on July 21st - this was 1 of only 2 times this summer we exceeded 90 degrees. We average only 4 such days in a typical summer season The coldest reading was the 4.8 degrees below zero low on January 31st Total precipitation was 55.10" (w.e.) which was 6.44" above our normal of 48.66" this was the 17th wettest year since 1894. Well behind the wettest year set just last year in 2018 when we recorded 79.21" Total snow fall was only 29.8" which was 6.2" below our annual normal snow total of 36.0" (our 63rd lowest total since 1894) No matter your weather this year I hope you all have a healthy and prosperous 2020! Paul

From JB after the 12z runs "The purpose of such extensive discussion on this is not to get into a fight over snow in central park, though I do think it will snow there and if I had to pick a number for snow by Mon am, there it would be 3. Its to get out in front of this, at the risk of being wrong, to explain why modeling is not the end-all to a problem, Say what you want, but there was no bowling ball rolling through with any hope a couple of days ago and this period Jan 5-12 has been on my radar for a while now. I can't help what happened before, and I see what is coming after, but in the meantime, there will be some triumphs with this storm as well as trauma. But this is not a backyard snow argument, for until the meteorology is settled the snow result is not clear, but with that warm water off the east coast, and the upper low coming right at it, I believe this low winds up between Cape May and Va beach, not north of that. As said, you may be 38 over 33 and raining and then bingo, the big wet flakes start coming down. The clipper on the euro spread snow further south than previous runs, and then next storm is further south. While the worst case ( lets say no snow south of I80 in the east and I 70 in the Ohio valley) is on the table, so is the best case as described in the earlier idea."

From JB today after 12z runs for the period before doom and gloom becomes full throated mid month!! "But there is a real chance here that the storm on the weekend does exit to the south and it does snow all the way to the coast. No longer are there just pressing height falls on the model. And this is what I am talking about, If you have different mass considerations, the movement of the mass, being lifted in one place, sinking n another, will bend the baroclinic ribbon, If you then focus the height fall center where the bend occurs you are in business, Truth be told, the 500 mb the Euro has is for a midwest to northeast snowstorm, it is still has to get some warm air out of the way, but they run at least makes 2 points. 1) it is not so far fetched that before the doom and gloom after day 10, there are winter threats and 2 ) Remember these are mathematical representations of a system that can not be tamed by men. Whether it happens or not, The 12z run while more bullish is likely not through correcting as it is desperate to try to string it out at the end, but that may be a function a feedback, You roll an upper low through the east like this and here is the problem btw the stringing out at the end and you probably are going to see it snow to the coast from the Delmarva north Of course the GFS had a nice little twist too it in the longer term And before that the GEFS jumps on a clipper but has nothing behind it and huge fight ensues with the Euro having less with the clipper and a cutter behind it, I like the middle. More clipper to push the cold, then a more southern track of the storm from Texas to the Va Capes. I think that storm will be further southeast, near the Va coast next week We'll see In the meantime there is room before the doom and gloom for some fun and games"

Dr Joe D "former Dr. Dewpoint" at WB from today's post... "This opens the arctic flood gates with coast to coast, border to border cold including at some point a Florida freeze threat"

AM Low here in East Nantmeal was 30.0 while down at Marsh Creek at lake level down to 22.7 - these higher AM min temps are killing any hope of making my December forecast ....not that hopes were that high anyway

AM low temps in spots just 2 miles away like down at Marsh Creek at 400 ft ASL made it down to a low of 25.8 while here a few hundred feet up almost 10 degrees warmer this AM at 35.6