ChescoWx

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

Beautiful day today across Western Chester County....great to see the pattern and analogs aligning for what should indeed be a memorable core of the JFM winter months of storms and rumors of storms....fun times ahead for those that like winter weather in this area!

Here in Chester County we have a 1 year of every 4 or 25% chance of having snow on the ground on Christmas Day. The last 10 years are aligned with that average as we have had 3 White Christmas Days since 2009. The most recent Christmas being 2017 with 0.3" / 2012 with 2.0" and 2009 with 4.0". The greatest snow depth recorded on Christmas was the 25" of snow on the ground Christmas Night following a 21.2" Christmas Eve storm that including frequent lightning and thunder on Christmas Eve 1966 - this followed the 8.8" that fell earlier that week on the December20th 1966. The next snowiest Christmas was from a storm that began at 8am on Christmas day back in 1909 and continued into the next day ending at 6:30am on the 26th (for both of these events I have attached the coop reports for the month for both years including W.T. Gordon's note from 1909 that it was "snowing furiously and very deep snow" and the Philadelphia Electric Company COOP in Coatesville reporting that "highways in bad shape" . Of note the Christmas 1909 Blizzard represents our 2nd greatest individual snowstorm in Chester County history as 38" had accumulated by the time the storm ended on the 26th. The only greater snowstorm in our history was the 3 day Blizzard of February 12-14, 1899 when a whopping 45.3" of snow fell with temps mainly in the single digits during the storm duration. Of note temps remained below freezing the remainder of December 1909 with 39" of snow on the ground on New Years Eve. The coldest Christmas Eve and Day occurred back in 1980 when the morning lows both days were below zero with the 24th at 2 below and Christmas Day at 6 below zero. Of interest just 3 years later in 1983 we also had below zero Christmas Eve and Christmas Day with lows of 1 below and 3 below respectively. That Christmas Day in 1983 was also the coldest Christmas Day with a high of just 6 degrees above zero. By contrast the warmest Christmas Eve was just 4 years ago in 2015 when we recorded a high temp of 68.5. Christmas Day 2015 was also short sleeve weather with a high of 66.7 just off the record high for Christmas Day of 67 degrees set back in 1964. The wettest holiday was the 1.63" that fell on Christmas Eve 1986 and the 1.92" that fell on Christmas Day 1967. No matter your weather I hope all of you have a Merry Christmas!! All the best, Paul December 1966.pdf December 1909.pdf

Temps on one thermometer have finally bumped above Freezing - about 12 hours of ZR - plenty of ice in trees and non-paved surfaces - roads seem fine

Been ZR here in East Nantmeal for almost the past 6 hours (since 6:10pm) temp slowly creeping up - now at 32.3...very icy on non-paved surfaces

1 is about 30 feet higher other 2 at same elevation...

Temperature has continued to fall across NW Chester County this evening now down to the low for the day at 32.1 (I have 2 other thermometers down to 30.0 and 31.1) we have a nice glaze on the deck and ZR continues to fall steadily here in East Nantmeal Township

Some mainly sleet here in NW Chesco with a few flakes mixed in temp at 33.8

Light snow and temp slowly dropping from 34.2 now down to 33.7 - schools closing early in Chester County

WWA for NW Chesco for up to 2" of snow but doubt we see more than mood flakes today. Just a few light flakes currently with a temp at 33.2. WXSIM has never been impressed with this "event" will need to keep an eye on temps this evening to see if any rain that falls freezes later on contact - but WXSIM keeps us above so should be no big deal

WXSIM for NW Chesco sees this as a pretty minor "winter" event with some light snow developing by 7am and continuing off and on through much of the day with around 1.0" of snow before mixing with IP by 4pm - then a pretty quick transition to plain rain heavy at times by 9pm in the evening

This event has been a mighty consistent storm track for the last week with a slight jog to the south over the last 2 days - JB and most guidance has always had the low to the south of the M/D line since last Monday ....what I suspect will happen is some initial snow with the overrunning warm front and then a pretty quick change to non-snow....but of course the further N and W you go from the I95 corridor the tougher it will be to scour out the LL cold - so some moderate icing (ZR over IP) likely from the PA Turnpike north and west. The bigger issue in my mind is how much precipitation is involved. Think we see a dry slot tomorrow afternoon and then many spots will rise to above freezing from the PA Turnpike south and east. Also, still keeping an eye on next weekend....could be a significant event from this vantage point.

Yep same here in NW Chesco....it's easy to change from Snow to non-snow of course....but going from ZR to plain rain is the problem....no doubt we will change to snow faster than progged but struggle to get above freezing especially the higher spots like around here....

Not looking like much front end snow....but sheesh if this amount of ZR were to fall...