ChescoWx

WXSIM with 6z data warmed about 1 degree from last forecast - still shows a mix of rain and S+ during heaviest precip but with the slightly warmer temps only a slushy 1/4 inch of snow - maybe we are back to a foot with the 12z GFS and NAM data! Since there is no real snow in the forecast we track WXSIM snow!! See you on the anticline this weekend! Friday night: Mostly cloudy to cloudy in the evening, becoming dense overcast after midnight. A mix of rain, sleet, and snow likely after midnight. Low 32. Wind chill ranging from 23 to 40. Wind east-southeast around 6 mph in the evening, becoming 13 mph, gusting to 20 mph, after midnight. Chance of precipitation 70 percent. Precipitation (liquid equivalent) mostly around half an inch. Snow or ice (on ground) accumulation about a quarter inch. Saturday: Dense overcast in the morning, becoming mostly cloudy to cloudy in the afternoon. A mix of rain and snow likely in the morning, then rain likely in the afternoon. High 40. Wind east-southeast around 15 mph, gusting to 21 mph, in the morning, becoming 6 mph in the afternoon. Chance of precipitation 80 percent. No snow accumulation expected.

LOL! That made me laugh!! Can you imagine if JB had access to this output? If so he would have no doubt sited it this week....he can always find the snowiest model or outcome!! The WXSIM programmer mainly designed it for forecasting temps....which like last weekend actually outperformed the NWS point and click for my area. The WXSIM steadfastly stuck with temps below freezing while the NWS said 37....Like any program it is only as good as the data it is ingesting....in this case the GFS for longer term and the NAM blended in for shorter term forecasts. Plus like any model when multiple days out it will not be as accurate. When it comes to snow forecasts it will often bounce around especially as it tries to account for my areas relative higher elevation mainly for storms like this upcoming weekend which have the feel of a March storm (which often has big differences over short distances based on just 200 ft of elevation gain etc.) it tries to nail the BL issues and will make a totally different forecast if the BL goes up a degree (like the latest 6z run this AM see below - where it is back to a mix with little accumulation) It should get more consistent as we get within 24 hours. I have had the tool for over 10 years and it is a fun tool for the weather hobbyist and really the only one that let's you make a true in your backyard forecast. But like any tool it is just one I would use if making a forecast....all of our go to forecasts should today and always remain the great team at the NWS in Mount Holly (we are fortunate to have the best office in the USA in my humble opinion!!) Paul

WXSIM with 18z data continues to see a real battle of precip types based almost entirely on relative elevation on Saturday. When the precip is heavy it see S+ as it lightens it's just rain. Temps never fall below freezing at the surface hanging between 32.7-33.7 with 850's just below 0c during the time of heaviest precipitation. WXSIM is back up to around 10" of very wet snow. Really feels like a March type snowstorm. In some ways reminiscent (of course not the amounts) of the March 1958 elevation driven event where just 6 miles up the road at my elevation Morgantown PA recorded 50" between the 19th-21st with 44" falling on the 20th alone with temps just above freezing for most of the event. The 6 days leading up to the event saw temps in the mid to upper 40's and the day after the snow ended went right back up toward the 50's and within 5 days all 50" was gone.

AM low this morning 16.7 2nd coldest reading this season behind only 12/19 at 15.6. Of note today marks on average our coldest day here in Western Chester County with an average temp of 24.0 - it's all uphill from here!

The WXSIM still shows 1" to 2" of snow here at around 685 ft but it's battle regarding precip type when heavy it's snow and rain when lighter. Looks like a typical March event with precip type being heavily elevation dependent. I could see spots under 400 ft with nada / 2" over 600 ft /up to 3"+ over 700 ft in the philly burbs and NW NJ

ruh roh! WXSIM trend is not our friend....with 18z down to 1" to 2"..... Saturday: Dense overcast. A mix of snow, sleet, freezing rain, and rain likely in the morning, then a mix of rain, snow, and sleet likely in the afternoon. High 35. Wind chill around 25. Wind east around 10 mph, gusting to 15 mph. Chance of precipitation 80 percent. Precipitation (liquid equivalent) mostly around an inch. Snow or ice (on ground) accumulation 1 to 2 inches. Above-ground freezing rain accumulation up to 0.1 inches. Saturday night: Cloudy in the evening, becoming dense overcast after midnight. A mix of rain and snow likely in the evening, then a slight chance of a mix of snow and rain after midnight. Low 31. Wind chill as low as 24. Wind north around 9 mph, gusting to 15 mph, in the evening, becoming west-northwest after midnight. Chance of precipitation 70 percent. Precipitation (liquid equivalent) mostly around a quarter of an inch. No snow accumulation expected.

took a deeper looks at the WXSIM forecast output when it thinks it is snowing....has winds ENE and temps nearing but just below 0c at 850mb....it will change with 18z!

Steve already down to only 6" to 10" trend is not our friend......

truncates NAM and all GFS once past NAM run window....

WXSIM with 12z GFS and NAM now down to "only" 6" to 10" of wet snow (keep in mind as someone questioned me on the last one - it's accuracy at this range is suspect at best - it simply takes a blend of the gfs and nam and makes a forecast based on local factors (elevation etc.) - verification will of course not be this... Friday night: Mostly cloudy in the evening, becoming mostly cloudy to cloudy after midnight. A slight chance of a mix of sleet, rain, and snow after midnight. Low 31. Wind east-northeast near calm in the evening, becoming 4 mph after midnight. Chance of precipitation less than 20 percent. Precipitation (liquid equivalent) mostly less than a tenth of an inch. No snow or ice (on ground) accumulation expected. Saturday: Dense overcast. A mix of snow and rain likely. Breezy. High 35. Wind chill ranging from 22 to 27. Wind east-northeast around 12 mph, gusting to 21 mph. Chance of precipitation 80 percent. Precipitation (liquid equivalent) mostly between 1 and 2 inches. Snow accumulation 6 to 10 inches. Saturday night: Cloudy in the evening, becoming dense overcast after midnight. Patchy light fog. A mix of rain and snow likely in the evening, then a chance of a mix of snow and rain after midnight. Low 31. Wind chill ranging from 23 to 29. Wind east-northeast around 7 mph, gusting to 17 mph, in the evening, becoming west-northwest after midnight. Chance of precipitation 70 percent. Precipitation (liquid equivalent) mostly around a quarter of an inch. Little or no snow accumulation expected.

Let's do this again - latest WXSIM for NW Chester County PA with 12z NAM and 6z GFS for next weekend- this could be a great example of an elevation driven event inland of the I95 corridor - not cold but just cold enough especially with a bit of elevation for a wet snow event....this will change a bit but I do believe this is something to keep an eye on as the week moves on Saturday: Dense overcast. A mix of snow and rain likely in the morning, then snow likely in the afternoon. High 34. Wind east around 10 mph, gusting to 17 mph. Chance of precipitation 80 percent. Precipitation (liquid equivalent) mostly around 2 inches. Snow accumulation 12 to 16 inches. Saturday night: Cloudy. A mix of snow and rain likely in the evening, then a chance of a mix of snow and rain after midnight. Low 30. Wind chill as low as 23. Wind north around 9 mph. Chance of precipitation 70 percent. Precipitation (liquid equivalent) mostly around a quarter of an inch. Snow accumulation about an inch.

JB riding the snowiest model - the Canadian for next weekend's potential event....call me stunned!

And yet this recently completed decade was the snowiest on record for Chester County PA.....weather like many things runs in cycles and of course the climate is always and will always be changing

Picked up 0.3" of snow with the squall that came through around 10pm temp down to 30.5

Latest Wxsim for next weekend with 12z NAM/GFS combo - of course we don't shovel model snow!! Saturday: Dense overcast. A chance of snow in the morning, then a mix of sleet and snow likely in the afternoon. High 31. Wind chill ranging from 11 to 18. Wind east-southeast around 7 mph, gusting to 16 mph, in the morning, becoming 10 mph, gusting to 18 mph, in the afternoon. Chance of precipitation 80 percent. Precipitation (liquid equivalent) mostly around 2 inches. Snow or ice (on ground) accumulation 12 to 16 inches. Saturday night: Cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog in the evening. A chance of a mix of freezing rain, sleet, and snow in the evening, then a slight chance of a mix of rain and snow after midnight. Low 30, but temperatures rising after midnight. Wind chill ranging from 19 to 29. Wind south around 10 mph, gusting to 20 mph, in the evening, becoming west-southwest after midnight. Chance of precipitation 60 percent. Precipitation (liquid equivalent) mostly less than a quarter of an inch. No snow or ice (on ground) accumulation expected. Little if any freezing rain accumulation.

Looking ahead to next weekend the WXSIM has light snow arriving by 7pm Friday night becoming all sleet by 10pm with heavy sleet at times through mid morning than becoming ZR in the PM and finally all rain by 4pm - total snow (mainly sleet) accumulation 3" to 4" - temps than plummet on Sunday with a low Monday AM of just 5 degrees with a high on Monday of 13 above

For our 2nd straight day a record high...and this time an all-time all elevation Chester County record of 64.4 at 1:44am besting the old mark of 61.8 set just 3 years ago. Also recorded 0.35" of rain with the frontal passage with a high wind gust of 24mph

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!!

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

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"