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WXSIM Forecasts for NW Chester County PA


chescowx
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Wxsim run with 12z data.....and wait for it - another big change based on the latest GFS/NAM runs

 

To simplify precipitation arrives Sunday at 1am and continues as mainly snow and sleet with a brief period of ZR.

Total precipitation is 0.80" thru Tuesday evening with still some light snow or flurries at that time.

 

5" to 8" of snow/sleet accumulation

 

 

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Latest Wxsim with 18z data continues a somewhat colder solution with GFS/NAM data

It has snow arriving by Sunday morning at 6am continuing at various rates with some mixing at times with sleet and for a couple hours ZR through 2am Tuesday. Temps remaining in the 20's during the entire storm. 

Overall about 5" to 7" of total snow/sleet before ending

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Latest Wxsim for NW Chester County PA with 18z data has some light sleet/rain mix arriving by 1am Monday becoming all rain by 6am (.02" falling as mix) then all rain with 0.22" before ending as some snow flurries by 10pm Monday night

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Wxsim with 6z NAM/GFS data trending a bit colder and wetter than yesterday - it now has 0.42" of precip with 0.26" falling as ZR.

Precip that falls between 1 and 7am Monday morning with temps just below freezing then temps rise a little above with just rain the rest of the day before ending as some flurries.

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Latest Wxsim has temps staying in upper 20's all day but very little precip .06" of course won't take much to cause some problems.

Wxsim also has a couple of inches of snow by Thursday AM rush hour and the start of another snowstorm on Sunday AM with a couple more inches on the ground at the end of the current run period

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Hi Andy,

Yes it actually does it's own tracking of actual from my weather station vs what it forecasts. It then tries to learn by incorporating errors. It really can only forecast temps the snow/rain etc. is just straight from the GFS/NAM combo it uses so as you have noticed it will swing wildly from the 12z to 18z runs but that is simply all it has to deal with. 

Paul

Just curious, do track the accuracy of Wxsim? Like 3 days out down to 1 day out?

Thanks for posting your Wxsim

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Latest Wxsim for the NW Philly burbs (15:1 ratio for Sat/Sun and 12:1 for Tues/Wed)

Saturday 1pm Light snow temp 20.9

4pm Mod snow temp 20.5 (1.1")

7pm Mod Snow temp 18.7 (1.5")

10pm Light Snow temp 17.2 (2.3")

2am snow ending temp 14.0 (2.7")

 

Tuesday

7pm Mod Snow temp 23.1 (0.8")

10pm Heavy Snow temp 21.4 (2.8")

1am Heavy Snow temp 21.2 (5.2")

7am snow ending temp 21.2 (6.5")

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Wxsim program with 18z GFS/NAM data with 10:1 ratios for NW Chester County PA

 

Light snow by 1pm Saturday temp 17.7

4pm Moderate Snow temp 20.2 (0.5" snow)

7pm S+ 20.6 (1.6")

10pm S+ 22.6 (3.8")

1am Heavy IP and snow temp 25.5 (5.8" snow/IP)

4am ZR/IP temp 28.1

7am ZR 29.3

10am precip ending temp 31.4 (total precip 1.04")

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Latest Wxsim with 6z data naturally ramps up the precip with the NAM influence and shows a heavy front end thump of snow with now up to 10" of snow to IP to ZR with temps never rising above 30.2 during the precip which ends by 7am Sunday by which time 1.65" of precip has fallen

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Wxsim with 12z data has snow arriving in NW Chesco by 1pm with Heavy Snow between 7pm and midnight then some IP/Snow mix thru 1am by which point it shows about 10" of snow/IP (1.09" w.e.) then finishes off with 0.21" of ZR before ending by 8am temp tops out at 29.8 at that hour.

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Wxsim with 18z GFS/NAM data for NW Chester County Pa

Similar story as before snow arrive by 1pm temp 16.3

Heavy Snow between 4 and 10pm with 7.3" of snow by 10pm

Heavy Snow mixed with IP by 1am with 10.5" of snow/sleet

then IP to ZR mix before ending by 7am

Temp rises to 27.6 by 7am

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Tom

You and me both....when have the GFS or NAM been correct this far out......but again the program is only as good as the GFS/NAM input - which only changes every 6 hours.  Tom, fortunately the Professionals have better tools than amateurs like you and I !!

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Tom

You and me both....when have the GFS or NAM been correct this far out......but again the program is only as good as the GFS/NAM input - which only changes every 6 hours.  Tom, fortunately the Professionals have better tools than amateurs like you and I !!

Thats what I dont get though, neither the nam or gfs show 10.5" of snow and temps staying below freezing the whole time.

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Tom as you and I both know that is the problem with taking any one numerical model or program's interpretation literally....which neither you or I fortunately ever do. They are only guidance and I have never seen a professional take any one run of the GFS/NAM/EURO ....or yes even a program that blends two of these inherently imperfect numerical models like WXSIM  into making a professional forecast. That is why you and I are what we are....amateurs and hobbyists and we leave it to the great professionals that we have in Mt. Holly to do what they do....we are fortunate to have what I believe are the best local NWS team doing what they do best and this year has really underscored that. No matter how much I like to look at other sources and there are some great ones like (Wxsim/WxBell/NYNJPAWeather etc). there is at least for me only one place I go for a real forecast that I trust...and I suspect you will agree with me!!

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Wxsim for NW Chesco with 6z GFS/NAM data

Snow by 1pm temp 19.6

S+ from 4pm-10pm (5.7" snow)

Mixing with sleet by 11pm with 6.6" of snow

ZR sleet mix after midnight ending - looks like 7" - 8"  of snow/IP before mostly ZR precip ends by 5am with temps rising to 27.7

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Hi Paul...I think the recent WXSIM output for your location seems good. Interesting to note the cold surface temps being shown. I continue to think models are warming the surface too rapidly in the NW suburbs, and there is a chance for more zr and little or no plain rain. We'll see.

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Latest Wxsim with 6z data for NW Chester County has a brief period of IP/Snow changing to ZR pretty quickly and then the struggle to get the surface above 0c....unfortunately it does not manage to do so till 8am on Monday morning by which time 0.75" of w.e. has fallen. Also of interest in forecasts my snow cover to be all gone by Wednesday - today is the 36th consecutive day of snow depth greater than 1.0"

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Latest Wxsim with 6z data for NW Chester County has a brief period of IP/Snow changing to ZR pretty quickly and then the struggle to get the surface above 0c....unfortunately it does not manage to do so till 8am on Monday morning by which time 0.75" of w.e. has fallen. Also of interest in forecasts my snow cover to be all gone by Wednesday - today is the 36th consecutive day of snow depth greater than 1.0"

I expect mine to be gone to by wednesday if the current forecasts are correct.

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