Snowfall Dose of Reality Needed?
After today's noontime run of the GFS a dose of reality check is needed after seeing some discussion on the internet about thoughts of up to foot of snow and thoughts of a big time snowstorm in Philadelphia proper based on what the GFS showed. Keep in mind these graphics are not human forecasts but merely computer model representation and even the representation has some broad interpretation as you will see.
I cautioned earlier this winter about the usage of Coolwx.com's precipitation soundings and said you need to take them with a grain of salt. If you looked at the noon time GFS run for Philadelphia today, you'll see according to Coolwx.com the following precip type breakdown and the following amounts in rain, snow, and some sleet in the changeover period. Going by Coolwx.com, the GFS computer model is saying about 8.6" of snow for this storm in Philadelphia at the airport.
One of the problems with Coolwx.com is that it, according to its website, it misdiagnoses precipitation type as sleet or rain...or sometimes I have found rain is diagnosed as snow or sleet although the actual GFS soundings for the storm say there is not enough cold air to produce snow.
Earl Barker's Wxcaster.com website has snow graphics of the GFS and NAM models. The above chart shows snowfall for our region from the Sunday night and Monday storm according to the noontime GFS model. Notice the huge cutoff between coating type accumulations in the western suburbs to 6-8" of snow in Bensalem and Levittown, with a foot being forecasted on the GFS in North Jersey. This could be a situation where Philadelphia International Airport sees a coating of snow and Northeast Philadelphia gets 4-5" of snow if this version of the GFS is right. Is it? I'm not sure. The NAM paints a much different picture and gives very little snow to the immediate region as the storm that is depicted is weaker and bombs out later on. In past storms this winter the NAM has performed poorly with storms but given that storm performance has never really been good on the computer guidance overall the NAM solution can't be totally discounted.
Many, myself included, have been burned by both sets of graphics -- Coolwx.com and wxcaster.com -- in analyzing what is going to happen. I have found that wxcaster.com snowfall graphics this winter is better in model analysis than Coolwx.com. That's not to say Coolwx.com is not a bad site but in any model analysis precipitation analysis needs to truly be take for a grain of salt. Given the lack of consistency in the model guidance and vast changes from run to run, forecasts should be and need to be low confidence. A 20-30 mile difference in development within the main focus of the storm will result in a significantly different final outcome and as a result there is huge bust potential in any forecast.
I cautioned earlier this winter about the usage of Coolwx.com's precipitation soundings and said you need to take them with a grain of salt. If you looked at the noon time GFS run for Philadelphia today, you'll see according to Coolwx.com the following precip type breakdown and the following amounts in rain, snow, and some sleet in the changeover period. Going by Coolwx.com, the GFS computer model is saying about 8.6" of snow for this storm in Philadelphia at the airport.
One of the problems with Coolwx.com is that it, according to its website, it misdiagnoses precipitation type as sleet or rain...or sometimes I have found rain is diagnosed as snow or sleet although the actual GFS soundings for the storm say there is not enough cold air to produce snow.
Earl Barker's Wxcaster.com website has snow graphics of the GFS and NAM models. The above chart shows snowfall for our region from the Sunday night and Monday storm according to the noontime GFS model. Notice the huge cutoff between coating type accumulations in the western suburbs to 6-8" of snow in Bensalem and Levittown, with a foot being forecasted on the GFS in North Jersey. This could be a situation where Philadelphia International Airport sees a coating of snow and Northeast Philadelphia gets 4-5" of snow if this version of the GFS is right. Is it? I'm not sure. The NAM paints a much different picture and gives very little snow to the immediate region as the storm that is depicted is weaker and bombs out later on. In past storms this winter the NAM has performed poorly with storms but given that storm performance has never really been good on the computer guidance overall the NAM solution can't be totally discounted.Many, myself included, have been burned by both sets of graphics -- Coolwx.com and wxcaster.com -- in analyzing what is going to happen. I have found that wxcaster.com snowfall graphics this winter is better in model analysis than Coolwx.com. That's not to say Coolwx.com is not a bad site but in any model analysis precipitation analysis needs to truly be take for a grain of salt. Given the lack of consistency in the model guidance and vast changes from run to run, forecasts should be and need to be low confidence. A 20-30 mile difference in development within the main focus of the storm will result in a significantly different final outcome and as a result there is huge bust potential in any forecast.
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