The dry slot is supposed to happen. The real show is when the phase happens allowing the precip to our west to explode over the area giving us our snow. Right now the interesting thing is the radar is actually west of where the models have this band of precip. And even more interesting is the backbuilding trying to occur across PA into NJ. The main show starts after 7-8pm:
I am having a tough time seeing some observations by people who think this low is moving faster than expected. Above we can see our low is really getting its act together and slowing down. Over the leas 2 hours it moved very little and the models show a big leap happening by next hour. This image tells me models are 1-2hrs too fast! Radar continues to not match up with models at all.
Models are missing this banding going on across DE/NJ. This impacts the models because it throws off the latent heat distribution and with the models favoring this farther east they knock down the ridge more allowing a faster more eastward movement. The sfc pressure image above is starting to back this up as the models should be too quick with the sfc low at 18z obs.
I think we all need to be realistic with expectations of what is going to happen this evening. Per NWS radar the band of snow coming through South Central PA is no more that 10 miles wide. It is simply a line of snow showers. I understand the 'models' are predicting this and that but all you have to do is look at what is happening on water vapor and IR to see that there is not going to be much more than a coating this evening. The core of the upper level low is over eastern Lake Erie and hence most of the energy transfer is up in Central upstate New York.
Things just didn't line up for southeastern PA this time.
Thanks SgtSnow. One thing to keep in mind is that everything I said earlier regarding lower tropospheric dynamics is still the case and one band of 2"+ per hour snow setting up for a while and the earlier forecast may verify after all, it will be interesting, we will get snow, it just does not appear as though it will be what the nws and I were expecting earlier.
There's a lot going on, and I can sum it up pretty quickly by saying this; the forecast this morning was based on a lot of things happening and some aren't going to, that's why the NWS and the models blew this forecast, it's not that we wont get anything but it won't be like earlier expected, though there was a lot of good science to back up that forecast which is why the nws issued it, (and also zero science behind the wild guesses of "a coating to 2" and the like, and if that turns out to be the case and those people take any credit for their dart toss of a forecast being correct then shame on them), I will say that for my area, central Montgomery county 3-5" looks good as of now.
3pm wsw Snow Accumulations 4 To 10 Inches...Along With Around A Trace Of Ice. Even If Accumulations Are Only Around 4 Inches The ...Combination Of Snow And Temperatures Falling Below Freezing Will Probably Become A Major Travel Problem During The Evening Commute...Especially After 6 PM. • Timing...Mostly Rain During Midday. Precipitation Changes Back To Snow Late This Afternoon And Evening. The Snow Will Fall Heavily For A Time...With A Period Of 1 To 2 Inches Of Snow An Hour Possible.
Ike 34, anything is possible. Pick the 5 right Powerball numbers and winning the lottery is possible. According to the NWS however, that scenario (develop and just sit over us) seems highly unlikley with a new forecast for just about the entire Philly metro area for no more than 2-4 (in fact most places even north of Philly are at 1-3)