What I will be tracking through the overnight hours is the intensity of the s/w seen over Canada extending down into the Northern Plains. The deeper this s/w can get the more precip we will see stream northward. The circle shows where precip is expected to develop in the beginning stages around 4AM. The intensity and timing of the development of this precip will give us clues on how the event will unfold downstream. The last thing is the cut off low off CA where it could aid in pumping up heights depending on strength and position.
This is the sounding for Philadelphia when the precip is moving in. One thing that stands out is the very cold temperatures throughout the profile with no threat of mixed precipitation. The sfc temperatures are very cold below -5C with a very deep dendritic growth zone. The reason I went slightly higher is because of this deep snow growth zone because it extends over 300mb! Notice as it falls from the cloud it moves through avery small layer of above -10C. This means the dendrites will have very little interference with supercooled water droplets.
This means we can expect big powdery flakes. The ratios will exceed 20:1 in some locations given the favorable thermodynamic profile and the snow growth layer extending so close to the ground. The main trigger for the precipitation will coincide with the lower levels as the WAA/isentropic lift move in:
Models and water vapor analysis have been showing the *potential* for a better looking coastal coming closer to the coast keeping in heavier precip longer. Eventhough the latest data suggest this won't come close enough to be significant but something to nowcast. The WV imagery looks more promising now with the s/w appearing better defined than models show, but differences are very minor right now.
The snow map: Will adjust if needed tomorrow morning!
Matt: I am pretty sure it will be, the questions are, how much of an increase, when does the phasing occur, how close to the coast does the low develop/intensify and where, how much does the above normal water temperatures and frigid air mass over the eastern U.S cause baroclinic forcing and is it more pronounced than currently indicated, these are a lot of unknowns so time will tell, it will certainly be interesting though, (man this was a run-on sentence haha). I am sure that the baroclinic forcing will cause a more powerful low than currently forecast, the issue is how close to the coast does it develop as a phased system.
weatherman71; That solution is a possibility if the S/W strengthens up and the heights amp up. It is unlikely but concerns me because it would only take a very small change to allow these systems to phase sooner and the trend has been higher qpf and low development closer to the coast, if we had a Greenland block and 50/50 low, things would be different, as I have said before, the NAO was almost exactly the same from start to finish for the '79 Presidents day storm so that is not the issue here.
P.S: The water vapor imagery from the southern states and GOM will give an indication as to how much moisture is entrained and assisting in increasing qpf, which the ECMWF seems to already be ahead of the curve if more moisture gets pulled northward than currently predicted. I understand that the majority of you guys already know this but as I have said before, if just one person learns something because they didn't know, it was well worth posting.
Hey, it's JPM again. Computer models do not handle WAA very well, the easiest way to know if totals will be higher then forecast is if the snow starts falling earlier then forecast, that may sound elementary and it is but it also means that the WAA wasn't handled properly and so totals would be a bit higher. My posts from a few minutes ago on the other discussions go into more detail on my thoughts regarding this event.
Hey everybody. Take a look at this Futurecast. Looks more juiced up dont you think? And the snow ratios are high so good news for snow lovers.http://hp6.wright-weather.com/wrf_nmmeast-radar-loop_1hour.gif
That is in line with my call for 2-3" for Philly yesterday .. but I think SE Jersey, Southern and Central DE and the eastern shore of MD, might get 3-5". They were predicting 0.05 of precip yesterday down here and we wound up with a 3-5" snowfall. Any sort of WAA in these temperatures will mean 1" or more snowfall rates per hour.
Well reasonable map mike and keep us updated! Well another storm with a close call, but now it's time to look beyond this! So once this storm rolls by when will out next best chance be for a storm threat? Keep us updated though for this storm!