It is not even December yet and already we have experienced much below normal temperature departures and we are about to brace ourselves for a Nor'easter set to strike tomorrow morning. This potent system is going to bring accumulating snow to the area, the first of the season for many, and some rain. Where the rain/snow line sets up is the toughest part of this forecast, because obviously if your area is mainly seeing snow instead of rain you will see higher accumulations.
ANALYSIS:
Due to a process called dynamic cooling, when falling precipitation helps cool off the atmosphere, there is a good chance many areas that may start as rain changeover to a heavy wet snow. The 00z EURO model last night showed 850 mb temps crash once the heaviest precip. began to fall. They go from 0 to -1*C down to -4*C for many locations. That means at the 850 mb level, the column is cold enough to support snow instead of rain.
From both water vapor imagery's, we can notice a couple of things. First off, heights along the east coast are positively tilted due to the strength of the STJ s/w (shown by a yellow "X" in southwest TX). The combination of a mid-level trough and a potent STJ s/w is helping heights along the EC to rise and allow this system to track up the coast. Secondly, check out how much the Gulf is helping to fuel this system down by Florida. A southerly flow is allowing convection (t-storms) to pop-up and we will have to see exactly how much of that convection comes up the coast along with the storm as it organizes down there.
Another key factor to watch is the 700 mb level. If an H7 vort closes of south or east of the area, that will increase VV's and help promote frontogenesis. This would surely increase precipitation rates and lead to higher snow totals. Right now, models are signaling the greatest lift will be along the coast. Check it out below:
TIMING:
Start (from south to north): 6am - 8 am
Heaviest Precip: 1pm - 3pm
End: 7 pm - 9pm
SNOW MAP:
Like I said before, this is a trough and tricky forecast. Determining where the R/S sets up is never easy. But I feel this system is going to track right along the BM and bring a heavy swath of snow to areas northwest of NYC. NYC itself will be right on the line. If colder air moves in sooner, they will be more in the 3-6 inch zone than the 1-3 inch. Honestly, a safe call for NYC is probably 2-4 inches. Coastal areas will struggle to see accumulations due to warming 850 mb and 700 mb temps, not to mention surface.
We'll see how this plays out! Stay safe and Happy Thanksgiving!
-Frank Paparatto
www.njstrongweatherforum.com
No comments:
Post a Comment