potential for a few (million) mangled flakes part 2

[tornadojay]

In the most general sense, when I see that sharp hook in the contour lines on the 500mb heights chart on the GGEM (near SE Pa hour 36), I know an intense storm is on the way.

Of course thermodynamically it reflects a pocket of high vorticity and a positioning of jets that allow an efficient transfer of air from a developing low pressure center to a high pressure center. But without understanding the underlying dynamics, I can always rely on the look and feel of the graphics to tell much of the story.

Yes.. the hook (or shorter wavelength) of the 500 mb height field implies an increase in the amount of curvature vorticity, which in turn, leads to greater divergence on the lee side of the trof. That in turn leads to surface pressure falls, in part, due to conservation of mass. The air above that diverges must be replaced somehow, and air parcels rise to fill in that void, thus lowering the surface pressure. So, among other things, the greater the voriticity advection, the stronger the storm.

[TheTrials]

GFS is nice for KBDR too after the inch of rain. That deform band is impressive

[Alpha5]

MM5 is not that great outside of 24 hours but the trend continues....high res vs low res models. I'd look for the Euro to follow a more NAM like solution

[eduggs]

I thought the 540 line looked a little weird on the UKMET and here is why. The surface is an unmitiaged torch for NYC. Here is the sounding. Its 3.4c with a dew in the mid 2's.

http://vortex.plymou...el&size=640x480

I don't recall ever having looked at text output of a UK sounding, but I know the graphical soundings I've seen are always too warm in the lower levels (often absurdly so). I've never investigated whether that was a software problem or bad data. But suffice to say I do not use the UK for temperature profiles.

[TheTrials]

FWIW, the Hi Res NMM and ARW are quite warm in terms of thicknesses with the ARW bringing the 850 line up to NYC like the GFS does.

EDIT: That was through 33, they cool at 36.

[TheTrials]

I don't recall ever having looked at text output of a UK sounding, but I know the graphical soundings I've seen are always too warm in the lower levels (often absurdly so). I've never investigated whether that was a software problem or bad data. But suffice to say I do not use the UK for temperature profiles.

Interesting. The Ukie soundings tough with the off hours, but they were colder in the lower levels yesterday when I looked at them.

[CoastalWx]

The fact that the low goes se of NY and the dynamics go through the roof might allow that ra/sn line to come awfully close to the city. As long as the lows don't go too far nw...this may change quicker than we think. Something to watch anyways.

[TheTrials]

Hi Res Sim Radar. Thicknesses begin to crash here

[CoastalWx]

The fact that the low goes se of NY and the dynamics go through the roof might allow that ra/sn line to come awfully close to the city. As long as the lows don't go too far nw...this may change quicker than we think. Something to watch anyways.

Change to snow quicker that is.

[earthlight]

SPC WRF, very far out of it's reliable range, is a nice hit. We can't see 850 temps or thicknesses. But we can see simulated radar/precip and surface temps.

Simulated radar

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/refd_1000m_f36.gif

Temps

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/t2ms_f36.gif

[famartin]

For reference purposes:

Winter Precip Types by Thickness Values

What Causes Thundersnow

Wet Bulb Calculations

General Winter Precipitation Forecasting

Relationship between Jet Streak and Vorticity Generation

Snow Sounding

Cold Rain Sounding

This post should be in its own pinned thread.

[TheCloser24]

That simulated radar just looks unreal! All that moisture going inland, that is going to be very heavy snow.

[ag3]

Every hi Res model has a period of intense snowfall for our area after hour 33.

[Nikolai]

One of my favorite memories last winter was the 1/26 storm... another example of crazy dynamics giving us an excellent outcome.

After the surprise snow in the morning, we had light rain/zr for most of the afternoon/early evening... I told my friends we were about to have a sleet t-storm and they didn't believe me, two minutes later... after that, they again were in disbelief that we were going to have a significant amount of snow... another hour or two later, we were absolutely ripping snow at 3-4"/hr.

I still think the city sees 4" when all is said and done, and the model wobbles are just that... while the NAM may be over-amped QPF wise, it's wise to remember recent QPF patterns and the fact that when it has precipitated this fall, it has often done so in an extraordinary manner (how else would we have had our wettest month on record...). If recent events are any indicator, the solutions that are showing the higher QPF-values (and accompanying intense dynamics) certainly have some merit.

[earthlight]