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December Banter 2018

George BM

By George BM,
in Mid Atlantic

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nw baltimore wx

nw baltimore wx

Posted
Posted
3 minutes ago, North Balti Zen said:

The lack of generally favorable digital snow in the runs is the most disheartening thing to me. Generally around here we see an uptick in that run over run which indicates a favorable period and some ops are coming up. Not seeing that remains a red flag. 

My take is that the operational runs will continue to look bleak until around the first and then suddenly start looking better. And it won't be just the elusive 15 day that looks better, but closer in like the 7 - 10 day. Of course that still doesn't mean it will snow, but at least that would give something for the frustrated to do.

As a side note, that January 7 storm might be something worth watching. Even a 1-3" event would be nice to see.

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87storms

87storms

Posted
Posted

i actually don't really care all that much as long as we get 2-3 decent events.  i tell everyone who doesn't know much about this area to expect that every year.  2-3 minor to moderate events is typically on average (in my mind at least) what the dc metro area is good for in every single winter, so yes, things could still change because it doesn't take longer than a 2-3 week window to get our 2-3 events.  we're a fringe snowtown.  that's how we roll.

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EastCoast NPZ

EastCoast NPZ

Posted
Posted
1 hour ago, North Balti Zen said:

The lack of generally favorable digital snow in the runs is the most disheartening thing to me. Generally around here we see an uptick in that run over run which indicates a favorable period and some ops are coming up. Not seeing that remains a red flag. 

Yes indeed.  We can capitalize on about 10% of digital threats ... in a good year.  When the models cant even produce fantasy snow?  Well..... 

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WxUSAF

WxUSAF

Posted
Posted
1 minute ago, WxWatcher007 said:

Awful. Just awful. 

I was never on board for an epic December, but I thought that we'd at least check in at normal for the month with snowfall. 

Yup. Not being able to fall into some front end slush or a random dusting is very unusual. 

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Scarlet Pimpernel

Scarlet Pimpernel

Posted
Posted
6 hours ago, WxUSAF said:

Epic January or February or not, not seeing a flake in December is pretty rare and sh-tty

 

Interesting.  Though I'd almost argue he's being a bit disingenuous or unfair or even overly strict, as there have been a few to several years with a mere trace of snow if not exactly "0.0" at all of the 3 local area airport locations in December (and a trace is really officially "nothing measured").  I can see his point though, that it's truly hard to get absolute zero in December...perhaps harder at BWI or IAD than at DCA.  Consider it the difference between a no-hitter and a perfect game, I suppose! :D

December 2015 is surely the standard for ultimate suckiness for any winter month...taking both lack of snow and torch-like temperatures into account.  DCA, in fact, recorded none (not even a trace!) of snow that December from what I saw.  BWI somehow mustered a trace.  IAD also managed a trace that year.  But nothing actually measurable.  Recall that's the December that had a +11 to +12 temperature departure for the month, and I'd argue that was *far* worse than how this December panned out.  At the least this year, we had some honest chill in the air at times.

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Maestrobjwa

Maestrobjwa

Posted
Posted
7 hours ago, WxUSAF said:

Epic January or February or not, not seeing a flake in December is pretty rare and sh-tty

 

Not to mention 2 of the 3 winters ended up pretty paltry! (And yet...the winters that happened the year AFTER all three of those winters were epic!) So...if we get denied this year...perhaps next year comes back with a vengeance! :D

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Vice-Regent

Vice-Regent

Posted
Posted
32 minutes ago, Bob Chill said:

18z gefs just showed a progression that is basically identical to week 3 on the weeklies. Lol. 

gfs-ens_z500a_nhem_65.png

 

Look at all that red my man. Sure looks like Hadley Cell expansion... for those less versed in this subject please have a read.

The major driving force of atmospheric circulation is the uneven distribution of solar heating across the Earth, which is greatest near the equator and lesser at the poles. The atmospheric circulation transports energy polewards, thus reducing the resulting equator-to-pole temperature gradient. The mechanisms by which this is accomplished differ in tropical and extratropical latitudes.

Hadley cells exist on either side of the equator. Each cell encircles the globe latitudinally and acts to transport energy from the equator to about the 30th latitude. The circulation exhibits the following phenomena:[1]

  • Warm, moist air converging near the equator causes heavy precipitation. This releases latent heat, driving strong rising motions.
  • This air rises to the tropopause, about 10–15 kilometers above sea level, where the air is no longer buoyant.
  • Unable to continue rising, this sub-stratospheric air is instead forced poleward by the continual rise of air below.
  • As air moves poleward, it both cools and gains a strong eastward component due to the Coriolis effect and the conservation of angular momentum. The resulting winds form the subtropical jet streams.
  • At about 30° latitude on either side of the equator, the jet streams become so much faster than the surface wind speed that baroclinic instability prevents the Hadley circulation from extending further poleward. This coincides with the beginning of the Ferrel cells.
  • At this latitude, the now cool, dry, high altitude air begins to sink. As it sinks, it warms adiabatically, decreasing its relative humidity.
  • Near the surface, a frictional return flow completes the loop, absorbing moisture along the way. The Coriolis effect gives this flow a westward component, creating the trade winds.

The Hadley circulation exhibits seasonal variation. During the solstitial seasons (DJF and JJA), the upward branch of the Hadley cell occurs not directly over the equator but rather in the summer hemisphere. In the annual mean, the upward branch is slightly offset into the northern hemisphere, making way for a stronger Hadley cell in the southern hemisphere. This evidences a small net energy transport from the northern to the southern hemisphere.[1]

The Hadley system provides an example of a thermally direct circulation. The thermodynamic efficiency of the Hadley system, considered as a heat engine, has been relatively constant over the 1979–2010 period, averaging 2.6%. Over the same interval, the power generated by the Hadley regime has risen at an average rate of about 0.54 TW per year; this reflects an increase in energy input to the system consistent with the observed increasing of tropical sea surface temperatures.[2]

Overall, mean meridional circulation cells such as the Hadley circulation are not particularly efficient at reducing the equator-to-pole temperature gradient due to cancellation between transports of different types of energy. In the Hadley cell, both sensible and latent heat are transported equatorward near the surface, while potential energy is transported above in the opposite direction, poleward. The resulting net poleward transport is only about 10% of this potential energy transport. This is partly a result of the strong constraints imposed on atmospheric motions by the conservation of angular momentum.[1]

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