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Discussion: Storm arriving

in: Cristina; Cristina > 2020-05-08

May 9, 2020 12:47 AM # 
blairtrewin:
As I put it in an e-mail to some colleagues a couple of days ago, 'EC at 00Z Saturday shows T850 below -8C as far south as New York'. I'm guessing you absorbed enough of the terminology while at the Meteorological Institute in Oslo to be able to understand most of that (even if most readers can't).

Certainly an impressive cold outbreak for this late in the season (and separately, there's an equally impressive one forecast for northwest Europe too). The flipside is abnormal heat on the other side of the systems in western North America and Siberia.
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May 9, 2020 1:55 AM # 
walk:
Polar vortex redux - snow forecast for tonight. Possibly 2”accumulation and close to record low and record low for high. Local forecaster was predicting -40 at high altitude. Not sure how that lines up with T850.
May 9, 2020 2:21 AM # 
jjcote:
T850 is about a mile up?
May 9, 2020 2:31 AM # 
blairtrewin:
T850 is the temperature at the level where the air pressure is 850 hPa. Normally that's about a mile up but it will be a bit lower in such an intense upper-level system. The -40 is at the 500 hPa level (normally around 5.5km, but again will be lower here), which is low even for winter and exceptional for May (I believe that if it happens it will be the first time it's happened in May at any site in the lower 48 states).

Our usual rule of thumb in southern Australia is that snow at sea level (exceptionally rare on the mainland and rare even in Tasmania) requires T850 around -6 to -7, but that applies to well-mixed maritime air masses (which a southerly/southwesterly in Australia almost always will be) - it's much more complicated when a continent is involved.
May 9, 2020 9:48 AM # 
walk:
No snow on the ground here but perhaps at Charlie’s.
May 9, 2020 11:05 AM # 
jjcote:
No snow on the ground at my place, but flurries at 7 AM.
May 9, 2020 11:55 AM # 
peggyd:
No snow here in DC but just above freezing at 7:30 am.
May 9, 2020 7:57 PM # 
Charlie:
No snow on the ground, flurries on and off here and at People's SF where we were walking this am. Plenty cold. 31 F when we set out this morning.
May 9, 2020 8:09 PM # 
Cristina:
We had flakes this morning but nothing significant. Blustery and cold today.
May 10, 2020 1:37 AM # 
walk:
We went through a decent squall on our drive this afternoon through Norfolk and Canaan. Drove out of it only to reengage back home. Nothing sticking though we did see a very tiny patch in Colebrook while looking at the wind turbines.
May 10, 2020 2:17 AM # 
o-maps:
In southern New Hampshire it was snowing pretty intensely around 8-9am. A solid inch or two on the deck, spottier accumulation on the lawn and in the nearby woods but I’d say there was more ground covered than bare. All melted by late morning.

Sounds like the same in central Connecticut, from cmorse’s comment on CleverSky’s log.

Then around 6pm there was a very brief but very intense squall that left a short-lasting accumulation of sleet or tiny hail. I was about to step out the door to run, held off a half hour, then the sun came out and it was gorgeous though cold (couple of degrees above freezing) and very windy.
May 10, 2020 2:19 AM # 
Cristina:
We had that tiny hail, started just as I was getting ready to run. Probably closer to 6:30, in the Fells. I was confused by the giant white globes of pollen on my windshield until I realized what it actually was.
May 10, 2020 2:40 AM # 
jjcote:
https://en.wikipedia.org/wiki/Graupel
May 10, 2020 2:57 AM # 
Cristina:
Oh, yeah, it probably was graupel!
May 10, 2020 5:00 AM # 
jjcote:
Nancy did grad school research on graupel.
May 10, 2020 6:14 AM # 
o-maps:
Oh of course, thanks J-J, it was for sure graupel.
May 10, 2020 9:49 AM # 
Charlie:
Deck and parts of the yard have a thin accretion of grapple this morning.
May 10, 2020 3:41 PM # 
cmpbllv:
We had hail just south of the NH border at about mile 14 of Anna's 20-mile hike. It did not improve morale. The dusting of snow on the ground / in the trees when we got started around 10:30 was pretty, though.

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