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February 20-21, 2019 -- Potential Overrunning Thump/Ice


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00z HRRR coming in rather impressive     

A lot of great analysis in this post, very much appreciated!

Quick note on this system... Recall this area of frozen precipitation will be occurring as it collides with a 500mb ridge (this is not unimportant). The anti-cyclone aloft provides flow out of the wes

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Just now, bscott4293 said:

It seems the heaviest snow shifted south this run, will be interesting to see how this evolves as we get into the more reliable range for mesoscale models beginning at 00z

That’s not the full run. As areas to the northeast just started snowing. The 18z gfs actually got wetter for the metro when compared to 12z

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1 minute ago, Allsnow said:

That’s not the full run. As areas to the northeast just started snowing. The 18z gfs actually got wetter for the metro when compared to 12z

The area of heaviest snow and highest totals shifted south on the FV3, I wasn't commenting on the northern extent of the snow.

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2 minutes ago, bscott4293 said:

The area of heaviest snow and highest totals shifted south on the FV3, I wasn't commenting on the northern extent of the snow.

 

I don't know if that's a meteorologically correct representation.

As was alluded to earlier, you would think that an area of heavier snow would mean an overall smaller area of snow, not bigger.

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Upton:

 

Quote

The synoptic pattern for the first storm system is not favorable for 
a significant winter storm across the region. The antecedent air
mass is the main ingredient to bring about a concern of front end
wintry precipitation before a wintry mix and then eventually rain.

High pressure gradually shifts from overhead Wednesday morning to
just along the New England coast Wednesday evening. The air will
initially be dry with dew points in the teens. Some concern that the
models are saturating this air mass too quickly due to the proximity
of the high pressure. Another factor of concern is deep layered
ridging aloft. The main shortwave trough and parent low is progged
to be located over the Northern Plains at 00z Thursday. The main
source of lift will be from warm advection/frontogenesis and the
potential of secondary low pressure to develop somewhere along the
Middle Atlantic Wednesday evening. The 12z NAM appears to be too
aggressive in developing precip early Wednesday afternoon and has
therefore been discounted. Have followed a GFS/ECMWF blend for
timing. Another factor to weigh in here is overall model performance
this winter has been subpar regarding similar PTYPE events, with too
much wintry precip forecast versus actual observations (the most
recent occurring last night into this morning).

This new forecast package shows the potential for snow to develop
for the Wednesday evening commute across the southern half of the
area. Its north and eastward progression will be determined by how
quickly it can overcome lingering dry air and surface and upper
ridging. The snow should overspread the rest of the region after 00z
Thursday. However, due to the unfavorable position of the high and
factors noted above, the snow should quickly transition to a wintry
mix and plain rain at the coast before midnight. This progression
will continue northward through early Thursday morning as warmer
air moves in both at the surface and aloft. Some lingering freezing
rain is possible across the NW interior if surface temperatures take
a bit longer to rise above freezing.

Have followed a conservative approach to snow/sleet amounts with
generally 1-2 inches across the region, with lower amounts across
eastern Long Island and SE CT. A reasonable worst case scenario with
a snowier outcome is for 1-3 inches east and 3-4 inches from NYC on
west. Of note is the 12z ECMWF EPS mean probability for greater than
3 inches is generally less than 30 percent. A tenth of an inch or
less of freezing rain is forecast across the interior. Overall
liquid equivalent amounts are around a half inch.

 

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8 minutes ago, ThunderSnow4 said:

Am I missing something? HRDPS was basically insane and no one posted it? 

The HRDPS is the prototype of a crippling snowstorm with 2+” per hour rates here in dc. Approaching NYC in the last frame, looks like a big hit there as well. Only if it were the EURO...

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7 minutes ago, ThunderSnow4 said:

Am I missing something? HRDPS was basically insane and no one posted it? 

Fronto band as depicted by it crushes MD/N DE into SE PA/SNJ. 

1d104007-b7e3-45e1-b949-afa4bcc36ae9.gif

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1 minute ago, Gian_Tancredo said:

The HRDPS is the prototype of a crippling snowstorm with 2+” per hour rates here in dc. Approaching NYC in the last frame, looks like a big hit there as well. Only if it were the EURO...

Banding as depicted would lose its punch on its journey north. But this will change several times before the event arrives. Those rates could be reached, but mind you they would be short lived. But during the height of it, it'd be pretty wild. 

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18z Euro came south/east with the heaviest banding.  12z had it south central PA.  18z has it in extreme NW VA, WV panhandle north into extreme southern central PA.  4-5" for 95 corridor along NOVA/DC/MD before the flip.  4" Philly.  2-3" in CNJ.  

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  • 33andrain changed the title to February 20-21, 2019 -- Potential Overrunning Thump/Ice
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