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Richmond Metro/Hampton Roads Discussion


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5 minutes ago, eaglesin2011 said:

ha ha I know its most likely Virga but a decent band was forming  that's why I asked if anything was hitting the ground....  If we dont have anything by 7pm I dont expect us to get anything measurable . This system is moving quickly 

Agree. I'll give it until around 7. If it's not doing anything then, I will wave the white flag. 

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A look at ground observations to the South of Richmond tells me that Nam's thermal structure profile on Skew-T forecast soundings was overly optimistic about a shallower layer of above freezing temperatures, than has actually transpired, up to this time of 2 PM.  Recall yesterday it showed an 814 ft depth about this time.  However, Gfs back then, showed a much greater depth, up at 1,450 ft, which I took note of late last night, and Gfs appears to be the winner on that greater depth of above freezing temperatures.  Depth needs to get *below* 1,200 ft.

With this gridded data, using GFS this time, it shows the magic change-over to occur between 4 PM to 7 PM.  Temperatures go from 0.4°C at that 1,450 ft layer, down to -2.1°, and the freezing level HEIGHT lowers quickly between 4 PM and 7 PM, at the same time moisture RAMPS UP from the 50%-tile UPWARDS to the 80%-tile.  Not quite the saturation ideally needed, but it comes close at 80%-tile in those trouble-some, pesky lower layers that are currently ABOVE freezing and that are the DRY layers.

So, based on this Skew-T sounding information, and the gridded data extracted that I highlight in yellow, should show things changing pretty quickly in those hours from 4 PM to 7 PM.  By the way, the 975 mb layer that I highlight is shown as 431 M in GPH, translates to 1,450 ft (431 X 3.281) to get height in feet, for that layer.  Visual included below.

***   Edited to add:   Also take notice in this visual below, that the RH, relative humidity, in the surrounding layers above & below the highlighted 975 mb layer go UPWARD as well in R.H. from the 52% to 61% at 1000 mb & 950 mb layers, -- at 4 PM --, going up to the 78% to 90% R.H. moisture, -- at 7 PM --, all while temperatures at those layers go to freezing, at 7 PM.  The 12 hr. highlighted at the top, correlates to 7 PM, which is 12 hours away from the initialization time at 7 AM this morning.  Have a see below.  

12Z Gfs.JPG

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Feb. 20, 2020

320 PM

 

Newest output on snowfall for Richmond:

12Z Gfs:  0.3"  (3/10", with 1/10" coming between 1 AM and 4 AM)

06Z Gfs:  0.5"

12Z Nam:  0  (Recall this one had been previously forecasting between 4 inches to 5 inches)

18Z Nam:  0.4"

00Z ECMWF:  1.00" ( 1 inch) 

12Z WRF:  Trace (LESS than 1/10")

12Z H-Rap:  0

Just taking the last 1-2 iterations of these models, as I can't use the 16Z to 18Z H-rap as its already tainted showing snow in Richmond by early afternoon, then this averages out to be 0.3"  (3/10") of snowfall for Richmond.   This meshes between a compromise blend of the 2 writings I released yesterday.  1st writing for 1/10" to 2/10"; followed by a 2nd writing of between 1/2" to 1".  So smoothing these 2 variations blends well, for 3/10".  

Notice above, that it's NOW ECMWF & CMC-RGem which is the HIGHEST-producing, lonely outliers showing the MOST snowfall for Richmond.  Recall yesterday it was the NAM going way upward to 4" to 5".  That all came to a screeching halt on this morning's 12Z output.   It is interesting to take notice that the last 2 iterations of the ECMWF have shown 1" to 1.2" of snowfall, but it, along with CMC-Rgem are ALONE in producing amounts of 1" or over, with CMC-RGEM, at 1.6".  

 

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