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Richmond Metro/Hampton Roads Discussion

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When it precipitates tomorrow, in Richmond, Virginia on Thursday, February 20, 2020, it WILL be ALL SNOW!

Here's why:

In Richmond, Virginia:  12Z forecast Skew-T soundings for tomorrow show that

--  The freezing level height begins around 814 ft, AGL, tomorrow, (~1000 mb), and for ALL LAYERS ABOVE 814 ft, at 1 PM on Thursday, Feb. 20, temperatures above that height of 814 ft will be BELOW FREEZING.

--  While temperatures from GROUND LEVEL up to 814 ft. are forecast ABOVE freezing, this is still permissible to have snow, as the snow forecasting guidelines provide that as long as the freezing level is BELOW 1,200 ft, then snow can still occur.  ( Reference Table IV, Forecasting Snow, cited at:  https://www.weather.gov/sgf/winter_checklist_paper)  Okay, so there's that.

--  The 1000-850 mb thicknesses are below 1,300 meters during the entire duration of this snow event for Richmond, VA,

(1,284 - 1,267 m).

--  The 1000-500 mb thicknesses are below 5,400 meters during the entire duration of this snow event for Richmond, VA,

(5,356-5,292 m). 

-- 850 mb temperature will be from -8 to -11°C.

-- Your 700 mb T is running at -7 to -10°C during the event tomorrow.

(Are there any NEGATIVES and PITFALLS to thwart the snow, at all?)

A couple negatives to start with.

#1.)  Your starting surface temperatures at 1 PM on Thursday are forecast to run at 34° by your Nam and 42° by your Gfs.  Rest easy, though, as SNOW can still occur with the SURFACE temperature ABOVE freezing.

#2.)  I do see an intervening DRY LAYER on Skew-T forecast soundings tomorrow on your Nam projections, from ground level up to 5,000 ft, ~ 850 mb at 1 PM on Thursday, Feb. 20.  The DRY LAYER depth is even greater at 10 AM, up past the 10,000 ft mark.  (What does this mean, effectively?)  It means it starts off as virga, until the lower-layers saturate from the top - down.

This is forecast to happen by 4 PM on Thursday, Feb 20, in Richmond, VA.  A saturated column profile is forecast by that time, and all layers are forecast to be at freezing.  (Nuh-uh!  Not the surface layers from Mos!)  Okay, at the surface Nam shows 33° at 4 PM and Gfs, at 40° at 4 PM.  Look for that 40° to be a bust at 4 PM.  Once it starts precipitation, ambient air temperatures start dropping quickly as it'll wet-bulb about 1/3 of the way down towards the dewpoint T.  And again, gang, don't be getting hung-up on the surface temperature, because it will STILL SNOW with SURFACE temperatures ABOVE 32°.  Wet bulb zeros are forecast so low, and dewpoint temperatures are forecast so low, in the 20 to 23° range.  

What this may effectively do is tear in to your snowfall amounts, too, at the START of the event in the EARLY afternoon.  By evening, though, saturation of the vertical depth of the troposphere will become MORE COMPLETE and WHOLE to produce better snowflakes, although Richmond is quite a far ways removed from the positioning of the surface low transpositioning, so don't be getting too overly excited about the amounts.

I'll produce another writing for Richmond, VA detailing snowfall amounts in a subsequent writing later on.


--  cyclogenesis. 

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call as of this morning from NWS  
Seems doable since it's going to ba more of 5:1 ratio and not 7 or 10:1. If you take a blend of the RGEM and 3kNAM it's right in line with those. Not a big storm but nice for what has been dumpster fire winter. Surface temperatures will cut back on snowfall maps from any model output

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February 19, 2020

--- This writing below ONLY APPLIES TO RICHMOND, VIRGINIA ---:

For Thursday, February 20:

On the snowfall forecast amounts for Richmond, Virginia:

Here's what I've decided.

1/10" to 2/10" of snow seems realistic.  How did I arrive at this projection??

I took 2 iterations of ECM, 2 iterations of Gfs, 1 iteration of CMC's Gem, 2 iterations of WRF.  I disregarded the Nam forecast.  (Disregarding reliable intelligence?)  Because it stands way OUT, as an OUTLIER; that's why.  

What if I include Nam in the composite rendering of projections of snowfall amounts for Richmond?

Then, I'll have to adjust the snowfall RANGE of variability between 1/10" to 1".  Nam's last 2 iterations of output have been 4.2" and 4.4".  Before that, from last night it was 6".  (Why the stark contrasting differences?)  The surface low position is FURTHER NORTH on Nam, than on Gfs & ECM.

ECM was actually furthest South with its 00Z projection for 7 PM Thursday, showing it at a junction of Savannah's latitude & Cape Hatteras' longitude.  Nam was at Myrtle Beach's latitude & Morehead City's longitude at the same time positioning on its 12Z morning projection for 7 PM Thursday.  

Also, too, the surface low is WEAK.  Only 29.92" at its closest point at 7 PM by ECM, and 1010 mb by Nam at 7 PM at its closest point.  The surface low only deepens once it begins moving AWAY from the U.S. East coast.  The upper level pattern is equally as lame, with a zonal flow impairment.   

Here were the exact amounts that each model detailed:

6Z Gfs: 0.2" of snowfall for Richmond, VA

12Z Gfs:  0.1" of snowfall for Richmond.

12Z, Tues morn, ECM:  0 snowfall for Richmond

00Z, Tues eve, ECM:  0.3" of snowfall for Richmond

6Z Nam:  4.2" of snowfall for Richmond

12Z Nam:  4.4" of snowfall for Richmond

00Z & 12Z WRF:  TRACE of snowfall for Richmond, LESS than 1/10" of snowfall.

12Z CMC's Gem:  0.6" of snowfall for Richmond.

What's more disappointing to you snow lovers are the TRENDS on probabilities of precipitation are dwindling & coming down on the Gfs mos product:

What was 66% from 18Z yesterday, fell to 49% at 00Z last night, fell to 43% at 6Z last night, fell farther to 37% from this morning's 12Z newest output from your Gfs.

How about Nam?  Nam has held solid at an 86% chance on this morning's forecast run.

(So how do you account for these wide discrepancies in a forecast then??   Snow??  Or NO snow??)

My interpretation on the subject is to CALL for snow to occur, but TRIM the amounts WAY DOWN.

(What will 1/10" of snowfall look like?)

1/10" of snowfall will be enough to cover cars & trucks with a thin surface of snow.  It won't completely cover your grass, though; although patchy areas will see some whitish hues.  

This will not create any traveling problems.

EVEN in the REMOTE sense that I DO CHOOSE to BLEND IN the NAM forecast projection, bringing a possible highest TOTAL amount to 1 inch, with it averaged in to the other models' consensus, even 1 inch of snow still will not be enough to create travel problems.  


I think the timing of said projected snow will occur between 2 PM and 10 PM on Thursday.  I also think you'll find on radar some finger sleeves of radar return echoes starting up as soon as late Thursday morning AIMING from Southwest to Northeast in our direction, but I expect this late morning echo returns to be VIRGA to start, with the lower levels too dry just yet.

I believe the more notable snowflakes that will become more visible will come in the LATE afternoon hours between 3 PM - 8 PM, for Richmond, VA, although I do expect you'll see snow flurries flying in the air as soon as EARLY tomorrow afternoon, on Thursday, Feb. 20.  Besides, it has to snow!  It's the 20th on 2020, and on the 02nd month!

Last thing to close with is this:  While there still remains a notable chance that no snow will accumulate, (not enough of it), I do still think you should get to see snow flurries falling lazily in the air on Thursday afternoon. 

--  cyclogenesis

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