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Tuesday 1/7/20 Disco snow event


MountainGeek
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HREF mean snowfall for the region is between 2-4" for a majority of NoVa west of I-95 all the way to the north in Central MD. Probability threshold for >4" accumulation is fairly low for a majority of the area, but there is a focal centered north of I-70 from Northern Frederick to the east across Carroll and Baltimore counties. The 1hr snow mean is actually pretty impressive for a 4 hr span beginning at 20z through 0z for the central MD crew showing a general 0.5/hr accumulation. but pockets of up to 0.75"/hr. Remember that what is shown is a mean, and not necessarily a slam dunk. 1-1.5"hr for an hour or two is very much in the cards, so localized amounts exceeding 4" north of I-70 is possibility. We know the usual suspects :lol:

A sharp gradient in snowfall totals is depicted as well toward the bay. Areas east of I-95 may struggle to reach 1 inch. A few in here have been pessimistic about their chances of receiving over an inch. It has merit, but that is just climo. Nothing much you can do. 

Final forecast is 1-3 " for inside the beltway(s), Alexandria, Arlington, and southwest of DC. 2-4" for areas north of the Potomac in MD, WV Panhandle, and northern neck of VA. 2-5" for areas north of I-70 stretching from Hagerstown to northern Harford County near Jarretsville. Best chance for the higher end is Parrs Ridge, MD line crew on a triangle of Emmitsburg/Mt Airy/Jarretsville.

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2 minutes ago, MillvilleWx said:

HREF mean snowfall for the region is between 2-4" for a majority of NoVa west of I-95 all the way to the north in Central MD. Probability threshold for >4" accumulation is fairly low for a majority of the area, but there is a focal centered north of I-70 from Northern Frederick to the east across Carroll and Baltimore counties. The 1hr snow mean is actually pretty impressive for a 4 hr span beginning at 20z through 0z for the central MD crew showing a general 0.5/hr accumulation. but pockets of up to 0.75"/hr. Remember that what is shown is a mean, and not necessarily a slam dunk. 1-1.5"hr for an hour or two is very much in the cards, so localized amounts exceeding 4" north of I-70 is possibility. We know the usual suspects :lol:

A sharp gradient in snowfall totals is depicted as well toward the bay. Areas east of I-95 may struggle to reach 1 inch. A few in here have been pessimistic about their chances of receiving over an inch. It has merit, but that is just climo. Nothing much you can do. 

Final forecast is 1-3 " for inside the beltway(s), Alexandria, Arlington, and southwest of DC. 2-4" for areas north of the Potomac in MD, WV Panhandle, and northern neck of VA. 2-5" for areas north of I-70 stretching from Hagerstown to northern Harford County near Jarretsville. Best chance for the higher end is Parrs Ridge, MD line crew on a triangle of Emmitsburg/Mt Airy/Jarretsville.

Thanks for taking the time to do this

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10 minutes ago, caviman2201 said:

The warm layer is so thin those of us E of 95 might be able to look up and watch our snowflakes melt.  Might be snowing at the top of the Legg Mason building in the innner harbor and raining on the street lol.

Side note, I wonder if thats ever happened somewhere with really tall buildings like NYC where the warm layer was so thin it was raining on the street but snowing on the tops of the ~1000ft+ buildings.

It happens somewhat frequently in marginal events. Especially NYC where being right on the coast can torch their boundary layer with an easterly wind. 

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Just now, yoda said:

I know its not the same... but wasn't the St. Patty's Day storm (March 2017 I think?) the same temp wise?  Got into the 40s, snow started instead of rain due to the DP/T depression?

Yes, March does not equal January... but that popped up into my mind

At this point there's plenty of data to think about and understand how that applies to each person's yard. My climo nearly always puts me in the middle on these types of deals. 1-2" is where my head is at. A clean 2" would be quite a victory. 

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2 minutes ago, yoda said:

I know its not the same... but wasn't the St. Patty's Day storm (March 2017 I think?) the same temp wise?  Got into the 40s, snow started instead of rain due to the DP/T depression?

Yes, March does not equal January... but that popped up into my mind

I’ve been thinking of that storm today. Was mid/upper 40s ahead of precip and precip started as snow IMBY.

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1 minute ago, Bob Chill said:

At this point there's plenty of data to think about and understand how that applies to each person's yard. My climo nearly always puts me in the middle on these types of deals. 1-2" is where my head is at. A clean 2" would be quite a victory. 

I'm always conservative and really don't like putting a boom or top end scenario I've thought from jump 1/2" - 2" for here. Sounds like it will be pretty for awhile even if not accumulating 

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Special Weather Statement
National Weather Service Baltimore MD/Washington DC
1058 AM EST Tue Jan 7 2020

MDZ003-004-503-504-VAZ052-053-501-502-505-506-WVZ051>053-071800-
Washington-Frederick MD-Northwest Montgomery-
Central and Southeast Montgomery-
Prince William/Manassas/Manassas Park-Fairfax-Northern Fauquier-
Southern Fauquier-Western Loudoun-Eastern Loudoun-Morgan-Berkeley-
Jefferson-
Including the cities of Hagerstown, Frederick, Ballenger Creek,
Germantown, Damascus, Bethesda, Rockville, Gaithersburg,
Silver Spring, Dale City, Manassas, Woodbridge, Lake Ridge,
Montclair, Reston, Herndon, Annandale, Centreville, Chantilly,
McLean, Franconia, Warrenton, Turnbull, Purcellville, Leesburg,
Ashburn, Sterling, Paw Paw, Martinsburg, Charles Town,
and Shepherdstown
1058 AM EST Tue Jan 7 2020

...PERIODS OF HEAVY SNOW THIS AFTERNOON...

Radar and surface observations just before 11 AM indicated a
sudden onset of heavy snow moving across eastern West Virginia,
northern Maryland and portions of northern Virginia. Visibility
was dropping from unrestricted to a half mile or less in the span
of 15 to 30 minutes, with snowfall rates of over one inch per hour
reported. This heavy snow is expected to reach Highway 15 by 11:30
AM, and approach Interstate 95 by 1 PM.

Remain alert for rapidly changing visiblities and quickly
deteriorating road conditions.
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16 minutes ago, caviman2201 said:

The warm layer is so thin those of us E of 95 might be able to look up and watch our snowflakes melt.  Might be snowing at the top of the Legg Mason building in the innner harbor and raining on the street lol.

Side note, I wonder if thats ever happened somewhere with really tall buildings like NYC where the warm layer was so thin it was raining on the street but snowing on the tops of the ~1000ft+ buildings.

Happens all the time as somebody who grew up in the city. During transitions, it can be snowing at the top level of a tall building and raining at The surface. Only lasts a minute or two

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