December 15-16 Mixed Bag of Precip

[NorthArlington101]

6 minutes ago, H2O said:

I get trying to keep roads safe but this brine stuff is gonna ruin our watershed over time. I’d almost prefer they go back to sanding as it happens

Beet juice! 

[H2O]

2 minutes ago, StormyClearweather said:

I know you said "sanding" instead of salting, but still an interesting piece on the issues with salting vs. brining. 

Road Salt Works. But It’s Also Bad for the Environment. - The New York Times (nytimes.com)

Thru my former line of work I know all too well the impacts that any salt or sodium based products are putting on our local watersheds.  I understand the need to make roads safe to drive but what seemed like a great idea a few years ago is affecting other things.  

 

Anyways, to be back on thread topic it looks like roads even around here might get slick if things hold as shown on models.

[RickinBaltimore]

5 hours ago, Weather Will said:

WB 6Z 3K NAM.  Other than mountains above freezing by 10 am.

Sleet bombs over Dundalk, hon. 

[mappy]

3 minutes ago, H2O said:

Thru my former line of work I know all too well the impacts that any salt or sodium based products are putting on our local watersheds.  I understand the need to make roads safe to drive but what seemed like a great idea a few years ago is affecting other things.  

 

Anyways, to be back on thread topic it looks like roads even around here might get slick if things hold as shown on models.

not to mention the salt will really screw over people's wells due to run off! 

[H2O]

14 minutes ago, mappy said:

not to mention the salt will really screw over people's wells due to run off! 

Yup.  Ground water and freshwater sources are getting affected by all this road salt in whatever form it is

[midatlanticweather]

12z NAM looks quite a bit more icy. Maybe warnings expand a bit? I dunno.

 

 

[Weather Will]

WB 12Z 3K NAM…except far western areas transition to all rain N&W between 10 and noon.

[BristowWx]

3 minutes ago, Weather Will said:

WB 12Z 3K NAM…except far western areas transition to all rain N&W between 10 and noon.

Thats quite a jump in Southern Faquier with .58...that ISW criteria for certain.

[Eskimo Joe]

37 minutes ago, H2O said:

I get trying to keep roads safe but this brine stuff is gonna ruin our watershed over time. I’d almost prefer they go back to sanding as it happens

 

32 minutes ago, StormyClearweather said:

I know you said "sanding" instead of salting, but still an interesting piece on the issues with salting vs. brining. 

Road Salt Works. But It’s Also Bad for the Environment. - The New York Times (nytimes.com)

Both are bad for aquifers and watersheds. We over brine and over salt too much. In Maryland, SHA has been reducing their usage of these products, but a major problem in Maryland (which is the authority having jurisdiction for the Potomac River, not Virginia) is nonpoint pollution from private companies over treating parking lots.

[NorthArlington101]

Thats quite a jump in Southern Faquier with .58...that ISW criteria for certain.

Not sure I buy it personally - temps aren’t really any colder than precious runs + heavier precip wouldn’t be particularly helpful in accretion.

[Eskimo Joe]

Icing is inherently tricky for forecast. This link was posted a few pages ago, but am posting again. Would encourage members to book mark this: https://training.weather.gov/wdtd/courses/woc/winter/fcst-hzds/ice-storm-accum/presentation_html5.html

It's only 20 - 25 min and well worth your time.

[Eskimo Joe]

Looks like LWX extending the WWA for the Mason-Dixon counties until 4pm tomorrow. Makes sense, dews seem a bit lower than forecast, it's cloudy today and surfaces are chilled.

[Buddy1987]

Question for the pros in here. How much emphasis would you put behind the NAM and CAD related events, especially seeing how much more it raised the ante with regards to expected accumulation of ice at 12Z? Do you feel like it's overdoing it or does it hold some weight in these scenarios if you were going to create a forecast using it in a specific setup like this?

[midatlanticweather]

2 minutes ago, Buddy1987 said:

Question for the pros in here. How much emphasis would you put behind the NAM and CAD related events, especially seeing how much more it raised the ante with regards to expected accumulation of ice at 12Z? Do you feel like it's overdoing it or does it hold some weight in these scenarios if you were going to create a forecast using it in a specific setup like this?

 

5 minutes ago, Eskimo Joe said:

Icing is inherently tricky for forecast. This link was posted a few pages ago, but am posting again. Would encourage members to book mark this: https://training.weather.gov/wdtd/courses/woc/winter/fcst-hzds/ice-storm-accum/presentation_html5.html

It's only 20 - 25 min and well worth your time.

Maybe check that resource! - I am going to now. 

 

[mappy]

6 minutes ago, Eskimo Joe said:

Looks like LWX extending the WWA for the Mason-Dixon counties until 4pm tomorrow. Makes sense, dews seem a bit lower than forecast, it's cloudy today and surfaces are chilled.

Oh yeah? Mmmm wondering if my kid's presumed 2-hr delay will become a day off. 

[DarkSharkWX]

Think everyone in advisory will close/go virtual or at the very least delay

[MillvilleWx]

Currently have a bit of a separation of camps setting up between the globals and the hi-res due to the obvious resolution concerns that crop up in the short range. In the short range, it's important to follow the trends in dew point obs and temps, as well as cloud cover advancement and increasing SE flow as the low begins to develop early tomorrow morning. 

The current setup is indicative for a period of icing for all areas, including east of the fall line, but I have my doubts the impact will be too substantial for the DC/Balt urban areas as temps will be borderline, at best for prime ice accretion. To the west of the fall line, there will be an extended period of icing that starts early AM and last until close to Noon for locations above 600' elevation and even longer for places out by I-81 where the warm nose will take more time to protrude deep in the boundary layer and warm up enough to switch from ZR to rain. 

Here are two pieces of guidance I like for the current indications of potential. Note, NBM is blended guidance and will not handle CAD as well compared to higher res solutions, thus the numbers a bit degraded compared to where they may end up. One of the trends I noticed on looking at models this AM is a period where the temps will warm slightly before falling due to evaporative cooling processes as the precip becomes "heavier". This is a solution that has merit, but I wonder if this will limit any ice potential for areas along I-95 and east. Highest impact will be the valleys west of Frederick up to South Mountain and the Catoctins. Also, the I-81 corridor from Winchester down to Luray will be a mess as the warm air will struggle to mix to the surface and temps hold between 30-32F for an extended period. 

Current thinking is the WWA/WSW are in the right places given the recent guidance and trends in the short term. KOKX around 0.25" of ice is certainly in the cards. 0.25-0.5" out by Hancock and along the ridges in Western MD. T-0.05" along I-95 and inside the beltways. 0.05-0.15" for areas along and west of the fall line. Catoctins will likely be WSW criteria, but because it falls in Frederick Co, they will remain a WWA due to the population center away from the mountains. 

[Solution Man]

12 minutes ago, DarkSharkWX said:

Think everyone in advisory will close/go virtual or at the very least delay

DS, what’s your thoughts on upcoming event for area?

[mappy]

18 minutes ago, DarkSharkWX said:

Think everyone in advisory will close/go virtual or at the very least delay

I knew a 2hr delay was pretty much certain, but seeing that sub32 temps may hang on longer than 10amish, probably means a full closure. At least up in my area. 

[WinterWxLuvr]

2 hours ago, SnowenOutThere said:

Lol, I have a spanish presentation where I need to memorize a script tomorrow, really hoping I can get out of it.

That’s the spirit!

[MDphotog]

Looking at the 3k Nam (12Z) and PWS temps, NAM might have been a bit over ambitious on temps rising this morning.  Will be interesting to see how to plays out today.  At least for the Frederick/Hagerstown area.

[mappy]

FWIW: low was 20 IMBY, currently 33/24

[Eskimo Joe]

@MillvilleWx excellent write up as always. Your thoughts mirror mine as well. My only two questions are:

1.) Does cloud cover minimize our high temps and we bust low.

2.) With this starting overnight, does the lack of insolation mean ice accretes more effectively?

[MillvilleWx]

3 minutes ago, Eskimo Joe said:

@MillvilleWx excellent write up as always. Your thoughts mirror mine as well. My only two questions are:

1.) Does cloud cover minimize our high temps and we bust low.

2.) With this starting overnight, does the lack of insolation mean ice accretes more effectively?

Thanks Matt! I think it'll be interesting to see if the temps can bust a degree or two low. That's going to be important with this setup since every degree counts in marginal icing events. I think if clouds can stream in prior to 1pm, it could certainly play a role in limiting diurnal heating and keep the temps slightly lower than forecast. 

As far as the overnight start time, this would certainly have a benefit for some, mainly east of the fall line because after sunrise, it's pretty much a given that we'll see sufficient mixing to erode any weak CAD signature hanging around. I think spots down by Harrisonburg/RNK are in a better icing setup due to the majority of precip occurring with a lack of solar insulation. 

[NorthArlington101]

Sun is still definitely making its way through the cloud deck in Arlington, but seems to have thickened up — 37/21.

If things were holding off a little longer tonight I’d chase this in Staunton for the hell of it. By the time the Survivor finale ends though (10pm) I don’t think I’d want to cross the Blue Ridge!

[katabatic]

31.8/15.6 in southern Garrett County. This will be an interesting next 36 hours out here.

[peribonca]

First radar hallucinations of the season... returns seem ahead of schedule. There I said it. 

[Eskimo Joe]

Ice map seems reasonable. Last updated 9:44 am this morning.

 

 

[WinterWxLuvr]

33/25 in Funchester

[MillvilleWx]

27 minutes ago, Eskimo Joe said:

Ice map seems reasonable. Last updated 9:44 am this morning.

 

 

I'm glad I still know what I'm doing