My snowflake prediction for Friday is 2 snowflakes. Exact percentages are 55% delay, and a 10% chance for closure. The reason I'm leaning towards a delay is because the HRRR is now showing a lot more additional ice on top of what we already have throughout the night. Although temps do rise above freezing, there won't be enough time for it to melt for a full day. I think there won't be a closure because temps will rise very quickly above freezing and melt all of the ice. Even though the ice won't accumulate that much on sidewalks and streets, there will be some slick spots in areas with the simulation the HRRR is showing, at the very least. Some streets and sidewalks could be completely covered in ice, especially in areas like Damascus. The storm looks to be overpreforming a bit right now. HRRR isn't picking up on the freezing drizzle that is happening right now too. Temps dont get above freezing until 7 am on the HRRR for some parts of the county. Because of these reasons, I am confident in a delay but not in a closure. Remember: what the HRRR shows is ADDITIONAL ice. The WWA goes until 10 am for Northern MoCo.
Good afternoon everyone! We have a winter storm threat to track tomorrow and Monday morning. This threat is looking more like an ice threat instead of a snow threat; but if you live north and west of I-95 you will still see some snow accumulation for this storm. Unless you're far north and west(along and west of I-81), you probably won't see an optimal amount of snow - if you like snow. This storm takes an inland track - so being even a little bit more west can make a difference. When the snow starts, it will be heavy, with rates 1-3" per hour. When it snows, it will thump. Wind gusts up to 45 MPH are possible with this storm, creating the possibility of downed trees and spotty power outages, especially when ice starts to take over the snow. I would recommend to stay off of the roads(if NW of I-95) on Sunday-Monday, as the snow with ice makes roads very slippery and impassible at times. There is a very cold airmass in place for the storm, so ice and snow will stick longer to untreated surfaces. Please note that freezing rain can happen even above freezing, if surface temps and wet bulb are still <32. There is a winter weather advisory for all of MoCo, with 1-3" expected and up to 0.1" of ice. Just north of us is in a winter storm warning, for 2-4" of snow and 0.1-0.3" of ice.
NAM12KM:
Note: at the time where it shows pink for our area(7 PM), I looked at a sounding for Germantown/Gaithersburg and it would seem as if it would be sleet, rather than freezing rain. Still, you can see everyone starts off as snow, and then the warm nose comes in, turning into sleet, then freezing rain, and eventually, when the CAD breaks, cold rain.
Ice total and snow total maps, pretty self explanatory.
NAM3KM:
The NAM high res shows everyone starting out as snow, then going to ice, and then going to plain rain. The NAM 3KM also shows some backend snow, which is interesting. However, it seems to be light snow, and probably wouldn't amount to much. A lot of the rain will wash all of the snow away, so even if 3" fell, it wouldn't look like it.
The reason why the NAM 3km shows a lot of ice is because of strong southeasterly upper level winds, forcing warm air into the atmosphere
and creating a warm nose that gets more dense as
time goes on. Eventually, the cold air at the surface breaks, and areas east of I-81 switch to cold rain.
One other thing I want to talk about is the wind gusts. At this time(8P Sunday), freezing rain is falling all throughout the region. With the strong wind gusts(40-50 MPH wind gusts), isolated power outages and downed trees is likely. I would recommend everyone north and west of I-95 to get ready to deal with some time w/o power, just in case.
*Editors Note: While I was writing this, the 18z NAMs came out, all of the models shown are from the 12z suite
My snow and ice forecast:
(I apologize for very low quality maps, Blogger won't let me put high quality pictures)
My next update for these maps will be tomorrow morning, after 12z mesoscale runs come in. I'm going bullish with my forecast because I think there will be heavy enough rates for a large enough area to get 2-4" before the changeover to sleet, freezing rain, and then cold rain. I think the NAM is too bullish on the warm air coming in very quickly and changing over to rain, so I didn't use the NAM that much in my forecast. Other models look pretty good for our region in terms of snow, such as the Euro, GFS, and HRRR. My final call WILL be tomorrow morning, after 12z HRRR, and both NAMs come in.
To conclude, I expect 2-4" of snow(possibly more in localized areas) for Northern MoCo and 1-3" for Southern MoCo. For ice, I expect 0.1-0.25" of ice for the general area, with possibly more in localized areas. Timing onset will be in the afternoon, at 1-3 PM. This will be a high impact storm, especially west of I-81, and also for NW of I-95, not just for snow, but for ice. I am very concerned about the ice threat, since CAD is usually undermodeled, especially on global models, and the ice combined with the strong wind gusts could create widespread power outages and downed trees. I'll have a quick update tomorrow, and then I'll do a nowcast.
There is an ice storm warning in effect for the whole county. This has not happened since February 12, 2008; which is over 13 years! From NWS:
"...ICE STORM WARNING IN EFFECT UNTIL 7 AM EST SUNDAY...
* WHAT...Two to three-tenths of an inch of sleet and freezing rain causing significant icing impacts.
* WHERE...The District of Columbia, and portions of central Maryland and northern Virginia.
* WHEN...Until 7 AM EST Sunday.
* IMPACTS...Difficult travel conditions.
* ADDITIONAL DETAILS...Roadways are becoming very icy and dangerous. Avoid all unnecessary travel.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Travel is strongly discouraged. If you must travel, keep an extra
flashlight, food and water in your vehicle in case of an
emergency. Prepare for possible power outages.
When venturing outside, watch your first few steps taken on
steps, sidewalks, and driveways, which could be icy and slippery,
increasing your risk of a fall and injury."
I can already report a tenth of an inch of ice here in Gaithersburg and a lot of sleet on the ground(over a tenth of an inch of sleet). Pre-treatments are useless, and I can clearly see a coating of sleet on top of the freezing rain. Tree branches are facing down and look like they will snap. It's really coming down here. Every single surface, even treated ones are covered in lots of ice and sleet. Do not travel at all. Power outages are possible, and tree damage will be done. This will be extremely dangerous. There are already so many accidents and injuries on the roads now. Stay safe inside and prepare for an extended period of time without power. Here are some links to help you: What To Do When Lose Power During An Ice Storm, Power Outage Checker(click on your state name), and the National Weather Service for the latest updates on winter weather.
