1/6/2024 Small Wintry Mix Event

We have a small wintry mix event for NW of 95 that will result in some minor impacts, with impacts increasing the further north and west you go. A low pressure system will track northeastward off the gulf coast and into the Delmarva as it intensifies over SE VA. Precip will overspread the DMV in the morning, starting out as wintry precip for most. Areas along and E of 95 are expected to see very minimal accumulations and a quick transition to a cold rain. 

As the event progresses, strong WAA will warm the 850 mb temps to above freezing as a warm nose is pushed northwestward, while cold air is still at the surface. Unlike a few days ago, this opens the potential to overall wintry precip rather than just snow to rain. These 850mb temps will vary, with the coldest temps being in the mountains and W of the Blue Ridge. Here, the primary ptype will likely be snow. It is very likely that everyone E of the BR will warm enough to see a wintry mix of sleet, freezing rain, and rain(more wintry precip the more NW you go).

The confidence of this storm is generally very low even this close to the event, due to the extremely tight gradient setting up near the RS line; this is going to be a nowcast event. A 1-3 degree difference will make or break this setup. Due to the preceding temps and low wetbulb temps, wintry precip(where it does happen) should stick pretty easily. The best confidence for significant snow is W of I81, the Catoctins and westward, into the mountain counties. Although it seems surface temps were colder than modeled, the 850 mb temps according to IAD sounding look just as modeled, this doesn't really mean anything yet. Nonetheless, most of the region will see some wintry precip, with accumulations starting as soon as you head N and W from the cities.

Making a snow map for this event was difficult, but here are my general thoughts as of now:

Everyone E of 95 sees all rain, this is medium-high confidence. At the very most a couple of flakes may mix in at the border parts, but very little to no wintry precip is expected here. 95 and just NW is looking to see a T-1"(trace does not mean measurable snow). I think everyone here sees at least wintry precip falling, even with a quick transition to rain. This area also has low confidence, and will setup the start of the very large gradient. The more snow accumulation the more NW you go. Immediately NW of DC/Balt(outside the cities), there is some chance for some very minor ice/snow accumulation. This will be washed away quite quickly however.

The light blue zone(for areas closer to DC) I think will see enough snow/sleet to accumulate, as well as some ice accumulation. This area is extremely uncertain though, with the lowest confidence. The dark blue zone is the same idea as the light blue, but more snow/sleet and more ZR. Again, extremely low confidence in these areas; small temp differences can make or break this.

However, the light blue area near I81 is likely going to see large ice accumulations(potential of 0.1-0.25"+ here). This area is W enough to have enough cold air at the surface but WAA will quickly turn most precip here into freezing rain. The predominant ptype here looks like freezing rain, but some sleet/snow will likely fall.

The purple area is much more confident as this area likely stays snow long enough to see moderate accumulations(3-5"). Even here, there is a slight concern that mixing will cut down a bit, but any mixing shouldn't be too long. The predominant precipitation type here is snow. The red area is the bullseye and the mountainous areas. These areas have higher confidence.

Here are the current onset and warning maps, WSWs are up for just E of I81 and westward, as well as Frederick/Carroll Counties. WWAs are all the way down to the metros, primarily due to ice concerns. Generally, if you can avoid travel near I70/I81, do so, but closer to DC, travel shouldn't be too bad. We see an areawide E of I81 transition to mix and then rain by 10AM to 2 PM.

March 12, 2022 Snow: Strong Winds and Near-Blizzard Conditions

Good evening everyone! Over the past week or so I have been tracking a winter storm threat for the DC area on Saturday. In the past 24 hours, models have consistently trended colder and more southeast, allowing for our region to garner higher snow accumulations. There is a winter weather advisory for I-95 corridor and north and west of that. 2-4" is expected in I-95 corridor, while 3-5" is expected NW of 95. The cold air will come in quickly and strong tomorrow. There will be a brief period of sleet while we transition over to snow tomorrow, which will help snow accumulate better. The freeze will also aid with this. The winds will be very strong tomorrow. Many areas will see wind gusts in excess of 50 MPH, up to 55 MPH. Due to winds and the heavy snow expected, blizzard conditions are possible tomorrow,  particularly between 8 - 11 AM. In the WWA, it states the possibility for this. Thundersnow is also possible, mainly when we transition into snow(soundings support it). Winds are quite undermodeled. Tomorrow morning, we will have an FGEN band that will setup west of DC, but east of I81 as the transition to snow occurs. Rates could be 1-3" per hour in this band. Because of this, I really think west of DC should be placed under a winter storm warning. Just because it was 60 today does not mean snow will not accumulate. There have been many times where there were mild temps before onset of snow, and areas got a good amount of snow(1/3 as an example). I'll show some of the 18z mesoscale models here.

 

HRRR: 

 

The HRRR has a very impressive snow accumulation, with the bulk of the snow falling in 6 hours. Latest runs of the HRRR are uptrending on snow accumulation too. I think this could be a legit overpreformer for our region, dynamics and FGEN banding are very impressive. The soundings from the HRRR scream FGEN band(winds rapidly veering with height, ample amount of omega and lift in DGZ) with good snow growth. I would cut totals by about 1/3 for a more realistic amount, but still a very impressive amount.

NAM 12KM:

NAM is quite impressive with snow accumulations, with a widespread swath of 6" and higher. Again I would cut totals by 1/3 - 1/2, but this was a big improvement from last run. The reason why is that NAM is slower, and colder and east, allowing for more snow accumulation. NAM 3KM supports this too.

NAM NEST(3KM): 

The NAM 3KM is very impressive with dynamics + FGEN and supports the low-resolution NAM's solution. NAM 3KM is also impressive with a wide swath of 6"+. Again cut totals by 1/3-1/2. Much better than last run.

NAM 3KM has an impressive FGEN band moving through the region as rain turns into snow.  A sounding reveals ptype being snow, with good dendritic growth. Winds rapidly veer, which indicates FGEN. There is good lift in the DGZ with nice omega values. This is a good sounding for heavy snow, and for strong dynamic cooling. This sounding also indicates some possible thundersnow in some areas. 

My snow map:

Here is my final snowfall map. In the red, you can expect 4-8" of snow(Blue Ridge, Catoctin Mountains, Western MD). North of DC, you can expect 3-6" of snow. Most of the region DC and south are in the 1-3" range. Far southeastern parts of our region can expect C-1". I went a little bit bullish on the snow map because of latest trends on guidance leading to more snow. The dynamics and setup from this event is quite impressive. Even though rates are still uncertain, a FGEN band that will allow for these totals to come to fruition. The north winds will help blow snow and help transport cold air here. When rain transitions over to snow at around 5-8 am for most of the region, there will be a brief period of sleet. This will help snow accumulate, including the flash freeze. This will be a nice event for March. Whiteout conditions at times cannot be ruled out, and near blizzard conditions for somewhere are likely at one point at time. Even thundersnow is possible tomorrow(transition to rain - snow). This will probably be the last snow event looking at long range models, so enjoy everyone! Main roads should be fine but secondary roads will likely cave to the high snowfall rates.

Final Call Snow & Ice Maps and Nowcast

 

These are my final call snow and ice maps. Almost nothing has changed for the snow map, but the ice map has took a change for the good: The 0.1-0.25"+ zone is now gone, and has been replaced with the 0.01-0.1"+ ice zone. Most people will only see up to a tenth of an inch of ice, but the plus is there for the mountains who will have cold air for longer, allowing for longer ice accumulations. Also some localized areas may see amounts just above a tenth of an inch. Cold air was undermodeled and WAA was overmodeled on high res models if you look at radar. This could mean a longer time period of snow, and just in general wintry precipitation. Surfaces will be below freezing for a while even when temps start to rise above freezing.

MLK Weekend Storm - What to expect

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.

Wintry Mix Tomorrow

Good evening everyone! Tomorrow morning, some freezing rain, sleet, and snow is possible for our northern areas. This event will not be significant at all, and I expect minimal accumulations, up to a coating of slushy snow; with all of the (possible) accumlation on grass, with roads staying wet.  Those small amounts may not even occur in the first place. A cold front pushing through this evening creates dew points below freezing, with surface temperatures in the 30s(mainly for northern areas). The event will start out as sleet or snow for northern areas, and then switch over to rain as soon as temps rise. Other than the mountains, icing/snow will not be a threat due to how warm its been recently.

These are the winter weather maps expected by the NWS:

 

 

Plume for Northern Maryland(Frederick):

As you can see, this plume shows all type of precipitation, with rain being the dominant precipitation. It shows pink(sleet), red(freezing rain), blue(snow), and green(rain). It shows it starting in the early morning, and then as temps rise, the cold rain starts to take over the mix, and eventually wins over the wintry precipitation. The plume mean shows a trace-dusting of snow for Frederick, Maryland. When the rain chances increase in the plume, thats when the precipitation get mixed with rain.

This is the 0z HRRR for tomorrow. It shows an early batch of rain quickly moving through before the snow and mix arrives. When the quick batch of rain arrives, its not cold enough at the surface to support wintry precipitation, so therefore the precipitation falls as rain. However, when the heavier precipitation comes to our area, upper level temperatures are cold enough to support wintry precipitation even with mid 30s at the surface. If the snow falls at a heavy enough rate, there could be a light coating on the grass in some areas. 

To conclude, a wintry mix that transistions to rain is likely if you live north of DC and I-66. It may lead to a possible slushy coating, especially in our more far northern areas. This event will not impact the roads or sidewalks, unless you travel north of the Mason-Dixon line, where WWAs are posted. Precipitation becomes less likely south of DC, and these areas will see just rain, with a very very low chance of mixing.

April Fools Storm Recap

In the morning, there were reports of mixed rain and snow for the northern part of the region and possibly some stickage in northern Frederick and Caroll counties. Throughout the day, north winds and bands from PA brought graupel, sleet, and mixed rain and snow throughout a lot of the region. Then, after 3 PM, bands were forming that had less mixing in them and more snow. Then, at 4-5 PM, a band formed that mostly pure snow and brought heavy precip rates for a lot of the part of our region! Snow was reported as far into parts of Southern Maryland! Thundersnow/graupel was reported, which is really rare(0.07% chance in snowstorms), and especially cause it is in April! Stickage was reported in some parts of our northern region, and I was able to get a dusting/coating of snow, which is often recorded as 1"! Some people saw snow in temps as warm as 45-50+! It dropped from 44-42 in less than 5-10 minutes to 39 for me! Visibility dropped to <0.50 miles! That shows you the power of dynamic cooling and north winds! Bands were still forming in PA and coming SE to hit the DMV region as the sun starts to set and temps drop. There were also a lot of gusty winds. As the night continued, bands started to hit regions and some people woke up to a coating of snow on their cars and surfaces as temps drop. This was a pretty unique storm to say the least.

April Fools Snowstorm Update

5:50 PM Update:

As many people saw snow from a heavy snow band that pushed through our area, many bands are still coming through and still forming in PA. We have a chance for snow bands to come through our region throughout the rest of the day and night, and even a chance early morning tomorrow! As north winds gust and pull in cold air and as the sun sets and temps drop, some of these bands may fall when its below freezing, and may cause some accumulation! Not much is expected though, only up to an inch; up to 2 inches at the very most. Sun angle issues will be removed, and if the temps are below freezing accumulation could easily happen. Keep hoping! This was better than a lot of models were saying.

7:30 AM Update:

As the main course of precipitation moves out of our region, there is still chance for some flurries/snow showers with mostly light but sometimes heavy-moderate snow to come south from PA throughout the day and into the night. In the night, it may be below freezing when they come. North winds will create showers in the afternoon that may have snow mixed with them. Snow was confirmed on radar in northern Frederick and Carroll counties and may have coated the ground there. However, mixed snow reports go much more further east and south than that, and I can confirm one here too. Anyways, we still have a chance to see some snow, mixed with times throughout the day if you don't live in a northern place and/or aren't an early riser. There is a chance for some accumulation, mainly after sunset when temps will start to plummet towards freezing. It won't be much unless that precip is heavy.

Tomorrow is the beginning of April... and to start it off we have a chance for some snow to fall. Models have been jumping back and forth with this system, and 12z runs weren't looking that good, but 18z runs look a bit better. The cold front is coming through, and has reached into western Maryland at 5 pm. I don't know if this is earlier or later than expected, but I'll assume this is around expected. I'll keep updating this specific post if anything major changes. Let's jump right into the models!

 GFS:

The GFS shows rain turning into an isolated part of snow before the main system moves out, and shows lingering rain/snow showers staying for a while before completely moving out. After hour 18(7 AM), the 540 line is south of our county. This is good because it means that our county is generally suitable to get snow. The lingering snow/rain showers between hour 21-27 should generally be snow, possibly mixed with rain.

Now I want to talk about the isolated snow spot at hour 18. We have northwest/north winds up to 700 mb in this sounding, which will bring in cold air. The precipitation type maps plus precip type on sounding all say snow. However, we are under the 540 line at this time, which isn't favorable for getting snow. We also have temps well above freezing. This would likely not be all snow even for Damascus and would probably be mixed with rain. These are somewhat heavy precip types and will cause dynamic cooling, something the models don't handle well so we will see how this plays out.

The GFS shows around an inch for that area in that spot of snow at hour 18. I wouldn't think this much would fall, since rain mixing would hinder with accumulation, but this could happen if we saw less mixing!

NAM(12km):

The NAM shows all rain on the ptype map for all of MoCo, but the thing is its glitching a bit. At hour 18(7 AM), most of the county is under the 540 line and still rain. Even if not snow, it would still at least be snow. 

This sounding shows north/northwest winds up to 700 mb, and temps at 39F. Even on the precip type guess, it says snow. It would be difficult to have pure snow with this sounding, so there would likely be mixing with rain. Even so, the ptype map is wrong and it should show some snow above 540 line.

It shows no accumulating snow for our region except for western Maryland, but this map is glitched.

European:

The European doesn't show any wintry precip for any of our region, but there is a high chance that in the break between hour 24 and 30 that there is some sort of wintry precip, mainly for our northern areas. I cannot see soundings or 540 lines so it's harder to interpret this.

The Euro(10:1 ratio NOT Kuchera) shows no snow except for northwestern Frederick County.

This event is very difficult to forecast. A small difference in temps could mean snow or no snow. A cold front is pushing through and a second cold front will push through tomorrow as well. If we don't get snow from the main event, we may get snow from the lingering snow bands after the main course of precip, and it may be below freezing when we might get them. For a snow forecast... it's too difficult to make one.  We might not see any accumulation at all or we could see 1-3 inches. North and west of MoCo has the best chance, but this storm favors more inland than more north(although being more north always helps)! Models won't be useful past this point, and its better to use other tools. This may be the last snow threat of the year. Either way, April Fools!

April Fools Snow?

Yes, you read the title right, I am tracking a storm that could potentially produce wintry weather in the DMV, and yes it's on April Fools Day. I guess this year Mother Nature is playing pranks of her own.  I didn't make a post about this earlier because it looked like it was going to miss the DC area except for western Maryland. But now, as models have been shifting the system more east and south, the DMV has a chance to see flakes fall, and some accumulation in our more inland, northern areas. Any part of eastern Maryland, even northeast Maryland, don't have much of a chance with this system. This system will enter tomorrow, but the main chance of snow is Thursday morning, as a cold front pushes through. It will be rain throughout Wednesday for everyone. This isn't a weak system too. A lot of models are showing 0.75-1+ inches of all precipitation amounts(total QPF) for a lot of our region. Dynamic cooling will help a lot here.

NAM(12km):

The NAM shows heavy rain transitioning into sleet, then snow as the low starts to move off and up the coast. It still shows temps above freezing, but somewhat heavy precip rates, so if there's any accumulation, it should be solely on the grass. A lot of areas won't even see any accumulation.

The NAM shows all the way from a coating in SE MoCo up to 3 inches in Northern MoCo. It will melt very fast when the snow stops though, and the April sun angle + temps above freezing will cut down on the totals. However, one thing I do want to point out is that the NAM and other models have been showing lingering snow showers even after the main course of the precipitation is done, and that may hit parts of the DMV at times. Shouldn't account to much, if any, as temps will be likely above freezing.

This is a sounding at around 4 AM EDT. The red represents temperature at the surface, and the green represents dew point. The precip here would likely be sleet because of a warm nose from 750 mb(1.25 miles up in the atmosphere) all the way to 500 mb(2.75 miles in the atmosphere). The snowflake would fall and refreeze into a sleet pellet. There are north/northwest facing winds to bring in cold air at the surface all the way up to around 700mb. It could also be rain though, since the sounding doesn't seem to go too past 0 C(freezing line) in the "cold air" area at 800 mb. There is more room for cold air up in the atmosphere, and the warm nose isn't that big to guarantee rain.

European:

The European shows heavy rain possibly turning into wintry precip(mix/snow) as the low moves off and up the coast. This has 6 hour breaks between pictures, so there would likely be some short of wintry precip in between the time from hour 48 and hour 54. 

Assuming 10:1 ratio(NOT KUCHERA), we don't see any snow ACCUMULATION, but that doesn't mean we will see a snow shower. The snow accumulation is awfully close to us though. It might have shifted a bit southeast, which is good for us.

GFS:

The GFS shows heavy rain turning into heavy snow as the low goes up and off the coast before starting to lighten out as the system moves out of our area. These are heavy precip rates, and would be enough to combat the sun angle + above freezing temps... if they occured.

The GFS shows all the way from a coating to a half inch, with the most snow in NW MoCo. It has trended southeast and stronger for this storm, which is good!

However, there is room for being skeptical when the transition happens. At 4 AM Thursday, the GFS on the precipitation maps shows heavy snow. However, when you look at the sounding, it says the precip type is... rain? The sounding supports it. It shows a warm nose from 875 mb to 625 mb with temps above freezing. Compared to the NAM sounding, the temps are warmer and the warm nose looks strong enough to cause a cold rain instead of snow. There are north/northwest winds up to 750 mb to pull in cold air which is good.

A small change could mean either cold rain or heavy wet snow. Accumulation isn't expected to happen anywhere but grass, and may not occur in the first place too. This will have to be watched, and dynamic cooling will play a big role here. North/northwest winds will start to occur as the low moves off the coast and will bring in a lot of cold air. We want more heavy snow before sunrise to alleviate sun angle concerns, but the transition seems to be happening around 4-8 AM. Even just 1-2 hours earlier would make a big difference in snow accumulation. I will make an update tomorrow with new models plus radar and soundings. Right now, it looks like a coating up to an inch for MoCo, with some localized areas possibly reaching up to 2 inches. No accumulation is pretty possible too. I am confident in flakes falling though.