A low-pressure system tracking in southern VA will bring our region snow again. It will move out fast, but will bring good dynamics with it, and intensify as it slides across, bringing heavy rates. Winter storm warnings are up for those in the I81 corridor and N of I66 for 4-6" of snow, with more in the mountains.
A strong 170-200kt UL jet will lead to divergence(therefore, rising air) on the left exit of the jet(over us). This, along with strong frontogenesis/WAA will support lift, which looks to stretch throughout the DGZ, leading to optimal snow growth and support for heavy banding. The intensifying low pressure will also deepen the lift in the DGZ even more, strongly supporting the idea of 1-3"/hr rates and higher accumulations; despite short duration.
A sounding in N MoCo indicates a favorable environment for snow growth barring the above-freezing surface temps. N of 66 and NW of 95 temps should be 30-32 during the peak precip, and we should dynamically cool to around 32 when the precip sets in.
Additionally, the 850 MB low(image 2) is in a favorable position for those just north of its track, and the SLP is in an ideal location. We will see strong WAA(image 1) and healthy PVA(image 3). Large dynamic cooling is expected given the rates of the precip and the profile being dry enough right now(image 4).
Thus, 1-3"/hr rates are expected with this system. The duration will be around 3-6 hours, but the impressive dynamics and rates will make up for the short period of time, in my opinion. The overall setup is just supportive of heavy snowfall rates, and ratios aren't horrible either(should be around 10:1, slightly higher in peak banding). Overnight timing also really helps here with any melting/sun angle concerns, so long as we are around or below freezing it will have no problem sticking.
Thus, this is why I went aggressive with my snowfall and forecasted widespread 4-6" N of 66, with mountains getting 6-8" because of orographic lift leading to heavier rates in banding(as well as being colder). Thundersnow is possible too due to the strong forcing and instability in the column. Heavy snow is almost a lock, but this event will almost fully wrap up by 7-8 am. Although the warm is ground initially, initial precip should help saturate the column and enforce dynamic cooling for the heavier rates. It will stick to roads due to the overnight timing and rates. Precip type should generally be all snow N of 66(maybe you might see a bit of rain mix in at the start but should transition quickly), S of there you should start as rain first but transition to snow. Overall, a solid snowstorm is upcoming for N and W of DC!
This will be a quicker post since I only have a little time today. But we went from a generally all-rain storm to potentially quick heavy snow in less than 24 hours. The South trends on modeling with this short of a lead time are quite remarkable, and I'm not sure if I've seen anything like this, at least recently.
A dynamic system will be approaching from the TN valley, bringing precipitation to the mid-Atlantic and Northeast, a lot of which will be snow. Winter weather advisories are up for those NW of 95 and N of I66.
We will start as rain, but likely switch over to snow and see accumulations in these areas. For us, we get cold enough to snow from dynamic cooling; this system will be very dynamic. It depends on rates, and the boom/bust scenarios are equally likely. The bust scenario would be that we do not get heavy rates and little to no accumulation; the boom is that we get heavy rates for a few hours. Despite marginal temps(33-34), heavy snow rates will accumulate, even on sidewalks/roads if heavy enough. This storm will be more of a latitude and elevation-based storm rather than longitude. That's why central/northern MD is more favored in this setup. Even with heavy rates, your ratios will be low and it will be a wet snow.
Precip will likely onset between 5-8 AM, with central MD expected to be all snow by 7-8 AM. Guidance is indicating heavy precip rates, which timed with the morning commute will make it hazardous. It's not more so about the actual amounts, but the heavy rates expected and the timing are perfect to impact the commute. This storm has trended so far south that Maryland gets in on the main snow shield; and not just the backend. Our storm's preformance will depend on these rates.
There is the potential for 1-3 hours of 1-2"+ rates during the morning commute. With these rates, it will accumulate, even on side roads and paved surfaces. Heavy rates always beat marginal temperatures or any other factor. The previous rain will also make pretreatment impossible. The heaviest rates will likely be just after the switchover(when dynamics are the most favorable), with thundersnow possibilities being hinted by guidance. We won't know what this storm will do until we get there; it is fully dependent on the level and location of banding.
Snow Map + School Predictions:
HREF forecast for the next 24 hours; 2-4" NW of 95 and N of 66 with 4-6" for 70 and north
This is my snow forecast for the event; I think there should generally be at least a solid inch for N of 66; further south should stay under an inch. 3-6" for elevated areas near the MD line and of course, the mountains look like a good call. especially with the recent trends. I would not be surprised at all of the warnings were issued last minute for those regions. The plus in the 1-3 zone is mainly for higher elevated areas. This is a very difficult forecast, with an equal chance for a boom and bust. 1-3" is just in the middle zone and I feel like it will either be a bust/boom. Either way, the morning commute is looking awful, and there will be impacts. As for school impacts...
Prediction: 3 Snowflakes I'd expect many school impacts, with widespread delays and even closures, especially for counties in the 3-6" zone. The timing of this is perfect to at the very least delay. There is also a 50/50 chance for a closure depending on how long the rates last, and how intense they get. If the rates last for long enough, schools will be forced to close, and there will be enough accumulation on the roads. With the current forecast in place. and the rates guidance is showing, there is really no way schools can open on time tomorrow.
Overall, a nice sneaky event. I think this is going to surprise a lot of people; enjoy the snow!
A vigorous shortwave/trough will move through the area around tomorrow at midday, providing strong lift to generate snow and sufficient dynamics from the strong upper jet, in addition to PVA and modest WAA. These dynamics will allow heavy precip to be brought about just ahead of the shortwave and a more expansive precip shield, which guidance has been trending to. Guidance, in addition to the more expansive precip shield, has brought the vort-max further south, allowing for higher amounts of QPF. The heaviest snow/concentration of precip will just be north of the vort-max; putting us in a more favorable position.
This is ahead of a great antecedent airmass, with already existing snow cover contributing to it even more. However, the absence of deep moisture, and generally low precip amounts, as well as the general storm being too progressive will inhibit this from becoming a major storm - despite the favorable H500 pattern. Nonetheless - a moderate storm for the area is looking likely, with ample cold. Ratios will be high due to a cold, saturated profile in the DGZ and the rest of the column, leading to modest dendrite growth. Surface temps will also be in the upper 20s and lower 30s the entire event; below freezing the entire time.
We should see a good thump of snow not too far from onset; making morning commute extremely hazardous. Shortwave forcing by that time is very good and would support locally heavy rates; despite low lift in the DGZ. This will likely be another high-ratio, generally low-rates event. Roads will become slick and snow-covered extremely quickly, with lingering snow expected to last through the evening rush hour. Thus, most schools/offices have closed in person. Snow will continue throughout the rest of the day, but will become lighter after the morning thump.
Snow Map
This is my forecast:
I went extremely bullish due to the uptrends today and the overall setup. The most snow will be N of I70 in NE MD due to great dynamics and precip from the IVT(which won't have that much of an impact closer to DC). N of I-66 should generally see 2-4"+ (why I brought my 3-5"+ zone further south), with the south of it generally seeing 1-3". Although this is bullish - please keep in mind that just cause a specific area is in the 3-5"+ zone doesn't mean they will be seeing the higher amounts of the range. Most areas S of 70 in that zone will likely stay under 5". The further north and east you are, the better for this setup(outside of the mountains). The exact location of the bands and the heaviest QPF/snow are uncertain, thus why I added the plus for any isolated spots above the range. The general consensus should be another nice high-ratio, low-rate snow event - on top of already existing snow, something that is quite rare in the mid-Atlantic. This storm will have a large impact on the morning commute and bring about hazardous travel.
Additionally, radar looks good right now, with virga saturating the column currently, as well as a decent precip shield in the OH Valley/Midwest. MPING reports confirm this is all reaching the ground over there. Earlier today, HRRR underdid the moisture in IA and didn't see the snow shield reaching Cincinnati (all related to our storm system). Current observations look good so far and aren't indicative of any major concerns.
Overall, the last-minute uptrend on the vort-max being further south and a more expansive, robust precip shield have led to totals becoming higher in the DMV.
Here are the current NWS warnings/advisories map, and precip onset:
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.
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.
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! Today is going to be a very nice day, with highs in the 50s to the2 lower-mid 60s. But as a cold front moves through, and a storm moves behind it, we will be tracking the threat for some snow. The NWS has most of the region(except for the southern part of the region, and western MD) in a winter weather advisory for 1-2" of snow, with local amounts up to 4" of snow. The onset of the storm will start out as rain/mix, but it will turn to snow quickly. Everyone will be snow by the time sunrise happens on Sunday. This will be a light event, and after noon you should be fine to travel. However there might be a refreeze after 4 PM, which could cause some slick spots. Most accumulations will be on grassy surfaces, however there could be accumulation on paved surfaces too. Minor travel issues and slushy spots are not out of the question. High resolution models are starting to pick up on an FGEN band that may occur at the start of the event, that would bring moderate-heavy snow rates. It would dynamically cool the atmosphere and combat warm surface temperatures. I'll look at 2 high-resolution models: NAM NEST & HRRR.
HRRR:
The HRRR shows precip onset as rain, quickly turning over to snow. At 1-3 AM you can see a moderate-heavy snow band in parts of the region. By 3 PM, snow is done for almost all of the region, but I skipped some timeframes at the end to show a backend snow band that the HRRR gives.
This is the total accumulated snow that the HRRR gives. Remember, not all of it will stick, so actual totals will be a bit lower than this. Gives a widespread 1-3", but I'm skeptical of the widespread 3"+ in parts of north central MD.
This HRRR sounding at 2 AM Sunday shows something interesting. In the sounding, there is intense lift in the DGZ, which allows for moisture and moderate-heavy precipitation rates. This is an FGEN band because you can see the wind barb directions rapidly changing. If you are a snow lover you want to see this happen for more accumulation. This is important because this will dynamically cool the atmosphere to be cold enough to support snow, and would help to quickly overtake the warm surface temps.
NAM NEST:
The NAM shows the inital onset as rain before quickly changing over to heavy snow. It also shows the heavy FGEN band between 1-4 AM, and is actually a bit more robust with the onset of precip compared to the HRRR. It also has the backend snow band, but not as robust as the HRRR.
The snow accumulations are bit more robust compared to the HRRR, but around the same.
The NAM NEST also shows a nice FGEN band setting up around 1-4 AM, with more lift in the DGZ than the HRRR, creating heavy snow rates. You can see the FGEN banding on the map below setting up, and on the sounding too. I explained what this means while talking about the HRRR sounding.
The bullseye of this storm will be western central VA, where a FGEN band will drop 3-6" of snow. The FGEN band looks to be better supported there with longer duration leading to more totals. I expect a general 1-3" for most of the region, with C-1" for western MD and C-1" for the southern part of our region. Most accumulations will be in the grass, but there could be some accumulations on paved surfaces too, especially where the FGEN band sets up. Some travel issues and slushy spots on paved surfaces is not out of the question.
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