2/17 Overnight Moderate Event for DC/Balt Metros

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! 

2/13 Rain to Snow Event for Morning Commute

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!

1/19 Light-Moderate Snow Event

Synoptic Setup 

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:

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.

12/10/2023 Accumulating Snow Event NW of I95

 Guidance has converged on an anafrontal system with a secondary low that provides the opportunity to see some snow, as moisture is thrown from the secondary low into the cold sector. Thus, this gives us to potential to see snow falling, with (light) accumulation prospects NW of 95.

SYNOPSIS:

A shortwave, which has already moved through the country and continues to do so has a cold front ahead of it and northern piece energy. The trough axis is delayed behind the front, so we set up an anafrontal event(not typical).

 This system overall is very dynamic and should have good PVA in front of it which induces cyclogenesis(intensification of the storm) and moisture advection. Temp gradient is also quite large, with the airmass behind the cold front being Canadian and the airmass in front of it being subtropical.

We also have a dual jet setup associated with this which pops a secondary low when the trough becomes negatively tilted, in the Carolinas. This directs winds and moisture return NW.

The large temp gradient should allow for frontogensis forcing, which will make precip rates extremely high. CAA driven snow will occur in the overnight hours after midnight for most people as temps drop.

One thing to note about this system is that surface temps are extremely marginal, but the rest of the atmosphere is <0C, allowing for it to snow. These heavy precip rates will allow for greater dynamic cooling and a saturated column.

    

OBSERVATIONS:
We are now less than 12 hours away from snow, and the use of models is useless. As of 23z(6P EST), the trough is netural-slightly negatively tilted over MS/AL.

This is ahead of schedule, as it was supposed to be this way at 7-8 PM. This will have better implications downstream as a earlier negative tilt will allow for cold air to fill in faster during the snow, and the secondary low to pop more/quicker in a favorable location.

The cold front was also ahead of schedule, and stronger than modeled, passing the BR by 515-530 PM. 

Temps are dropping quite quickly behind the front, with some station reporting degree drops every 4-5 minutes. Although it is worth noting that sfc temps are warmer than on NAM, they are colder than on HRRR(behind the front), and it just initalized at 22z

The rate temps are dropping behind the CF, catching up to NAMs temps wouldnt take too long either. It's running too warm for some parts of nova at 0z anyways. We'll see though, eitherway temp wise we look good.

And now we look at the radar, we are starting to see the backside precip fill in and amplify. It looks very good with convection off the Carolinas. This system is absolutely juiced, and is exceeding expectatations. 

So overall, it might be safe to say that this event is going slightly better than expectations. Observations look great so far and is expected to continue into the event. 

Overall:

Overall, despite uptrends, the general picture is the same: accumulating snow for NW of 95, mainly in higher elevations. Temps will be very marginal(32-36), but we might push colder during heavy bands due to CAA. That being said, we need heavy snow rates to stick. Otherwise, it will not stick; moderate or below will not do it. Mesoscale banding features are too hard to resolve at this range, so there is no really saying where it will be, but if I had to guess it would be somewhere around here(NW of the fall line): 

As for snowfall, there will be an extremely sharp cutoff on I95. I have trouble thinking anyone inside or east of the beltway will see more than just white rain, with little to no accumulation. Elevation is just too bad there to get anything substantial. Temps will be too marginal there for anything. Even further NW, temps will remain 32-36 for most of the storm, with the exception of lower temps 1000'+ or in the bullseye areas. The reason I'm even going this bullish on accumulations is because of the puking snow rates that will set up somewhere that will stick to the ground despite temps. The rates cannot be moderate or light, they have to be heavy, but we know it will set up somewhere,, and that area should see nice accumulations. Having heavy wind should also help blow the snow around and even help with stickage as wind removes latent heat release; it would help us more than hurt us. This, along w/ heavy rates will make for low visibillity conditions. 

As of N of the fall line, I gave the highest amounts to areas 700'+ elevation and west of I81. The bullseye for this storm overall will be the Blue Ridge and the Apps, as expected. Locally, the bullseye is probably the Parrs Ridge if I'm betting.  In the Parrs ridge, there could be a spot of over 3"+ if everything goes right. I went extra bullish based on new data we have, but this could very well bust. I feel like this is a boom/bust type setup; either we do really well with banding and get puking snow for hours accumulating to over an inch, or we generally stay mostly rain with no acccumulation even if it snows. Ratios will be very low; likely 4:1-7:1 depending on your location.

And as for school impacts, models have trended earlier with the event, generally wrapping snow 5-7A through the region, but before that it will be absolutely puking, along with strong winds as the low intensifies and moves NE. The snow will melt extremely fast afterwards, but I still think theres a chance we could pull off a delay. I'll go 2 snowflakes(50% delay) for this event, if band is a bit later then we'll probably delay. If we can get a WWA in place we probably delay, but it can go either way. Accumulations will mostly be on grassy surfaces, but depending on rates, could be on some side roads and sidewalks. Overall, this event should lock in Dec measurable snow for most areas, and should be really nice to see. 

Winter Outlook 2023-24

full 36 page read/analysis: https://tinyurl.com/223zv9ec

Analogs:

Top ENSO analogs: 1957/1965/1991*

MEI Analogs: 1986/2009

Top Pacific Analogs: 1965/1972/1995

Polar Analogs: 1957/1965/1987/2009

EMI/Orientation Analogs: 1982/1991*/2015

1957/1965/1972/1987/2009 are my highest weighted analogs

DJF Weighted Temp/Precip Composite

The ENSO will likely end up as a basin-wide(with more of a western lean like 1957/65 as Nino 4 warms and Nino 1+2 cools), with periods of Modoki forcing. I do not think that this is a wall to wall cold and snowy winter, but rather bouts of favorable patterns/timeframes, with most of the bulk being in the second half of the winter(Feb). I think we overall end up N-slightly AN for the winter, with Feb being BN, and Dec slightly AN, with Jan being around N. There’s too much variability and unpredictability to pinpoint specific temp anomalies for those specific months, but I still think we overall end up N-slightly AN.

Snowfall:
 

The range this winter is extremely large, with the maximum high-end potential being a top 5 winter or another horrible, low-snow winter. Strong+ ninos tend to be very boom or bust winters. With the exception of 1994/95, every analog year I had was either under 10” or over 30”. As I mentioned before, the main thing that will determine the fate of this winter is the polar domain. With the -QBO/++AMO, as well as bouts of favorable forcing setting up at times, the polar domain is looking good for this winter. While we have a -PDO, the strong El Nino will win out and override the state. The warmest anomalies being over and east of the dateline is a very good thing and very different to the forcing we’ve been seeing over the past few years. The active STJ should provide us with plenty of storm opportunities and ample moisture, snow or rain regardless. Thus, this is also the best chance since 2016 for a HECS/KU. Even if we don’t get a KU, the active STJ provides many opportunities for multiple SECS/MECS. 

That is why I went well AN for snowfall for this year. I doubt we see a near-normal year; either much BN or much AN. There is a lot of potential this year, and as of now, things seem to be looking good. The warm Atlantic will also provide extra moisture for storms. Going around the mid-range this year for snowfall doesn’t appear to be a good idea. This year definitely won’t be that cold overall, but we don’t need extreme back-to-back cold anomalies to get snowfall. All we need is one wave to time up right. With a Nino, the Pacific shouldn’t be too much of a problem this year. ENSO influences PDO, not the other way around; especially at this strength. 

I also went for a more N/S gradient in my map than a W/E gradient. The big nino years here had a more north-south orientation for the gradient than a west-east(obviously being more west still favors more). Although we’ll see some CAD storms, especially earlier in the season, I don’t think we’re going to be seeing too many of them overall. I think the PNA this year will average out to be neutral-slightly positive, with the western ridge flexing at times, increasing in frequency as the winter progresses. This should favor more Miller A/C type storms, which generally aren’t as W/E gradient oriented. 

Given how things appear to be progressing, and the best-looking year in several years, I believe that going bullish on a high snowfall winter is the right decision to make.

Summary:
 

Overall, I am sold for a well AN snowfall winter for the Mid-Atlantic and SE, and BN for NE. The strong Nino and STJ should heavily favor the MA/SE, and lead to suppression issues not much further north. ++AMO favors further S blocking, which in turn favors a further southern displaced track. Along with the STJ and other factors, the main focus of this winter on the EC will likely be the MA.

 

December, although not favored by Nino climatology, doesn’t look that bad anymore, and might be AN in snowfall, with a -NAO setting up for the early part of the month, and forcing returning to favorable phases by mid-late month. Although I expect it to still end up slightly AN, there’s definitely the possibility of the month ending up near normal. We should have a generally transient warmup in mid-Dec before returning to a favorable period later in the month. Although climo before mid-Dec is at best dubious, it is certainly possible to get some events, especially with the pattern setting up. For the month, I could see us getting a few minor events, and maybe even a moderate event. The very end of the month seems to be the best time period for something. I do not expect the PNA to be overall positive, but we could get a few transient +PNA flexes, along with HL blocking around this time. HL blocking setting up in December; and an -NAO is a very good sign for the winter and for higher-magnitude blocks to set up later in the winter. 

 

January looks to be alright, with the favorable forcing from late Dec continuing into the early part of the month. As stated previously, this month will generally be transitional, but the pattern at the start of the month will remain favorable. Thus, after early Jan, it appears to be quiet for a bit, until the end of Jan, where the pattern will become favorable again and continue into Feb. This is also when peak climo starts. Again we might see some +PNA flexes, but it should remain generally variable throughout the month. We should end up around N for this month temp-wise, and snowfall.

 

February will easily be the best part of this winter, with everything lining up: frequent +PNA flexes, favorable forcing setting up, HL blocking, active STJ, and overall peak climo should make Feb exciting. This isn’t too much of a surprise though, as Nino climatology heavily is backloaded and protrudes Feb as the coldest, snowiest month. We should definitely end up BN for this month in temps and AN in snowfall.

 

As for indices:

 

• PDO: slightly BN; -0.4 to -0.9

• AO: slightly BN; -0.2 to -0.5

• PNA: N-slightly AN; -0.1 to +0.3

• NAO: N; -0.2 to +0.2

• ENSO peak: 1.7-2.0(under super)

• ENSO Orientation: West-Tilted Basin-Wide
  
   

overall, should be a fun winter to track w/ the first real nino since 2015