psuhoffman

What model in the 3 days leading into the storm showed 0" at DC? And what model showed 15"? And don't post some clown snow map with a faulty algorithm if you use those to predict snow then you got problems. I mean a model that actually showed 15" at DCA if you looked at soundings and took out the fake snow from wave 1 with a big warm layer. The real range was 3-9 on 90% of all runs the last 3 days. There were a couple outlier runs that showed 10-12" but it was never the consensus. Not a single one showed 0 or 15. Your full of it. Btw if you ever ever ever ever ever even say persistence or imply it won't snow because it hasn't so far in any future winter I'll troll the living hell out of you with facts. We had every pattern imaginable this winter. From average temps and snowy in December to frigid and bone dry to warm and wet and finally cold and snowy. This year proved persistence only works in hindsight and is BS in forecasting because patterns break at any time and chaos matters too.

RIP

The problem with persistence based forecasting is you don't know when the pattern will break. And there can be wet periods embedded within longer term dry patterns. Some of us had over 1" qpf last week. Either way yes dry feeds back and can cause more dry but it can and will break and so all this dire saber rattling that it can't rain or snow because it's dry is overdone. Yes it's dry. No one is refuting that. But it's part of long term cyclical patterns. Dry wet it goes back and forth and will balance in the long run. This isn't anything out of the realm of normal long term variance. We have had droughts like this before and we will again. And it will end at some point.

DCA avg snowfall 1970s: 14.58 1980s: 17.08 1990s: 12.94 2000s: 12.68 2010s: 18.4

Adding march 2015 as an example of an epo driven pattern with no Atlantic help that worked. again the negatives are centered to our north. In this case we needed a wave to run north pulling the boundary through then a second wave got us.

You're welcome. I enjoy it. The thing is it's rare to get the ideal setup. Most of the time the trick is looking at all the variables and how they trade off each other to see if we can place the boundary just south of us as a system comes along. The atmosphere acts like waves and these things we call epo,pna,ao,nao are just our measure of how the waves are behaving in a specific location. It's good to quantify that but the truth for getting snow here is all about how all the waves in the jet play off each other to determine the location of a synoptic system along the temperature boundary as it passes our longitude. There are a ton of variables at play and each one changes exactly what we want from the others. What combination of things will get a system to track just to our south. That's the game. There are lots of ways to get there but it's complex predicting how all the factors influence each other.

We can add more of these but one thing you will notice with almost all of the is no big huge blue ball over the eastern US. We want the lower heights at H5 centered to our north, and preferably to our northeast to get snow. That is the most important and most common theme of all of our snow events both big and moderate. Keep an eye on where the troughing sets up next time if the EPO reloads. Hopefully not right over us or to our south next time.

And sometimes we just get lucky with almost nothing going for us. This looks like crap but the PV lobe over quebec and the ridging on the west side of Hudson Bay forces that system out of the southwest to bowl east under us and we got our only decent snow of the 1997 winter in a crap pattern.

Our only snow event in 1995 was primarily PNA driven with a lucky trough axis in the east that worked out.

What if we don't have NAO or 50/50 help. The best bet in that case is to root for a gradient boundary storm. A wave along the boundary mostly moving west to east of southwest to northeast. Something overly amplified is very unlikely to work in that setup. And it will require a better EPO to offset the other missing pieces. This is a good example. Now we have a positive NAO and a WAR. You would think uh oh, but the EPO is textbook and again notice the center of the lower heights are to our north. In this case the setup places the boundary south of us and a wave was able to ride along and we win. The key here is where the lower heights set up downstream from the EPO placing us right along the boundary. Early March 2014 and feb 1996 are other examples of a gradient boundary storm that worked out. Different moving parts but similar in that the lower heights centered to our north and a system rode the boundary set up through our area.

But what about some looks if we have to go it without NAO help? There are ways to get snow without that kind of textbook blocking but it requires trade-offs with other variables. So what about an EPO driven pattern with a positive NAO. This is the early December 2002 storm. A LOT of these storms coming up will be the "thread the needle" type. NAO blocking gives us that HUGE window. With most other setups the problem is minus that blocking we have to rely on a tradoff between other pattern drivers to line the trough axis up just right. If the trough sets up just west we rain. If it sets up just east we watch a fish storm pass by. We don't have a large margin for error. Still most of our snow comes from less then perfect setups with a little luck. This one was primarily EPO driven. We did line up a favorable 50/50 and even though it was transient it was there at the right time to promote confluence and cold right as the system approached. Most of these h5 plots are the day before the storm to show the setup. You see the indication of the system coming at us from the southwest but you DONT see some big huge trough over the east. Again on almost all of these you will notice the lowest height anomalies are centered to our north or northeast NOT over us or to the southwest of us. Keep that in mind when we start to see how this next pattern is evolving. We dont want some huge blue ball over the United States with high pressure blasting down to Arkansas if we want snow. Here the extreme EPO combined with a favorable 50/50 set the table for a good storm minus any NAO help.

So I liked this example of a pretty good storm from 2004 across our area because it deals with the trade off between the PNA and atlantic. In this case the blocking and 50/50 location would be way too suppressed if it weren't for an absolutely crap pna pattern. There is a trough in the west there but thats actually good here because look at where the 50/50 is. If it werent for the attempts to pop a ridge in the east and cut something to our west anything coming at us from the south would be suppressed. This worked out because the system tried to go west and was forced under us. So too much of a good thing in the atlantic was offset by what would normally be a worse PNA look. If we actually had what we usually consider a "good PNA" there it would have been cold/dry and a snowstorm along the southeast coast maybe.

With the down period we're in I thought it was a good time to resurrect this thread and further the discussion from last year. I realized lately that while we did a good job touching on what is a perfect pattern for snow that we didn't really discuss all the different variables that factor into the "trade off" that happens when there is a less then perfect pattern. And those scenarios make up 90% of our snowfall events so it's not really useful to only focus on the textbook perfect HECS setups. So first of all its important to look into the WHY of the textbook HECS cases first for comparison. This is the composite H5 mean of our 6 unquestioned HECS events in the last 40 years. So what makes that the "perfect" look. The single most important feature is what sin the box there...the ridge over trough in the north atlantic centered over greenlands longitude. The ridging over greenland is what we call the greenland block. The trough south of it is the 50/50 low. The ridging forces systems under it which promotes the troughing into the 50/50 locations. The combination of flow around the Greenland high and the 50/50 low promotes cold air into the northeast US. Also, confluence (merging of air flow) promotes high pressure. The confluence of the flow around the 50/50 with where it meets the westerly flow of the jet coming across the CONUS promotes high pressure to our north. This is even more pronounced with a split flow. Also keep in mind these features arent all or nothing. That isn't JUST a -NAO, its a greenland block. Not ever bit of ridging over greenland is a block. Yes it helps but that look there is classic because its a perfect block. The strength of that block will really slow down the flow and force systems under it. Keep that in mind when we look at the other features on that map. The indication of an STJ is there with the lower heights down along the gulf coast. That is of course desirable. But look at the Pacific. Without that look in the atlantic that would be crap. I made the point about the blocking because people keep throwing around the whole Pacific v Atlantic thing and its not an all or nothing debate. With just some nao ridging that pacific would probably blast pacific air across. Yes there is a split flow indicated there but that trough location off the west coast isn't gonna cut it without the atlantic blocking. So yea if we only have some nao help having a crap pacific will ruin it. But if its one of those rare cases with off the charts 3std blocking then you actually WANT the crap pacific. The attempt at ridging in the east virtually ensures that a system will attack the blocking from the southwest. But with that blocking...the chances of a cut to our NW are low so when ends up happening is it attacks the high, runs right into it, WAA thumps us to high heaven, then gets forced east under it. Its our dream scenario. Without the less then favorable pattern out west we would just be cold and dry. Notice there is no big blue ball of death over the eastern US. If there was we would be cold/dry with that blocking. You need there to be an attempt at ridging up the east coast to back the flow and force a storm up into the blocking. But that ONLY works with that level of blocking. Without it that same look is a cutter pattern. There are lots of variables playing off each other. So this is a closer in view of the surface and h5 for 1996, the perfect example. Notice where the flow is aimed. With that H5 low where it is, without the blocking holding in the confluence to our north that storm would have cut. But it cant. Most extra tropical cyclones are baroclinic meaning they develop along tight temperature gradients or fronts which provide potential energy. Once they occlude they can become baratropic where the temperature profile is more uniform around the low. But that process rarely happens before our latitude in the development cycle. So for our purposes storms will follow the path of least resistance and fuel source along the temperature gradient boundary. That boundary cannot penetrate up the east coast inland past our latitude because of the resistance from the flow around the high to our north. So the low is going to transfer to where there is a natural baroclinic zone, the coast. The temperature gradient between the land and ocean creates a natural location for the storm to jump. This places us in the battleground. The WAA from the south trying to overrun the cold is tremendous. The circulation from the high increases the CCB and convergence with enhances lift. Its perfect. And the blocking combined with the attempt at ridging into the east gives us a HUGE window of opportunity. Basically a low that tracks anywhere into that box is going to transfer to where we want it off the VA capes. Once there we are good no matter what happens. That is what makes this the perfect setup, the combination of what would usually be a trough axis too far west forcing a system right up at us but then running into a cold air mass blocked in by the north atlantic pattern. Its our money pattern. I am reviewing all this because once its obvious WHY this is the perfect pattern and all the variables and trade offs that play into that we can then look at different looks and examine the different trade offs that make less then ideal patterns work out for us.

Vice Regent says we're all gonna be under water. This guy thinks we're heading for scorched earth. Can we stick them in a room and let them fight it out?

You win. Your right. The earth is scorched. The apocalypse is upon us. It will never rain again. Fleas and ticks will rule the earth. Flee scurry run for our lives. The great dryness is upon us.

I am being flippant because I think he is going too far with this. Yes we are in a low level drought. And I don't mean to be rude towards farming interests and other areas where it is having an effect. But right now what we're experiencing is part of typical cyclical weather. And it's an effect not a cause when we discuss snow. The Nina pattern among other things is causing both the lack of snow and precipitation. Droughts are an effect more than a cause. If droughts caused drought then we would never get out of them. Droughts tend to persist as long as the pattern causing them persists and then it ends and so does the drought. So sorry if I came off dismissive but I'm tired of the agendas. Between the global warming and the drought and the government conspiracy and NWP arguments we can't keep anything on topic anymore.

Oh look a thread where we can talk about drought. Crazy. I think your taking something fairly mundane and blowing it way out of proportion. We're in a drought. We have had many like this in my lifetime and we will have many more. We also have floods. Weather goes through these cycles. It will rain/snow and balance out eventually. We're not to the point where things are dire yet. That's the take of this false prophet of populist belief.

Crap you just unraveled this whole thing

Where do you see severe?

Yea it's a lot more complex then I got into. And someone else (like you) is probably better then me for those that really want to get into the fine details of this. I did get into some of that stuff in my meteorology classes but I haven't used it all that much and that was 18-20 years ago now. Most of us including me probably aren't pouring over all the plots needed to get into each meso scale factor. Wish I had that kind of time. The h5 vorticity is a good poor mans way to get a basic quick look at what's going on. Plus usually when we hear a lot of vort max talk it's because we're dealing with a pretty pathetic surface system (like last night) and we're relying on the lift associated with the h5 vort to give us a little something. In this case to pop a weak surface reflection and a very small band of precip. I love this stuff. I've wasted days reading through my old textbooks on meso stuff. Of course it's funny cause when it comes to looking at longer range stuff which is usually what I'm doing this year (ugh) the meso stuff could be a waste of time. Even from 48 hours I could spend time looking at where the best lift is based on meso features then the whole synoptic setup shifts 50 miles and it's pointless. Really want to go back and finish my meteorology degree but I'm not sure how I would use it. I like teaching (assuming I don't lose my job due to the current financial crisis in Maryland) and have a family to consider. It's probably something I'll do later on just for my satisfaction. Perhaps then get duel certified in science and find a school that would let me teach it as an elective or as a major unit in earth science.

Usually when we say vort we mean a vorticity maximum embedded in the 500 mb flow. It's a measure of vertical vorticity or spin along a vertical plane. Positive vorticity advection or pva is important in a basic sense because it enhances lift which is what causes precip. The h5 map below shows a vort max. The specifics can get complicated and I am tired but this is a really good explanation I found a while ago. http://www.weather.gov/source/zhu/ZHU_Training_Page/Miscellaneous/vorticity/vorticity.html if you still have any specific questions I'd be glad to try to answer them

These 3 were pretty much locks given the h5 heading into them. Notice the lower heights to our northeast on all 3. That is the most consistent feature across all our big snow events. Also notice the higher heights up to our north in general. In 1996 it was breaking down (not uncommon) but the damage was done. That "blocking" tends to help in several ways. It can displace the PV south and aid in cold pressing down to our latitude. It promotes lower heights to develop under it, which we need. And by forcing systems under it it prevents systems from cutting up toward the pole and promotes the sliding under which usually gets them into the 50/50 position. Called the 50/50 low (its near 50 lat and 50 long) that is the lower heights to our northeast. That is important because it creates flow out of the north into New England. This promotes cold transport into our area and when combined with the return flow of the approaching system creates confluence (where two streams merge) which promotes high pressure there. Now below is a closer look at 1996 over the CONUS. Looking at h5 is better because that is about the mid level of the atmosphere in terms of thickness and tends to be the level that has the most influence on driving the pattern. Think of it like currents in flowing water, or waves. Troughs and ridges slide around within the flow usually finding the path of least resistance. And within the flow you get buckling where a major areas of low and high heights can build up and become road blocks that divert and influence everything around them. Kind of like a whirlpool in the water. Looking at h5 is looking at the steering currents. On the H5 below I highlighted some of the key features that made this a can't miss classic setup. There are several things to check off. 50/50 low to suppress the flow enough to prevent cutting. Higher heights over the top leading up to displace things south. Then a monster system digging into the TN valley with enough room to pump ridging in front and allow it to amplify and ultimately cut off completely and bomb a system up the coast. But with the 50/50 and suppressed flow across Canada it cant lift north so its forced east under us. That's also why the western atlantic ridge or WAR is such a problem for us, put a ridge where we want that 50/50 low and a system that digs in and amplifies will simply lift north and the low will cut to our west usually. As a system amplifies it wants to lift poleward along the east side of the trough, so if you don't have a blocking feature were in trouble unless we get perfect timing. On the other hand, put a road block to our north, get a strong system trying to come north but being blocked right at our latitude and suddenly were getting crushed. More resistance means more "convergence" and more lift and thus more potential for heavy precip and in these cases with cold in place feet of snow.

I was talking to friends of mine from NYC about favorite storms and was saying how this past week was great but that it didn't make my top spot. Of course that storm having such a localized area of truly historic totals like that made it hard for them to understand but being here that one was epic and I am not sure anything will ever top that. On top of everything you said, it was a huge over performer, I think our forecast was only 10-16" going into that event. Plus it was only on the radar for a day or two before, there wasn't this long long LOOOONG build up and wait. Being nervous every model run that something will go wrong. The chase is fun but personally I kinda liked how that one just came out of nowhere and slammed us. For all those reasons, the CRAZY rates of heavy wet snow in the initial thump, the crazy deform bands in the wraparound, true blizzard conditions, total snow on the ground when it was over, and the surprise factor...It would take a lot to knock that off the top spot, even if another storm technically dropped a few more inches I am not sure it would top it.

how much did this area get during march 93? I assume there was a lot of sleet mixing even out here with that one.