ILMRoss

Tbh the big, smothering 1040 high is one of the most promising features of this setup thus far .

Some thoughts; This is an uncommon, although not unheard of, setup that exists because of the thermal gradient. Check this out: There is a very intense thermal gradient here with a trough in the NE and a strong ridge poking in from Florida. The general mechanism for winter mischief is that any blip or impulse riding this gradient will be able to kick up precipitation from frontogenesis and general warm air advection (which sounds scary but in pure scientific terms is another way to produce lift. WAA = lift!) The high pressure also helps. I’m not really focusing on the potential coastal closer the euro has until a few more days pass. The issue here is the high 500mb heights; it may not be very cold throughout the entire atmosphere and *whatever* this is may evolve into a delicate mix forecast as cold air still has potential to undercut things at the surface. Synoptically, I think a similar event is 1/28/14 (which eventually brought a moderate snowfall along a wave riding a big thermal gradient) although not a perfect analog. It’s an imperfect setup but there’s a higher ceiling than most events due to the potential duration/moisture supply.

The system on Thursday very much has legs. Let's be clear- Not a very high ceiling system! The best case scenario is probably a 1-3 inch event on the northern half of the state! But, beggars can't be choosers. The difference for the last few runs of the GFS is a much healthier merge between the two parent jet streaks on the shortwave. when it's exiting Texas.

Thursday definitely has the potential to be a meat and potatoes, flat, light to moderate snow event. CMC solution is pretty tame and reasonable given the pattern. That other models don’t show a big snow i think is more indicative of how noisy/unpredictable to field of shortwaves is coming in after that. Short wave interaction is what could kill this opportunity and I think we’ll see inconsistency for one more run cycle or two before we know for certain this is worth keeping track of. The storm next weekend will be interesting, although unless something In the mid levels/high arrangement changes I don’t think the cold air will be robust enough for anything outside of a Acela corridor snow. Would love to be wrong though!

I wouldn’t overlook the system coming next Thursday. The shortwave takes a nice track; it just gets sheared apart and just loses its integrity. Otherwise, it’s heading into a nice modeled air mass. If future runs begin to maintain the shortwave a bit further, Thursday gets more interesting.

It wouldn’t take a lot of repositioning to make this shortwave on the euro a bigger deal. Perfect high. Something to keep track of.

I would not write off some token flakes on Friday night, but those curling edges of the “front ends” are hard to predict 12 hours out, not just 5 days. Whatever falls would then have to be beefy enough to not evaporate in the residual dry air mass. So I wouldn’t put hard money on that. Next week looks cool, with ample opportunity if the structure of the pattern holds, but most veterans here know how quickly that can sour. Would not yet focus on any particular time period.

Keep an eye on Tuesday. If the shortwave nudges a little deeper/stronger keeping with previous trends, I-40 corridor could be in for a quick treat.

GFS... All the wrong trends were there. As Bill Belichek would say... we're on to New Years.

GFS with an OK but not great run. The ULL is encouraging. The red flag here was the overall strength of the ULL coming in- about 6dm higher At the ULL core than previous runs. I will continue to bang this drum until we get to mesoscale models- more convective feedback issues here- check out the MCS that goes from Miami to Bermuda in the span of 24 hours. That’s a feature that both impacts the behavior of the entire system and probably won’t happen. No reason to abandon ship here but some colder runs would be nice.

Ok. Everyone needs to chill out a second. Let me list some things out to keep in mind when discussing a storm like this: 1. This is 180 hours out and pinpointing a "corridor" of snow right now is a fools errand. Multiple models still have the scenario of this thing diving into Florida and being a mild rainstorm with a stiff east breeze for the Carolinas. Including the Euro. 2. A bowling ball low pressure diving SE-ward then bombing off the coast is incredibly anomalous. 99% of the time, it's not how we get snow here. The "tracks", the imaginary snow walls (Wake County), the highways, and everything else that get used to establish a forecast will likely not work if a GFS-like scenario came into fruition. 3. I can't stress enough how much convective feedback is going to screw with the surface reflection and ultimately moisture transport with this storm. I would not pay attention at all to the precip shield or anything like that for the time being. The snow maps are fun, and in "paste bombs" could look historic- don't take the bait. If you're just learning, convective feedback is an issue some models have when forecasting convection (think: thunderstorms). Global models' grid spacing makes it tough to accurately render convection, and this can "fool" the models into forecasting inaccuracies since convection has a major role in how these synoptic scale will behave. Case in point; the 00z GFS, here is 850mb vorticity: Essentially, the GFS is treating almost every thunderstorm as its own spinning entity. Chances are our system won't be this completely elongated, and moisture transport will be better to our NW.

Truly, what an unorthodox system. I would beware of any modeled precipitation field given the convective feedback on any global model right now. I will be willing to bet the pressure field won't verify like this, no matter the setup. Chances are, the secondary low will not be near Bermuda.

To the pessimists: The GFS is an outlier. Temperatures are barely marginal. About 6 things need to go right for this scenario to come into fruition. Good luck accurately predicting how the vorticity will contort itself as it journeys over the rocky mountains. To the optimists: There is definitely a future on the table that includes this trough getting its act together and becoming a sharp trough or even an ULL. The GFS shows this scenario would unleash full chaos mode with a wild coast storm and potential for snow even with marginal temperatures. Yeah, a major coastal storm with patches of heavy snow in select lucky areas is an irresponsible forecast. But this is still worth keeping an eye on.

So the 6z GFS is probably the worst case scenario for this storm. The shortwave “survives” and pairs with a textbook (like, actually stick the modeled high placement and strength in a textbook) CAD scenario that returns the Carolina power grid back to the 1870s. As I said yesterday these shortwaves that travel across the south west are finicky and praying that they “hold up” or don’t get “strung out” is usually a fools errand. And I still kind of think that. That being said it is being pretty consistently modeled that a 1040+ high will cross the northern states. And that’s concerning. The “textbook CAD” is typically the toughest ingredient for these systems. 12z models will be worth watching with how that shortwave behaves, because the margin between “chilly day Thursday” and “ice storm” is pretty close.

Not to be a buzzkill but I have been around this forum long enough to play the “maybe the Baja shortwave will change and work in our favor this model suite” game. It doesn’t work out a lot. Seems like we’re going to be stuck in this cold/active pattern for a while; my advice is to take the energy focused on this storm and instead direct that energy in completing your holiday shopping this weekend, so that you can track models and speculate on forums stress-free by the end of December

Cold vs moisture will be a fun race for anyone to track at work tomorrow. Some competing biases here- you kind of expect the cold advection to underperform, although at the same time precip via frontogenesis always seems to overperform. Think a lot of places see 10 minutes of decaying snowflakes while laying 36/33, which in November is always a W.

this snow threat is kind of cute but i'm mainly just POed that it's cutting the tail off of the fall golf season. courses will be brown and soggy by november

Big, strong high pressures are usually coupled with strong upper features and disturbances. Strong high pressures are only possible with a ton of sinking air throughout the atmosphere... many different processes (jet exit/entrance regions, vorticity, warm air/cold air advection) work together to create this monster highs. On the flip side, with such strong jets/troughs creating the high on one side, the other side (eastern side) will feature rising air and different types of advection to provide moisture in the region.

Wow, the FV3 GFS has absolutely shown killer consistency, right to the end. If this storm follows it's script, what a coup! Nice to have a trustworthy (at times) tool in the the toolbox, or at least moreso than the current iteration of the GFS.

From what I understand thunderstorms oriented perpendicular to the storm track essentially act as a firehouse of moisture into a system, whereas storms oriented parallel to the storm track can basically act to cut off the conveyor belt of moisture by disturbing the inflow into the storm.

I like cranky, and I think he can have some moments of brilliance, but often I find his reasoning to be oversimplified... like right here. Gee, if it were as easy as looking at cirrus clouds, I'd be out of a job right now.

RGEM has a sharper, more negatively tilted wave as early as 36 hours from now, which is causing the stronger solution. I don't know much about how the RGEM handles synoptics but I wouldn't attribute the run to mishandling of convection.

My guess is that the suppression trend is partly tied to this: the trend is for the ULL to "landfall" into Baja California as a more and more positively tilted wave. This positive tilt has ramifications downstream for its orientation, how amp the wave gets, and where some temperature profiles set up because a more negative tilt can raise heights downstream.

Something I’d watch out for in this next suite is cyclogenesis along the Atlantic- so far not a single global has represented this well to my eye. The mesoscale models look more believable. Here’s what I mean: Cyclogenesis is favored to occur in areas where there’s already a distinct low level vorticity axis (think: frontal boundary! “Low level vorticity axis” sounds like an intimidating weather term but it’s really just represents a wind shift!) In CAD regimes, there’s always a super distinct axis just off the coast between the CAD Airmass and the coastal front. Thus, as that area has some lift imparted on it, you’d expect pressures to drop and cyclogenesis to initiate. The globals don’t show this. Here’s the GFS: it has not signature along the Gulf Stream at all... and I’m not sure I buy that. Here is the nam in comparison at the same time: In the nam, there’s a much more distinct signature of this taking affect, and this represents what “supposed” to occur in this scenario. I think this is helping toss everything more northward in the NAM. Now, obviously, meteorology doesn’t always bend towards what’s “supposed” to happen, as any seasoned weather enthusiast knows. That being said, I wouldn’t be surprised to see a “CAM vs Global” battle emerge today as more CAMs get in range. Lastly- CAM = convection allowing model- think NAM, RGEM, HRRR, etc. They don’t have to parametize convection with their higher resolution. .

All I’m going to say is, Fish loves ensembles, and Fish loves certainty, and the ironclad nature of 1 inch + totals on the ensembles have probably weighed on that team.