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Brick Tamland
Guest
Yeah, I think this could have a few surprises in it, too. The last Euro was very encouraging. Not saying I'll get 4 to 6, but just encouraging that it increased the totals.
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Wintry Palm Sunday NC and VA Winter Storm
- Thread starter Webberweather53
- Start date
Webberweather53
Meteorologist
Areas upstream of NC have been shifting their winter storm watches to the SW, areas north of the VA border definitely have to be at least a little concerned about a lack of precipitation here limiting wintry precipitation potential.
SimeonNC
Member
Yeah, as Webber said earlier there is a major bust potential for this storm.
Yeah, could just be a cold rain or nothing. This is a very unusual trajectory, and late March snow is like hunting unicorns! I have no doubt Roxboro sees 2”-4” on the ground atleast, and mountains could do 6” plus. RAH= flurries/with rain!
Avalanche
Member
Places along the banks of the apps could see some wet snow mixing in with the rain during this weekend storm.
RAH is saying to prepare for lots of rain this weekend, with maybe some sleet in areas north of I-85. Sleet more likely than snow in areas that get wintry precip.
RAH does a great job, never wrong! Just like Brad P.
Webberweather53
Meteorologist
I actually meant to respond to this earlier, but yeah I think this argument has some legitimacy to it, as I explained to cold rain, even if we assume the cold high to our north in Quebec and Ontario is weaker than forecast and we have less synoptically driven cold air damming (which would argue for warmer surface temps), models often poorly handle and underestimate cold air damming that's attributable to diabatic heating.
Ya know, we can actually still get cold air damming without a big surface high to our north or even if it's very far offshore New England and the Mid-Atlantic, but it's created in place over the Carolinas, GA, and/or VA (or "in-situ")! The primary processes that dictate this sort of CAD dome involve a dichotomy in phase of change processes on a large-scale with height in the atmosphere especially in the cold season. As hydrometeors form aloft in the low-mid levels, the change of phase processes involving condensation (vapor>> liquid) and deposition (vapor >> solid) release heat into the surrounding air and this condensate is deposited most vigorously in the low-mid levels (meaning they'll warm the most).
Meanwhile, below this, as these snowflakes fall (& raindrops if it's above freezing or a drop hasn't interacted w/ an ice nuclei and is supercooled), they evaporate (liquid >> gas), sublimate (solid >> gas), and if it's above freezing, they also melt (solid >> liquid). These processes warm the mid levels and cool the atmosphere closer to the surface, inducing an inversion (warm over cold), which since cold air is dense, surface pressures rise slightly in response, and this creates a geostrophic adjustment process essentially where this rise in surface pressure on the eastward side of the apps allows the coriolis force to pile more mass and dam this cold air against the mountains, creating an along-barrier component to the flow that blows parallel and down the side of the apps. Once the CAD becomes established, further warming aloft due to condensation/deposition will reinforce and "lock" in the CAD dome as the air near the ground becomes relatively more stable/dense in comparison. Here's a graphical depiction of what I'm talking about and a corresponding animation (although this really isn't the best or even a good example of in-situ CAD because large-scale advections dominate, nonetheless these processes are still working in tandem with the advection to enhance the CAD).
Here's a crude cartoon explanation of what I'm talking about earlier wrt condensational deposition at the end of that 2nd paragraph.
Essentially where there's both strong upward vertical accelerations and a lot of moisture still left in the parcel is where you're going to see the most heating due to condensation (& possibly deposition although it's not explicitly stated here). The levels where this occurs is somewhere around 600-700 hPa or so and not surprisingly this is also where the peak of the "notorious" mid-level warm nose is located. This is actually not some strange coincidence, there's a good reason the warm nose likes to develop there (it's observed to occur here even absent of the Appalachians in areas not adjacent to significant topography (i.e. I'm referring to how height of the appalachians can influence the height of the CAD dome and level of the corresponding warm nose)!
(The height of maximum condensational/depositional deposition can also partially explain where the level of maximum wind is located in tropical cyclones)
The upward vertical accelerations are maximized in the mid-troposphere near 500mb whereas mixing ratio is highest at the lifted condensation level (LCL) (or also the cloud base) where all the vapor remains in a parcel and it decreases with height as the water vapor is condensed out along its way upward to the mid-upper troposphere & it often decays exponentially with height because temperature decreases with height and since water vapor increases exponentially as a function of temperature (as the temperature warms the amount of water vapor the atmosphere can hold increases even faster!)
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Wow, The 12z Euro close to a foot here and the 18z NAM NOTHING? What in the world???
NAM seems to be trending further north and Euro trending further south. What's the deal ?
Webberweather53
Meteorologist
Just about every other model has been trending south and suppressed on this afternoon's 12z suite, I would like to see what this model shows on its 0z and 6z runs when new RAOB data is ingested, this has occasionally made a big difference in its solution this year in the short-medium range.
MichaelJ
Member
Unfortunately for most of us, I would tend to trust the Mesoscale models over the Globals at this range. Tomorrow mornings runs will tell the tale IMO but the 18Z NAM is VERY troubling even if it appears to be on an island at this time.
Is the NAM a reliable model within 48 hours ?
Avalanche
Member
Yeah, need to prepare for rain as this system will give us overcast skies and rain at times.
Oh, yes I agree 100%. 18z RGEM looks warm to me! I could be wrong though!!
Webberweather53
Meteorologist
I think after 2 or 3 0z/12z more suites we will know if this is mainly a VA or NC threat or both east of the mountains. Thereafter it will come down to exactly where the elongated frontogenetical band of intense precip sets up which determines the amount of dynamical cooling we see and the intensity of the CAD dome both of which are very hard for the models to pin down more than 24 hours out (if at all). We at least have the diurnal cycle going for us, getting the heaviest precip between midnight and sunrise as currently progged is optimal and is a baby step in the right direction of getting snow/sleet for many on the board. Regardless it’s nice to see the forum so active once again for what will probably be the last time this winter unless Apr pulls a huge rabbit out of the hat.
Blue_Ridge_Escarpment
Member
18Z GFS looks very similar to the Euro.
Yeah I think you can probably tos the NAM.
packfan98
Moderator
Happy Hour on the GFS looks good for some. The surface low definitely tracked a little further south:
Does the GFS map account for sleet because RAH said sleet would be the likely precip type instead of snow.