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December 11 Frontal Wave Snow Event


WxUSAF
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43 minutes ago, leesburg 04 said:

To my untrained instincts the further SE the jack zone gets means the cold is lagging in its chase of the precip. I'm sure it's a banding thing as well but just sayin. Buyer beware 

Looks to me like the cold is in place as the last piece of energy rides up. Front looks to lie in the SE parts of the region right along the coast- perhaps this is part of the reason we are seeing some guidance shifting the heavier snow chances towards DE and NJ.

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Just now, C.A.P.E. said:

Looks to me like the cold is in place as the last piece of energy rides up. Front looks to lie in the SE parts of the region right along the coast- perhaps this is part of the reason we are seeing some guidance shifting the heavier snow chances towards DE and NJ.

The gefs has been targeting further east consistently and it’s something I’ve noted as I’m seeing everything else slowly adjust towards it. 

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1 minute ago, C.A.P.E. said:

Looks to me like the cold is in place as the last piece of energy rides up. Front looks to lie in the SE parts of the region right along the coast- perhaps this is part of the reason we are seeing some guidance shifting the heavier snow chances towards DE and NJ.

This is going sound weenie'ish and not meant to sound my backyard'ish, but if there's leftover energy running up the front tomorrow morning, I'd bet it's west of where it's depicted now.  IMO, it's rare that cold air intrudes this area as fast as models depict.

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35 minutes ago, nw baltimore wx said:

This is going sound weenie'ish and not meant to sound my backyard'ish, but if there's leftover energy running up the front tomorrow morning, I'd bet it's west of where it's depicted now.  IMO, it's rare that cold air intrudes this area as fast as models depict.

At the risk of sounding weenie-ish myself, I like seeing the guidance depicting the heavy snow bands just to my east.

Its a tricky set up for sure, and one I think is truly anafrontal, as it seems like the front will be through as the final impulse moves in and precip will be falling into cold air- although right at the surface it will be a bit warmish to start. It didn't always look like this would be the case(precip behind the cold front), but it seems looking at latest guidance it is evolving that way.

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14 minutes ago, C.A.P.E. said:

At the risk of sounding weenie-ish myself, I like seeing the guidance depicting the heavy snow bands just to my east.

Its a tricky set up for sure, and one I think is truly anafrontal, as it seems like the front will be through as the final impulse moves in and precip will be falling into cold air- although right at the surface it will be a bit warmish to start. It didn't always look like this would be the case, but it seems looking at latest guidance it is evolving that way.

If it comes down heavy enough, column cools and we are in business. Of course, we know how these things work out. 

Runs today will get wetter into the afternoon

Everyone will be hugging the HRRR around 8pm tonight as it shows some heavy blues over the area 1-3am

Reality: sparse precip, temps never get to freezing, usual places get 1-2"

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Just now, mappy said:

If it comes down heavy enough, column cools and we are in business. Of course, we know how these things work out. 

Runs today will get wetter into the afternoon

Everyone will be hugging the HRRR around 8pm tonight as it shows some heavy blues over the area 1-3am

Reality: sparse precip, temps never get to freezing, usual places get 1-2"

Probably. My gut says there will be 2 maximas for snow potential- the usual places NW of the cities, and another along the coast- probably east of me. In between, it might end up being more spotty.

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3 minutes ago, C.A.P.E. said:

Probably. My gut says there will be 2 maximas for snow potential- the usual places NW of the cities, and another along the coast- probably east of me. In between, it might end up being more spotty.

I think thats a good forecast. I'm going for about 1" IMBY, but could see it being less than that. NAM being so dry so close to the event gives me pause. 

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3 minutes ago, C.A.P.E. said:

Probably. My gut says there will be 2 maximas for snow potential- the usual places NW of the cities, and another along the coast- probably east of me. In between, it might end up being more spotty.

I'm hanging my hat on the area that has the front just to its east.  That 5-10 mile stripe just to the west of that is where it will be best due to lifting and dynamics.  P sure the mets and Wes have always said that where subsidence from the cold high and moisture being pushed up over that front is where the best rates happen.  Like squeezing a sponge.

edit to say that what I just described is really bad technically but reduced into laymans terms.  Or as i call it: dumbed down for the masses and those masses are one(me)

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Classic looking frontal circulation for this setup. The temperature gradient associated with the SW-NE oriented front strengthens as the boundary moves eastward, creating a thermally direct mesoscale circulation about the front, with warm air on the SE side of the boundary rising and sloping westward with height. This circulation is associated with the right entrance region of a jet streak that also strengthens with time as the thermal gradient intensifies.

front1.thumb.png.a95278eab07c2130a57d6bf14ff55ee7.png

The frontal circulation can be seen on forecast cross-sections normal to the orientation of the boundary, where enhanced frontogenesis slopes westward with height. Additionally, there is some relatively low stability air above the frontal surface. In the cross section below, you can see the small closed contour of 320-K theta_e between -12 C and -18 C, indicating convective instability within the dendritic growth zone. This environment would be very favorable for ice crystal generation and growth.

front.thumb.png.897d6ee5cc8cf91fc8381fc23311a7d5.png

This cross section also highlights the marginal boundary layer temperatures for this event (typical for these anafrontal precip setups), where the 0-C contour extends above the frontal surface to around 700-mb. The above freezing temperatures will limit the period of snowfall to a narrow window of favorable frontal dynamics and sub-freezing temperature profiles. Right now, it's hard to say how long this window will be.

Finally, you can also see the advection of low-level dry air on the cold side of the front which may lead to more sublimation of ice particles and less snowfall at the surface, especially during the tail end of the precip.

front2.thumb.png.67ab57be0223939aa17cfc1c4f9036d8.png

It should be an interesting event to watch, and perhaps I will finally see some snowflakes this season!

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1 minute ago, H2O said:

i tried to google "nerd snow charts" and got this.  Coke snowman

Image result for walmart let it snow sweater

 

i wish i had seen that at the walmart i go to, would have bought it just for the lols. 

also, we should probably stop bantering in this thread, sets a bad example ;) 

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13 minutes ago, MN Transplant said:

12z HRRR went inverse-HDRPSRDSRSD.  0.0" along the 95 corridor and not much better elsewhere.

These type of setups rarely break in our favor. They always look more robust 2-3 days in advance and then evaporate inside 24 hours.

I think 95 corridor sees flakes with minimal stickage. NW sees up to 2”.

We know this song and dance, unfortunately.

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19 minutes ago, MN Transplant said:

12z HRRR went inverse-HDRPSRDSRSD.  0.0" along the 95 corridor and not much better elsewhere.

That's pretty much the only model with such low snow totals. Cranky is saying there's lots of moisture with this system and is leaning high but we'll see. Even the nam has higher totals I think but I'm too lazy to check 

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1 minute ago, JakkelWx said:

That's pretty much the only model with such low snow totals. Cranky is saying there's lots of moisture with this system and is leaning high but we'll see. Even the nam has higher totals I think but I'm too lazy to check 

NAM can't decide if it wants to give a NAMing, or just be dry. 

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1 hour ago, mappy said:

If it comes down heavy enough, column cools and we are in business. Of course, we know how these things work out. 

Runs today will get wetter into the afternoon

Everyone will be hugging the HRRR around 8pm tonight as it shows some heavy blues over the area 1-3am

Reality: sparse precip, temps never get to freezing, usual places get 1-2"

Correct. 

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