• Hello, please take a minute to check out our awesome content, contributed by the wonderful members of our community. We hope you'll add your own thoughts and opinions by making a free account!

Freezing Rain, Sleet, Snow, Rain...Kitchen Sink (12/15-16)

RGEM in past winter storms has a bit of a cold bias. Also if temps are in the 31-32 range like the NAM shows with moderate to heavy zr the accrual rate will not be very good. ZR accumulates best when rates are light and/or temps are 30F or colder. If I remember correctly, the heavier rates of zr can also cause latent heating which warms the surface above freezing quicker vs a lighter rain.
 
I
snowlover91 said:
RGEM in past winter storms has a bit of a cold bias. Also if temps are in the 31-32 range like the NAM shows with moderate to heavy zr the accrual rate will not be very good. ZR accumulates best when rates are light and/or temps are 30F or colder. If I remember correctly, the heavier rates of zr can also cause latent heating which warms the surface above freezing quicker vs a lighter rain.
Click to expand...

Its lighter stuff like this which is honestly the bigger problem, it can make up for surface temps around 30-32 889FBB08-8E8F-4E96-AA27-675C3FAFB423.png
 
I wouldn't be entirely shocked to see a brief period of freezing drizzle or light freezing rain for some areas north and west of downtown Raleigh. It's really close at onset with wetbulbs around 30-32 but quickly pushes above freezing
 
snowlover91 said:
RGEM in past winter storms has a bit of a cold bias. Also if temps are in the 31-32 range like the NAM shows with moderate to heavy zr the accrual rate will not be very good. ZR accumulates best when rates are light and/or temps are 30F or colder. If I remember correctly, the heavier rates of zr can also cause latent heating which warms the surface above freezing quicker vs a lighter rain.
Click to expand...
Brad P made a post about ZR being a self-limiting process. Heat leaves the water as it freezes and warms the air around it, so the heavier rates would heat the ground level up much faster than lighter ZR.
 
snowlover91 said:
RGEM in past winter storms has a bit of a cold bias. Also if temps are in the 31-32 range like the NAM shows with moderate to heavy zr the accrual rate will not be very good. ZR accumulates best when rates are light and/or temps are 30F or colder. If I remember correctly, the heavier rates of zr can also cause latent heating which warms the surface above freezing quicker vs a lighter rain.
Click to expand...
This is correct but we aren’t looking at heavy rates with this system. Light to moderate is about the most you’ll likely get from this system.
 
FamouslyHot said:
Brad P made a post about ZR being a self-limiting process. Heat leaves the water as it freezes and warms the air around it, so the heavier rates would heat the ground level up much faster than lighter ZR.
Click to expand...
The lighter precip occurs near and prior to the onset of the event when global or even regional high res NWP models can’t and often don’t properly resolve it. Even when you consider sub cloud evaporation, I wouldn’t be surprised if freezing drizzle and/or light sleet started being observed in the Piedmont significantly earlier than forecast perhaps as early as midnight tomorrow night given the mid level warm advection and isentropic upglide that starts showing up by 4z. This underrepresented precipitation thru diabatic processes (mid level warming thru condensational deposition and low level evaporation) also would help “lock-in” the CAD dome ever so slightly sooner, potentially providing a few additional hours for low level cold advection to work its way down into the Carolinas


1607971240882.png


Notice that precip on the 3km NAM doesn’t start breaking out for another 4 hours after this frame above. The aforementioned information and prior experience in these events supports this idea but we’ll see

1607971395690.png
 
The NAMs warm nose is stout throughout nearly the whole event. EURO and RDPS it there but more marginal. QPF here is between .8 and 1.0 between the 3 of them. NAM may start as a little IP but seems all ZR if not going to plain rain. The other 2 are more of a mix with RDPS switching back to snow late. I am betting on the NAM but not expecting the temp to recover all the way to above freezing unless we bust high Tuesday night.
 
From past expierence. Precip always gets going sooner in these events as webb alluded to. 4-6 hrs not uncommon in 9 out 0f 10 cases from past expierence.

Also never, ever disregard the Nam thermal profiles. Look deep into it. It's not always accurate , but usually can sniff out the hidden piece of info in these events.

Those canadian maps I posted are usually your coldest, but not by much. They show the possibility if the CAD is a degree or 2 stronger or stays longer. Thats never a given but always a possibility because models have a tendancy to always underestimate both.
 
You must log in or register to reply here.
Back
Top