Ed, snow and hurricane fan

Change to ice comes sooner. I don't know about change to snow, although 12Z NAM was too warm comparing the sounding to the RAP generated current condition. NAM had a warm nose, RAP model which is initialized more often had their 850 mb below freezing. Or Wichita Falls looks like mostly snow. DFW, no idea. But the change to frozen may come a few hours early just based on NAM and GFS being too warm 5-6 hours after initialization. If SPS is a guide, the change to snow may come sooner as well. SPS (Wichita Falls) obs to freezing rain, but that may be automated and they are sometimes wrong.

5.6C at Love field at 17Z, 12 km NAM predicting 6.9C at 18Z. And the area is cooling down, not warming up. GFS forecast 18Z temp is 7.5C. SPS reporting snow and 30F (may be auto observation), NAM sounding is sleet at 18Z, SPC Meso analysis off RAP says 850 mb freezing line is about there.

I am trying to see if the 12km NAM and 3 km NAM run the same physics. I remember the ARW, NMM and such, even if I had no clue what the differences are. The 12Z 3 km and 12 km NAMs are more different for tomorrow's DFW winter event than I'd expect just from finer resolution.

Most snow maps use a 10:1 ration liquid to snow, and most don't differentiate between snow and sleet. Sleet tends to be 2:1 to 3:1, or a 'clown map' 10 inches of snow (with 10:1 ratio) might be 4 inches of snow on top of a couple of inches of sleet.

Verbatim, 6Z GFS is more ice or sleet than snow. I think the hard to answer question is ice or sleet. The 3 or 5 inches of snow at the end will make it look nice. 6Z 3km NAM is a little ice, then a fair amount of sleet, followed by a little snow. That would be better case scenario but too early to lock in.

I think Nowcast on actual P-types. Looking at 6Z GFS, major ice versus heavy sleet in DFW is a degree difference in temps and a small difference in the depth of the below freezing surface layer. Then a nice snow for the scenery but if there is half an inch of ice, nobody who has a choice will be driving and some trees will come down on electric lines.

0Z HRRR is initialized off the 23Z RAP, it doesn't have the data the NAM or GFS will have on their 0Z run. It was designed as a very short term model, mostly for severe weather prediction.

A couple of hundred meters of thickness of the subfreezing layer, a half a degree C an ice storm that leaves thousands powerless or a sleet storm that makes driving dangerous but not impossible.

12 km NAM isn't super high resolution anymore by modern mesoscale standards. And maybe weenie casting, I don't know why it would be, but 3 km NAM looks a smidge too warm by early morning Thursday, especially for the higher res.

Even 6Z Euro if a degree or two F too warmer than reality is a big deal. 12Z mesos should be getting into range for at least Wednesday night into Thursday morning.

Looking at the 6Z GFS and temps, tiny temp differences means everything between damaging amounts of freezing rain and less dangerous sleet in the Metroplex. FWD AFD mentioned ice accumulating above 28F because wind is removing heat from surfaces and rain. There was a post yesterday to that effect. Does an NWS met secretly visit the forum?

All my family in Bedford/Hurst/Euless have underground supplied electricity, so ice would need to be enough to take down larger above ground major transmission lines, usually taller than surrounding trees and thicker than neighborhood transmission lines. No idea if Dallas is the same. Neighborhood lines thinner and vulnerable to tree branches falling/

Fact from last big Houston ice storm- spraying CaCl2 brine solution on the road keeps bridges and overpasses ice free ***only*** if significant liquid rain doesn't fall first and wash it off. Houston highway flyways were treated and still a disaster.

18Z Euro may be trending closer to GFS. No school at least Thursday in DFW. I want Hwy 6 in the action...

I wouldn't get too confident on anything until Euro and GFS converge. Globals not known for low level temp resolution, either, but it seems like mesoscale models aren't really good outside 48 hours, or Tuesday earliest to get *super* excited.

I actually have no idea how to guess sleet over freezing rain, but cool 850s and subfreezing 925, I'm guessing sleet.

Looking at 12Z GFS 925 mb temps, DFW would get half the frozen as sleet, not ice. Sleet on ice bad for driving, but powerlines wouldn't be coming down.

Houston lost our ice storm, but with GFS and Euro having a pretty serious ice or sleet storm, they have to start putting out alerts. The question is how much is freezing rain, (enough for trees on powerlines) and how much sleet. My Mom and two sisters (Mom lives with 1) in Bedford have underground power cables, a good thing, but worst case, mostly freezing liquid and an inch, major trunk lines would go down and even underground neighborhood power doesn't protect against that.

My Grandma is buried in Marshfield. She was from there. I'm only 1/8th English (her father was a Lane, her mother was sailed from Galway) but per my brother's Ancestry research, ***THREE*** Mayflower ancestors. Price is right style, Marshfield, 35 inches.

GFS in 6 days has the mother of all ice storms in Dallas, surface freezing line to Houston suburbs with rain, and the last post before just now was 6 hours ago. Euro has the cold, not the precip. You guys are lucky, the land of 400 page threads for one storm.

0Z GFS has Houston very close to an ice storm Thursday night and Friday. Euro has the cold, not the precip.

Was James the Coast Guard(? Air Force?) guy from Cape Cod? I saw a comment about COVID page 1.

I don't remember if it was this forum or NYC, but there used to be model comparisons at initialization through the current valid time, some posters used to actually look at water vapor loops and satellite and try to judge which model seemed to be most correct at an early frame. That was about 10 years ago, but it gave confidence that one model may have a better handle than others just based on initialization and 3 and 6 hour forecasts vs actual conditions.

Silly question- from seeing weak and sheared tropical systems where the center absolutely chases the convection, with some runs suggesting a warm core and a warmer than normal Atlantic off the NE, maybe surface lows chasing convection out towards the Gulf stream might make some sense. Does that make sense?

Totally OT, but I'm old enough to remember when one had to ride a bus from North Quincy to Dorchester/Fields Corner to catch a train to visit the certainly dead by now Mom's Great Aunt Mary Lydon in the projects on probably what would be considered the Dorchester/South Boston border. G.A. Mary was the only relative I ever met (not counting in-laws) who had an accent. Later, when visiting Grandma, in North Quincy, I road in to Andrew Square, road down to Ashmont, and took the trolley because someone said it was the only trolley line to run through a cemetery.