02/09/11 FCST: Southern Plains

[Jacob Ferden]

It appears winter isn't finished with Oklahoma and Texas just yet. The GFS has been bringing in another potentially significant snowfall on Wednesday, and while this doesn't appear to be as widespread and severe as last week's blizzard, it looks like another snowy and windy period may be in the offing for parts of the southern plains.

12z GFS 120 hr. snowfall for central Oklahoma:



12z GFS 24hr. accumulated precip. for 00z Thursday:



Obviously, we're still quite a ways out, and I think the GFS is probably too bullish on the snowfall. But given the OKC area is just finishing the process of digging out of last week's storm, this isn't the most encouraging scenario at the moment.

 

[Mike Smith]

Both 18Z NAM and GFS models have the heaviest snow in KS. Way too far out to say at this point.

 

[Jason Boggs]

Yeah, it's too far out to pinpoint snow totals, but I sure hope that 120 hr GFS verifies. We sure could use 6-12 inches on snow around here.

 

[Patrick Marsh]

Both the Canadian model and ECMWF (both of which are statistically better than the GFS) have the highest QPF across OK -- and more than with the last system.

The big question the models are struggling with is how to bring in the arctic air. Previous runs (prior to 18 UTC today) of the GFS were considerably faster with the cold air surging south and thus the short-wave trough struggles to amplify over the cold air and thus doesn't until farther east. Thus, OK was left out of most of the precipitation. The Canadian and ECMWF are slower in bringing the cold air south and therefore allow the main short-wave trough to amplify over western Texas and therefore a significant winter storm is forecast. I should point out that the 18 UTC run slowed down the arctic intrusion, and is coming more inline with the Canadian and ECMWF.

As for the largest snow totals being in Kansas, the 18 UTC NAM only went out until 06 UTC Wednesday, which is about the onset time of heaviest precipitation in Oklahoma, so of course the highest snow totals would be across Kansas (and most likely owing to frontogenetic forcing and not a deformation zone associated with the amplifying / closing short-wave trough). As for the GFS, I think the question there is precipitation type (initially) across OK (isn't it always?), leading to a reduction in snow totals across OK compared to Kansas.

Regardless, the short-wave trough is still way offshore and won't be sampled by our upper-air network for awhile. There are a lot of questions needing answers before we'll have a better idea of what will happen.

Just me $0.02

 

[Patrick Marsh]

00 UTC NAM from tonight at F84 paints a very ominous picture across the southern plains for mid-week. Strong fontal zone moves into Oklahoma late in the evening on Tuesday with precipitation developing along and post frontal. Although model soundings support all snow, knowing models tend to under-forecast the strength of the warm layer aloft (especially in deepening cyclones) suggesting a possibility of freezing rain / sleet will exist in addition to snow across Oklahoma. (Cold air should remain deep enough across Kansas to support primarily snow.) The H500 vorticity maximum and H500 90kt+ speed maximum are still in western Arizona poised to dig slightly setting the stage for a relatively prolonged precipitation event somewhere in the southern plains.

 

[Trey Thee]

I'm glad someone got a thread up because that was on my agenda for tonight. This is not good, the main highways are finally passable at reasonable speeds, side streets are still a mess, main roads are hit/miss up here in Tulsa but are generally passable with varying speed. Downtown Tulsa is still downright terrible.

If we get another 8 to 12 (God forbid 12+) the entire metro will be in massive trouble. There's snow piled up 3 to even 8 feet high along the sides of various roads and intersections, theres just no place to put it and no significant melting that will take place between now and Tuesday.

 

[RMacDonald]

Just ran my SmartModel for the Tulsa area. Looks like a small window of FZRA from 08 Feb 06Z to 08 Feb 11Z, then transition to Snow, only able to capture to 09 Feb 01Z picks up on Snow with .1 to .3 accum per hr. Winds will also be an issue but nothing like you saw this last storm. Hope to get a couple more runs to lock it down better.

 

[Mike Smith]

Snow with .1 to .3 accum per hr.

Is that what you meant to write? That would be a slow rate of accumulation.

Mike

 

[Trey Thee]

Is that what you meant to write? That would be a slow rate of accumulation.

Mike

I wonder if he meant precipitable water? That would be 1 to 3 inches/hour snow.

 

[Patrick Marsh]

I wonder if he meant precipitable water? That would be 1 to 3 inches/hour snow.

This would assume a constant 10:1 snow-to-liquid ratio, which is rarely the case. The snow-to-liquid ratio changes based on the amount of available moisture, temperature, and pressure at the level of ice crystal formation. Thus, it changes throughout the event. General rule of thumb is the closer the surface temperature is to 0C, the lower the snow-to-liquid ratio is.

Just an example, in the blizzard last week, Oklahoma City officially reported ~12" of snow, which melted to 0.6" of liquid. This would yield an average snow-to-liquid ratio of 20:1.

 

[Trey Thee]

This would assume a constant 10:1 snow-to-liquid ratio, which is rarely the case. The snow-to-liquid ratio changes based on the amount of available moisture, temperature, and pressure at the level of ice crystal formation. Thus, it changes throughout the event. General rule of thumb is the closer the surface temperature is to 0C, the lower the snow-to-liquid ratio is.

Just an example, in the blizzard last week, Oklahoma City officially reported ~12" of snow, which melted to 0.6" of liquid. This would yield an average snow-to-liquid ratio of 20:1.

Of course it changes, it could be higher or lower based on a variety of factors...and yes that was an assumption on my part. I wasn't trying to imply (and I dont think I did) that its always 10:1. I was trying to figure out exactly what the original intent was of the post.

edit: If the post actually meant total snow accumulations of .1 to .3 inches/hr then we'd have to get 20 or 30 hours of straight snow to meet the accumulations currently being shown by most of the models. I'm really anxious to see how this system unfolds the next 24 hours. The models should get a pretty good handle on it.

I'm particularly concerned at this point about a tenth or quarter inch of ice glazing the recently cleaned streets and then getting an additional 6 to 10 inches of snowfall. That could make travel an even bigger mess.

I've got a lot of family in OKC and travel is just now back to somewhat normal down there, both major metro's in the state could be crippled by another major storm.

 

[Jesse Risley]

The most recent run of the ECMWF still wants to hold the QPF maxima (app. 0.50" - 0.75") from all of central OK eastward into the Lower Mississippi River valley between 00z WED - 00z THUR. A few specific values for locations in the general discussion area are as follows: OUN - 0.48", DFW - 0.30"; LZK - 0.42"; TUL - 0.49" and ICT - 0.38". The ensembles show the mean SLERs beginning closer to 10:1 across S KS and N OK, gradually shifting to > 15:1 into WED. The ECMWF is less aggressive with colder 2m temps than the GFS. The GFS Skew-T profiles show 2m temps across central OK (OUN) < 0C at 00z WED, whereas the ECMWF Skew-T profiles are less aggressive, showing SFC - 850 mb temps > 0C across the region until closer to 06z WED.

 

[RMacDonald]

Hello sorry for not being clear, I was showing .3" of snowfall per hour. Just uploaded fresh 18Z SmartModel runs for LA, TX, OK, AR, AL, GA, MS. starting to caputure the winter weather moving in.

 

[Trey Thee]

Hello sorry for not being clear, I was showing .3" of snowfall per hour. Just uploaded fresh 18Z SmartModel runs for LA, TX, OK, AR, AL, GA, MS. starting to caputure the winter weather moving in.

Thanks for the clarification

 

[Andrew Francis]

OUN planning on posting WSW tomorrow. Preliminary totals, in general north of the Red River, being 3-6 inches. Higher the further north you go.

EDIT: Nevermind, issued tonight for most of OK.