Texas winter wx thread (2009-2010)

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Re: Texas winter wx thread (2009-2010)

#4481 Postby wall_cloud » Tue Jan 26, 2010 8:29 pm

wxman57 wrote:The one thing I'm not clear on as far as that Fort Worth AFD is the mention of freezing drizzle. All the vertical profiles I've seen indicate that once the surface temps drop to freezing that all the moisture above the surface will be in a sub-freezing layer. That means snow would be more likely than freezing drizzle, as freezing drizzle requires a warm layer aloft. There could be a brief period as the rain changes to snow that small warm pockets aloft could melt the snow on its way down, resulting in some light freezing rain. But such a changeover should occur quickly in the strong cold air advection behind the surface low.


remember that you are looking at a model sounding. typically model soundings underestimate the strength of the warm nose above the low level inversion. If this were the case, you would end up with a very shallow dome of subfreezing air, resulting in freezing rain/drizzle. keep in mind that the cold advection does not occur along a vertical line. the cold front slopes back over the cold air meaning that despite the cold advection at the surface, there is still typically warm advection above the frontal zone.
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Re: Texas winter wx thread (2009-2010)

#4482 Postby wall_cloud » Tue Jan 26, 2010 8:31 pm

wxman57 wrote:
weatherguy425 wrote:Guys, he's saying that most of the precip totals are coming from the rain along and ahead of the front, and a sooner front arrival would just mean an earlier onset to the squall line and would have little affect on frozen accum.


Right, but it DOES depend upon your location. For example, we have to consider the orientation of the cold front. What we expect to happen is for frontogenesis (a front to form) on an east-west orientation across southern Oklahoma early on Thursday. As the upper-level trof moves in later on Thursday, heavy precip breaks out in advance of it. A wave/low will form along the east-west oriented frontal boundary and the cold air will rush southward from the Texas Panhandle into west Texas. From the wave/low, the front will extend to the southwest. East of the low, the front will be oriented east-west.

So OKC-AMA will be in the cold air from the start, as frontogenesis will occur to the south of these two cities. The D-FW area would be south of the developing frontal boundary - in the warm air - when the heavier precip moves across. The only way there could be a significant winter event farther south is if the frontogenesis takes place farther south, because once that NE-SW oriented front trailing out the back side of the low/wave moves through D-FW, for example, that means the upper-level trof is moving through and there isn't much moisture to work with in the cold air.

What governs the location of the frontogenesis? It's the path of the upper-level vorticity center. So we're not watching for the front to move south faster than forecast, as it's not really there yeet. We're looking for a change in the path of the mid to upper-level energy that would shift the frontogenesis zone southward.


correct...if the front moved south quicker, DFW would likely be looking at more of a icing event than heavy snow.
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#4483 Postby msstateguy83 » Tue Jan 26, 2010 8:33 pm

wall cloud so whats your overall thoughts on this system, your thought on best areas of heavy snow, heavy ice if you care to share?
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Re: Texas winter wx thread (2009-2010)

#4484 Postby txtiff » Tue Jan 26, 2010 8:35 pm

by PETE DELKUS / WFAA-TV

Posted on January 26, 2010 at 6:54 PM

******
Related:
•More News 8 Weather

WFAA-TV Chief Meteorologist Pete Delkus has a preview of the next big storm system headed to North Texas: A winter mix of snow and sleet that is forecast to arrive on Thursday night starting as heavy rain.

"We're going to be right in the middle of some sleet, freezing rain and freezing drizzle and even a little bit of snow," Delkus said, adding that ice accumulations are possible.
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Re: Texas winter wx thread (2009-2010)

#4485 Postby rainman » Tue Jan 26, 2010 8:47 pm

wall_cloud wrote:
wxman57 wrote:The one thing I'm not clear on as far as that Fort Worth AFD is the mention of freezing drizzle. All the vertical profiles I've seen indicate that once the surface temps drop to freezing that all the moisture above the surface will be in a sub-freezing layer. That means snow would be more likely than freezing drizzle, as freezing drizzle requires a warm layer aloft. There could be a brief period as the rain changes to snow that small warm pockets aloft could melt the snow on its way down, resulting in some light freezing rain. But such a changeover should occur quickly in the strong cold air advection behind the surface low.


remember that you are looking at a model sounding. typically model soundings underestimate the strength of the warm nose above the low level inversion. If this were the case, you would end up with a very shallow dome of subfreezing air, resulting in freezing rain/drizzle. keep in mind that the cold advection does not occur along a vertical line. the cold front slopes back over the cold air meaning that despite the cold advection at the surface, there is still typically warm advection above the frontal zone.


Another thing to note is the dry slot that is forecasted to move over the dfw region. For optimal snow production in the clouds...you need near saturation in the -10C to -20C layer for crystalization to occur. Currently this layer looks dry and the most likely precip would then be freezing drizzle. However...a few small flakes or even sleet is also possible. Snow production is more than just "is it below freezing all the way up?"
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Re:

#4486 Postby wall_cloud » Tue Jan 26, 2010 8:48 pm

msstateguy83 wrote:wall cloud so whats your overall thoughts on this system, your thought on best areas of heavy snow, heavy ice if you care to share?


right now I'm think that the heaviest snow will fall somewhere along the path of the Canadian River (runs just north of Amarillo to Canadian, TX). Once into OK...the heaviest snow SHOULD be along and north of I-40 from near Elk City to Stillwater. The heaviest ice accumulations will likely occur across NW TX from near Childress into south central OK.

This is a very dynamic system to say the least. I was not working during the Christmas storm but worked several days ahead of time to help set it up. From what I am seeing, this system is in the same ballpark with that storm. Its just a matter of the cold air phasing with the strongest forcing and keeping that upper low on a path consistently shown by the GFS over the past 2+ days. I think the band of heaviest snow may see amounts approaching a foot, if not locally higher. wind blow snow will create visibility issues as well, creating near blizzard conditions thursday afternoon across portions of the TX panhandle and western OK. I really haven't focused much at all on the areas downstate (DFW).
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Re: Texas winter wx thread (2009-2010)

#4487 Postby wall_cloud » Tue Jan 26, 2010 8:49 pm

rainman wrote:
wall_cloud wrote:
wxman57 wrote:The one thing I'm not clear on as far as that Fort Worth AFD is the mention of freezing drizzle. All the vertical profiles I've seen indicate that once the surface temps drop to freezing that all the moisture above the surface will be in a sub-freezing layer. That means snow would be more likely than freezing drizzle, as freezing drizzle requires a warm layer aloft. There could be a brief period as the rain changes to snow that small warm pockets aloft could melt the snow on its way down, resulting in some light freezing rain. But such a changeover should occur quickly in the strong cold air advection behind the surface low.


remember that you are looking at a model sounding. typically model soundings underestimate the strength of the warm nose above the low level inversion. If this were the case, you would end up with a very shallow dome of subfreezing air, resulting in freezing rain/drizzle. keep in mind that the cold advection does not occur along a vertical line. the cold front slopes back over the cold air meaning that despite the cold advection at the surface, there is still typically warm advection above the frontal zone.


Another thing to note is the dry slot that is forecasted to move over the dfw region. For optimal snow production in the clouds...you need near saturation in the -10C to -20C layer for crystalization to occur. Currently this layer looks dry and the most likely precip would then be freezing drizzle. However...a few small flakes or even sleet is also possible. Snow production is more than just "is it below freezing all the way up?"


correct...dendrites tend to grow between -12 and -18C. the 18Z Nam soundings for the DFW area show this region fairly moist. haven't looked at the GFS soundings...but it is something to consider.
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#4488 Postby Peanut432 » Tue Jan 26, 2010 8:50 pm

Wall cloud..what are your thoughts for the Childress and Wellington area during the storm? Is 12+ really possible or will there be more rain there? If the precip is rain, will it be freezing rain? Thank in advance
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Re: Texas winter wx thread (2009-2010)

#4489 Postby Portastorm » Tue Jan 26, 2010 8:50 pm

A quick shout out and big THANK YOU to wall_cloud and rainman for sharing their professional expertise this evening!

Oh ... and for you model watchers ... the 0z NAM is running.
Last edited by Portastorm on Tue Jan 26, 2010 8:52 pm, edited 1 time in total.
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#4490 Postby msstateguy83 » Tue Jan 26, 2010 8:52 pm

same here thank you guys
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Re: Texas winter wx thread (2009-2010)

#4491 Postby rainman » Tue Jan 26, 2010 8:54 pm

wall_cloud wrote:correct...dendrites tend to grow between -12 and -18C. the 18Z Nam soundings for the DFW area show this region fairly moist. haven't looked at the GFS soundings...but it is something to consider.


Dewpoint Depressions in this layer are around 10C with the NAM and around 12C with the GFS....may see some ice production out of this...but most precip will be FZDZ or IP with some light snow maybe mixed in.
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Re: Texas winter wx thread (2009-2010)

#4492 Postby wall_cloud » Tue Jan 26, 2010 8:56 pm

rainman wrote:
wall_cloud wrote:correct...dendrites tend to grow between -12 and -18C. the 18Z Nam soundings for the DFW area show this region fairly moist. haven't looked at the GFS soundings...but it is something to consider.


Dewpoint Depressions in this layer are around 10C with the NAM and around 12C with the GFS....may see some ice production out of this...but most precip will be FZDZ or IP with some light snow maybe mixed in.


the sounding I'm lookin at shows 4C
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Re: Texas winter wx thread (2009-2010)

#4493 Postby Tireman4 » Tue Jan 26, 2010 8:57 pm

Portastorm wrote:A quick shout out and big THANK YOU to wall_cloud and rainman for sharing their professional expertise this evening!

Oh ... and for you model watchers ... the 0z NAM is running.


Amen Porta. A HUGE shout out. Amazing breakdown of this event.
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Re: Texas winter wx thread (2009-2010)

#4494 Postby wall_cloud » Tue Jan 26, 2010 9:02 pm

I'd do it far more often if I had the time.
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Re: Texas winter wx thread (2009-2010)

#4495 Postby srainhoutx » Tue Jan 26, 2010 9:15 pm

Thanks wall_cloud and rainman. It's great to see our Mets chimming in and adding great info to the Topic. Looks like a near record event for some folks.
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Re: Texas winter wx thread (2009-2010)

#4496 Postby Portastorm » Tue Jan 26, 2010 9:21 pm

I notice the 0-degree isotherm is further south at 42 hrs per the 0z NAM as compared to the 12z NAM

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/00/images/nam_pcp_042l.gif
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Re: Texas winter wx thread (2009-2010)

#4497 Postby msstateguy83 » Tue Jan 26, 2010 9:21 pm

from what i can tell might be wrong further south track per the 00z nam
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#4498 Postby txtiff » Tue Jan 26, 2010 9:26 pm

So you don't think it is going to take a more southern track?
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#4499 Postby msstateguy83 » Tue Jan 26, 2010 9:28 pm

i ment from what i can tell it seems it is... anyone else wanna chime in?
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Re: Texas winter wx thread (2009-2010)

#4500 Postby Portastorm » Tue Jan 26, 2010 9:28 pm

Again, I'm comparing the 0z NAM running now against the 12z NAM from this morning. Thru 60 hours, looks like the upper level trough isn't as sharp as shown this morning. Kinda flatter and not quite as deep. I wonder if that is a sign of it shearing out some. HPC earlier today mention that might happen.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/00/images/nam_500_048l.gif
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