Well… it didn’t take long to fully swing into spring… with the March 30th severe weather event in central/eastern KS-NE-OK and what looks to be an ominous looking tornado setup in Southwest Kansas tomorrow, April 1st.
I’ll let the GFS 4-panel model graphic (a 36-hr forecast valid 6pm CST April 1) below do the talking, for those of you who know how to interpret these charts. About as classic a setup as you can ask for in early spring. A negatively tilted upper trough slowly moving into the high plains at the peak-heating of the day. A formidable dryline will shape up from Western KS into the eastern TX Panhandle. Just amazing wind shear at all levels with abundant moisture and a warm front lifting north during the day. I’ll be working this one (not chasing), I can’t wait! I love working these kind of events… it’s why I do what I do If there’s significant tornadoes, lets just hope they stay in the open farmland like they’re supposed to out here.
Well as any good forecaster should do, I’m here to verify my forecast from yesterday’s virtual chase. My primary northern target to intercept the first supercells of the day in north central KS west of Highway 81 didn’t really pan out. Storms developed in the target area around 17z or so just as I had though, however too many storms developed given the lack of a “cap” and the orientation of the convection was north-south…with prevailing mean shear vectors being of strong southerly component, that did not allow for discrete cells to develop, but rather a messy line of marginally severe cells (see left radar panel below). My southern (secondary) target in southern Oklahoma worked out a little better. A classic supercell developed near Duncan, OK by mid-afternoon which did produce at least one tornado near the town of Velma, according to a few storm chaser accounts.
A classic mid latitude cyclone is moving across Kansas today. This appears to be shaping up to be a setup very similar to work done by Jon Davies regarding tornadoes near the 500mb low/potential vorticity max coincident with the cold-pool aloft. Here is a forecast I posted to a storm chasing forecast discussion group regarding today’s virtual chase target:
WV loop mid-morning shows nice mid level drying working into western
KS. You can see the subsidence/lift couplet near the mid level PV max
on the water vapor loop pushing east at a fairly healthy clip. I think
initiation by 17-18z in an area north of I-70 east of HLC...with the
first storm(s) evolving into supercells by 18-19z with first tor report
maybe by this time? Looking at the DDC short-fuse composite
(weather.gov/ddc/shortfuse/shortfuse.php) a nice persistence moisture
flux convergence max betw HLC and HYS with nose of steepening low level
lapse rate and theta-E/CAPE working up into this area as well. I'd like
to be near Smith Center KS around 18z if I could be out. This event
does have components of the cold-core pattern with the 995 sfc low/sfc
wind vertical vorticity max positioned very close to the H5 PV max and
cold pocket of -20 to -22ish. I guess you could call it a hybrid...
maybe somewhat similar to April 10th last year or even March 27th
Kinsley KS event in 2004. After 20z, the whole warm sector should light
up, but I don't usually like being directly under the H5/3 jet core
which should be flying through most of KS today/Nrn OK. So, I'd either
stay along the KS/Neb line near the cyclone occlusion or farther south
in the southern half of OK. Good luck to all out today, I'm jealous!
With compact mid level lows like this one today, I like targeting the area very close to the mid level potential vorticity max. This is usually marked by the darkest “dry spot” on a water vapor image. This is an area of strong subsidence in a maturing cyclone that contains some air from the stratosphere which contains a lot of “potential vorticity”. Just downwind of this PV max (northeast in a northeasterly moving cyclone) is where the best lower tropospheric “response” will be , where frontogenesis is usually maximized and lift is strongest. When there is potential instability involved (usually diagnosed by CAPE fields or theta-E ridges at the surface) near this area, then this potential instability is released vigorously along with the extra deep lifting from all the other “dynamics” involved. To make a long story short, “low-topped” supercells are favored in these areas. Today, between 18z and 20z, the “sweet spot” for all this appears to be setting up in far north-central KS for these kind of storms. Tornadoes usually occur in this area. So, I’d be favoring strongly the Smith Center to Mankato KS area to Osborne to Beloit around this time if I could chase.
The storm came…. and went on this, the vernal equinox of March 20th. We snowed in Dodge from about 5:30am through most of the day. The snow began to let up in the mid afternoon after about 6″ at the airport. Around 6 and a half inches will the offical total here as it’s still snowing lightly as I type. The most snow fell just north of the strengthening 700mb low from the Sublette to the Garden City area, just as I had discussed might happen based on what the GFS and the other models were showing. Unfortunately, the whole system was rapidly occluding and weakening as the afternoon went on and most of Kansas was left in a large dry slot with only scattered snow/rain showers east of a Dodge City to Hays line. This resulted in a busted snowfall forecast (predicted 10-14″+) for areas northeast of Dodge City…especially heading into portions of central and northeast KS. The upper cyclone underwent fairly explosive deepening early this morning in the western OK Panhandle and as quickly as it deepened and matured… it began the weakening process only hours later. A very dynamic meteorological situation with high bust potential for some forecasters… which indeed did happen. There were forecast successes, though, for western Kansas and much of Nebraska where predicted 8-12″+ amounts did indeed verifiy… with amazing 20″+ amounts in Central and Northern Nebraska since Saturday night.
Well just as planned, we changed over from the sleet mix to all snow at about 5:30am. I’m not sure I like the radar trends… looks like a dry slot is rapidly advecting north out of northwest Oklahoma towards southern Ford County. Hopefully this will keep filling in, which I *think* it will. I don’t like being on the edge with these things!
at 4:30am, I’m hearing the “tink-tink” of ice pellets hitting my front window… we are getting a rain/sleet mix at this time. We were all rain about a half hour ago. Garden City airport has been reporting snow in the last hour or so. This sleet period should only last an hour or two before a complete changeover to snow. The radar imagery is pretty impressive right now, verifying the models quite nicely up to this point.
Everything appears to be on track for some rather significant snow accumulations for Dodge City and points surrounding in western Kansas. The GFS nailed the ~06z convective burst several runs back, as evident by the regional radar shown here (05z). This is the genesis of the impressive wrap-around warm conveyer leaf as the storm matures overnight just southwest of southwest KS. I still foresee thundersnow in the 12-15z window across southwest KS, including DDC. At the heaviest, snowfall rates may easily exceed 2″ per hour, mainly during the mid-morning hours. All versions of the RUC model (including the development RUC on the FSL/RUC webpage) through 12 hours show a significant amount of QPF through 18z (noon) Monday. See no reason to doubt this from a simple pattern recognition standpoint with a fully maturing mid-latitude cyclone strengthening along the “golden path” for Dodge City. According to all the model soundings I’ve interrogated, it appears we will change over to snow here in DDC nearly at the onset of the big “blob” of (convective) precip heading northeast towards SW KS as seen on radar. It will initially be a rain/snow mix, but quickly change to a sleet/snow mix then all snow just before 12z. See the Skew-T graphic, a 9hr forecast from the RUC model. Look at the massive warm-advection signature (winds veering with height) in the lower 300mb or so of the sounding! More later. It’ll be tough for this weather weenie to get some sleep knowing what’s coming!
Saturday evening model runs are in. No huge surprises with this run actually. Getting into the day Monday is where the NAM begins to diverge from the slower GFS/Canadian solution. Slower solution pretty much = more snow for here in Dodge City, as I mentioned in the previous post. Here is the 48hr fcst from the Canadian 00z run valid 6pm Monday evening:
This canadian run is actually fairly consistent with the placement and timing of things from the 84hr fcst valid the same time that I posted yesterday. It continues to show a near 1″ 12-hr QPF bullseye near the track of the 700mb low. The “bullseye” in the QPF field is a bit farther northeast than the 84hr forecast, however this is what we call “white noise” in the model details. The main signal of interest is that there will likely be a 1″ QPF hit in a 12-hr period during the day Monday along and immediately north of the 700mb track. The Canadian model is very similar in placement of the 700mb almost along the OK/KS border near Medicine Lodge at 21/00z (6pm Monday). The 00z run of the GFS and the NAM show a rapid cooling of the 800-700mb warm layer from 06z to 12z Monday morning changing any rain over to heavy snow by sunrise or shortly before. When the precip changes over to snow in SW KS near Dodge City, there may in fact be some thunderstorms involved. I haven’t experienced a thundersnow since 1993. This would be a real treat!
The 18z GFS model is revealing a “best-case scenario” for a major snowstorm in Dodge City. Taken at face value (which is a dangerous thing to do with any model!), the 18/18z rendition of the GFS evolves a very deep, slow-moving, compact 700mb low across far southwest Kansas during the day Monday 20th. Below is a 6-panel graphic I whipped together, graphics taken from the ARL-Ready website. In events like this where deep cyclogenesis is involved, I love to use the 700mb low track for the placement of the heaviest snow with the “meat” of the storm. An old-school heavy snow forecasting tool is the 700mb low track, and to me, in situations with strong 700mb cyclogenesis like in this case, it is a very good tool. Very impressive snow rates can exist with deep, slow moving, and compact 700mb lows. Well, we have a beauty of one showing up in all the models for Monday. The track of it is extremely critical. If the 700mb tracks just north of Dodge, then the Ness City to Wakeeney corridor will get a foot or more of snow. If the 700mb low tracks where the 18/18z GFS suggests, then the areas from Garden City to Dodge City to Larned will get an easy foot… given the moisture at play. The key? A deepening, and crawling 700mb low. That’s how we get the footers here in SW KS. The trends in the model runs continue to support this. This is getting rather exciting!
The huge winter storm is still on track to blitz much of the central plains from southwestern KS into the southern Dakotas. It appears there will be two waves of winter precipitation. The first wave will be developing late this afternoon over eastern Colorado which will expand into northwestern KS tonight and into Nebraska. This wave will produce moderate to heavy snow amounts in central/northern Nebraska into South Dakota. Then the main storm will begin to eject out of New Mexico tomorrow night. The rain snow line will slowly shift south Sunday night from the I-70 corridor down into Southwest Kansas overnight. We will probably change over to snow here in Dodge probably around or shortly before dawn Monday Morning. There will be a warm pocket at 800mb to overcome before we go over to all snow. Just massive warm/moist advection late Sunday night into the first half of Monday. The classic 500/700mb low tracks would actually put the heaviest snows from roughly WaKeeney into north central KS to just north of Kansas City. This is certainly indicated in both the GFS and NAM snowfall outputs, as shown below. This will be one for the books, certainly, for someone in northern KS and central Nebraska. The southern portion of the snow storm, closest to the 500/700mb lows, may see some thundersnow. We will be near the gradient here in Dodge between a ton of snow and not-so-much snow. It’s very tricky. If the 700mb low tracks just south of Dodge, we will likely see very heavy snow for several hours, piling up to near a foot by late Monday. If the 700mb low tracks along or just north of Highway 50, then the I-70 corridor will blitzed. Either way, SOMEONE will see well over a foot when all is set and done. A very nice, and MUCH NEEDED widespread precip event for the farmers all across the central plains!