High Plains Drifter

"Panhandle Magic" begins the Great Plains tornado season!  At least a handful of chasers witnessed and documented the first Plains tornado of 2007 as a few supercells developed over the eastern Texas Panhandle early this evening.  Below is a radar image with a few of the storm report icons from around that time.  Apparently the tornado north of McLean was the one that was observed by several chasers… Not much has happened yet in Southwest Kansas but I think that’s about to change per the water vapor loop… tremendous upward motion is about to impinge on Southwest Kansas and dewpoints are rising into the lower to mid 50s just south of Dodge City.  More later…

71 today… blizzard tomorrow!  High plains weather never ceases to amaze me.  We had a high of 71 degrees today in Dodge City… and at this very time tomorrow afternoon… it could very well be 30 degrees with northwest winds of 40 mph gusting to 55 mph and moderate to heavy snow with blizzard conditions.  The storm appears to be developing farther south just a bit…with the surface to 700mb lows developing just a little bit farther south.  Even the new 12z ECMWF shows a 500mb low center over the TX Panhandle now tomorrow morning.  I’m at home briefly, but expect to be called back into work in a couple hours when storms start developing.  A tornado watch and a blizzard warning are in effect over parts of the Dodge City NWS county warning area… how about that?  We’ll see what the real atmosphere can produce tonight and tomorrow… it looks really interesting. 

Western Kansas blizzard still on track.  All the models are still on track in developing the surface and mid level cyclone during the day Saturday as it moves across Kansas.  The kinematic and thermal fields are all quite impressive for fairly decent precipitation west of the low — suggesting a 9 to 12 hour duration blizzard over portions of western Kansas.  Below are a few NAM forecast charts I put together from the latest 00z model run:

850mb temperature prog shows air cold enough for snow diving south across western Kansas by midday Saturday 2/24.  700mb moisture is shown to wrap significantly around the system during the day

500mb low will be positioned near Pratt, KS per the NAM model with a very deep ~530dam minimum height.

For "wrap-around" precipitation around a powerful low, forecasters tend to look for a nose of warm, moist air in the mid levels from roughly 750 to 550mb.  Above is the 700mb temperature forecast showing an axis of warmer 700mb temps nosing back into the Hays-Wakeeney corridor just northwest of the 700mb low center.  The temperature gradient at 700mb between this warm nose aloft (more popularly called "trowal" by forecasters) and the axis of cold air to its immediate west over far northwestern Kansas and northeastern Colorado…will be a zone of enhanced precipitation.

Next update on this storm may not come until late tomorrow night as I may be pulling some overtime at work with severe weather ahead of this storm.

1st Severe Thunderstorm Outbreak on the Plains Tomorrow Night!  I have modified the dates on my blog of this event from the 24-25 to 23-24 as the system will be fairly quick moving…and the fact that Friday night the 23rd looks more and more like a potential nasty night for widespread severe thunderstorms along the dryline and advancing cold front aloft.  Take a look at the 00z NAM forecast from tonight’s run below.  It’s the 500mb Heights and 250mb Isotachs showing the upper level jet streaks.  This is a classic Great Plains severe weather pattern given adequate moisture in the warm sector:

Northern branch of polar jet and subtropical jet will spread into the southern Plains by late afternoon into the early evening on 2/23

Below is the 24hr NAM forecast of 850mb relative humidity and wind vector.  Ordinarily in the warm season, low stratus is not much of concern in the warm sector east of the dryline… however being so early in the season (late February) the northward transport of high moisture content will likely result in a lot of low clouds given the cooler lower troposphere this time of year.  All the models suggest this, and is a big concern for "chaseable" severe storms on the dryline tomorrow:

24hr NAM forecast valid 6pm CST 2/23 indicating low clouds likely east of the dryline the afternoon of 2/23

Regardless, it appears the massive cold advection in the mid levels will overcome slight deficiencies in the lower troposphere especially after 6pm tomorrow — including portions of Southwest Kansas.  SPC Day 2 forecast had a "moderate risk" of severe storms from roughly Ness City, KS south along the dryline and points east into Oklahoma.  I will likely be working my first severe event of the season tomorrow in the Dodge City forecast area… should be interesting!  Next post will be about the latest on the possible blizzard behind this storm on Saturday!

27hr NAM forecast valid 9pm CST 2/23 showing surface wind vectors, CAPE (convective available potential energy), and 500mb Temperatures.

An intense, fast-mover.  It appears all the major models have a decent handle on this storm now as we enter the 60-72 hour forecast window.  All the models suggest intense deep tropospheric cyclogenesis over Southwest Kansas early Saturday with the 500mb low bottoming out in the lower 530s.  I made a comparison graphic below, which shows the NAM and the UKMET the slowest solutions.  The ECMWF is still the fastest and farther north with the upper low track.  Regardless of which solution is favored, there will be a swath of intense winter precipitation and wind over a 6-12 hour time frame over portions of western Kansas.  

Comparison of 5 models of the 500mb low position at 6pm CST 2/24

The UKMET solution would favor intense snow and wind here in Dodge City with perhaps a few hours of near blizzard conditions if the snow accumulates enough.  Interstingly enough, the UKMET shows more QPF in the "wrap-around" comma head of the storm over western/northwestern KS than any of the other models.  The UKMET traditionally shows less QPF than any other model in just about any situation.  I would argue that the numerical models are going to struggle with QPF in such strong cyclogenesis during the day Saturday and there very well could be significant snow of 5 to 8" to go along with 40-50mph winds somewhere over the western 1/3 of Kansas by midnight Saturday night.

72hr UKMET 12-hr precipitation forecast valid 6pm CST 2/24

. . . A bit farther south? . . .

The new Feb 21 00z run of the GFS suggests the mid level upper low will close-off over the Texas Panhandle around +84hr to +90hr… a classic scenario for significant precipitation over Southwest Kansas.  As a blizzard lover, this is exactly the kind of 500mb pattern I would be looking for — but there is one problem:  the magnitude of warm air ahead of the system and the overall lack of low level baroclinicity.  At least for here in Dodge City, we may be too warm for significant snow… at least as it stands right now.  That said, it is actually quite a feat to get this kind of deep tropospheric cyclogenesis without cold enough air for snow in Southwest Kansas in February.  A 535 decameter 500mb is usually deep enough to "generate" its own cold air through the column for snow at this time of year.  The question will be how quick this can happen.  A big "kicker" Pacific jet will keep this system on the move, so any blizzard conditions would likely occur for a 6 to 9 hour period perhaps over portions of western Kansas — a lot of uncertainty though.  When it does snow though, the snow rates may be quite high and with 30-50 mph winds… blizzard conditions would most likely be met… including here in Dodge City should this latest GFS run be any accurate.

96hr GFS run valid 6pm CST 2/24 showing the upper low and surface low nearly stacked along the OK-KS border.

Storm chasing this system?  There still remains a possibility of a chase Saturday if a) I am not needed for any overtime at work b) if Dodge City area remains out of the blizzard risk.  I will not chase if it appears we may get blizzard conditions in Dodge City with this storm.. (that’s the blizzard freak in me!).  Anyway, below are two charts from the 21/00z run of the GFS… the first is the 400mb RH and the 2nd is the surface wind and Lifted Index.  (I like to look at 400mb RH because I think it shows the mid-latitude cyclone dry intrusion subsidence and warm conveyor best and roughly the level in the troposphere that water vapor is depicted on the WV satellite imagery)… anyway, using these two charts, and *if* this were a perfect prog, then there should be an enhanced tornado threat over far south-central Kansas shortly not too long after 18z, if any insolation is realized in the mid level dry intrusion.  We’ll see how this plays out in subsequent runs as well as other models.

400mb RH… I like looking at this as a prog for what the water vapor satellite image might look like

Surface wind and surface-based LI suggesting an area of instability near the OK-KS border… notice this area is progged to be at the nose of the mid level dry intrusion in the image above.

. . .The 533 Low. . .

Boy is this looking interesting.  For the past several days, a majority of the major global spectral model solutions were suggesting the possibility of significant mid-latitude cyclone development over the plains the weekend of Feb 24-25.  Even at the National Storm Chaser Convention this past weekend there was a "buzz" about this upcoming storm… and even research meteorologists and weather enthusiast extraordinaire Howie Bluestein was showing the Day 7 GFS progs before his radar talk. 

What I am seeing here in the models is a storm that may very well rival November 27, 2005 in regards to development, size, and impact over the Great Plains.  The GFS shows a ~533dam 500mb low center near the OK/KS border Saturday 2/24.  Surface development will also be very impressive with a large warm sector ahead of the low.  A surface low will likely track from Southwest KS into Northeast KS…deepening significantly… perhaps to lower-mid 980s millibar MSLP center.  The surface low may actually develop fairly close to the 500mb low center which may enhance the possibility of low topped supercells much like 11/27/2005.  The other thing that is interesting is the fact that I"m off work Saturday, so if the system slows down enough such that central or southern KS looks like a reasonable possibility of low topped supercells, then it’ll be my first chase of 2007!  I’ll try to keep my blog up to date with regards to the latest thoughts I have of this storm through the week…including the blizzard aspect of the storm…as it appears very likely there will be a major… perhaps crippling blizzard over some portion of the Great Plains northwest of the low track.

One thing to note here that is important.  This is still in the 120-144hr time frame… and all the models are now in a really good agreement with each other today.  While this "super ensemble" method of agreement implies increased confidence, it doesn’t mean these models all have a handle on the evolution of this downstream development. Tomorrow, the models may show something quite different… but there will still be a big storm… it’s just the synoptic and subsynoptic details that will not be clear until a day or two out.  One of the things I want to do here on this blog is document the various shifts in model solutions, similar to some of my previous winter blog posts.  

500mb Heights & Vorticity showing the low center over KS/OK