A nice synoptic - sized cyclone will be developing late this weekend and moving towards the east (as usual) right through the Missouri region tomorrow afternoon. The combination of frontal lift, along with a nice influx of moisture from our good friend the Gulf Coast (the non-oil, all moisture component) and a little dry air (elevated mixed layer) advecting into the southern Missouri/northern Oklahoma area AND the fact that the middle Midwest is right between an upstream trough and downstream ridge (implying upward vertical motion due to upper tropospheric dynamics) is promising for a decent triple point warm sector set up.
Analysis via the NAM model (12 UTC 2 Apr 2011 run):
Synoptic Scale Forcing: 300 mb wind/height between (12 Z Sunday and 00 Z Monday) map shows the western Illinois, Missouri south to northern Oklahoma regions between an upstream trough and downstream ridge, implying upward vertical motion within this region. This is where the cyclone will develop. 500 mb maps (same time-frame) show similar setup, with southwest winds ~60 knots at this level. Vorticity map shows some nice positive/negative anomaly couplets in the Missouri region, and sometimes can be a nice first order indicator of developing convection (though in case the features are small and could just be noisy vorticity data, but I think there is some legitimacy to this). The cyclone and it's respective triple point (including developing warm and cold front) can easily be seen at the 850 mb level (temperature maps) during this same time frame, with the triple point of the system residing near the La Crosse, WI region at 00 UTC Monday. Both the 850 mb and 925 mb maps during this time show strong warm air advection and moisture advection from the south central US meeting with cold air that has resided over the northern US for quite some time, with wind speeds ~50 knots in extreme southeastern Missouri, and still near 40 knots throughout most of Missouri at 00 UTC Monday at 925 mb (between 30-40 knots at the same pressure level since 12 UTC).
Bottom line: Synoptic forcing due to upper level dynamics inducing, as well as strong warm air and moisture advection from the gulf fueling development of a synoptic cyclone, AND dry air (elevated mixed layer) advection from southwest seem to favor a nice triple point style setup over the central US.
Mesoscale Forcing:
Moisture: As mentioned, moist air advection from the Gulf will be present due to the low level jet in the south central US, which will intensify overnight between 6-9 UTC Monday (and transform into the fan-favorite NOCTURNAL LOW LEVEL JET). Dewpoints are forecasted to be in the 60 degree Fahrenheit range easily throughout a nice portion of Illinois south through Missouri and into Oklahoma and Arkansas, with a strip of near 70 deg. dew points along a line from western Illinois through west Missouri south through eastern Texas at 00 UTC Monday. This along with warm air temperatures at the surface will allow for a nice moist boundary layer to develop.
Dry Air Cap: A nice elevated mixed layer will advect over this same region throughout the day due to strong southwesterly winds at 700 mb throughout the day. This will provide for a nice initial cap, and may actually be somewhat difficult to break before dark in some areas, such as eastern Missouri and the southern tip of Illinois. Nevertheless, this will allow for daytime heating to build up a nice "loaded gun" sounding-esque situation that, if broken at the right time, could fire up some nice thunderstorms, including supercells.
Instability: nice values of CAPE (Convective Available Potential Energy) are present throughout this region, with some areas approaching 2000 J/kg (see map below). Therefore, this region will be very unstable, and lifting mechanisms such as daytime heating and frontal forcing will allow for strong to severe thunderstorms to develop.
Shear: 0-1 km relative helicity values are favorable throughout Missouri and Illinois (~ 175-200 m^2 s^-2 range). Soundings (like the one below; note all soundings shown for 18 UTC-00 UTC Monday for north-central Missouri) show some nice veering of the winds with height, and definite speed shear (also, see discussion above about strong lower tropospheric winds). Since the shear is present in regions of favorable instability, supercells and tornadoes are definitely possible in the triple point region.
LCL heights: NAM is showing relatively low LCL heights (~1000m above ground level) throughout Missouri and western Illinois, which is nice for getting some funnel clouds to reach the ground :)
Bottom Line: Okay, there's plenty more to talk about, but I'm getting lazy and have plans this afternoon, so to summarize briefly:
elevated mixed layer + low level jet + shear + instability + high lapse rates (which I didn't cover extensively, but I pseudo-cheated and noticed discussion about this in SPC's breakdown) = supercells + some tornadoes
Key Drawbacks to Tomorrow: Too much CIN throughout the morning might prevent "loaded gun" scenarios from "firing," or in simpler terms, may prevent development of strong updrafts and firing of supercells during daytime hours. Also, I noticed a small gap where CIN diminishes too early, and composite reflectivity is generating a mini-MCS in this spot (see 2-panel plot of CIN and composite reflectivity at 00 UTC Monday below; feature circled). This worries me, because if thunderstorms in the triple point become too organized, then forget about chasing supercells. Also, the sun still sets fairly early, so chasing hours may be limited.
Go Zone: Basically north-central Missouri, then maybe Western Illinois overnight (but mainly north-central Missouri). A few cells may fire in southern Missouri, but with warmer temperatures, dew point depression values are a little higher (also, region is farther from triple point, warm front).
I'll throw out a storm report forecast tomorrow once HRRR is in range of forecasting this thing :)
Peace out,
Helicity
P.S. Again, all plots from Twister Data (www.twisterdata.com)
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