Forecasters have been talking about a wide variety of weather risks for the Plains on Wednesday, as a strong low pressure system develops over Kansas. Models still differ somewhat in the placement of the low, and especially in the quality of the moisture return ahead of the system. Let’s look at the risks we’re fairly certain of, first:
This risk is looking to be higher in the overnight hours into early Thursday. The image below (courtesy PivotalWeather) shows 7am CDT Thursday as forecast by the GFS model.
That’s showing 35-40 mph wind on the back side of the low, through western Kansas. If anything, I suspect that’s a little underdone. Given that it’s on the cold side of the system, I don’t think it will be a big factor in fire risk, but we could see some tree damage, especially the Bradford Pears, which seems to be in full bloom in much of the state.
While the threat of significant snowfall still looks to be mostly in northeastern Nebraska, western Iowa, South Dakota and Minnesota, some areas of Kansas could pick up a few inches of snow from this system. This loop is from the NAM model, and shows forecast total snow depth from 7pm CDT Wednesday through 10am CDT Thursday:
What’s less certain at this point is the severe weather threat. While there are several parameters in various model runs that look like north central Kansas could see severe hail, wind and perhaps a few tornadoes, there are fairly strong concerns about the quality of the moisture the system will have to work with. In the 24 hours before the storm, mid- and upper-level wind will be more from the desert, and the system that plowed through the Houston area yesterday ended up pushing most of the rich Gulf moisture offshore. Winds at the surface really only pick up in the 12 hours prior to the event. So dew points are forecast in the 50’s in most of Kansas to low 60’s right up along the state line:
This loop is 7am CDT Wednesday to 7am CDT Thursday. Green is dew points in the 50’s, blue is dew points in the 60’s — in both cases, the darker the color, the higher the dew point.
But I have an issue with this forecast: how do we get a jump of the 60+ dewpoints from southern Oklahoma/Arkansas (hour 54, 1pm Wednesday) to the eastern half of Kansas (hour 57, 4pm Wednesday) to the Nebraska state line (hour 60, 7pm Wednesday) with 25-mile an hour south winds at the surface?
For comparison, the GFS forecasts dew points above 60 degrees only east of a Marysville to KC-metro area, and only at 7pm.
Because of this uncertainty, I’ve not invested the time to do a full forecast based on the 12z Monday models. I will do one tonight based on the 0z Tuesday models, and post a full briefing Tuesday morning. For now, a quick look at the SPC risk area and a few sentences from each of the affected forecast offices’ morning forecast discussion:
Hastings, NE discussion (relevant for Beloit, Concordia and vicinity):
Bottom line: this will be a multi-hazard system with svr tstms possible Wed PM, snow (potentially heavy for some) Thu into Thu eve, and very strong winds combining with snow Wed night into Thu to create near-blizzard or blizzard conditions in areas with heaviest snow. The worst of this system will be centered on Thu.
Goodland, KS Discussion (relevant for Goodland, Atwood, Colby, McCook, and Norton areas):
Based on the speed of the system and sounding profile, there will be a gradually change from rain to a mixture and finally to all snow. As show yesterday, the most accumulation will be in the northern third of the area. No matter how much snow falls, which will be key, windy to very windy conditions will be the most certain part of this forecast.
The extremely tight pressure and mixing will spread these conditions from west to east across the area. Mixing shows that 50 to 60 knots could get mixed down. Did increase the winds accordingly but there is potential for these winds to be even stronger. If enough snow falls and falls fast enough, blowing snow could become a significant impact.
Topeka, KS Discussion (relevant for Clay Center, Manhattan, Abilene and points east):
There continues to be notable guidance spreads in the surface low placement and speed Wednesday into Thursday as the upper low deepens and begins to rotate northeast and this plays a large role in conditions for these periods. There is better agreement in rapidly-falling heights resulting in mid-level cooling steadily weakening the capping inversion through Wednesday evening with ML CAPE values just ahead of the surface low around 1500 J/kg with a 500 mb jet core overhead near 60 knots. General parameters lead to significant shear/cape combination though much remains to be determined on hodograph specifics with the likely fast-moving storms.
Wichita, KS Discussion (relevant for Russell, Great Bend, Ellsworth, Lincoln, Salina areas)
S-SW winds would really ramp up Wed afternoon & evening & with the airmass becoming DEEP & dry adiabatic sustained 25-35 mph speeds with gusts around 40 mph are likely, certainly mid-late Wed afternoon. This would easily send the Grassland Fire Danger into “Very High” & perhaps even “Extreme” country Wed afternoon.
The NW winds wrapping around the sfc cyclone are STRONG, spreading from W & NW KS to the NW corridor of the KICT forecast area early Thu morning. Another Wind Advisory may be required for Russell & Barton Counties late Wed Night/very early Thu morning.
More tomorrow morning when it becomes more clear!