As this system slowly works it's way ENE it will slowly intensify and you'll see the stronger mid-level jet core move east as well, continuing to show how strong this system really is as wind speeds at 500mb near 90kts.
There is already plenty of moisture up into the central plains out ahead of the sfc low and as that deepens moisture, aided by the strong low level winds, will be thrown up and over the front back into the cold air to help get the deformation band of snow going. 850mb winds but in the warm sector and in the CCB will be very strong. You will have blizzard conditions into parts of western SD near the Black Hills/Rapid City.
With more than abundant moisture in place, both aloft and at the surface, lots of forcing and enough cold air, snow will begin to develop rapidly during the day tomorrow and reach peak intensity tomorrow night as the deformation zone takes shape and will almost stall out as the sfc cyclone occludes tomorrow evening allowing for heavy snow to sit over parts of SD for a long duration of time.
Some of the snowfall amounts being forecasted by the models are just insane and hard to even believe. The NWS is staying on the conservative side being the numbers are so high, it's early October so the sun angle is still fairly high as well as the pavement and ground temps so snow could have a hard time sticking as well. Blizzard warnings are up across western SD for 7-15" with locally higher amounts as well as wind gusts to 70mph! This is all the models forecasted amount for Rapid City, SD.
Now onto the severe side of things....lots of chasers will be out tomorrow trying to see one last tornado before winter gets here next month or so. An unseasonably deep through coupled with lots of moisture (dew points in the mid-upper 60's) will great for a very volatile environment tomorrow afternoon and evening. As the sfc low deepens tomorrow across eastern NE, the sfc winds will quickly respond the the pressure falls and back along and south of the warm front with winds aloft veering around quickly with height creating a lot of speed and direction shear in the low levels. As you can see here, the sfc winds are very backed by late afternoon and evening tomorrow across western and northwest IA.
And when looking at the sounding/wind profile you can see this much better throughout the entire atmosphere with ESE winds at the surface veering to WSW winds at mid-levels.
Now I haven't mentioned how much instability yet but let's just say it will be there, and in a big way for this time of the year with CAPE values climbing to 3000 j/kg in the late afternoon hours. So we have lots of moisture, lots of instability and lots of shear, both low level shear and bulk shear...but will we get discrete storms to take advantage of this environment? It can happen but I'm still worried about more parallel mid-level winds closer to the cold front and getting linear storms quickly and the amount of cold air advection just behind the cold front. I think a sleeper target is somewhere in northeast IA along the warm front where the 500mb flow is more WSW'ly allowing for possibly more discrete storms to ride the warm front but the big spot to me is northwest IA. The last image is the STP or significant tornado parameter which will combine several things like instability and low level shear to get a value of where the best chance for tornadoes and/or significant tornadoes might occur. This is valid for 7pm tomorrow evening.
Tomorrow is going to be the most exciting day in a while meteorologically speaking and I can't wait to geek out even more to it.
Matt
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