04/13/06 DISC: Northern Plains

[Howard Robinson]

THE NWS rated the Iowa City tornado to be a F2.
Full report on all the tornados in Iowa, can be found here.
http://www.crh.noaa.gov/crnews/display_sto...d=2228&source=0

 

[Kenny Drake]

It probably feels like a major kick in the *** when a SVR watch is issued and something like last night happens. However, If you were to ask anyone tomorrow morning if there was going to be a tornado in southern Iowa most would have laughed it off completely. The fact that you caught it before initiation in southern Iowa (even if only SVR) is great. I'm not quite sure what puts spotters on alert but I'm assuming either SVR or TOR watch would. The people in Iowa City knew the tornado was coming. When something like last night happens noone can justify blaming one person. It simply just means that what we know about weather wasn't enough to foresee what happened last night. This will make an excellent case study and hopefully there is one as I will definitely be interested in it. This year has seen many good looking days across the plains by models but the DPD's have been too high in reality. I would have never have been able to foresee a tornado such as the one in Iowa City last night (4-13) with 1500m LCLs.

I think meteorologist and climatologists in general will learn a lot out of this entire year. Even now, in the middle of the year, evidence is mounting increasingly that the drought over the past few months has been a negative feedback to moisture across the plains and the models have not been picking it up. Do models even consider surface moisture (trees, etc..)? Or do they just look at the time of year and make assumptions on what the amount of moisture should be? To me this just seems odd that the numerical models wouldn't take into account something that seems so relevant. But I just realized, there are no recorded measurements on the amount of moisture from the surface... and how would one quantify it? I suppose there could be a way to quantify it from soil temp & air temp oscillations due to diurnal heating.

 

[Michael P. Morris]

Do models even consider surface moisture (trees, etc..)? Or do they just look at the time of year and make assumptions on what the amount of moisture should be? To me this just seems odd that the numerical models wouldn't take into account something that seems so relevant. But I just realized, there are no recorded measurements on the amount of moisture from the surface... and how would one quantify it? I suppose there could be a way to quantify it from soil temp & air temp oscillations due to diurnal heating. [/b]

It's both. The land-surface parameterization scheme (the Noah land surface model) currently in use by the operational NAM requires some estimate of the surface greeness fraction (which has an annual cycle) and the soil composition. However, these values are typically estimated from satellite measurements and may not be truly representative of one single point. Not everyone has direct boundary layer flux measurements like the Oklahoma Mesonet . The consistent high bias in afternoon dewpoint temperatures is also a byproduct of the Noah's physics. They do take all the surface inhomogeneities into account, but they are somewhat smoothed and the data used to initialize Noah are derived from the Eta Data Assimilation System so any errors in the EDAS or its forecasts are going to propagate ahead in time. It's not perfect but it's the best we have.