High Plains Drifter


disclaimer:  "The meteorological views/forecast thinking expressed are those solely of the author of this blog
and do not necessarily represent those of official National Weather Service forecast products,
therefore read and enjoy at your own risk and edification!"

December 8, 2007

Great Plains Winter Storm Dec 8-10 [post 6]

Filed under: General Weather & Forecasting — Mike U @ 5:43 am

Canadian Ensemble Forecast for late Monday into early Tuesday looks very impressive!    Well, I woke up fairly early this morning (still recovering from the midnight shifts), and it is extremely slick outside.  The temperature is  26 degrees and  radar still shows light freezing drizzle over Dodge City.   At any rate, the purpose of this post is to discuss and show the very interesting prediction from the Canadian Ensemble.  Very briefly, ensemble numerical prediction is necessary to try to capture the degree of uncertainty in a forecast.  The more members of an ensemble of solutions the better, because then you can run statistical analysis on the solutions to come up with means, standard deviations (assess the degree of uncertainty), and even generate composite charts to show local max/min from each members of a certain parameter.  The Canadian  model, GFS model, and ECMWF models all have their own ensemble "suite" if you will.  Only the Canadian and GFS ensemble prediction output are available on the internet.  I like the Canadian ensemble very much when it is showing a strong  "clustering" signal.  I took a look at the 72-84 hour forecast of precipitation for the Monday night-Tuesday wave that will more than likely affect western Kansas.  The 12-hr precipitation forecast is actually quite ominous!  I remember seeing such impressive QPF (quantitive precipitation forecast) signals from last year’s December 29-30th  major High Plains winter storm. (albeit not for such a long period of time like that very rare, extreme event)

Img 1For the 12-hour period ending 6am Tuesday 12/11, nearly all 20 ensemble members are showing a significant QPF "bullseye" or axis across the Central Plains.  The average maximum within the axis or bullseye from all the members is  about 25.6mm , which equals 1.00".   Averaging out all 20 members, there is a large 10mm contour (right panel in Img 1)  encompassing much of Kansas.  A mean of nearly a half inch from all the members is very significant — it’s a very strong signal from the model, and at 84-hours from a global spectral model, it’s something to really take note of.  There is substantial confidence in a major winter precipitation event across the central Plains, including Southwestern Kansas Monday night… an some of the early indications from GFS model soundings suggest that much of this may very well be freezing rain, given such impressive warm layer aloft expected to spread north atop the shallow cold near-surface layer.  Stay tuned, this could be pretty big!

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