Storm Potential Update: It is very early in the winter storm forecast game. The two main NWS models have trended toward an axis of moderate snowfall along a Des Moines to Waterloo axis tapering off quickly north of a Carroll-Ft.Dodge-Mason City Line. The Baron 15km in-house run is just a few miles south of this solution but close enough at this point and has shown good consistency this winter. Heres what to consider now: 1. Probability of 3 inches of snow or more is increasing with an axis of 5+ possible. 2.There could be a period early afternoon of enhanced snowfall and another after dark for a couple hours. 3.Strong winds are likely Saturday evening, so continued light snow and blowing will result in 1 mile or less visibility. 4. The system has not yet come out of the mountains in the southwest US and must reform its structure, and until it does, it will be poorly sampled so variation in track of 60 miles or more between now and tomorrow afternoon are likely. 5. An approaching Arctic front Saturday night may help shunt the system south, in fact one model run (Adonis/Weather Central) has no snow for Des Moines...but if the timing of the SW Low and the fronts arrival are more coincident, we may see a period of phasing which would intensity snowfall amounts where that occurs. Models have been pointing to banding for the past 24 hours. 6. Temperatures near 32 will keep snowfall ratios around 10:1-12:1 limiting accumulations we would see if temps were in the 20s. 7. At this point, prepare for the potential of adverse winter weather, especially after noon on Saturday, but realize the forecast tonight and tomorrow evening will increase in accuracy considerably. 8. We have a saying here the past two decades... Dont pull the trigger (warnings, etc) until you can see the whites of its (the storm systems) eyes. That means when the system makes it out of the mountains and we see what happens in western TX/OK etc. That will be tomorrow morning.
Posted on: Thu, 01 Jan 2015 22:28:00 +0000
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