Effects of Upstream Soil Moisture on NW Flow Snow Events

For those who have not been participating in the discussion group related to NW Flow Snow in the southern Appalachians, I wanted to briefly pass along a very short summary of some interesting model simulation work on the impacts of the immediate upstream boundary layer that Doug Miller at UNC-Asheville as been working on. He is expecting to have a paper published in Weather and Forecasting in the next couple of months I think. The focus is on a particular high impact event from Dec 6-8, 2010 in which upstream trajectories were NOT coming from the Great Lakes (a well-known source of moisture and latent heat flux), but rather from across the northern Plains and southern Ohio Valley. The ground not only had been fairly warm in the days leading up to the event, but also saturated with copious amount of rainfall. The gist of the model simulation work was to show how important these immediate upstream conditions were, and associated heat fluxes, to the amount of precipitation a high res WRF produced over the southern Appalachians (and the model actually did fairly well with the forecast amounts). While Doug points out that this may be tend to be a more important influence earlier in the season (when upstream ground conditions are commonly more moist and unfrozen), this season (which has been unusually warm and moist in the Ohio Valley), I think we recently saw another example of this on Jan 2-3. I’ve uploaded a couple of images that show the trajectory, soil moisture anomaly, and final snow accum map (at least for the Blacksburg CWA) to the bottom of this post.

A presentation that Doug provided back in the Fall was recorded, and is available at the following URL:

http://www.werh.noaa.gov/SSD/Rose/RecordedTraining/nwfs/doug_miller_unca.wmv

Also, some of us in the NWFS collaboration group continue to work on assessing synoptic scale patterns associated with many NWFS events over the last 5-6 years, assessing correlations with various aspects of these events, and developing composite maps for the major large scale patterns. We’ll try to share some of these results in this forum as they are available.

I you have any questions about what we’re doing within the ongoing NW Flow Snow group, which spun out of previous CSTAR research efforts, feel free to ask! You can also visit the following site for recent minutes from calls and other resources or case studies we’ve made available:

http://www.erh.noaa.gov/gsp/localdat/NWFS_discussion_group/nwfs_discussion_group.html

Steve Keighton

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