Friday, December 13, 2013

Final Call for 12/14 Storm

12z runs are in and there haven't been any significant changes to the forecast. The latest wrf-nmm (posted below) continues to paint a wintry scenario for much of western VA as we head into the overnight hours into tomorrow. It did relatively well depicting the last 2 events earlier this week.
One of the toughest parts of this storm will be pinpointing where the early morning overrunning band of precipitation sets up. Looking at the latest HRRR, it appears that this will likely setup somewhere north of Lynchburg-with better chances as you head north into the Shenandoah Valley. It will be from this band that I expect north-western areas of Virginia to pick up their most substantial snowfall since it will be during the early morning hours when the sun has yet to take effect and upper level temperatures are still well below freezing.
After looking at this afternoon's data, it's looking more and more likely that some areas of the Shenandoah Valley (especially the northern half) will stay wintry through the entire event. Snow pack across some of this area will aid in locking in the colder air. With that being said, I haven't increased amounts due to the fact that this same area will likely be dry slotted pretty quickly in the afternoon as energy is transferred from the primary western low to the secondary coastal off the coast. This happens every single time there's a Miller B (type of storm involving transfer) and the transfer occurs north of our latitude. Below is a futurecast showing the dry slot working into the area by afternoon on Saturday.
This is showing up quite well with total precipitation amounts across the models. Here's the 18z nam for example..notice the driest area on the map across the mid-atlantic is in western va where this dry slot takes over early on:
With all that being said, here's my final call. Expect the higher end amounts as you increase in elevation and vice versa:

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