I believe no two weather events are exactly the same, but I also believe that analyzing past storms and reviewing climatology can reveal some similarities to an approaching storm. With that said, the more I look at regarding the WED/THU Mid-Atlantic winter storm, the more I am reminded of the January 25, 2000 storm - except this one seems to be a more western version of that storm. Those with an excellent memory will recall that was a big storm for areas near the Chesapeake Bay, I recall measuring 13" from that snowstorm, which to this day is the fourth biggest snowstorm I have ever witnessed. Here were the snow totals from that storm:
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| Fig. 1 - Mid-Atlantic snow totals from the 25 January 2000 snowstorm (http://www.erh.noaa.gov/lwx/Historic_Events/jan25-00-mdva.gif) |
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| Fig. 2 - A real 'Carolina Crusher' impacted central NC on 24-25 January 2000 (http://www4.ncsu.edu/~nwsfo/storage/cases/maps/accum.20000125.gif) |
What seems to be the main difference with this system is that the 850mb low tracks further inland (as depicted on today's 12z ECMWF below; Fig. 3 & 4), as opposed to just along the coast like with the January 2000 storm (Fig. 5) . If correct, the further inland track of the low will allow for snow to change to rain, thus limiting snow accumulations for southern Delmarva. It is worth noting the GFS/NAM are slightly more favorable with the track of the 850 low, and would lead to higher snow totals for a larger portion of Delmarva.
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| Fig. 3 - 12z 2/11/2014 ECMWF 850mb forecast for 7am Thursday, 2/13 (Weather Underground WunderMap). At this point, 850mb temperatures begin to rise above freezing, thus introducing warm low-level air which would begin the transition from snow to rain. |
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| Fig. 4 - 12z 2/11/2014 ECMWF 850mb forecast for 1pm Thursday, 2/13 (Weather Underground WunderMap). Low-level warm air advection has spread across all of Delmarva, with precipitation likely falling as rain east of the Chesapeake Bay. |
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| Fig. 5 - Observed 850mb analysis at 12z on 25 January 2000, depicting a coastal 850mb low moving northward along the coast, which limited the westward advancement of warmer air and thus the rain/snow line. |
As far as climatological indices go, this storm is otherwise very similar to the 25 January 2000 storm. Back in college, I researched major Delmarva snowstorms (at least 12" snow observed somewhere on Delmarva) to discover what the NAO/PNA/ENSO tendencies were. In total, I found 22 major snowstorms during a 55-year period of record from the winter of 1950-51 through the 2004-05 winter. Of those 22 storms, there was a very strong correlation with a Negative NAO (18/22 cases, 82%); slightly less strong correlation for positive PNA (14/22 cases, 64%) and a weak correlation favoring El Niño conditions (12/22 cases, 55%). Interestingly, the 25 January 2000 was one of only two major snowstorms to impact Delmarva with a combination of positive NAO, negative PNA, and La Niña conditions (the other being 24-25 February 1989). The difference being the two was the synoptic climatology classification type - the 1989 storm was a "Miller B" (essentially, a primary storm moves in from west, then secondary storm develops along coastal baroclinic zone), while the 2000 storm was a "Miller A" (essentially just one primary storm that develops over southeast/east coast and tracks northeastward along coastal baroclinic zone). So with respect to climatological indices and synoptic classification types, it is neat that the 25 January 2000 storm was unique among the 22 major snowstorms studied from 1950-2005.
It just so happens that the approaching snowstorm, a "Miller A", is also modeled during a period of positive NAO, negative PNA, and La Niña (albeit weak) conditions. Should the ECMWF be wrong in that the 850mb low has a more coastal track like the 25 January 2000 storm, it could be a very big snowstorm for much of Delmarva. However, it is hard to ignore the consistency and supreme skill score of the ECMWF. If 850mb temps really do warm to +8C, there will be a lot of rain on Thursday, for a lot of Delmarva. I can tell you from experience, once it changes over to rain, it almost never goes back to accumulating snow. It is worth noting that the SREF also has a fairly low probability of snow for the southeastern half of Delmarva after daybreak on Thursday (Fig. 6).
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| Fig. 6 - SREF probability that snow is the dominant precipitation type at 12z on Thursday, 2/13 (http://www.spc.noaa.gov/exper/sref/sref.php?run=latest&id=SREF_prob_snow_precip_01__) |
Latest SREF probabilities indicate no higher than a 30% probability of snow being the precipitation type from 12z (5am EST) onward. So how much snow falls before changing to rain?
After examining the 12z ECMWF and latest SREF guidance, it is quite apparent there will be a wide range of snow totals across Delmarva. Probably ranging from 0" snow and a lot of rain on the MD/VA beaches to closer to 12" of snow for far northwestern locations (near and north of US-301). For my hometown of Cambridge specifically, I think 2-5" of snow seems a reasonable forecast for now, before the changeover to rain. I am banking on an SREF/ECMWF blend, with the beaches receiving mainly rain, while the heaviest snowfall totals occur across central portions of Virginia and Maryland. However, an 850mb low track further east by just 50-100 miles will substantially increase snowfall totals to near a foot for back home. Oh the joys of forecasting major winter storms!
