Friday, March 7, 2014

March 11-14 Potentially Significant Snowstorm

As I discussed back on February 25th, we're looking at the potential for a significant winter storm in the March 11-14 timeframe, narrowed down from the original March 12-17 timeframe.

The ECMWF model's 500mb vorticity forecast for March 12th is shown above, and we see the two ingredients for our storm on this map. We see the main piece of energy as an elongated swath of positive vorticity stretching from Nevada to Missouri, with our second player dropping south on the lee side (east side) of the ridge stretching across the West Coast. We also see a piece of energy in the Gulf of Mexico which will do its part to interrupt the severe weather aspect of this storm, which is why we'll be focusing on the snowy side.

The ECMWF develops a 997 millibar low centered over southern Illinois on the morning of March 12th, with overpowering high pressure to the north suggesting we aren't likely to see any big northward shifts with this storm in the future. Model verification confirms this idea. As far as the projected storm, this 997mb low is just the elongated system, not accounting for the system dropping from Canada which will eventually phase with the aforementioned system in Missouri.

By the morning of March 13, the system is rapidly deepening in the Mid-Atlantic as the two pieces of energy have begun to phase. This means that they are combining into a single storm system, which only intensifies the snow potential for this event. From March 12th's jet stream forecast, I would expect we see the system try to push east due to a rather zonally-oriented jet stream across the United States, which isn't that favorable for the system to shoot up the coast. However, by the time it hits the coast, the jet stream is essentially laying out the red carpet for the system to go northeast and affect the Northeast.

The snow map for the ECMWF would dump amounts of upwards of 12" across much of the Northeast, including coastal regions, while laying down over 6" in Ohio and a portion of Indiana. This would all depend on phasing of these two systems, which the folks at the National Centers for Environmental Prediction (NCEP) indicate may not be so likely. They indicate that models tend to phase systems too often, when in reality, they don't end up phased. This could be one of those situations, but I guess we'll just have to wait and see.

The GFS model, on the other hand, is much less enthusiastic when compared to its European counterpart. We see both systems shown above, valid for the same timeframe as the 500mb vorticity map we looked over at the top of this post, but in the GFS' case, the layout is different. The GFS model keeps the system back in the Southwest, on a positively-tilted axis, meaning the strongest vorticity values are pointing in a southwest direction. I have a feeling the GFS might not be grasping this system correctly. The NCEP agency also states that models in general have a bias to keep storms in the Southwestern US for too long, when in reality they eject from the Southwest quicker than forecasted. This would work in favor of the ECMWF's solution. However, the GFS does not phase the two systems, which results in noticeably less snow and precipitation in general. We'll need to watch both models for this system in the next few days, as both appear to be hanging on to one bias while letting go of another one. In this case, the ECMWF may be phasing the systems too eagerly but not holding the energy back in the Southwest, while the GFS looks to be keeping the system in the Southwest but not phasing the storms.