Ph.D. Student - Earth System Science (UC Irvine), B.Sc. - Atmospheric Sciences (Cornell University)
By: Zachary Labe , 8:30 PM GMT on December 04, 2011
Current teleconnections do not support an east coast snowstorm. The record breaking Arctic Oscillation has reached nearly +5.4 which is record highly anomaly for the month of December. The NAO is also very high and corresponds to limited blocking across the north Atlantic. The current jet stream flow is very transient and therefore limits the potential for east coast nor'easters. In fact the threat of east coast snow is diminished by nearly 50% or more in a +AO and +NAO regime.
"Current NAO and PNA Predictions"
(Courtesy of NOAA)
In this unfavorable regime, snow can still be possible in near ideal setups. Current GFS guidance has been supporting the concept for a southern stream system moving along the Middle Atlantic coast and up along the eastern seaboard. The energy is ejected from the southwest. The PV will be displaced across the Hudson Bay, which will help to funnel the cold air south along the east coast. Current GFS prognostics suggest a low pressure developing in the southeast along the remnants of the washed-out cold front. Cold air will be lacking, but H85s will generally be at or below 0C from the Mason-Dixon line on northward and generally west of I-95.
Typically in a La Nina, the southern stream remains very weak and therefore limits the potential for southern storm systems such as this possibility. But given the series of waves moving along the front, this is certainly possible.
Model guidance remains at odds with this possibility... The ECMWF supports a relatively similar H5 prognostic, but instead holds back the S/W energy and allows for a flatter wave traversing across the central Middle Atlantic. Although recent antecedent runs have generally become more amplified. The GFS remains most amplified with a 996mb coastal runner spreading heavy snow northwest of I-95 in a very Nina-like snow/rain line setup. Other guidance such as the UKMET is generally a middle ground run between the ECMWF and GFS, while the GGEM remains even flatter heading straight out to the sea. Many GFS ensembles support a storm system in this period with remarkable consistency in the 12z run with the GEFS mean supporting the OP GFS.
12z GFS 12/04/2011 run...
The GFS run as posted above is about as perfect as a storm system can look for snow lovers in this dreaded teleconnection nightmare. Current model accuracy verification charts for days 3-6 remain very poor for both the GFS and ECMWF. But it is important to note the consistency in the GFS ensembles supporting an amplified wave in this period.
With weak blocking, it is very simple for this shortwave to take a simpler approach as a flat wave off the east coast, but there is definitely the possibility for this storm system to take a GFS-like track with inland snow.
I still am not quite sure what will happen given this setup. I actually remain a bit on the optimistic side of the forecast for snow lovers for locations northwest of I-95. I can definitely see how this wave becomes amplified enough for a similar solution and given the remarkable ensemble consistency, I believe this period needs to be monitored. Given the lack of boundary layer cold air, it is likely this will not be a snow threat for I-95 south of New England. I will have a new blog Tuesday morning...
"Local Harrisburg Radar"
(Courtesy of WGAL)
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