Potential 2/1/20 Storm

Our next chance of precipitation will be as a result of a strong coastal storm.

The upper level disturbance partly responsible for a potential early February coastal storm is currently entering the Pacific Northwest United States, bringing rain to coastal areas and snow to interior parts of Washington, Oregon, Idaho, and Montana. This disturbance will slide eastward over the Rockies then move south into Texas as an area of unsettled weather with light showers. This is fueled at the upper levels by a digging trough shifting from a positive to a negative tilt as it enters the Gulf of Mexico.  Once it taps into moisture from the Gulf of Mexico, the area of low pressure will experience more rapid pressure falls, bringing heavy rain to the southeast United States. Strong positive vorticity advection (PVA) over the southeast and a strengthening subtropical jet streak will enable further strengthening. A redeveloped area of low pressure will develop off of Cape Hatteras late on Jan 31 2020 or early on Feb 1 2020.

As a strong area of PVA moves to the northeast it will interact with a northern digging trough positioned over the Great Lakes region. It is unclear whether or not these two features phase, leading to rapid surface pressure falls. The difficulty in predicting the interaction of these two features is as a result of the subtropical jet moving quickly and zonal flow south of 45N. A missed connection will result in a weaker storm, but a late or early connection has important ramifications for the west/east position of the storm as it intensifies and moves along the eastern seaboard. This, along with cold air in place will be crucial for determining precipitation types and where accumulating snow will fall. Mild air will likely be in place during the daytime, so if the northern stream and southern shortwave connection takes place such that the storm intensifies and moves across 70W/40N in the overnight hours, this would guarantee sufficient location and thermal background for accumulating snow in the New Jersey region. However, given the warm background state, it would be unlikely to experience snow ratios higher than 10:1 unless there is extreme mesoscale banding where large omega intersects the snow growth zone (-20C to -12C). These details are not close to being resolved, as this storm is 84+ hours away.

Similarly, we are not yet close to resolving the track of the low pressure. The average locations for the past 4 GEFS runs at 18Z on Feb 01 2020:
06z Jan 28 2020: 36.5N, 71W
00z Jan 28 2020: 36N, 72W
18z Jan 27 2020: 36N,73W
12z Jan 27 2020: 34N, 74W
The clear trend is for a slower and more eastward track. Still, there is substantial model spread in the most recent GEFS run. This run also highlights the potential for a track inside the 70/40 benchmark with a few members north and east of the mean:

Screenshot from 2020-01-28 10-31-54.png

It should become clearer by the 00z GEFS run on Jan 30th 2020 where this storm will track, and at that point we will dive into precipitation types and snowfall totals. The last four GFS runs have been too volatile with snowfall totals (0 to 6″) to take them seriously.

The GEFS is still simulating a blast of cold air from Alaska across much of the CONUS between 2/4 and 2/5. Because this event is controlled by a large-scale perturbation to the stratospheric polar vortex, I have high certainty about this shot of cold air. We may finally see an extended period (5 days at least) of below average temperatures.

Coupe

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