Written by Sebastian Harkema
On December 18th/19th, the National Weather Service (NWS) produced over 40 snow squall warnings in the northeastern portion of the United States. Snow squalls are fast moving and are extremely hazardous, as snowfall rates can exceed 1 in/hr and drastically drop the visibility to near zero. One such squall created whiteout conditions in midtown Manhattan for a short period of time and another caused a major pileup on I-80 in central Pennsylvania.
The first snow squall warning was issued at 1815 UTC on 18 Dec. 2019 near the Finger Lakes region of New York. From this point forward the NWS had numerous snow squall warnings over the next 6+ hours from Pennsylvania to Maine. Two hours after the first warning was issued, the NWS issued the first snow squall warning for New York City which provided residences with at least 10 minutes of lead time before whiteout conditions would occur. The ability to identify these snow squalls highlights the hazards that these phenomena are associated with, and could be lifesaving now and in the future.
With a temporal resolution of 10 minutes, forecasters can use our NESDIS merged snowfall rate (mSFR; Meng et al. 2017) product to track snow squalls with the heaviest snowfall rates. SPoRT has collaborated with NESDIS to transition this experimental product to the NWS forecast offices. Figure 1 (above) highlights the mSFR product from 18 Dec. 2019 at 1300 UTC to 19 Dec. 2019 at 0250 UTC, with NWS snow squall warnings popping up in light blue. Throughout the event, there is good spatial and temporal correlation between the warnings and regions of heavier snowfall rates. At 2100 UTC, the mSFR product indicates snowfall rates at or above 1.5 in/hr around New York City (Fig. 2; below). Around this time, numerous videos were produced showing the visibility dropping drastically in a short period of time.
Additionally, something interesting shows up in the mSFR product data over New Hampshire. A snow squall warning was issued at 2318 UTC for central New Hampshire with the squall associated with snowfall rates exceeding 2 in/hr (Fig. 3; below). Over the next 60 minutes, it appears as though the snow squall “bows out” and quickly dissipates just as the snow squall warning expired at 0015 UTC on 19 Dec. 2019. Again, this demonstrates the benefit of the mSFR product, which can be used in tandem with other methods and/or observations to identify mesoscale snow squalls.
With meteorological winter officially starting on Dec. 1st, we are likely to see numerous snow squall events in the coming months. Be aware and stay safe, especially if you’re caught on the road, when one of these snow squalls moves through. The mSFR product enhances situational awareness for many winter weather scenarios including the ability to track these mesoscale snow squalls. See the JPSS Quick Guide and a past JPSS Science Seminar for more product information.
Meng, H., Dong, J., Ferraro, R., Yan, B., Zhao, L., Kongoli, C., Wang, N.‐Y., and Zavodsky, B. (2017), A 1DVAR‐based snowfall rate retrieval algorithm for passive microwave radiometers, J. Geophys. Res. Atmos., 122, 6520– 6540, doi:10.1002/2016JD026325.