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On the morning of February 20th, an expansive area of strong (~1048 mb) high pressure located from the Rockies to the Midwest was slowly building to the southeast. Weak low pressure was developing along a frontal boundary draped from the Gulf coast to just off the Atlantic coast of FL/GA. Aloft, a northern stream upper level shortwave trough was diving from the northern Great Lakes to the Ohio Valley, while a series of fast-moving southern stream upper disturbances in W-WSW (zonal) flow aloft were moving from the southern Plains to VA and the Carolinas. The upper shortwave tracked from the OH Valley to VA/NC from the afternoon of 2/20 to the early morning of 2/21 while the surface low slowly intensified as it tracked to the northeast (well offshore of the Carolina coast).

Temperatures were mainly in the low-mid 30s across much of the area with an overcast mid-high cloud deck Thursday morning. However, it was quite dry below 10000 ft. While regional radar mosaic showed precipitation overspreading the area by midday-early afternoon off the GA/SC coast, nothing (save for a few sprinkles) was reaching the ground. In fact, it had warmed into the low 40s across much of the area by 1-2 PM with dew points in the 20s. This resulted in wet-bulb temperatures in the mid to upper 30s across southern VA/NE NC, with low-mid 30s across the northwest half of the CWA. However, the atmospheric column over southern VA/NE NC quickly saturated from the top down during the 2-3 PM timeframe. Temperatures quickly dropped into the 32-36F range (a couple degrees below the wet-bulb). This was likely due to latent cooling as falling snow melted/sublimated as the column first saturated. Precipitation quickly changed to snow by 3-5 PM across most interior sections of SE VA/NE NC. Even by 5 PM, the low-levels remained too dry for precipitation to reach the ground northwest of a Farmville-Petersburg-Salisbury (MD) line. Snow continued to fall for the next several hours across interior SE VA/NE NC. Snow began from the Richmond metro to the VA Eastern Shore at 5-6 PM  (where temperatures quickly fell to 31-33°F) before ending a few hours later.  Precipitation eventually changed to mostly snow in areas near the coast by 7-9 PM, but temperatures remained in the 34-36°F range for the majority of the night in areas very close to the coast (due to strong NNE flow off the 45°F water). See the "Observations" section for more detailed surface obs during selected hours of the event (which showed the warmer air coming off the water from the NNE). These slightly warmer temperatures prevented any appreciable accumulations near the immediate coast. The snow ended from northwest to southeast from the late evening on 2/20 to the early morning hours on 2/21. Snowfall amounts were generally 1-2" from the southern Richmond metro to the VA Eastern Shore, with 2-5" over interior S/SE VA and NE NC. Amounts decreased closer to the coast, with generally less than 1" in areas near the immediate shoreline of the bay/ocean.

Despite the relatively long duration of the snow across parts of the area, there was not a single observation of heavy snow across the area. In fact, rates were largely 0.5-0.75" an hour or less throughout the entire event. Some banding associated with a WSW-ENE oriented band of 800-700 mb frontogenesis was evident on radar across SE VA during the mid afternoon-early evening. However, radar echoes diminished slightly in intensity after 7 PM, with mainly light snow observed after 6-7 PM. However, since the sun had set, the worst road conditions occurred after 6-7 PM as the wet snow started to stick to some roads. RAP/NAM analysis did show that the main band of frontogenesis (mainly from 800-700 mb) was located below the dendritic growth zone. In addition, soundings from SE VA showed some steeper lapse rates during the mid-late afternoon in the 650-500 mb layer, where there was perhaps some conditional/slantwise instability in the DGZ during the late afternoon-early evening (when radar echoes were most intense). However, this signature disappeared by 7 PM. See the "Environment" section for more details.

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