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Dangerous Heat Continues in the West; Multiple Areas of Excessive Rainfall Possible Today

Dangerous heat continues across the West with widespread Excessive Heat Warnings and Heat Advisories. The West should see relief from hazardous heat by Friday. The heat will expand into the northern Plains on Tuesday. Heavy to excessive rainfall today in the Mid-Atlantic to Carolinas, southern Rockies, and west Texas into the ArkLaTex may lead to areas of flash, urban, and stream flooding. Read More >

Overview 

An upper shortwave ejected ENE into the central High Plains the morning before the event (1/30). That shortwave continued tracking east-northeastward through the Plains during the day on the 30th. The associated strong surface low followed an east-northeast track through the Plains as well. Meanwhile, a cold Canadian airmass was in place over much of the eastern US. During the night of the 30th into the early morning hours of the 31st, the upper shortwave formed into an upper low as it continued tracking ENE as the parent surface low approached the central Appalachians. Clouds were already on the increase over the local area by early Sunday morning with temperatures at just below freezing area-wide. A leading band of snow associated with mid-level (700-500 mb) frontogenetical forcing was right at our western CWA border by 06z/1 AM on the 31st.

During the remainder of the morning on the 31st, a secondary surface low started to develop along a stalled warm front well to our south as the parent low dissipated as it approached the mountains (classic "Miller-B" setup). High pressure centered from just south of the Hudson Bay to near Burlington, VT was ridging south into the area, helping to create a cold air damming situation. A more substantial area of precipitation moved into the area from W-E between 5 and 8 AM. Thermal profiles were still cold enough for this to be all snow at the onset (even down to Norfolk/Chesapeake/VA Beach). However. strong warm air advection (especially from 925 to 700 mb) took hold during the day, and snow quickly changed to sleet, freezing rain, then rain from SSW to NNE. The snow was heaviest in the 30-60 minutes immediately preceding the transition to sleet/mixed precip. Fairly strong 850 mb frontogenesis was noted during the day on 1-31. No freezing rain was observed closer to the coast, where snow simply transitioned to sleet then rain. By late afternoon, precipitation had turned to rain in most areas, but remained freezing rain across our far NW counties (where CAD typically lasts the longest and temperatures failed to rise above freezing during the entirety of the event). In total, 1 to 2 inches of snow was common across south-central and interior SE VA, with 2-5" over the Richmond metro, and 4-6" (and some light icing) across our VA Piedmont counties. In some areas in the southern Richmond metro, this was the first accumulation of snow on roadways since December 2018.

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