It was almost hard to believe that Monday morning started with ice when afternoon highs soared well past expectations into the 50s and lower 60s (high of 60 at Blacksburg, 57 at Roanoke), thanks to an earlier exit of precipitation, more sunshine and a faster eroding of the cold wedge than expected . It’s symptomatic of an unusually strong surge of warm, moist air from the Gulf of Mexico that will reach southern Canada, pulled up by a strong upper-level jet stream trough digging into the central and eastern U.S. It’s more typical of something we would see in April rather than late January. Usually when such a surge of warm, moist air occurs in spring, it is swept aside by a cold front of Pacific or Canadian air mass — not a full-fledged Arctic front that may make our Thursday highs 30 degrees cooler than our Wednesday highs. In this collision of air masses, heavy rain and storms will develop, posing a significant tornado risk in the lower Mississippi River valley on Tuesday. In our region, on Wednesday, it is possible that downdrafts will bring some of the extremely strong winds to the surface, and we may see gusty winds (50 mph or greater) with a squall line during the afternoon or evening. Instability does not appear to be sufficient to support a widespread outbreak of severe weather in our region — cloud tops may not even be high enough for thunder and lightning, so whether these will truly be “thunder”storms remains somewhat in question. But because of the high-wind-gust risk, the Storm Prediction Center has placed us in a slight risk of severe weather for Wednesday. Also, we are likely to see 1+ inch of rain of rain as the cold front pushes and lifts the warm, moist Gulf air.
We’ll return to fairly typical late January/early February temperatures for several days after the frontal passage (30s-40s highs, teens-20s lows, generally), with northwesterly winds blowing over the mountains and possibly an Alberta clipper-type disturbance or two triggering a few intermittent rounds of snow showers. We’ll continue to watch next week to see if a system moving out of the West will interact with the cold air for a larger scale winter storm.