Flash flood watch 020520

Drought is not going to be a problem for parts of Virginia going into early spring.

After a January that finished basically normal in rainfall with a little more than 3 inches in the Ronaoke and New River valleys, February may easily reach that amount in its first week, with more periods of rain likely in the days and weeks to come. 

A flood watch has been posted through noon Friday, as a thick feed of Gulf of Mexico moisture, more like something we'd see in April or May, will pour into the region ahead of an approaching low-pressure system and cold front. Widespread rainfall of 2-4 inches is expected across our region, with locally heavier amounts, on top of a few tenths of rain that has already fallen in Wednesday showers. With hillsides covered by fallen leaves and no green leaves and live vegetation siphoning the water from the ground, the runoff of this rainfall may be enough for some localized small stream flooding, ponding in roadways, and possibly some flooding of large-scale rivers. Most of this rain will happen on Thursday, especially the afternoon and evening, though the watch continues into Friday morning for some margin.

While we've had much milder than normal temperatures, a "backdoor" cold front has slid southward, bringing cooler air southward across the region. This is allowing a wedge of a cooler air to develop, banked against the mountains, as rain falls into it. This is an important feature, as it will likely spare most of our region from the threat of severe storms on Thursday, with little instability to go along with strong lift, deep moisture and strong winds aloft. Such will not be the same across the Carolinas, where warmer temperatures will spike instability, and the boundary between cool and warm may enhance atmospheric spin. Some of this may make it into Southside and Central Virginia, where a better chance of severe storms with strong wind gusts or even an isolated tornado exist. There is enough lift and wind dynamics aloft that some thunder or wind gusts can't entirely be ruled out in our region, but the cool wedge will limit the threat substantially. It won't, however, sap the threat of heavy rain causing thunder.

A cold front will push through early Friday with gusty westerly to northwesterly winds bringing in colder air. This will be more akin to a spring cold front, taking us back to 30s and 40s temperatures, rather than an Arctic front, as most of that air remains bottled up in the far northern latitudes behind a polar vortex that is approaching the strongest level on record. Some snow showers may blow across the mountains over the weekend, and a disturbance approaching Saturday may enhance the snow showers some. Do not be surprised to see snowflakes in the air, but widespread accumulations are very unlikely.

Speaking of snow, many locations in a strip across west Texas -- all the way to Mexico border -- north through Oklahoma into the Midwest and Great Lakes got 3-6 inches of snow on Wednesday, with some locally heavier amounts.  Places like Abilene and Midland, Texas, are now running ahead of the Roanoke area in 2019-20 snowfall. With no big punches of Arctic air to work with, but some colder air bleeding down from Canada from time to time, snow developing behind large-scale storm systems appears to be the most likely way it will happen across much of the nation. 

However, it is looking more likely that high pressure ridging over the Southeast will bump these storms well to our west and northwest, with mostly warmer than normal temperatures for our region most if not all of this month, with repeated wet weather episodes. While a quirky wet snow behind a system like Texas got can't entirely be ruled out, it is absolutely looking like it will be a no-show this winter for our region.

Will it traipse in late for the party again in March? That may be a very bad thing where fruit trees start to bud in warm February temperatures to come. But somehow, deep down, it feels right that there will be some weird cold spell and/or snow event once we're all ready to be over a no-show winter. Warm or cold, at least it doesn't look like we'll be dry going into spring, but hopefully not overly saturated.

Contact Kevin Myatt at kevin.myatt@roanoke.com. Follow him on Twitter @kevinmyattwx.


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