UPDATE 8:15 AM, 4/11: Fire risk by day, freeze risk by night as dry, cool Canadian air mass tightens grip on SW Virginia
UPDATE 8:15 AM, 4/11: Let’s just roll this over a day, except it will be considerably cooler today (50s for highs, some 40s), just a little less windy (though still windy and dry enough for high fire danger) and likely even colder by Thursday morning, with freezing temperatures over a much wider area (winds and clouds held temperatures a little above freezing in most of Southwest Virginia overnight) and a frost threat if winds die down in time. Link here and scroll down for the latest patchwork of freeze and fire advisories. A rapid warmup is expected over the weekend with highs in the 80s by Sunday through Tuesday. END UPDATE
UPDATE 7:45 AM, 4/10: The freeze watch has been updated to a freeze warning for early Wednesday generally along and west of the Blue Ridge, including the Roanoke and New River Valleys. I added an inset of this unusually colorful National Weather Service map splitting the region between blue for the freeze warning and red for the red flag warning, mainly because it is interesting. However, the map linked here gives a little bit more accurate view, showing the purple region in the middle where fire and freeze threats overlap. END UPDATE
Red flag warnings for fire danger and freeze watches overlap across Southwest Virginia. It seems very odd at first glance, but really, it has the same root cause: A dry, cool, Canadian air mass being shoved into our region by the circulation of high pressure to the west and low pressure to the northeast. Tuesday is again expected to be a breezy to windy day as the strongest in a succession of dry cold fronts — mostly dry, in this case, as I’ll explain below — pushes through. This is the front that will bring the coldest weather of this April cool snap, with near-freezing low temperatures possible Wednesday through Friday mornings, and highs that may not reach 60 on a couple of those days. On Tuesday, it will add more wind to a very dry situation in the air and on the ground, putting the region in critical fire risk according to the Storm Prediction Center (the same folks who issue tornado watches, in case you wondered). An existing large fire in Craig and Alleghany counties will likely continue, and new fires could quickly get out of control anywhere they are started. That’s why the red flag warning has been renewed in much of the area for Tuesday afternoon and early evening — the warmer part of the day has the lowest humidity with greatest difference between temperature and dew point, and winds will pick up a bit during this time as well. Wednesday may provide another period of at least somewhat heightened fire danger, but after that, winds will diminish. That will reduce the fire-spreading threat but may lead to more widespread frost and colder temperatures by Thursday and Friday mornings.
Northwest wind flow behind Tuesday afternoon’s cold front may trigger some light showers in eastern West Virginia and perhaps the far western rim of Virginia as moisture is squeezed out as the winds blow over the slopes of the Appalachians. By early Wednesday, some of what is showering may be snowflakes. A disturbance passing through Wednesday night may be enough to trigger ground-whitening snow in the higher elevations of eastern West Virginia, and perhaps a few flakes may drift into higher elevations across the state line in Virginia, too. Moisture is scarce, though, so amounts will be very light, with no more than an inch expected. Downslope wind flow should dry up any rain or snow showers before they can get into the Roanoke and New River valleys.
By the weekend, a rather sharp warming and gradual moistening trend will begin as high pressure shifts off the East Coast and turns our prevailing winds more to the south and southwest. 80 degrees is possible by Sunday or Monday.