UPDATE 11:45 PM, 4/18: Significant rainfall continuing today; an even bigger soaking rain likely by weekend
UPDATE 10:45 AM, 4/18: Many locations in Southwest Virginia, and farther north into mountain areas suffering wildfires, have already seen rainfall amounts of more than a half-inch (dark blue colors on this radar map) with rain continuing to fall on this Wednesday (current radar linked here). Some locations, especially along the North Carolina border in Grayson and Carroll counties, have seen more than 1 inch, more than 2 in some cases. The map I have posted at left shows the potential for 2-3 inches of rain areawide — and it has absolutely nothing to do with today! This is the newest Hydrometeorological Prediction Center rainfall projection map for the weekend (8 a.m. Saturday to 8 a.m. Sunday) in conjunction with a major eastern U.S. storm system. Today’s rain is substantial and very much needed, but it remains but a preliminary act to what is likely to be a weekend soaker — though one that still appears likely to occur mostly after Saturday morning’s marathon in Roanoke, with some other weekend activities having a few dry hours during the day Saturday. END UPDATE
UPDATE 11:45 PM: Rain has been overspreading the region from south to north through the evening, and this will continue overnight. Some locations near the North Carolina border have already got over an inch of rain, but dry air has stymied the rainfall farther north. The atmosphere will continue to saturate more in the overnight and early morning hours. Rain falling through dry air will also cool many areas into the upper 40s and low 50s, and temperatures will struggle to rise on Wednesday with rain continuing. END UPDATE
UPDATE 9AM: Let’s take a new look at the 5-day precipitation map from this morning. Rainfall amounts through Wednesday evening have been upgraded to 1/2 to 1 inch for much of Southwest Virginia as a wave of low-pressure develops along a stalling front and throws moisture back over us. The map shows heavier 1-plus-inch rainfall developing over western Virginia in the 48-hour period ending Sunday morning, as well, with the possible strong low-pressure system we’re discussing. It appears the best shot of rain the next 36 hours or so will be Roanoke and southward, while the wildfires are mostly to the north. So count us in for 2 possible periods of substantial rainfall in the next 5-7 days or so. END UPDATE
A strong storm system and cold front in the central U.S. has been the focus of recent days, especially after Saturday’s severe weather outbreak. And that cold front will pass through Tuesday and hang up into Wednesday, providing a focus for some scattered showers and thunderstorms, and also knocking some degrees off the summerlike highs we’ve experienced Sunday and Monday (89 at Roanoke on Monday, 1 short of the April 16 record from 2002; 81 at Blacksburg, tying the 1994 record for the date). Though we may warm up close to 80 again in some places after the midweek showers, Monday was likely the last summerlike day we’ll have for many days, maybe weeks.
But for Southwest Virginia, this storm system may be upstaged by what could turn into a powerhouse spring storm for the weekend and early next week. Forecast models are converging on the development of a strong low pressure system near the Gulf Coast late this week, moving north or north-northeastward, over the weekend into early next week. If this occurs close to what is projected, our region could be in line for a soaking rain (the map linked here is only through Saturday evening), as moisture would be drawn over us from both the Gulf of Mexico and Atlantic Ocean. Severe storms would also be a possibility if the storm takes a more inland track and we end up in the “warm sector” east of the low. The low may also wrap in enough cold air for high-elevation snow on its backside. It is possible the low will move very slowly or even become so wrapped up it is pulled more to the west after it moves north of us, so this could be a prolonged episode of showers, storms, wind and eventually some unseasonably cool weather into next week. Much remains uncertain in regard to the development and timing of the weekend storm. Many in the Roanoke area will be concerned about Saturday’s third running of the Blue Ridge Marathon, which was damp 2 years and absolutely soaked a year ago. There is some indication at this time that the rain will not get going in earnest until late Saturday, so don’t write it off as another soaker just yet. The weekend rain will be very beneficial for ongoing forest fires in the mountains north and northwest of Roanoke — here is a photo I shot of smoke and “pyrocumulus” clouds from one of those fires on Roanoke’s western horizon, as seen from the Mill Mountain Star Overlook this evening.
There are some indications a cooler overall pattern may close out April and move us into May, as blocking high pressure possibly develops over Greenland and near the North Pole, features missing during most of our mild, nearly snowless (except Feb. 19) winter. The correlation between these features and the onset of cooler than normal temperatures diminishes the later on the calendar we get, as the mean jet stream position lifts northward, but it could still be enough to induce cooler weather in mid-spring. Plus, we’ve been so warm relative to normal for much of the last 5 months or so, that even just “normal” would seem cool.