PHOTO OF STORM MOVING OVER DOWNTOWN ROANOKE — ESTIMATED 45 MPH WIND GUSTS

LATEST VIEW OF SOUTHWEST VIRGINIA RADAR

While the greatest threat for severe weather and greatest risk for widespread heavy rain will pass well northwest of our region, a cluster of showers and storms with some heavy rain has developed along the I-77 and I-81 corridors in Southwest Virginia and is moving northeast through the New River Valley this evening. The heaviest activity is likely to be primarily west of I-81, but some of it may slip eastward into the areas along the Blue Ridge and into the Roanoke Valley as well. This is being caused by an upper-level impulse slipping northeastward through West Virginia. We’re catching the southern fringe of its influence, but that could be enough for some localized flooding with heavier downpours this evening. A localized severe wind gust can’t be ruled out entirely, either. There could be additional rounds of showers and storms overnight and into Saturday before a cold front clears the region by evening. Sunday still looks to be somewhat cool (60s highs, 40s lows) but mostly clear day for Mother’s Day, and we could be dealing with some frost and possibly freezing temperatures, especially  west of Roanoke, by Monday and Tuesday mornings. And then it could be 80 again by Wednesday afternoon. Jump on the spring roller-coaster, with a few rumbles and some splashes along the track this evening.

Roanoke recorded its first 80-degree high of May on Thursday. 2009 is the only other time in the last decade it took 9 days in May to reach 80 degrees. We may see another 80 in Roanoke, and 70s to the west (it was 74 Thursday in Blacksburg) on Friday. A cold front is approaching from the west, and will arrive by late Saturday (at left). There could be some showers and storms by Friday evening, more likely during the day on Saturday. It looks like neither a widespread heavy rain event or a ballistic severe weather episode, though some locally heavy rain and severe storms (58+ mph wind gusts, 1-inch or larger hail) are possible with warmth and some moisture streaming ahead of the front. Fronts from the west not supported by low-pressure systems moving from near the Gulf to provide more moisture and southeasterly upslope wind flow often leave us with weaker showers and storms, because of the  mountains’ effects of shortening updrafts and drying downslope wind flow. But the odds at this point do favor us getting wet on Saturday, with some rumbles of thunder. It should pass quickly, though, and leave behind a gorgeous Sunday for Mother’s Day, with lots of sunshine and mild temperatures rising into the mid 60s to lower 70s.

We will see two cold mornings on Monday and Tuesday, with some range in guidance about just how cold. The upper end would suggest mid 30s to low 40s lows; some of the lower guidance would lead to the latest freeze on record at Roanoke with widespread mid 20s to low 30s. We’ll take a closer look at the frost/freeze potential over the weekend as we move closer in time. The middle to latter part of next week could see quite the opposite, with some highs in the 80s possible.

We’ve been talking about this cut-off low since before I took my 3-day absence a week ago, so I’m quite ready to move on — and after 3 days of cool rainy days I’m sure most of you are too. Looks like we get to do that on Thursday, as it finally pushes northeastward away from us. The remaining residual effect may be some scattered afternoon showers and storms as highs push above 70, boiling up some of the moisture, plus any weak disturbances or boundaries that can rotate around the backside of the low. The Weather Prediction Center is showing very minimal amounts of rain for the next 24 hours. We likely get three consecutive days of highs in the 70s after six days in a row when it has failed to reach 70. A cold front pushes in Saturday, but it looks likes more like our typical spring cold front from the northwest, with a quick shot of showers and storms Friday night and/or Saturday rather than anything like the marathon rain we just experienced.

I’m going to go ahead and post this graphic — Tuesday morning’s projected lows on the 12Z GFS (courtesy Allan Huffman’s RaleighWx forecast models page) — even though it’s still a bit far out to get specific about this. The GFS has been consistent in showing lows dipping below freezing west of Roanoke and very near freezing to the east on Tuesday morning (and almost as cold on Monday morning). Behind this weekend’s cold front, high pressure may eventually settle right on top of us, which could lead to a clear, calm night or two in which radiational cooling will be maximized. The 32 on the graphic is very close to Roanoke’s position — a freezing temperature on May 14 would set a record for latest freeze if it occurred, the standing record being May 11, 1966 (nearly happened May 22, 2003, when it dropped to 33).  A freeze occurred as late as June 11 in 1972 at Blacksburg, but the record low for May 14 is only 31, set in 1996. Next week will bring drier weather, so temperatures may shoot up from these cold morning lows well into the 60s and 70s in the afternoon. While it may not end up quite as cold as this model is showing, it’s important for us to keep this potential freeze/frost situation in mind because of its potential disruptive impact on gardening and agriculture throughout the region.

UPDATE 4 PM: The flood watch has been lifted for Southwest Virginia. Some flood warnings remain in effect for local rivers, such as James River at Buchanan in Botetourt County. END UPDATE

FLOOD WATCH RE-ISSUED FOR MOST OF WESTERN VIRGINIA THROUGH THIS EVENING

A large area of moderate to locally heavy rain is moving southeast from West Virginia into Southwest Virginia. That’s right, I said southeast — after two days of odd east to west/southeast to northwest motion on rain and storms we’ve returned to a “regular” direction of movement, because we’re now behind the low, centered just north of us. This will add to rain totals and may exacerbate flooding or at least slow runoff in some areas still suffering it. (Latest information on rivers/creeks linked here.) Rain will obviously be more widespread in Southwest Virginia than earlier thought and likely with heavier amounts than previously anticipated (more than a half inch for most, an inch plus for some.) The system is continuing to slowly unwind and drift northeast, though, and will probably be (mostly) out of our hair by tomorrow.   Check out local radar for the latest. 

TODAY’S WEATHER JOURNAL COLUMN: Cold, snow dip far south in May

WEATHER JOURNAL COLUMN: Cold, snow penetrate deep to the south this May.

UPDATE: 9 AM, 5/8: A large area of moderate to locally heavy rain is moving southeast from West Virginia into Southwest Virginia. That’s right, I said southeast — after two days of odd east to west/southeast to northwest motion on rain and storms we’ve returned to a “regular” direction of movement, because we’re now behind the low, now centered just north of us. This will add to rain totals and may exacerbate flooding or at least slow runoff in some areas still suffering it. Rain will obviously be more widespread in Southwest Virginia than earlier thought and likely with heavier amounts (more than a half inch), at least for some. The system is continuing to slowly unwind and drift northeast, though, and will probably be out of our hair by tomorrow.   Check out local radar for the latest. END UPDATE

Cut-off upper lows die slowly. Each day, this one is becoming just a little less organized, and rainfall is becoming more sporadic and diurnal — or connected more and more to daytime heating rather than remaining organized through the night. That doesn’t mean it can’t rain at night — some showers will be ongoing at almost all hours — and it certainly doesn’t mean there won’t be some heavy rain, though it’s getting more and more localized. But just as Tuesday’s rainfall spinning around the upper low tended to be more patchy than Monday’s, Wednesday’s will likely be even a little more sporadic. The North American Model simulated radar for Wednesday afternoon at left shows a fair amount of showers, storms and rain bands blowing up with daytime heating (you can see the swirl of the upper low, expected to be centered over Virginia, sliding a bit northeast from its North Carolina position much of today.) The Weather Prediction Center projects most of the area to get a quarter to a half inch in the 24 hours through Wednesday evening – more likely, this will be an averaged-out amount rather than evenly brushed, with some spots getting more (a couple of inches would not be out of the question in a localized downour) and many getting less. The cut-off low had a cold enough center on Tuesday for some snow to reach the surface above 6,000 feet in the western North Carolina mountains, and for hail to develop in storms that typically wouldn’t be tall enough to support hail this time of year. Because of the presence of this cold air aloft, hail will be a possibility in some of the stronger storms on Wednesday.

By Thursday, the cut-off low will finally become not so cut off, pulled north and east away from us. That day could easily end up being sunny and quite warm (70s) with only minimal chances of showers and storms with some residual moisture and influence from the departing storm. A weekend cold front will bring the next organized chance of showers and thunderstorms Friday and Saturday — the kind that will move west to east, not this weird east to west we’ve been watching on radar the last couple of days. Early next week there may be a couple of frosty mornings — keep that in mind for outdoor vegetation.

SEVERAL FLOOD WARNINGS ISSUED AS STREAMS/RIVERS RISE FROM RUNOFF OF MONDAY’S RAINFALL; PARTS OF NEW AND ROANOKE RIVERS WILL REACH OR EXCEED FLOOD STAGE; FLOOD WATCH CONTINUES THROUGH TUESDAY NIGHT.

We are not done with rain yet from the cutoff upper-low that continues to spin in place roughly over Chattanooga, Tennessee. I do think most locations in Southwest Virginia have seen at least two-thirds of the total rainfall they’ll get through Wednesday, when the low finally wiggles eastward or northeastward and then gets tugged northward away from our region. But the upper-low will continue to spin some spokes of energy around, and tug in additional moisture off the Atlantic, for a few more rain bands and maybe even a few thunderstorms that could add to rain totals that have generally run 1 to 3 inches with some locally heavier amounts. Overnight and early Tuesday, showers and storms in North Carolina, some of which have been severe with some large hail, may connect and drift northward for rain in at least some of our region. Additional bands of rain and a few thunderstorms may recharge during the day Tuesday — the Weather Prediction Center shows much of the area getting at least a quarter to half inch of rain (dark green color in map at left) with a few spots of more (dark blue)  in the 6 hours from 8 a.m. to 2 p.m. on Tuesday. The concern overnight will be continued runoff from rain that has already occurred, plus any additional rain, raising creeks and rivers to near bank full or in some cases slightly over their banks. Barring an additional infusion of much heavier rain than expected, this does not appear as if it will be a major flooding episode, but beware that some lower elevations near creeks and rivers may become covered in water. As the National Weather Service regularly tells drivers who face water covering the road: “Turn around, don’t drown. “

UPDATE 9PM: SEVERAL FLOOD WARNINGS OUT AS STREAMS/CREEKS/RIVERS RISE FROM RUNOFF OF MONDAY’S RAIN; FLOOD WATCH CONTINUES THROUGH TUESDAY NIGHT 

Bullseye, Southwest Virginia. That’s what the Weather Prediction Center is showing for rainfall over the next 3 days, with the red colors indicating 3+ inches of rain with some localized spots of 4+. This will be the result of a slow-moving upper-level low, now making its way through northern Alabama and Georgia. The cold core of the upper low is no longer supporting snowfall as it did, unprecedented for May,  in the Ozarks of Arkansas and Missouri on Friday and Saturday morning, but has been supporting some hail in storm cells that wouldn’t typically be hail producers, as the freezing levels are unusually low over the Deep South. The counterclockwise flow of this low has already begun pulling thick moisture into our region off the western Atlantic — that was the curtain of low clouds and drizzle that moved in during the afternoon after a morning that had some sunshine. As this Atlantic moisture continues to be pulled in by the slow-moving low tracking south of us, the moist flow up the higher terrain and periodic disturbances rotating around the low will cause bands of rain to develop and move through. Some locations in northwest North Carolina have already topped 2 inches from periodic rain band through the day on Sunday. Rain looks to be showery on this Sunday evening with mostly light amounts in most of Southwest Virginia, but some heavier bands are likely to develop Monday and Tuesday, before the low moves to our southeast and eventually turns northeastward away from us. Rainfall amounts of 2+ inches will be capable of causing some streams and rivers to overflow, and 4+ inches may cause more serious flooding for some. It will just be a matter of monitoring how the bands develop and move the next couple of days to determine just how bad the flooding threat will be and where it will be the worst.

Temperatures will continue to be unseasonably cool. Roanoke and Blacksburg were 16 and 19 degrees cooler than normal with highs of 57 and 50, respectively, Sunday.  With rain and easterly wind flow around the low, temperatures will remain similar overnight and through the day Monday, and likely much of Tuesday too. That will mean some extraordinarily chilly 40s in many higher elevations (the blue colors on the NOAA map at left; some of the other numbers may be a bit generous). When the upper-level low pulls out by late week, there is no cold air mass behind it, so we may see a few days of seasonably warm (or even slightly warmer than normal) temperatures before another cold front moves through during the weekend or early next week.

Check on where the rain is now with the Weather Journal’s radar view

UPDATE 4 PM, 5/5: FLOOD WATCH EXPANDED TO INCLUDE ALL OF ROANOKE/NEW RIVER VALLEYS WESTWARD/SOUTHWESTWARD ALONG BLUE RIDGE, I-81 AND I-77 CORRIDORS — Widespread 2-4 inches locally 4+ projected through Wednesday evening — Heaviest rain likely Monday and Tuesday. END UPDAATE

UPDATE 7:45 AM: Most forecast guidance this morning suggests the main area of rainfall will not arrive in the Roanoke and New River valleys until late in the afternoon or perhaps even this evening. It will slowly advance through the area west of Interstate 77 today. The heaviest rain is not expected until Monday and early Tuesday. END UPDATE

The swirl centered over Arkansas on Saturday evening is plainly visible in this water vapor satellite shot, with the bright bands of moisture streaming around and spiraling toward the cold center. This is the cut-off upper-level low that is starting to edge eastward, with all the speed of a snail in molasses. This constant spin to our west for the next couple of days will mean a consistent flow of moisture off the western Atlantic into the higher terrain of the Appalachians. Bands of rain now crossing Georgia, Tennessee and Kentucky — just edging into far southwest Virginia late on this Saturday night as I type this — will ever so gradually edge eastward. It’s difficult to tell exactly when the rain will start at any given location, but the Roanoke and New River valleys may get in some (or maybe most) Sunday daytime hours dry or with just a few showers before the bulk of the rain arrives. Once it arrives, though, it will rain intermittently for a couple or three days, and some of those amounts could be heavy, especially from Sunday night through Tuesday morning. Projections of rainfall are generally in the 1 to 4 inch range for our region. The Blue Ridge will provide the greatest lift for the wet southeasterly breezes, and that is where a flood watch has been issued through Tuesday morning, for Roanoke, Montgomery, Franklin, Floyd, Carroll, Patrick and Grayson counties, with some localized 4+ amounts possible, especially toward the North Carolina border. Though accumulating snow fell as far south as northwest Arkansas underneath the chilly swirl, it appears unlikely that this will occur as the low moves eastward — the cold center of trapped Canadian air is slowly warming, and moist southeasterly breezes off the warm ocean waters are likely to keep temperatures and dew points aloft too warm for snow even at the highest elevations. If there is any at all, it would probably occur at 5,000+ elevations beneath the upper-level swirl late Monday or Tuesday. High temperatures, though, will be well below normal with highs on Sunday and Monday possibly not getting out of the 50s in most Southwest Virginia locations, depending on when the rain starts.

Once this low finally lollygags to the East Coast and then possibly gets caught by the jet stream and pulled northeastward, we will probably get a few days of warmer, drier weather.

FLOOD WATCH ISSUED SUNDAY NIGHT-MONDAY NIGHT ALONG BLUE RIDGE ROANOKE AND SOUTHWEST

This is the traffic jam of highs and lows over and near North America, as depicted for Sunday night by Friday’s 0Z European model (courtesy Allen Huffman’s RaleighWx website — with the H’s and L’s drawn in by me.)  The L over the circles in the Southeast U.S. is the much talked-about “cutoff low” that will drift ever-so slowly eastward from its position over Arkansas and Missouri tonight (where it is STILL dropping ridiculously late snowfall in the Ozarks, up to 5 inches in extreme northwest Arkansas on Friday, the latest on record for the whole state). Because it can’t go very far east or northeast against the high pressure systems in the Northeast U.S. and in the western Atlantic, which are in turn stuck behind low farther east over the Atlantic, it is going to spin moisture against the Appalachians for 3 to 5 days, starting Sunday. We may not see rain continuously, but rather in several bands circulated around the low as it moves east, and then perhaps finally northeast as the northern branch of the jet stream finally catches it about the middle of next week. As it stands Friday evening, it appears the bullseye of heaviest rain will be south of us, in the Smokies of North Carolina/Tennessee southward toward northern Georgia — but 2+ inches of rain may still occur in Southwest Virginia, especially along the Blue Ridge south of Roanoke. Rather than torrential downpours like we get with a tropical system, this is more likely to be a long-term moderate rain event with some heavier periods. With the ground relatively moist from about 3 1/2 of frequent rain and snow, that could pose some risk of flooding for streams and rivers early to mid next week. As the low finally eases by, we’ll go from rain bands to more showery stuff, before it finally comes to an end about Thursday or so, the timing of the end still uncertain.

Saturday still looks pretty decent for outdoor events, such as the Strawberry Festival and Chili Cook-off in downtown Roanoke, though easterly breezes may seem a bit nippy with highs probably not getting out of the 50s and 60s in most locations. No pouring rain is expected, and probably no precipitation at all beyond maybe some morning drizzle along the Blue Ridge.

It’s been an oddly cold and snowy spring in much of the U.S., but you might be surprised to learn that the warm spurts edged out the cold periods just enough that Roanoke and Blacksburg each averaged 1.4 degrees above normal in temperature for the month of April. Essentially, April averaged to a near-normal month, with rainfall within a half-inch of normal at Roanoke and within 0.14 inch at Blacksburg. Because of April 4, snowfall was third heaviest on record for April since 1952 at Blacksburg, and fifth heaviest at Roanoke since 1912. Yet, Roanoke also had its eighth earliest 90-degree day on April 10. You can click here for the full April climate reports on Roanoke and Blacksburg.

A strong upper level low in the process of “cutting off,” or becoming separated from the jet stream with a bubble of cold air aloft in its doughnut hole, is continuing to deliver highly abnormal and in some cases historic early May snowfall to several states in the central U.S. Early reports indicate that snowfall of 10-18 inches has set new state snowfall records for May in Iowa, Wisconsin and Minnesota. (Check out this time-lapse video of 15 inches of snow at Owatonna, Minn.) Tulsa, Okla., reported its latest snowflakes on record Thursday, Kansas City had its first May snowfall since 1909, Omaha had its deepest May snow ever at 3 inches and a winter weather advisory was issued for four counties in northwest Arkansas for the first time ever in that state during May with overnight/early morning sleet/snow mix expected. Record cold will also follow, with freeze warnings deep into Texas. Meanwhile, as is so often the case, extreme warmth and dryness is leading to fires on the West Coast. Our concern with this cutoff low is likely to be a prolonged period of rain, some of it heavy, early next week, as the low slowly drifts eastward and southeast winds rotating around it with counterclockwise circulation sweep moisture against the Appalachians for two days or possibly more. Early projections suggest 1-3 inches of rain, possibly more, will be a good bet, especially in the period from Sunday evening through Tuesday. Flooding may become a concern if locally heavier amounts develop — especially along the eastern flank of the Blue Ridge, where upslope wind flow will particularly enhance the rainfall. While record cold and widespread snow are not expected, the low will bring with it unseasonably cool weather with highs possibly not getting out of the 50s on a couple of days. The cloudy, cool, damp weather will not be in a hurry to leave, as the low will probably linger until late next week with periods of showers after the heaviest rain has pushed eastward.

Other than it being somewhat cool (40s lows, 60s highs) with easterly winds continuing to bank against the mountains, along with some morning fog and patchy drizzle, Friday and Saturday both look to be decently dry days, though mostly cloudy.  Some of Sunday may be salvageable, too. Take advantage of them if you have outdoor plans, for work or fun. There will be rainy days afterward.