Now that Roanoke has its first 90-degree high of 2012 — coming after the National Weather Service’s  5 p.m. climate statement on Tuesday — it may waste no time going all the way into the mid 90s the next couple of days (Wednesday and Thursday) as the core of the hot high-pressure dome builds overhead.  Even Blacksburg may push 90 degrees — which would tie a record high for June 20. (Roanoke’s highs the next two days are 101, which very likely will not be challenged). You can never rule out a few afternoon storms with this kind of heat, but underneath the stagnant to sinking air of this high pressure dome, afternoon convection will be more limited than we’ve seen the first couple of days this week. Storm chances will pick up by Friday as a cold front nears the region. Forecast models are now leaning more toward a jet stream trough digging southward by early next week, which would temper the heat considerably. Still some uncertainty at that range, but for now, it looks more like the original idea of a 2- or 3-day hot spell rather than a prolonged heat wave, at least for our region.

Here’s a surprising little statistic that seems to swim upstream against the fact that the March-April-May period was the warmest spring on record for Roanoke — it still has not hit 90 degrees on any single day (high was 89 of 4 different days). And it won’t get close to that today, because of what is known as an “in-situ” wedge of cooler air. The wedge is created by persistent showery weather creating a pool of cooler air east of the spine of the Applaachians, rather then more familiar wedge pushed in by high pressure from the northeast (what we would call “cold-air damming” in winter).  Most areas won’t get out of the 60s today.

So, whenever it finally makes 90 (possibly the weekend), it will be Roanoke’s latest date for its 1st 90-degree high since at least 2004 (June 11) and if it delays much later, since 2003 (June 20).

I’m back home and recovering from an unusual and intense Virginia Tech storm chase trip. More on that later.

Three quick links for a cool early June Sunday morning in Southwest Virginia:

Spring 2012 — March, April, May on the meteorological calendar was the warmest on record at Roanoke (dating to 1912) and at Blacksburg (dating to 1952). While April and May averaged above normal in temperature, it was really the extreme March that was the key in the spring warmth record.

The National Weather Service at Blacksburg will be looking into whether or not a tornado touched down in Botetourt County on Friday, based on a photograph by Botetourt View reporter Cathy Benson.

And finally … the Virginia Tech storm chasers had a good day Saturday tagging intense thunderstorms in southeastern Colorado and the Oklahoma Panhandle. We’re expecting to leave Guymon, Oklahoma, where we’ve been four straight nights, for eastern Kansas and a possible heightened risk of supercells and perhaps a few tornadoes on Sunday. At this late hour … I’ll leave it to fellow chase trip co-leader Chris White to provide some words and pictures from our day.

The graphic linked here shows the multi-day progression of Storm Prediction Center forecasts and how the tornado outbreak aligned with it in the Plains states on Saturday. The SPC had the region outlined with a risk of severe storms 7 days in advance, covered with a moderate risk of severe storms 3 days out and a high risk 2 days out. While identifying where exactly tornadoes will touch down remains difficult until within minutes, this early notification of a high-end severe weather threat was a tremendous forecasting success for the SPC and the weather service offices in the region, and it undoubtedly contributed to the low fatality count of five deaths. Click here to see several videos of tornadoes from the outbreak both Friday and Saturday.

Roanoke’s high temperature of 86 on Sunday was the hottest so far this season, 18 degrees above the normal for April 15 and only 3 degrees below the record of 89 for the date set in 1936. Blacksburg’s high of 81 only missed the standing record by a degree, set in 2006. Monday will be a similar day of temperatures, perhaps a couple of degrees cooler with some additional clouds as moisture builds slightly. The problem for anyone wanting rain this week is that the main energy of the Plains storm will move into the Great Lakes region and into Canada, taking away the dynamics, lift and some of the moisture flow from the Gulf of Mexico that could potentially trigger more rain and storms. As a weak cold front slides into the region Tuesday, some showers and storms could develop. On Wednesday, a weak wave of low pressure moving along the front may slightly increase shower activity. But as you can tell by Sunday night’s 5-day rainfall projection from the Hydrometeorological Prediction Center, amounts in our region are expected to be meager, a quarter-inch or less in most cases. That won’t be enough to head off any developing dryness or provide serious relief for the ongoing wildfires in the higher elevations north of Roanoke. Thankfully, those fires are considered about two-thirds contained as of Sunday.

The midweek system won’t hugely drop temperatures, just pull the mercury back from the summerlike highs of Sunday and Monday. But there are growing signals of a punch of colder air with frost/freeze implications possible by the weekend or early next week. This pattern of alternating warm and cold periods is fairly typical for April. Historic “normal” temperatures in the 60s for highs and 40s for lows this time of year are really the average between up-and-down extremes, not so much an expectation of steady temperatures through the month. Unless and until low-pressure systems dig farther south toward the Gulf of Mexico, Southwest Virginia will not see much rainfall or very many severe storms.

FREEZE WATCH ISSUED EARLY SATURDAY MOST OF SOUTHWEST VIRGINIA, INCLUDING ROANOKE, NEW RIVER VALLEYS

Another interesting statistical tidbit about March 2012: It was only the second month in any year since official records began at 1912 that Roanoke averaged 10 or more degrees above normal. March’s average of 57.4 was 10.1 degrees above normal. January 1950, at 47.5 degrees, was 10.9 degrees above normal. For the record, there have been 5 months averaging 10 or more degrees below normal: December 1917, January 1918 (yes, back-to-back months), March 1960, January 1977 and February 1979.  The coldest month on record relative to normal: March 1960, with an average of 34 degrees, a whopping 13.3 degrees below normal. That might not be too surprising in a March that produced 30 inches of snow.

Since 1912, there has never been an April that has averaged cooler than the March that preceded it. I don’t think this April will, either, but next week may give it a fighting chance. Signals are growing that the bill is about to come due for the warm March with a several-days period of cooler than normal temperatures starting about the middle or latter part of next week.  A cold front that passed through Wednesday evening will help bring an installment of the cooler weather in for the late week and weekend. Highs will struggle to make 60 Thursday and Friday, with some lingering showers especially south of Roanoke, and lows may be near or even a little below freezing in many locations across Southwest Virginia by Saturday and Sunday morning. Though Easter will start chilly for sunrise services, very dry air moving in behind the front will be warmed quickly by the sun, with highs again jumping into the 70s in many locations by Sunday afternoon. A strong cold front arriving around Tuesday or Wednesday of next week will punctuate a developing shift in the weather pattern that features strong high pressure and, therefore, above-normal temperatures over the Rockies with colder air pulled into the Eastern U.S. around the high’s clockwise rotation into a deep low-pressure trough, or southerly dip in the jet stream. With the Rockies high flanked by similar low-pressure troughs both east and west, this pattern may not break down very quickly. The result is likely to be a period of below-normal temperatures, and perhaps even some downright cold weather at times.  (Normal temperatures for early/mid April are mid-upper 60s highs/low to mid 40s lows for Roanoke, and low 60s/mid-upper 30s for Blacksburg.) Certainly, some frosty mornings appear likely late next week, and a hard freeze is not out of the question on at least one morning. This does NOT appear to be a repeat of the extreme 2007 April freeze, in either intensity or duration, but considering the early growth many plants have shown in the June-like days of mid to late March, damage will be a concern if there is even a morning or two when temperatures are below freezing. There might even be a bit of snow next week, particularly as cold, northwest winds blowing upslope over the Appalachians squeeze out moisture behind the midweek front. As of now, this does not appear to be a long-term pattern change, and warmer weather may well return not long after the cool snap.

You didn’t really expect to have that March heat wave without some kind of April cold spell, did you?

It’s going to take some time to fully digest the March “heat wave” of 2012, which has not merely rearranged but absolutely demolished record books across many parts of the eastern two-thirds of the United States. Through Friday, there were already more than 7,500 new daily record highs nationally, and more than 300 new record highest temperatures for the entire month of March, centered in the Upper Midwest.

Not reflected on the links above, many locations have set records for the warmest average temperatures for March, including Roanoke and Blacksburg. A recapping of the records at those 2 sites  below:

Roanoke:
• Warmest March average temperature, 57.4 degrees; previous record, 57.2, 1921.
• Warmest March average low temperature, 46.2; previous record, 43.4, 1921.
• Third warmest March average high temperature, 68.5; standing record, 71, 1921.

Blacksburg
• Warmest March average tempreature, 51.6 degrees; previous record, 48.5, 1976
• Warmest March average low temperature, 39.3 degrees; previous record, 35.7, 1961.
• Warmest March average high temperature, 64 degrees; previous record, 63, 1976.

Also from some preliminary research, I know it is Roanoke’s warmest January-March period on record, dating to 1912. January to March averaged 47.7 degrees; the previous record was 47 degrees in January-March 1990. I’ll have some more on January-March temperatures through the century in the days ahead.

As for the weather on this Sunday, the first day of April, there is no fooling that it will be just about a picture-perfect day for racing at Martinsville Speedway or any other outdoor activities, with sunny skies and highs in the 70s. Another weak cold front arrives overnight or early Monday with a slight chance of showers or thunderstorms, the air mass behind the front being just enough to keep the first of the coming week from having runaway heat as we thought might happen a few days ago. The stronger cold front is due about Wednesday or so with possible showers and storms after three days flirting with 80 for a high. We may settle into a few days of 60s highs/30s-40s lows after that.

UPDATE 11:30 PM, 3/23: Intermittent showers are expected to continue overnight across Southwest Virginia. There is potential for strong to severe storms on a Saturday once the sun pops out when a dry slot moves in during the day, destabilizing the atmosphere with surface warming that could lead to strong updrafts into colder air aloft with the approaching upper-level low. Exactly where the biggest severe weather threat will be in the Carolinas or Virginia remains a bit in question. I’ll plan to put up a new blog post sometime Saturday morning taking a closer look at any severe threat. END UPDATAE

UPDATE 5:20 PM: Roanoke has its first record high of the March hot spell: 84 degrees, breaking the previous March 23 record of 82 set in 2007. Today’s high is 24 degrees above normal and equivalent to normal nigh for June 15. Blacksburg reached 78 for the second day in a row, again 2 degrees short of a record. Showers and thunderstorms are building in from the southwest. Some heavy rain and gusty winds are possible with the stronger storms this evening. Latest National Weather Service-Blacksburg radar linked here. END UPDATE

High temperatures on Thursday of 80 in Roanoke and 78 in Blacksburg missed daily records for March 22 by 4 and 2 degrees, respectively. Friday provides one more opportunity, with forecast highs expected to be near Roanoke’s March 23 record of 82 degrees set in 2007 and Blacksburg’s record of 80 set in 1968. It may come as a little surprise that, as warm as it’s been on a consistent basis, Roanoke has yet to set a single daily record high temperature this month (unlike Blacksburg, that has set 3). Friday may be the final chance for several days.

We finally have something significant weatherwise to talk about other than potential record highs and scattered afternoon summerlike pop-up storms. The massive, slow-moving upper-low in the central U.S. — the big pinwheel on the satellite photograph at left — will begin to affect our weather by Friday evening. Its broad circulation will pull Gulf of Mexico moisture in several bands, and that will lead to intermittent periods of rain and some thunderstorms Friday night and Saturday, lingering into Sunday as the cold upper-air pool at the center of the upper-low drifts overhead. It’s always difficult to forecast the timing and amounts of rainfall in a broad upper low like this, but national forecasters are projecting widespread amounts near an inch through Sunday evening as slow-moving bands of thick moisture are pulled through the region, with southeasterly upslope flow perhaps enhancing lift and squeezing out a little more.  The upper level low may also pull through some dry slots. It is possible one of these dry slots arrives Saturday afternoon, allowing sunshine to destabilize the atmosphere a little. Warmth, plus moisture, plus strong winds aloft created by the upper-level low may lead to a risk of severe storms with hail, strong winds and possibly even isolated tornadoes on Saturday, especially east of the Blue Ridge.  At this time, a major outbreak of severe weather is NOT expected, but anytime it’s been as warm as it has been, there tends to be a heightened risk of stronger storms.

The air following a front this low will pull through by Sunday is greatly modified, with no real Arctic connection, so temperatures will only retreat slightly behind the front. We may have a day or two — Sunday/Monday, perhaps — with highs in the 60s (low 70s if there is lots of sun) and lows in the 40s. The overall warm pattern rebounds next week, at least back to widespread 70s for highs (maybe not as many low 80s), but there continues to be  signs the core of it shifts westward and weakens somewhat, as shown in the 8 to 14-day temperature map from the Climate Prediction Center, with much of Virginia out of the red colors in the white “equal chances” of warm, cold and normal area. A westward shift in the mean position of the upper-level high-pressure ridge that has caused the prolonged March warmth may also allow its clockwise circulation to pull down a few more cold fronts into the East in the long-range — the Northeast U.S. may be at particular risk for a post-warmth freeze, with no clear indication yet that level of cold air would extend as far south as Southwest Virginia. For now, there is no signal of a major pattern change, just some indications that summer-in-March will undergo some gradual erosion and won’t hold on at full strength throughout April.

Record highs for March 22 and 23 are likely to be challenged at Roanoke and Blacksburg. We are likely to see more sunshine than Wednesday as a weak upper-level disturbance shifts southeast and high pressure becomes more entrenched. Those records for Roanoke are 84 on March 22 (set in 1938, probably will stand on Thursday), 82 on March 23 (set in 2007, good chance to be tied or broken Friday); for Blacksburg, they are 80 both days, set in 1968 for March 22 and 1966 for March 23 (upper 70s to near 80 are projected each day). Scattered showers and thunderstorms are still possible each day (though likely to be less numerous than Tuesday), so it’s still possible a random storm or outflow or clouds from one nearby could stymie the warming at either site or elsewhere in Southwest Virginia.

More showers and storms are likely over the weekend as a slow-moving cold front pushes into the warmth. The cold front will bring only slightly cooler weather for a day or two after its passing — 60s highs, 40s lows, perhaps — with the warm overall pattern continuing afterward over the central and eastern U.S. There are a few signals that the pattern may start eroding somewhat, allowing a few more cold fronts into our region the next week or two, but any erosion will be slow.

TODAY’S WEATHER JOURNAL COLUMN: Cleaning out the winter notebook, looking at the 10 least snowy “winters”  (actually includes fall and spring, too) in Roanoke history. 2011-12 is NOT among them.

The summerlike weather pattern is slated to continue through at least Friday, with highs 15 or more degrees above normal in the 70s (and some low 80s) common, lows mostly in the 50s (near the normal highs for mid to late March) and chances of thunderstorms each day as moisture and outflow boundaries hang around from the previous days’ storms (such as those Tuesday that produced several reports of large hail, mainly east of Roanoke). By the weekend, a front will push in with a more widespread chance of rain (and perhaps some more organized strong storms), but it looks like only slight cooling behind before another rebound to warm next week.

With 11 days left in the month, I am already calling this as the warmest March on record for Blacksburg. Blacksburg’s records go back to 1952, and the previous warmest March was 48.5 degrees in 1976. This March through 20 days is already averaging 48.8 degrees. Blacksburg has had 2 consecutive days when both its high and low set records for warmth (77/50 on Tuesday to set new March 20 standards). The rest of the month must average only 48 degrees for Blacksburg to set the hot March record — looking at the overall weather pattern, that seems very likely to occur.

Roanoke’s records go farther back, to 1912, so they encompass very warm Marches in 1921 (57.2) and 1945 (56.0). At 54.9 degrees, this March would already finish third if it were over, and it has more time to close in and possibly pass the two ahead of it. It needs to average 61.8 degrees over the last 11 days to take over the top spot. The last 7 days have each averaged at least 61 degrees, and it seems many similar days are yet to come. So consider Roanoke to have a very good chance of setting a record for March warmth.

UPDATE 12:30 AM, 3/20: I’ll let this ride another day. Highs in the 70s, maybe some low 80s. Scattered showers and storms possible. After hitting 78 to set a record high on Monday, Blacksburg’s record March 20 high of 75 from 1968 may also be overtaken (if early showers don’t happen to stop it). Roanoke’s record of 83 from 1945 and 1968 probably stands. END UPDATE

UPDATE 11:50 AM, 3/19: The area of showers and storms affecting much of the region this morning has mostly dissipated. With the sun popping out, widespread highs in the 70s appear likely. Afternoon heating combined with thick moisture and an upper-level impulse sliding southeast from the Ohio Valley may fire a few scattered storms during the afternoon and early evening. END UPDATE

UPDATE 8:45 AM, 3/19: We’re starting off on the damp to downright soggy side this morning. Not only have fog and low clouds settled in to much of Southwest Virginia, but an area of showers and storms with some heavy rain has been affecting much of the area north and east of Roanoke. That’s a flip from much of the past several days when the action was mostly south and west of Roanoke. Some of the cells developing on the back end of the system in West Virginia may drag through the Roanoke and New River valleys later this morning.  Click here for latest National Weather Service-Blacksburg radar.  Temperatures this morning are already near or somewhat below the normal high temperatures for mid-March in the 50s (57 at Roanoke, for example, with a normal high of 59 — and normal low of 38) so the “much warmer than normal” part is on track again despite the rain and fog END UPDATE

Wednesday’s toasty highs in the mid 70s to low 80s could have easily been the start of a long period of similar high temperatures. But the last four days, instead, have had interference from upper-level disturbances from the west, a backdoor cold front from the northeast and a weak flow of cooler, moist air off the Atlantic. The result has been hard-to-predict periods of clouds and showers and rather erratic daily high temperatures. Highs Thursday through Sunday were 58, 69, 72 and 64 at Blacksburg and 69, 73, 75 and 66 at Roanoke –  all above normal, though none of them as extreme as they could have been. The leftover moisture from the past few days, some more disturbances moving in from the Ohio Valley and a persistent weak low hanging around the Outer Banks may trigger additional showers and storms the next few days.  (Amounts up to a half-inch are projected the next 3 days in our area — also note on this map the 5-8 inches projected in parts of Texas, Oklahoma and Arkansas with a major, slow-moving storm system there that will likely also trigger plenty of severe storms and some tornadoes.) This will again make projecting daily highs and rainfall chances a bit difficult — clouds and showers at any location on a given day can shave several degrees of highs, but then again, warmer highs at a given location can create more instability for afternoon showers and storms to develop. We are still under the effects of the warm dome of high pressure that has dominated the central and eastern U.S., so any day this week will easily reach the 70s and possibly some low 80s IF there is sufficient sunshine. That should be the general expectation each day through at least Friday — highs mostly in the 70s, maybe some low 80s, with some showers and storms possible any of those days to shave some degrees off the daily temperatures. It’s a summerlike pattern that is likely to continue through this week, with at least some signs it may change to a bit of a cooler springlike pattern by the weekend or early next week following a significant cold front passage.