UPDATE 8:20 PM: Moist wedge building in overnight; record hot July pace for Roanoke; widespread U.S. drought
UPDATE 8:20 PM: Easterly winds are banking relatively, cool moist air against the mountains. The upslope effects plus some temperature contrast are triggering small but heavy showers, perhaps accompanied by some thunder, in and around the Roanoke metro area, southward along the Blue Ridge through Franklin and Henry counties. (Radar linked here) Brief periods of heavy rain will be possible with these showers. As the easterly winds continue to bank moisture overnight, a layer of low clouds and scattered drizzle is likely to develop — such a layer kept much of northern Virginia in the upper 60s and low 70s throughout today. How long this layer can hold in place on Sunday will determine whether we have a cooler day with a high in the 70s or a warmer, sticky day in the 80s. END UPDATE
This weekend: Warm and sticky, highs mostly in the 80s, with scattered showers and storms possible as daytime heating interacts with a stubborn front and thick moisture. Some will get heavy rain (like Galax did Friday evening) and/or gusty winds, others will get lighter rain and a little thunder, and yet others will get sprinkles or nothing. Can’t really be much more specific than that. Same old midsummer dog days refrain.
We are 20 days into July, and Roanoke is on track for some possible monthly record heat. As with the record hot summer of 2010 and runnerup in 2011 (a merely normal June average temperature may make it hard for this summer as a whole to equal the previous two), it’s more about warm overnight lows than hot afternoon highs. Through Friday, Roanoke’s average high temperature for July is 91.9 degrees — that would rank fourth were it an end-of-month average. But more impressively, the average low has been only 71.2 degrees. Should a similar number be posted after 11 more days, it would crush the current July record of 69.9 degrees set just last year and even overturn August 2007′s record 70.6 for 
warmest average low for any month. Roanoke low temperatures have been no lower than 66 on any day this month and have been 70 or above on 12 of 20 days. The normal low is 67 — only July 12 at 66 has been below that, every other low has been 1 to 9 degrees above normal. Averaging the mean high and low together produces an average temperature for the first 20 days of July of 81.6 degrees, which, were it a month-end average, would set a new record for hottest July and be just less than half a degree off the 82.1-degree record warmth of August 2007 for hottest month on record. I bring this up now because we are two-thirds through the month with absolutely no sign of a significant weather pattern change. High temperatures go down with cloudy days like Friday (only 82 at Roanoke, 76 at Blacksburg) and passing cold fronts, but muggy low temperatures are hanging on even in the somewhat cooler periods because truly cool, dry air from Canada has been blocked from coming this far south.
Drought begets more drought. Drought begets more heat. More heat begets more drought. Vicious cycle much of the U.S. is in. We’re on the eastern periphery of the real trouble (Thursday’s Drought Monitor map shows the darker colors mostly to our west), but until there are major 
pattern changes that can bring large-scale storm systems to soak at least some of the very dry areas, there will be little change to prevailing mostly hot, mostly dry weather. Short of a large tropical system moving deep inland, an unlikely event for now because of an infusion of Saharan dust that has tracked westward from Africa over much of the Atlantic basin, those kind of drought-busting events probably aren’t going to occur for at least another 45 days, if not longer, when seasonal changes in upper-air patterns begin to take hold. So we’re pretty much stuck with a dome of hot, dry air over the central U.S., expanding or wobbling eastward over us at times, and at other times aiding in pushing at least some fronts and disturbances southeastward into the Appalachians and Mid-Atlantic regions. The heat and lingering humidity (plus terrain factors in the mountains) will be sufficient at times to fire scattered afternoon storms, but at other times hot, dry air moving aloft will block upward growth of storm clouds. A dip in the jet stream into New England may be able to erode the heat dome near us in coming days and weeks, which might lead to a somewhat cooler pattern — but widespread, general rainfall remains doubtful.
July 21, 2012 - 12:17 AM
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Doug, the CPC shows kinda what you were talking about……the El Nino rain influencing the southern tier of states in the fall and winter, all the way from California to Georgia. I’d like that to move up north a bit, but time will tell.
http://www.cpc.ncep.noaa.gov/products/predictions/multi_season/13_seasonal_outlooks/color/p.gif
As hot and muggy as its been recently, its almost Fall like outside this morning. Heavy overcast with occasional light rain and mist with a cool and steady NE breeze. Temp at 8:55 AM is a very comfortable 66 on our porch. I’ll take it.
Some important things to remember about El Nino:
(1) It’s not happening yet. It’s still possible it won’t develop.
(2) Sometimes the weather pattern doesn’t behave like it’s expected to during an El Nino, because of its relative strength and/or other weather/climate factors. 2007 is the classic case, when the winter’s wet weather went into the central U.S. (which would actually be a huge blessing for that parched region), while leaving the Southeast dry.
(3) When an El Nino or La Nina reverts to neutral conditions, it’s often the case tha the overall wind flow pattern keeps looking more like the El Nino/La Nina for weeks or months after it ends.
Another 70+ low for Roanoke (71). If July sets a heat record, so many mornings not getting below 70 will be the major reason, even more than 90+ days.
Kevin, June was famous for a lot of tropical activity in the Atlantic (Gulf and Carribean) basin. Nothing in July. Yes, I remember that historically, June and July are slow in the Atlantic. I have not heard you speak much about the tropics lately
I’m kind of shocked that after an early start to tropical cyclone development that we haven’t seen much out of it.
A lot of folks fail to realize that much of our water demands hinge on tropical systems making landfall and pushing far inland. Not that I wish the coast to get pounded, but I would very much like to see a few mild/week tropical systems develop and make landfall and get the ground nice and soaked.
I’ve pretty much gave up on my garden. After good amounts of rain in May and early June, my ground is toasted and the insects have all but destroyed it.
Rick: There hasn’t been much to speak of in the tropics lately. I hope you caught my Saharan dust mention above.
I just thought it was strange that we had all that tropical developement in June, near our coasts and then it just stopped. Why? I did not expect anything to come off Africa until August.
The Saharan dust overspread the entire Atlantic basin — all the way to the Gulf and Caribbean. It provided some unusually colorful sunsets in Florida. Studies have showed that when this Saharan dust layer blows west like that, it tends to shut down tropical development.
That may not explain all of why there hasn’t been much lately. Historically, years with early tropical development aren’t all that more active than years that don’t — average of about 1 more named storm. 2004 was a super active year, especially for the continetal U.S., that didn’t have a single named storm until the waning hours of July 31.
Nate: You are exactly right. Part of why places like Georgia and Texas have been in so much drought in recent years is a lack of tropical systems. I’ve always tried to emphasize there is nothing inherently evil about tropical storms and hurricanes — they are absolutely essential for the the proper function of our atmosphere, transferring tropical heat northward to cooler climes, burning off some of that heat with wind and precipitation, etc. And they are part of a healthy precipitation diet for much of the southern and eastern US in late summer and fall. But of course, none of that is much relief if your home or city is in the path of a major hurricane and its storm surge.
In case you’re wondering why Charlottesville to DC is holding in the mid 60s to lower 70s today — this satellite picture circles the “wedge” where cool, damp air has banked against the mountains, with low clouds holding temperatures down. It also marks the approximate position of the front where the most storms are firing.
http://blogs.roanoke.com/weatherjournal/files/2012/07/satelliteVa0721b.jpg
Rick, former (alleged) snow-hating cohort, thanks for posting that CPC map (first comment on this thread) of the temp outlooks for the following months/year. The pattern of rain along the southern tier, just as you (and KM in years past) alluded to, is straight out of the El Nino playbook, especially the one for the Nov-Dec-Jan period. But in the El Ninos of especially 1997-98 and also for the winter of 2003, El Nino also led to big precipitation for us. I have a feeling that it will happen again this time, too, but nowhere near as wet as the epic wet winter of 1998. Maybe a couple of 5+-inch “rainfall” months (rainfall including the rain equivalent of snowstorms) between November and March. Now that I have mentioned it, it probably won’t happen.
About the lack of tropical activity in the Atlantic/Caribbean: great that you mentioned the Saharan dust, KM. Also, I had TWC on at Oh-Dark-30 (before work, and we now arrive at 7 AM, not 7:30), and they gave a recap of Atlantic season to date and also showed the “norm.” 4 named storms so far, 1 hurricane, no strong hurricane (Category 3 or higher). But that is still well ahead of the norm. Normal (I think through July, but perhaps only through July 20 or 21) is 1 named storm, and no hurricanes!
The other factor has to do with El Nino. Kevin, you have mentioned that an El Nino developing tends to limit Atlantic tropical activity. I agree with your three points about El Ninos that you mentioned in your 9:07 comment, but after being a skeptic in March and April and possibly into May, I believe that we will have some sort of El Nino. Each month’s prediction plume has shown higher temps in the 3.4 area for the 2nd half of this year than the previous month’s plume, possibly with the exception of the one that was just issued this week. Just when the Atlantic tropical season should be gearing up in the last ten days of August and into September-October, El Nino may be gearing up too. But we shall see. As you have mentioned before, Kevin, all it takes is one big hurricane to make landfall and come inland and we could be swamped with rain. And other times, such as that season just a few years ago, we had leventy-leven named storms and quite a few hurricanes, but NO U.S. hurricane landfalls.
Updated the blog to note cool, moist wedge rolling in on easterly winds (low clouds rapidly building at ridgetop level east/northeast of Roanoke) and some heavier showers that have developed as the moist winds encounter higher terrain/warmer air.
Wedges are often hard to break. If this one hangs on a long time Sunday, it could be a cooler day than many forecasts show.
Seems you can smell just a hint of ocean on that breeze. Never will forget being swallowed by the wedge hiking on Mount Pleasant along the Blue Ridge east of Buena Vista one time. Sunny, hot day turned foggy, damp, chilly fast.
Oh, one other interesting graphic from The Weather Channel this morning. They should the drought monitor map for the state of Indiana at two different times. In mid-May, there were some pockets of the pale yellow “abnormally dry,” and quite a bit of white for no drought. In the latest issue (Tuesday?), the predominant color is red (D3. Extreme drought?) with a patch of intermediate tan (D2) in the NW and SE corners of the state. Getting worse every week, I guess.
I am amazed that you have not made any comments about the drought in Arkansas, Kevin. There is a pocket of dark brown (D4!!) roughly in the center of Ark., with over 50% of the rest of the state in D3. I was hoping that friends, relatives, former co-workers would have contacted you with descriptions of how bad it must be there. I for one would like to hear about it. Are lakes way, way down or disappearing?
Is there any chance that the wedge could stick around for even part of Monday? I have the good ol’ “monster” route again. A high in the low 80s would be infinitely better than one around 91 with humidity.
Doug, I have heard accounts of trees turning brown and dying off in some parts of the state. As for the wedge sticking around Monday, it’s doubtful, with the front washing out to the south and some indication a little piece of the dry heat dome spreads over us a day or two.
We are getting RAIN here in Hokieburg. More than drizzle that appears in the forecast.
The time for getting real rain with this is early in the evening when we still have the temperature contrast with the warm day. As the wedge builds in overnight, it’s likely to stabilize the atmosphere and we’ll have scattered drizzle or some very light rain.
The green radar blob is over us and we are getting a nice slow rain. Roanoke looks high and dry.
Roanoke city is mostly dry (I see a tiny shower in NW Roanoke near Hollins), but there is a persistent heavy patch just north in southern Botetourt County. Stuff is continuing to pop up and get carried southeastward by the upper-level wind flow over the easterly surface flow.
… hope some kind of rain shower can get over the industrial fire in NW Roanoke near 581 … 2 firefighters transported to hospital.
Photo I shot earlier this evening showing smoke from the large industrial fire in NW Roanoke getting carried on easterly winds. As the smoke interacted with the moist layer just above the surface, it formed clouds.
http://blogs.roanoke.com/weatherjournal/files/2012/07/NWFire2.jpg
Hoping the rain that is a couple miles away holds together to make it here. I just used some of our collected rain water to water the flowers – they are getting parched. “Rain, come on down!”
Yeah, Nancy was sitting on our porch and alerted me to that fire about 8:20 PM. I noted to her that the wind was out of a somewhat unusual direction, especially for this time of year, the east, blowing westward. I bet parts of “my” 24017 zip code have been affected by the smoke.
Kevin, on the 6 PM newscast, Jay Webb of “7″ showed a small rainstorm south of downtown Roanoke, along the 220/Tanglewood/Clearbrook corridor. Did you get any of that at your home? Of course, Khan was directing it, …. not a drop here.
Radar and my wife’s observations confirm that we only got a little bit out of that.