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In Southwest Virginia, the Memorial Day weekend looks to be a fitting kickoff for summer, with highs in the 80s each day and lots of sunshine. There is some chance of showers and even thunderstorms starting on Memorial Day itself as the area begins to be affected by a low pressure system slowly meandering through the Gulf of Mexico, eventually moving inland. But even that will be scattered, not widespread, so at this point it's definitely not a reason to cancel outdoor plans.

The summerlike pattern across much of the nation gives us no real target zone as we start Virginia Tech Storm Chase 2009 today.  The upper-level winds have simply died out across much of the nation. Should be great travel weather as we wander ... to what, if anything, we don't know yet.

After 4 days in self-imposed dry dock, Virginia Tech Storm Chase 2009 finally leaves from Blacksburg on Thursday morning. Unlike mariners soothed by calm seas, we will be searching for the violent thunderstorms in the wide spaces of the central U.S., primarily the Great Plains region that parallels the Rockies hundreds of miles to the east from Canada to Mexico.

This looks to be an especially challenging trip. Strong winds aloft, typically dipping and diving across the nation, have retreated to Canada, more like late June or even July rather than late May. The rich Gulf of Mexico moisture that typically moves unhindered northward over the prairies has been stymied, first by a chilly Canadian air mass sinking southward and now by a persisent low pressure system whirling counterclockwise, pushing north winds into the Gulf.

Thunderstorms will probably be widespread this weekend over much of the central and northern Plains as weak disturbances tap moisture primarily of Pacific origin, having surged northeastward in a "monsoon" like fashion across the Desert Southwest, a phenomenon also more typical of mid to late summer. The challenge for us will be finding regions where rotating severe storm structures will be possible. The best chance of that now appears to be in the northern High Plains of western Nebraska, eastern Wyoming, southwestern South Dakota and perhaps eastern Colorado, where east winds blowing uphill may be able to pool enough moisture for convection under moderately strong winds aloft that can give some storms a spin.

Throughout next week, there is little hint of any large-scale weather pattern change, but additional cold fronts from the northwest and disturbances from the west ... plus at least a modest return of Gulf moisture ... might be able to trigger a few severe storms here and there. No outbreaks appear in the offing, but we're not really looking for one: Just one special supercell.

For more on Storm Chase 2009, please also visit the Virginia Tech Storm Chase blog linked here.

2009 chase team members:
Anthony Phillips, junior, Snowville, Va., geography (student trainer, returnee from 2005 trip)
Andrew Smith, senior, Mechanicsville, Va., civil engineering (student trainer, returnee from 2008 trip)
Erik Ferryman, senior, Chesterfield, Va., geography
Nathan Horne, junior, Spencer, Va., geography
Samantha Huddleston, sophomore, Roanoke, Va., engineering
Jiyoung Jeon, senior, Seoul, South Korea, geography
Phillip Long, junior, Newport, Va., geography
Andrew Martus, junior, Fredericksburg, Va., geography 
Ashley Shim, junior, Berryville, Va., biology
Kevin Shutta, freshman, Waltersville, Md., business 
Brian Smith, senior, Salisbury, Md., aerospace engineering
Byron Wiedeman, senior, Vienna, Va., physics
David Carroll, Virginia Tech meteorology instructor, trip leader
Kevin Myatt, Roanoke Times/roanoke.com weather columnist
Bob Oliver, visiting assistant professor, geography, Sarnia, Canada
Jim Stroup, Tech photographer

Roanoke set a record low for May 19 on Tuesday, dropping to 37, eclipsing the previous record of 39 set in 1994. The temperature is about to make a huge rebound upward. Though Wednesday will start out cool, with temperatures in the 40s, the afternoon will heat quickly into the 70s, maybe scraping 80 here and there. Highs above 80 are likely Thursday through Saturday.

It was a chilly morning across Southwest Virginia this morning. A repeat, maybe a tad colder, is likely on Tuesday morning. The National Weather Service in Blacksburg has issued a frost advisory for most of the New River Valley. A freeze warning is in effect for some of the mountainous counties to the north along the Virginia-West Virginia border. Don't even be surprised if the Roanoke Valley dips below 40 tonight.

The dry air that has settled into the area is allowing nighttime temperatures to plunge to near the very low dew point. The flip side is that that same dry air will warm more quickly in the day as the week goes along, and we will probably top 80 by Thursday. Warm days and cool nights, with wide departures between high and low temperatures, are likely to be the mode this week.

Each of the last four years on the annual storm chase trip, we have had some period of time that resembles the current weather pattern: strong western/central U.S. high pressure, deep dip in the jet stream to the east, cold front entering or crossing the Gulf of Mexico. Such a pattern shuts down the typical spring thunderstorm pattern in the central U.S., as moisture flow from the Gulf is cut off and storm systems from the west that could trigger severe weather are largely blocked by high pressure.

Last year, we sat out a 7-day mid-trip lull similar to this pattern. Dead periods lasting 3 to 5 days occurred in the 2005, 2006 and 2007 trips.

But this year, Virginia Tech meteorology instructor Dave Carroll and I, after days of watching forecast models converge on a solution that would almost inevitably lead to several days of quiet weather, made the unprecedented decision to delay the trip four days, leaving on Thursday and remaining out as much as four days later than scheduled on the back end. We expect to return on or before June 3.

Part of the decision to delay was simply because we could, due to the scheduling flexibility of everyone  on board. The biggest reason is that this pattern looks especially negative for severe storm development, essentially anywhere east of the Rockies. An added factor is the potential for a strong low to develop in the Gulf of Mexico later this week, which threatens to further cut off moisture return flow to the Plains that would otherwise be expected to develop.

There was no point spending four days worth of gas and lodging, with the chances of significant storms appearing to be just about nil, when we could save that for four more days at the end of the trip, when the pattern might be different. There is no guarantee of that, and the forecast models are offering very mixed signals, none of which, as of now, portend any kind of classic severe weather outbreaks.

But, as Dave likes to say, we don't need an outbreak, just one supercell.

Prospects for storms in the open Plains do begin to increase by late this week into the weekend, though in some atypical ways that do not scream "severe" at us. That's when we'll go and roll the dice. Storm chasing is always a gamble based on our best guesses at uncertain factors. We learn from the hits and misses.

Click here for more on how the storm chase trip is advancing Virginia Tech toward a possible meteorology degree program

It's not often you can talk about frost and a possible tropical system at once. The cool air from Canada settling into the region will make it sweater-weather for most folks by Monday morning, with widespread lows in the 30s and 40s, but just a few counties north,  including Alleghany and Bath counties, there are frost and freeze advisories out  for Monday morning for what could be a late nip on some plants.

Meanwhile, the feature at left has been showing up for days on virtually all computer forecast models (this frame is from Saturday evening's Global Forecast System model run, projecting Thursday). The models continue to show an upper-level low circulation developing somewhere near Florida or Cuba and drifting northwest or north through the Gulf of Mexico. In some runs, the system takes root at the surface and appears to develop tropical characteristics. A slow-moving low pressure system is likely in the Gulf of Mexico this week. Though the official start of Atlantic hurricane season is still more than two weeks away (June 1), forecasters will be keeping a close eye on this system just in case it shows signs of becoming a depression, tropical storm or subtropical storm over the warming waters of the Gulf. In time, whatever this system becomes will likely move inland and may affect Virginia's weather a week from now, give or take a day. Lots of time to watch and see if there is a pre-season exhibition of tropical weather.

There have been several heavy rain and flooding reports (and a few hail and high wind reports) from thunderstorms in Southwest Virginia this afternoon and evening, mostly north and south of the Roanoke Valley. By late this evening, most of the storms have fused in a solid area of rain, with some embedded thunderstorms, though not as intense as they were earlier in localized pockets.

Among reports turned in to the National Weather Service in Blacksburg:

* Numerous roads closed from flooding in Carroll County.   
* Rock slide on Highway 52 North near Fancy Gap.   
* Water over Route 687 near Bacova in Bath County, 4 miles north of Hot Springs.
* Water on U.S. 220 at Bath/Alleghany County line, 1 mile south of Carloover.
* 3/4 inch hail, 2 miles south-southwest of Natural Well in Alleghany County.
* Tree blown down at Goshen in Rockbridge County.

Below in the extended entry (click "Read More" in full blog mode) is a list of rainfall amounts around the area through 10 p.m.

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Something besides thunder rattled things in Cave Spring this morning. I remember waking up and stuff was rattling, and I wondered if it was a gust of wind, but it seemed like stuff inside the room was rattling too. It was a magnitude-3.0 earthquake.

It's not really weather, but the National Weather Service did put out a public information statement about it early this morning (the magnitude has since been upgraded slightly):

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE BLACKSBURG VA
457 AM EDT SAT MAY 16 2009

...PUBLIC INFORMATION STATEMENT...

AT 408 AM EST...THE NATIONAL EARTHQUAKE CENTER IN BOULDER DETECTED
AN EARTHQUAKE 4 MILES WEST SOUTHWEST OF ROANOKE. THE EARTHQUAKE
MEASURED 2.6 ON THE RICHTER SCALE. SO FAR...REPORTS INDICATE THAT THE
QUAKE WAS FELT IN THE ROANOKE...VINTON...AND SALEM AREAS.

INFORMATION RELEASED IN THIS STATEMENT IS PRELIMINARY.
UPDATES...INCLUDING RICHTER SCALE MAGNITUDE...WILL BE PROVIDED AS
MORE INFORMATION BECOMES AVAILABLE FROM THE NATIONAL EARTHQUAKE
CENTER IN BOULDER COLORADO.

A major weather pattern change is ahead. By Monday, a mass of cooler, drier Canadian air will push through the area, giving us several sunny, dry days with cool mornings and warm afternoons (lows in the 40s, highs in the 70s). But the front at the leading edge of that will push into the sticky, soupy air over us now, and several rounds of showers and thunderstorms will be likely Saturday and Sunday.  Again, some places could get locally heavy rainfall, while others get much less, though everyone should get at least some rain. Don't be surprised if there are few strong to severe storms with hail or gusty winds, though a lot of the atmospheric dynamics don't seem to be in place for widespread severe weather.

The coming pattern change is having an impact on the annual Virginia Tech storm chase trip. We are postponing our departure date from Sunday to Thursday, in an effort to get past the calm, cool, dry weather that will envelop much of the nation east of the Rockies behind the front. Yes, we we are delaying on account of good weather!

Many people got rumbles and rain last night. A few folks got extremely heavy rain, as thunderstorms "trained" or moved over the same locations repeatedly. The U.S. 460 corridor both west and east of Roanoke seemed to be a focus for this, with 2-plus inch rainfall amounts common both in the Christiansburg-Shawsville area and also around Bedford County and Lynchburg. A flood warning remains in effect until early afternoon for Salem, and western Roanoke County and central Montgomery County for some overflowing streams that feed into the Roanoke River. Below in the extended entry (click "Read More" in full blog mode) are a list of rainfall amounts through this morning from the National Weather Service.

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