Live Blog: Saturday April 27, 2013
Posted on: 4:20 pm, April 27, 2013, by Brandon Chambers
We’ll post frequent updates to this live blog on the developing severe weather situation.
Storms have been rumbling across the Tennessee Valley throughout the overnight hours, with more storms that have popped up behind the main line that had developed and is now moving into northwest Georgia. There have been no severe storms, but the stronger ones continue to produce frequent lightning, with small hail and wind gusts greater than 40 mph possible,along with heavy downpours.
There are no current warnings, but hail is being produced in some of these heavy early morning storms. Pea size hail. Frequent lightning and heavy rain are likely. Winds are only in the 20-40 mph range.
The severe thunderstorm watch has been dropped for all of North Alabama.
From the Storm Prediction Center. The severe t’storm watch may be dropped early due to lack of instability:
MESOSCALE DISCUSSION 0571
NWS STORM PREDICTION CENTER NORMAN OK
0856 PM CDT SAT APR 27 2013
AREAS AFFECTED…NRN AL…FAR NWRN GA
CONCERNING…SEVERE THUNDERSTORM WATCH 143…
VALID 280156Z – 280300Z
THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 143
SUMMARY…SVR THREAT ACROSS WW 143 CONTINUES TO DIMINISH…WITH THE
STRONGEST STORMS LIKELY CAPABLE OF PRODUCING SMALL HAIL. IF TRENDS
CONTINUE…WW 143 MAY BE CANCELED EARLY BY LOCAL OFFICES.
DISCUSSION…RADAR TRENDS HAVE INDICATED CONVECTION HAS STRUGGLED TO
INTENSIFY WITH EWD MOVEMENT INTO A LESS UNSTABLE AIR MASS ACROSS
NERN AL AND FAR NWRN GA. THE LOSS OF DIURNAL HEATING…ALONG WITH
SLIGHTLY WARMER MIDLEVEL TEMPERATURES ACROSS THIS AREA /AS NOTED IN
28/00Z FFC SOUNDING/…SUGGEST MARGINAL INSTABILITY IS PRESENT.
ALTHOUGH SOME SMALL HAIL MAY ACCOMPANY THE STRONGEST CORES…CURRENT
OBSERVATIONAL TRENDS AND RECENT SHORT-TERM GUIDANCE SUGGEST THAT
THIS CONVECTION WILL STRUGGLE TO INTENSIFY.
Gusty winds blowing across Marshall Co. ahead of heavy storms to the southwest. Just got this note on Twitter:
“@starchick7003: @simpsonwhnt high winds blowing garbage cans and anything not tied down around Albertville #valleywx”
Just a reminder, if you want to report weather conditions, Twitter is a great resource! Use the hash tag #valleywx or Tweet us directly: @simpsonwhnt … @BChambersWX
Beautiful double rainbow looking toward east from Valley Grove Baptist Church at Tuscumbia, AL from Greg Beasley. This came behind the heavy storms in Colbert County.
Severe t’storm watch is still in effect until midnight for all of North and most of Central Alabama. The only severe thunderstorm in progress is in eastern Fayette County just east of the Fowler’s Crossroads area. If that storm holds together, it’ll move into Walker and Southwestern Cullman Counties.
We don’t typically post things straight from the NWSChat on the blog or on social media, but this is an interesting statement that really doesn’t need to be re-worded:
“Everyone, we are still focused on the storms moving across Walker and Winston counties–mainly presents a lightning & gusty wind threat as it moves into Cullman County.
There are some in-cloud lightning flashes occurring well north of these storms across Lawrence and Morgan Counties, but they are not attached to the “real” thunderstorms to the south.”
So those rumbles you’re hearing in Morgan and Marshall Counties as well as Blount and northeast Cullman are not connected to the severe storms. They’re mainly in-cloud lightning!
This is a photo Christy Simmons took in Russellville earlier this evening as the storm was passing north of there. It’s hard to say exactly what this is, but I think we all know what it looks like!
Sometimes there are tornado/funnel cloud look-a-likes that can fool the best of us when we’re spotting storms. In this situation, if the feature persisted for more than a few minutes and showed obvious signs of rotation, we’d be able to confirm a rotating wall cloud. Since it’s a still image, it’s almost impossible to know for sure.
There are no active severe weather warnings in North or Central Alabama. There is still a heavy thunderstorm with frequent lightning moving across northern Walker and southern Winston Counties. Dual-pol radar shows no signs of large hail, but the rain is really coming down hard!
If you are around or know folks who are down around the Duncan Bridge, Arley, Cold Springs, Brushy Pond areas on Smith Lake, let them know a big storm is on the way and that they should probably pack it in for the evening. Again, the severe threat is fairly low this evening; hail is the biggest issue.
A Severe storm in southern Marion Co., AL has a threat of some stronger winds near US 78/I-22. This image is the velocity product from the Columbus, Miss. NEXRAD. The beam is about 2,000 feet above the ground. So far, there have been no reports of damage in Marion County, so we believe the strongest winds are staying aloft, but there is very heavy rain, hail, and frequent, dangerous lightning in Marion, Walker, and Winston Counties.
Additional storms will develop throughout the evening hours, but we still believe the biggest threat will be damage to your car or rooftop due to HAIL than any other form of severe weather.
The HRRR model suggests the air over northeast Alabama will remain stable this evening through midnight (5:00 UTC). Unstable air over west-central and Northwest Alabama remains rich enough to maintain a risk of some strong or severe storms through the expiration of the watch.
The main risk tonight will be hail. Wind shear is lacking, but you can never totally say there is zero risk of one or two significant wind gusts or even a short-lived tornado. I do not expect that to happen, but we will keep you posted IF that kind of thing does look possible.
The severe t’storm warning for Colbert and Franklin (AL) counties has expired… the storm has weakened substantially
View of the elevated base of the storm passing north of Russellville; while this looks ominous, it’s a good sign. The higher-based these storms are, the less likely it is that we’ll have anything more than some hail or some gusty winds. Thanks to @RodCox4Bama for the photo…it’s looking NW from Russellville toward the SW flank of the storm. That’s the spot you’d be looking at if you were to find a wall cloud or funnel cloud. There is not one there. Anytime you have pics or observations to send us, you can email photos to email@example.com…or tweet straight to Brandon or me. He’s @BChambers_WX and I’m @simpsonwhnt.
Helicity in the lowest 1km of the atmosphere is very low; that’s a measure of shear in the lower levels of the atmosphere that is available for a thunderstorm to take advantage of. Low shear environments rarely yield extreme weather events. Hail will be the biggest threat this evening – especially west of Interstate 65. Although the watch goes all the way to the Georgia border, the severe weather threat gets less as storms move that way.
The National Weather Service in Huntsville tells us that they are in the process of outlining a Severe T’storm Watch for all Tennessee Valley of North Alabama Counties. That would include all of the WHNT News 19 viewing area except counties in Southern Tennessee.
Dual-pol “HCLASS” from the Columbus NEXRAD still showing some hail potential; the over-all storm intensity is decreasing. Pea-size to nickel-size hail a possibility near Littleville by 5:30 to 5:35 PM. If it stays strong, it will impact northwestern Lawrence County near AL 157 near Hatton and move on up toward Town Creek and Courtland.
This is mainly a heavy rain/hail/lightning producer…there have been no reports of wind damage or excessively large hail. That’s good news. We can deal with these storms as long as they behave!
The Storm Prediction Center is considering a watch of some type of Watch (probably a Severe T’storm rather than a tornado watch in my opinion) for the Tennessee Valley this evening. Here’s their take on the situation:
MESOSCALE DISCUSSION 0565
NWS STORM PREDICTION CENTER NORMAN OK
0454 PM CDT SAT APR 27 2013
AREAS AFFECTED…NERN MS…NRN AL…FAR NWRN GA
CONCERNING…SEVERE POTENTIAL…WATCH POSSIBLE
VALID 272154Z – 272300Z
PROBABILITY OF WATCH ISSUANCE…60 PERCENT
SUMMARY…AN INCREASE IN TSTM INTENSITY HAS BEEN NOTED OVER THE PAST
COUPLE HRS ACROSS NERN MS/NWRN AL. THIS ACTIVITY SHOULD CONTINUE
ADVANCING EWD NEARLY PARALLEL TO A WARM FRONT DRAPED ACROSS THE
AREA…BUT INTO A PROGRESSIVELY LESS UNSTABLE ENVIRONMENT.
CONVECTIVE TRENDS ARE BEING CLOSELY MONITORED FOR A POSSIBLE WW.
DISCUSSION…RADAR LOOP SHOWS A SUPERCELL MOVING ACROSS
FRANKLIN/COLBERT COUNTIES IN AL…WHICH IS LIKELY ANCHORED INVOF A
WARM FRONT ANALYZED FROM ROUGHLY 20 N TUP TO 25 NNE GAD TO 20 E
ATL…WITH RECENT REPORTS OF LARGE HAIL ASSOCIATED WITH THIS STORM.
ACTIVITY FARTHER S IN THE WARM SECTOR HAS SHOWN LESS
ORGANIZATION…BUT OCCASIONAL UPWARD PULSES IN INTENSITY HAVE BEEN
NOTED WITH ASSOCIATED POTENTIAL FOR HAIL.
DESPITE FAVORABLE DEEP-LAYER SHEAR IN THE PRESENCE OF A MIDLEVEL
JET…INSTABILITY REMAINS QUITE MARGINAL…AND DECREASES WITH EWD
EXTENT INTO PARTS OF NERN AL AND NWRN GA…WHERE SFC DEW POINTS ARE
ONLY IN THE LOW-TO-MID-50S F. MOISTURE ADVECTION SHOULD INCREASE
LATER THIS EVENING ACROSS ERN PORTIONS OF THE HIGHLIGHTED AREA AND
SHOULD MAINTAIN MARGINAL INSTABILITY BEYOND THE ONSET OF DIURNAL
COOLING. GIVEN THE UNCERTAINTY REGARDING THE POTENTIAL FOR STORM
INTENSITY TO BE MAINTAINED FARTHER E…A WW IS STILL
QUESTIONABLE…BUT CONVECTIVE TRENDS WILL CONTINUE TO BE MONITORED.
The severe storm in southern Colbert and Northern Franklin Counties is still moving east at about 20 MPH; slow moving storm may produce large hail and wind gusts greater than 50 MPH.
Golf ball size hail was reported near Belmont, Mississippi with this storm. While it has shown signs of rotation, the tornado threat is rather low across the Valley this evening. Storms are building in an area of high instability to the southwest of Huntsville, but as they move east this evening, they should show some signs of weakening as they move into a slightly more stable air mass.