I just wanted to share a couple of radar stills from the tornado outbreak of last Monday. The come courtesy of Plymouth State University’s NEXRAD archive. The first shows the cell that passed through Norman. The hook is muddled somewhat by the toads and county lines, but it is still there. Other local radars, such as the one housed by Oklahoma University, have better angles on the storm, but aren’t publicly available yet.
The second comes about an hour earlier, and is a of a storm near Wakita (if you have heard of Wakita, this might be why). It has perhaps the most pronounced hook of any storm that day.
I have nothing to add, really. It’s 6 days in the past, and this was a very well documented, well warned system among people that are used to such weather. Really, I just wanted to link to these, because they are definitely images that make a full blooded meteorologist say “whoa”.
Yesterday, a dynamic system moving into the Southern Plains organized and triggered a tornado outbreak over Oklahoma, the center of the tornado universe. In fact, the scientists at the National Weather Center, home to a combination of the Storm Prediction Center, NWS-Oklahoma City office, and a meteorological research campus of the University of Oklahoma saw a tornado out their window. They self reported! Unfortunately, this marks the second deadly outbreak of the year after last month’s twister that cut across Mississippi. 5 are dead and many more are injured in Oklahoma, most in Norman, just south of Oklahoma City where the NWC is located.
The images from this storm are incredible. We will look at some radar stills next week, when we don’t have forecasts scheduled every day. Speaking of forecasts, this is technically a verification post, which is why Nebraska was mentioned. Omaha was on the northern end of the system, and they mercifully only saw rain out of it. Temperatures were kept cool by persistent wind, and clouds. The rain didn’t start until Monday, which didn’t give Victoria-Weather the victory, it merely increased the margin of victory.
Actuals: Sunday – High 62, Low 38
Monday – .59 inches of rain, High 54, Low 48
May is the time most people start to think of warm weather, sunshine, and the fun summer activities ahead. However, Mother Nature likes to sometime put a monkey wrench into our cheery outlooks. An area of low pressure is developing today over the Central Rockies and will push into the Central Plains by later this evening. A slew of moisture is streaming up from the Gulf ahead of it and will get wrapped around on the north side of it, and will result in some snowfall over the Northern Plains. In addition, as the low shifts eastward through Friday evening, another swath of snow looks to fall over northern MN and WI, with a couple inches possible. We’ve had a ludicrously warm spring we’ve had here in the Twin Cities, we haven’t had snow since February 23rd which led to our first ever snowless March and April on record, so this possible snowfall isn’t going to make people in Central MN and WI very pleased. Snowfall isn’t uncommon over the northern tier of states in early May, but after the warm spring this part of the country has had so far, it’s certainly not a welcome visitor.
When I look at a surface map, I think of it like a topographical map. The high pressure is like a mountain, low pressure is like a valley. The closer the lines are (the isobars, lines of constant pressure) the greater the change in elevation on our topographical map. The air is like, say, water. It will always try to flow downhill, and will move faster in steeper elevation changes.
This is obviously an over simplification, especially since it doesn’t accurately describe the directionality of the winds. Due to forces like friction and the rotation of the earth, the wind blows roughly 90 degrees to the right of a straight high to low pressure line. Basically, if you stand with your back to the wind and lift your left arm, you are pointing to the lower pressure. That said, it does do a slightly better job describing the speed with which the wind will blow. A steeper pressure gradient does mean stronger winds, just like my mental topographical map would indicate.
This is, by the way, one of the most fundamental things a meteorologist knows. The first thing I remember learning about in my meteorology class was high and low pressure and the immediate effect on wind. I remember walking home from that class lifting my left arm, trying to figure out where the nearest low was. Memories…
The past 18 months or so have been tough for the folks from State College. They have been missing on a lot of short term forecasts and have been putting out some ludicrous long range forecasts, Well, this past month, they managed to stay at the top of the standings with several quality prognostications. It came down to the last forecast in Allentown, however, when they had the top forecast and The Weather Channel came in 4th, allowing Accuweather to sneak by the denizens of Atlanta for the top spot. Congrats Accuweather, it’s been a long time coming.
Now here is a look at some tornado safety tips.
There isn’t any “official” start to the severe weather season, like the start of hurricane season is June 1, but it’s been a fairly quiet spring so far as far as severe weather outbreaks across the country. Outside of one outbreak over the Carolinas in late March, not much has happened. That changed in a hurry last week when many severe storms erupted ahead of a very strong occluded/cold front over the Southern Plains and Lower MS Valley over April 22-24. A couple days ahead of time the Storm Prediction Center (SPC) issued a moderate risk for the region, and on the morning of April 24 the SPC issued a rare High Risk, the first one this year. This came to fruition when a supercell dropped a tornado in far northeastern LA then rolled into MS. By the time the tornado finally dissipated, it had tracked for an incredible 149+ miles, one of the longest on record. Sadly, 10 people perished from this storm in 3 separate cities as it inflicted EF4 damage in cities across the state. The NWS out of Jackson, MS has a nice write-up and summary of the outbreak. With another strong cold front looking to move through the Central US over the next couple of days, it always pays to be vigilant to weather forecasts and heed warnings when they are issued. We know it’s tempting to want to go outside and take pictures or even chase after these storms, but please leave that to the professionals and seek safe haven for yourself. While there are hundreds of storm chasers across the US documenting storms, relaying storm reports to the authorities, and hoping for each cell to drop a funnel cloud, they never want to hear about them hitting towns and causing fatalities, since human life is worth infinitely more than any picture is worth.
This is the current Unisys analysis. I have no idea why, but they decided to outline South Dakota in white. I can’t think of any possible significance, other than the fact that someone there must REALLY like Mount Rushmore.
More from the deadly tornado that cut Mississippi in half on Saturday. CNN has a video of the looming EF4 tornado that eventually devastated Yazoo City and a large swath of Mississippi. It ended up having a path of almost 100 miles, at times wider than a mile and a half. Fortunately, a twister of this duration and intensity is rare, but is the reason meteorologists so intently monitor the weather, and why storm chasers are so important. Naturally, Victoria-Weather extends our condolences to those who lost friends and loved ones in last weekends storms.
Yesterday, I highlighted the risk for severe weather in the Lower Mississippi Valley, and we did see widespread severe storms, especially along a line from north central Arkansas to eastern Texas. Most of this was because of wind, as the front rocketed east at 60mph, with thunderstorm gusts compounding the situation.
A merging of the cold and warm front (cold fronts move faster than warm fronts) happens at something called an occlusion, which is representative of the surface low, which works its way down the cold front and introduces an element of turning in the atmosphere that can turn those straight line wind events into widespread tornado outbreaks, as happened today (and the SPC correctly labeled a “high risk” day). A large wedge tornado was on the ground for 200 miles from northeastern Louisiana and across the state of Mississippi before finally lifting.
The long lived twister killed 10, with most of the hardest hit communities were near Vicksburg, Yazoo City and Holmes County. Another tornado dropped near Meridian, and the active pattern has also led to strong thunderstorms in and around Saint Louis, where funnel clouds were also reported. The energy associated with the storm system is still present, and will allow the continued development of strong thunderstorms overnight. Even now there are severe and tornado warnings in the Birmingham area, and any residents of the southeast should be aware that overnight, deadly tornadoes are a distinct possibility.
A strong system is coming out of the Rockies is generating the southerly flow we expect out of a good Spring severe outbreak. The system doesn’t have the typical vorticity of a massive tornado outbreak, however the storm is strong enough and there is enough potential energy that the storm prediction center has put out a moderate risk for severe weather in the lower Mississippi Valley. It’s projected for where the front will intersect with the strongest inflow from the Gulf will intersect the boundary, which actually isn’t entraining a lot of cool air. Here is a look at where the SPC is most concerned.
The threat is enough for tornadoes that the region, from Nebraska to Missouri and south into Texas, Louisiana and Mississippi that tornado watches are littered about the area. Only a few tornadoes have been reported so far today, a far cry from yesterday when the low over the High Plains generated dozens of mercifully remote twisters. Today, the storms will likely be more of a wind and hail threat for the south central US than tornado, but the threat is enough that residents should be wary. We’ll see how this moderate risk forecast verifies tomorrow.