As expected, there have been significant changes to the Storm Prediction Center’s severe weather outlooks for this week. The most notable change is with the Thursday outlook which, as of this post, has the outlook area covering states much farther to the northeast that in previous outlooks. Regardless, we’ve a busy weather week ahead. Let’s first take a look at Wednesday.
Wednesday’s Slight Risk has been expanded and now covers a large area from south-central OK into southern Iowa and western Illinois. Several major metro areas are within the Slight Risk and include Oklahoma City, Tulsa, Kansas City, Wichita, and all surrounding suburbs. Warm, moist air is flowing northward across the risk area and will provide the fuel for the storms. In western Oklahoma, Kansas, and northwest Texas, a “dryline” (which is a sharp demarcation line between dry and moist air) will be the focal point for storm development. In the early hours of Wednesday, storm formation will be deterred by a “cap” which literally stops warm, moist parcels of air from rising and forming storms. Eventually, ingredients in the recipe will come into play that will allow the cap to “break” and storms will develop. Once that happens, storms that develop should rapidly become supercell thunderstorms with heavy rainfall, large hail, strong straight-line winds, and the potential for tornadoes. The SPC specifically addresses the tornado threat with, “THE AMPLY MOIST BOUNDARY LAYER AND FAVORABLE LOW-LEVEL SHEAR — PARTICULARLY NORTHWARD INTO KANSAS NEARER THE ADVANCING SURFACE LOW — WILL LIKELY BE SUFFICIENT TO SUPPORT RISK FOR TORNADOES.” In other words, plentiful moisture for storm “fuel” along with wind shear that will allow storms to rotate will be present. There’s no reason to panic, just be aware that “tis the season” and any storms that form in the right environment have tornadic potential. Some forecast data hints at storms being somewhat isolated from each other, but any storms that do form will quickly become severe. As the evening progresses, storms will likely become more numerous, less isolated, and a reduction in the tornado threat may occur, but the large hail and damaging straight-line wind threat will continue. Flash flooding will also be an issue with any location that experiences torrential rainfall. Flooding kills more people every year than all other weather hazards combined and, in my opinion is a greatly underrated weather hazard. Now let’s take a look at Wednesday’s SPC Severe Weather Probabilistic map.
WEDNESDAY’S SEVERE WEATHER PROBABILISTIC MAP
The purpose of this SPC map is very simple, but certainly not meant to frighten anyone. It simply shows the probability of severe weather, including significant events, of occurring within twenty-five miles of any given point. Not every location within the Slight Risk 15% area or the significant severe “hatched” area will see storms. Some locations may not even see a drop of rain. It simply lets you know that within these areas, particularly the “hatched” area outlined in black, has a higher probability of severe weather being reported. This doesn’t mean an imminent disaster, but the Slight Risk also doesn’t mean storms will be “slightly” severe. At this time, SPC forecasters feel that storms within the hatched area will be pretty potent…which means if you live in or will be traveling through this area, expect a severe thunderstorm or tornado watch, numerous warnings, and some robust storms that won’t hesitate to show off how much shake, rattle, and roll they can make. It does not mean the end of the world or “death raining from the skies” which, unfortunately, is the message that many attention hungry fear mongers will convey through social media. If you have a well stocked emergency kit, a disaster/shelter plan in place, have good sources of watch and warning information, and heed all warnings and advisories only from official sources (your local National Weather Service office and the broadcast meteorologists of your choice), you will be safe. If you’re in an area where a warning has been issued, do not run outside with your camcorder to capture your ten seconds of YouTube fame, jump in a car and decide to become and impromptu “storm chaser,” or panic and try to drive out of the path of a storm. Those actions will expose you to lightning, high winds which can make driving difficult, low visibility, traffic congestion, and flash flooding which (with only two feet or less of water) can sweep you and your vehicle away. Plan ahead (as in now) for a day of severe weather, stay weather aware, and you’ll be fine. Now we can turn our attention to Thursday.
At the risk of sounding like I’m blowing my own trumpet, when I first saw this map, my immediate thought was, “Ah-Ha! Just as I thought. The severe weather threat area has been shifted to the north and east! Wednesday’s storms have overturned much of the atmosphere and laid out tons of outflow boundaries! What a mess…and forecasting nightmare.” I’m beginning to think that almost forty years of being a “weather geek” is paying off. But enough of me, back to the SPC severe outlook for Thursday. Due to the previous days severe weather and certain changes in the atmospheric “recipe,” this day presents (as stated in the SPC outlook), “SUBSTANTIAL CHALLENGES WITH RESPECT TO THE CONVECTIVE FORECAST.” In other words, severe weather is very likely, but what a headache it is trying to narrow things down to when and where. Wednesday’s storms will have had an effect on the atmosphere that will change where and when new storms form. To make matters more challenging, computer forecast models are not fully in agreement on where storms will be at the beginning of the day and where they will form as the hours pass. The threat for large hail and damaging straight line winds will definitely be present and the risk for tornadoes could be somewhat less than on Wednesday, but don’t let your guard down. Any storms that form Thursday will be just as potent as Wednesday’s storms and you should heed official information on watches and warnings with the same degree of caution. In spite of the possibility that Wednesday’s storms may have taken some of Thursday’s severe weather energy, it will be a day you’ll want to be keenly weather aware, especially in the red 30% area for parts of Illinois and Missouri. Once again, there’s no need to panic or worry. Simply be prepared, avoid the fear mongers, stick with official sources of weather information, and you will be fine. Let’s take a quick look at Friday.
By the time Friday rolls around, much of the “energy” for storms will have moved to an area stretching from Georgia northward to the DelMarVa region. Time will tell, but it appears at this time that damaging straight line winds and large hail will be the primary threats. As is the case with previous days, what transpires Friday will depend a great deal on Thursday’s storm activity. If you live in or near the 15% probability region, keep a reliable source of official weather information handy. As is always the case, as each specific forecast time draws nearer, the SPC forecasters can be more specific as to where and when storms will occur and what threats will be most prominent.
It’s my hope that these posts are helpful in your preparation for an active and interesting episode of weather. If anything, I hope to give those of you that have a degree of anxiety or phobias towards storms a sense of being in control by acquiring knowledge. Knowledge being power, and a sense of empowerment begets a calmer state of mind. In our contemporary world where divisiveness on the most menial of topics runs rampant, the human species needs all the “calm” we can get.
Let’s meet again tomorrow and take a look at this show Mother Nature has on the schedule. Who knows what changes she’ll have up her sleeve by then. In the mean time, check your NOAA weather radio, emergency kit, and plan your day accordingly. If you’d like to see all of the SPC’s information, you can find it here. If you need information from your local National Weather Service office, click your location on the “NWS Forecast Offices Map” and follow them on Twitter and Facebook. Finally, if you need information on NOAA weather radio, you can find it all here.