Quiet Wednesday, stormy on Thursday
By Thursday, a storm system will bring another risk of severe weather to the area.
Today and Tonight: Wednesday will offer one more tranquil and warm afternoon. High temperatures will make it into the mid 80s with some sun, but clouds should tend to increase in coverage through the day. Expect south winds of 10-15mph. Showers and thunderstorms are expected to move into the area overnight and into Thursday Morning. Temperatures will hang around 70 degrees with south winds of 10-15mph.
The National Weather Service (NWS) Storm Prediction Center (SPC) has issued a “slight risk” for severe weather on Thursday. This means scattered severe storms are possible within the forecast area. An isolated intense thunderstorm is possible. On a scale of 1 (lowest) to 5 (highest) severe weather threat, this event is a 2. Another way of describing the threat is that there is a 15 percent chance of experiencing severe weather within 25 miles of a given point in the risk area.
*There is some forecast bust potential with this setup. If thunderstorms develop along the Louisiana Coast first, much of the energy could be robbed from inland storms keeping severe weather at a minimum. Additionally, the position of a pocket of slower winds aloft will limit storm potential somewhere in the region. It will be difficult to pinpoint where that sets up until tonight.
1) Large Hail – could exceed 1” in diameter in the strongest storms
2) Gusty Wind – possibly in excess of 58mph
3) Other – heavy rain, isolated tornado can’t be ruled out but seem less likely
Precipitation: The NWS Weather Prediction Center (WPC) is forecasting 1-3” of rain for the 13 Parish, 3 County Forecast Area through Thursday. Most locations should receive the lower amounts, but particularly heavy thunderstorms will tip gauges toward the higher amounts in a few locations.
Estimated Timeline: Most of the action is expected early Thursday. Showers and thunderstorms will arrive after midnight and persist through midday. 2am – 2pm seems to be a reasonable window at this time. Of course, the Thursday Morning commute falls right in the middle of this timeframe. So, regardless of severe weather, rain, storms and possibly some delays can be expected for drive time.
Impacts: Large hail can damage property such as plants, roofs and vehicles. Strong wind is able to break off large branches, knock over trees or cause structural damage to trees. Driving in hail can cause your windshield to shatter creating a high risk for injury. Being outdoors or near windows during high winds can leave you vulnerable to be struck by flying debris.
Actions: Move valuables under a sturdy shelter. Tie down loose objects. If there is a weather warning active during your drive, consider waiting until that storm passes. Have access to watches and warnings such as with a NOAA Weather Radio or from the WBRZ Weather Team on Facebook and Twitter. Additionally, the *free* WBRZ WX App. sends push notifications to Apple and Android devices if a watch or warning is issued for your location. Remember, a watch means “conditions are favorable, and a particular threat could develop” and a warning means that “threat is happening and you should take action immediately.” For much more detailed severe weather safety, CLICK HERE.
Up Next: Clearing is expected on Thursday Night. On the other side of that storm system, humidity may go down a touch and this will be best noticed with Friday and Saturday Morning temperatures in the upper 50s. Highs will remain above average with afternoon readings near 80 degrees. Another short stretch of sunny days is expected before yet another impact storm system late weekend.
THE SCIENCE: A shortwave trough is moving across the Midwestern U.S. and into the Mid-Mississippi River Valley. As this happens, a surface low and attendant cold front will slide from Oklahoma to Missouri by Thursday Afternoon. By that time, this system will feature a highly divergent and diffluent jet stream with 90+ knot wind speeds at 250mb. In addition, the shortwave trough axis will begin taking on a negative tilt as it moves east and this trend can be seen on forecast models down to 500mb as well. The strong wave will result in a strong area of positive vorticity advection and thus ample mid-level lift. 700-500mb lapse rates will be in excess of 7°C with a dry pocket noted as well. Surface based CAPE is expected to be in the 1,500 – 2,000 range. As such, thunderstorm updrafts will be quite intense with the dry air intrusion increasing the likelihood of negative buoyancy and therefore downdrafts with gusty winds as well. Helicity is forecast to be below 200 which would fortunately keep the tornadic threat a bit lower. At this time, fairly unidirectional wind fields seem to favor the formation of an MCS and straight line winds, while a low freezing layer and strong instability bring an unusually high threat for hail. There is one, potentially crucial, mitigating factor to this event. If showers and thunderstorms initiate in coastal areas first, this would cut off some of the energy and greatly reduce inland severity on Thursday Afternoon. So yes, there is some bust potential in this forecast. The National Weather Service continues to note a “coupled” jet stream showing up on forecast models. Per their discussion, it will be where the northern polar front jet stream and southern subtropical jet stream meet that severe weather is most likely to occur. This may not be known until morning observations on Thursday. The Storm Prediction Center has outlined the entire WBRZ Weather forecast area in a “slight risk” for severe weather for this event. It would not be surprising to see this upgraded as this threat seems much higher than this past weekend. The frontal passage will allow some slightly drier air to settle in for 24 – 36 hours with Friday and Saturday featuring mainly clear skies and low temperatures in the upper 50s. Highs will not change much. The next storm system will come racing into the Lower 48 and toward the Gulf Coast by Sunday Night. This one is taking a more southern track which presents perhaps the greatest threat for severe weather of the four waves we’ve seen in the last week. In addition, forecast models are being rather aggressive with rain. Between the Thursday and Sunday/Monday events, 3-6” will be possible.