I’m not going to bury the lede, here. There is the potential for severe weather on Wednesday and into Thursday for south Mississippi.
All modes of severe weather will be in play, but the main concern will be for heavy rain, frequent lightning and gusty wind with every storm that develops.
Some storms will be strong with all of the above and small hail.
Few storms will be severe with all of the above and larger hail (up to the size of tennis balls) and the potential to produce a tornado. And perhaps even a strong tornado (EF2 or EF3).
From the Storm Prediction Center
The SPC will kick out their “Day 1” threat overnight and into Tuesday morning, but for now, here is the latest from the SPC:
Here is the latest discussion:
…Synopsis…
A vigorous upper low moving across central portions of the U.S. will once again be the primary upper feature of interest, as it tracks from the Texas/Oklahoma Panhandle vicinity early, to southern Missouri through the end of the period. Ahead of this system, moderately strong/accompanying flow will spread across the lower Mississippi and Tennessee Valleys and central Gulf Coast states with time. At the surface, a low is forecast to cross Oklahoma during the day, and then should cross the Ozarks through the evening eventually reaching the western Illinois vicinity by 18/12Z. Widespread thunderstorms, and substantial / accompanying severe risk, can be expected in advance of this system.
…The AR/LA vicinity eastward to portions of TN/GA and the FL Panhandle…
Showers and thunderstorms are forecast to be ongoing from Kansas southward to Texas ahead of the advancing upper system and associated cold front, and eastward across the central Gulf Coast states in a zone along a west-to-east warm front. Some ongoing severe risk will likely exist at the start of the period. With time, as moisture streams northward from the Gulf of Mexico beneath steepening lapse rates, modest heating will push surface-based CAPE into the 1000 to 2000 J/kg range with a broad warm sector stretching from the AR/LA vicinity eastward to the southern Appalachians.
Convection is forecast to increase in response to the destabilization, as persistent UVV occurs not only in the vicinity of the cold and warm fronts, but also more broadly within the general warm-advection regime. Southerly low-level flow, veering and increasing to around 50 kt from the west/southwest at mid levels will provide shear favorable for supercells. Additionally, ample low-level shear is expected to evolve through the day — particularly near the aforementioned warm front which should drift northward across Arkansas and align west-northwest to east-southeast from far southern MO to central GA by early evening.
As such, tornado risk may be maximized near this boundary — across the AR area during the day, and then later increasing eastward across AL and perhaps into GA as well, as low-level flow increases into the evening/overnight. In addition to tornado potential — including the risk for a couple of significant tornadoes across a broad area represented by the ENH/30% risk area, large hail and damaging winds will also occur in some areas.
Risk will continue through the overnight hours, tapering from west to east across the lower Mississippi Valley but continuing across the central Gulf Coast states and into the southern Appalachians through 18/12z.
Courtesy: spc.noaa.gov
As noted above, the SPC is more concerned about tornado development near the warm front. This is something we discussed yesterday as a possibility.
Karrie Meter is adamant about threat
The Karrie Meter has been kicking back numbers between 4.2 and 5.3 for about 10 days. I ran the numbers for Karrie Meter off of the late night (00z) data as well as some of the 12z data (ECMWF and got an average of 5.07 across the model data used.
The interesting thing to see was the spread within the data. Some models were running “hot” like the HRRR while others were coming in “cold” like the HRW-NSSL. All model data, except the 00z GFS showed a “TOR” number higher than the Karrie Meter. When the TOR number is higher than the Karrie Meter (that is the “Ratio” row), that indicates an increased risk for tornadoes across the area. The higher the Ratio, the higher the risk. If the ratio is below “1” the risk diminishes, but is not zero.
Looking over at the Karrie Meter map from the NAM-3km computer weather model, it shows a slightly different story than the average, but you can compare the numebrs above to the map below..
The NAM-3km data continues to kick back a solid swath of “4s” across most of the area through most of the day. And recall that the quickest way to compare the Karrie Meter to the SPC numbers is to simply take the Karrie Meter and divide it in half. From there, you can – generally – get an idea about the SPC risk.
That map shows the movement from 7am Wednesday through 4am on Thursday. And it shows a heft portion of south Mississippi in the yellow from about 1pm through 7pm.
You may be curious about how the Karrie Meter values (around a 4) are so different from the SPC values (a solid 3). is may be highlighting the area with an Enhanced Risk (as of this writing), the Karrie Meter is held back from higher values by lower shear values and helicity values within the model data for the NAM-3km data.
Timeline & Threats
Right now, it looks like the timeline of events will be two potential rounds of storms.
Round One
The first round would be in the morning between 6am and 10am. If storms develop – and that is a reasonably big if – they would have the chance to be supercellular and severe. The main concern in the morning would likely be heavy rain, gusty wind and large hail. In fact, if any storm develops during this time I think the main concern would be hail bigger than quarters.
The tornado threat may be limited by a lingering inversion, but the threat for tornadoes would be dictated storm-to-storm and not something on the wide scale that could be determined as higher or lower. And the threat for tornado development would increase later in the morning.
Round Two
The afternoon / evening event will be Round Two. This will be between 11am and 8pm. This is when individual storms ahead of the front will develop and move across the area from southwest to northeast. Storms may not truly get going south of the Highway 98 corridor. So if you live south of highway 98, a severe threat may never truly develop for you – but it is something we will continue to monitor.
Storms will have the ability to get rooted, organized and develop supercellular characteristics during this time. These storms have the potential to turn severe pretty easily given the environment.
The main threats in the afternoon will be heavy rain, frequent lightning, wind gusts up to 65mph, hailstones up to the size of tennis balls, and tornadoes. A strong tornado (EF2 or EF3) can’t be ruled out, either.
Round Three
The third round will be as the cold front passes through between 9pm and 4am. These storms may not be as potent, depending on how much the atmosphere is worked over by rounds One and Two. But it may have some stronger storms with heavy rain, frequent lightning and some gusty wind at times.
The Bottom Line
Showers storms and the potential for severe weather will persist during the next two days – both Tuesday and Wednesday. But the main threat for the most significant severe weather will be on Wednesday.
The timeline of events on Wednesday leave the area with an “all day” event where the potential for storms exists for longer than 12 hours and may start before some people wake up and linger around until after some people go to bed.
This doesn’t mean it will be storming all day long. There may be times during the day on Wednesday where it is actually “nice” outside. But, there may also be times when it is raining sideways, lightning is flashing and hail is pummeling your rooftop. Determining when your specific house or workplace will see rain, storms and severe weather is still a bit out of reach.
For now, just make sure you have your NOAA Weather radio setup with fresh batteries. Make sure it is set to the right channel and, if capable, that it is set to alert you when a warning is issued for your county. Also, download a weather app to your phone that will ping you when a warning is issued for your area. Having multiple ways to receive a warning is like setting two alarms to make sure you actually get up in the morning! Redundancy is key!
I’ll have another update tomorrow by midday as more data comes down!
