The Storm Prediction Center has bumped parts of Mississippi up into a Moderate Risk for severe weather. That is a “4” out of “5” on the 1-to-5 scale where “5” is the highest risk for the most significant severe weather.
For south Mississippi, a Slight / Enhanced Risk persists for most of the area with a sliver of Moderate Risk introduced to the north.
A reminder that these Risk areas on a map do not have “hard” lines in real life. Within the outlooks, the SPC notes that the different risk levels on the map indicate the threat/risk within 25 miles of a point. So the farthest southern tip of the moderate risk on the map indicates a Moderate Risk up to 25 miles south of that point.
From the SPC
The Storm Prediction Center has shifted things slightly for parts of south Mississippi, moving the highest risk to the northern side of the area.
Broken down into the individual threats (Wind, Hail Tornadoes), the maps look like this:
The black-hatched area on the maps above indicate a 10-percent chance of a significant severe weather event. That would be hail larger than golf balls and tornadoes stronger than an EF2.
Here is the latest Discussion:
…SUMMARY…
A broad area of substantial severe weather potential — including risk for large hail, damaging winds, and several strong tornadoes — is anticipated Wednesday from the Arkansas/Louisiana vicinity eastward across the central Gulf Coast states/southern Appalachians.
…Synopsis…
A compact/vigorous upper low initially over the Oklahoma area is forecast to move steadily eastward through the period, spreading strong flow aloft and a broad zone of enhanced ascent across the south-central and into the southeastern CONUS. This low will reach the Ozarks overnight, flanked by ridging across the Rockies, and along the East Coast. At the surface, a 998 mb low is progged to advance eastward along a similar track, crossing northern Oklahoma/southern Kansas through the day, and then the Ozarks overnight.
A trailing cold front will shift from eastern portions of the southern Plains and across Arkansas/Louisiana through the afternoon, and then across the Tennessee Valley and central Gulf Coast states through the end of the period.
Meanwhile, a warm front extending eastward from the low across northern Arkansas/southern Missouri and then east-southeastward across the Tennessee Valley into Georgia will linger in place on its eastern fringe, but will lift slowly northward in advance of the progressing low. These two fronts will outline a broad/moist warm sector, which will gradually destabilize through the day supporting a widespread/potentially significant severe weather event.
…Southern MO/AR/LA vicinity east to the TN valley/western GA…
Scattered showers and thunderstorms are forecast to be ongoing ahead of the cold front from eastern Oklahoma/western Arkansas southward into east Texas, and east-southeastward along the warm front across the Tennessee Valley area to the southern Appalachians. As the synoptic system advances, convection over the central Gulf Coast region/Southeast should remain generally north of the warm front, while some decrease in pre-cold-frontal convection is also expected through the morning. This should permit some heating of the moist (generally mid 60s dewpoints) warm-sector boundary layer, pushing mixed-layer CAPE values into the 1000 to 2000 J/kg range by early afternoon.
New storm development is expected to occur from the southwestern Missouri vicinity southward across the Arklatex region by early afternoon. Strong shear — including veering of the wind field with height from southerly to southwesterly — will support ready evolution of rotating updrafts, with some long-lived storms likely evolving with time. Along with large hail potential, locally damaging winds will be possible, along with a steadily increasing tornado risk through the afternoon. As storms move into central and eastern Arkansas, at least a few intense supercells are expected, within the broader area of storms.
Potential for a couple of significant tornadoes is apparent, with this risk spreading into southwestern Tennessee and northern Mississippi with either pre-cold-frontal storms moving eastward into the region, or with other cells developing in a zone of increasing low-level warm advection in the warm sector/near the warm front. During the evening and into the overnight hours, substantial strengthening of the low-level southerlies across the central Gulf Coast region is expected.
While some diurnal decrease in instability is expected, this should be more than offset by the increasing low-level and deep-layer shear. As such, risk for additional/significant tornadoes is anticipated to last through the overnight hours, focused particularly across much of Alabama. Hail and relatively widespread damaging winds will also be possible across this same region.
Courtesy: spc.noaa.gov
Updraft Helicity streaks
A lot of you that have been following these updates over the years (seven! holy moly!) have learned that the Updraft Helicity streaks within the model guidance can do a good job to help highlight where the most potent storms may be. This isn’t a perfect estimate, but it is a good first look at what may occur and a good “ballpark” for overall coverage.
The maps above are courtesy of Pivotal Weather and they highlight three different estimates – from lower threat to higher threat – within the modeling. The interesting thing to note is that all three produced a potent storm that moves from SW to NE right through the heart of south Mississippi.
Again, I want to stress that none of the above maps are “right” or “wrong” but instead are used as guidance to come up with a forecast for where the highest potential may develop…
Above is the areas that show to have the highest potential for seeing the strongest storms for south Mississippi only.
If you live within the orange – and particularly the red – I would really encourage you to keep extra tabs on the weather during the day on Wednesday. This doesn’t mean if you live outside of these areas you can let your guard down, but it means that if you are inside of these areas, you should pay a bit more attention to Mother Nature.
In the orange circled area, Bay Springs, Leakesville, New Augusta, Purvis, Collins and tAylorsville, and points nearby and points between.
The red circled area includes places like Hattiesburg, Petal, Ellisville, Laurel, Waynesboro, and Richton. Points nearby and points between.
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 for some guidance, the early morning data (6z) for others and got an average of 5.00 across the model data used.
The interesting thing to see was the spread within the data. Some models were running “hot” like the HRRR, HRW-ARW and NAM-3km while others were coming in “cold” like the HRW-NSSL and GFS. 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
Not much has changed here. It looks like the timeline of events will be two or three potential rounds of storms. And Round Two looks to be the most potent.
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!
Thank you Nick, as always for your diligence in trying to keep us in the know!