As we head toward the end of 2020 it is only fitting that the year end with a chance for life-threatening weather. Shows and storms will develop as early as Wednesday and look to last through Thursday for the Gulf Coast. This may be a multi-day event for some places. That means one round of storms one day, and then perhaps another round of storms in the same spo the next day.
This year has thrown everything at us, all year, so the Year figures, ‘what is one more shot for storms, am i right?’
You are wrong, 2020. And I’m glad you won’t be around much longer.
From the Storm Prediction Center
The SPC has already pegged the region with a chance for a few severe storms. for both Wednesday and Thursday.
Keep in mind, like I always say, that just because the SPC highlights things this far in advance doesn’t necessarily mean the storms will be that much more potent. It is more so that the meteorologists at the SPC have identified a situation where they are confident that severe weather will occur.
From the SPC:
The medium-range models move an upper-level trough across the southern Rockies and central High Plains on Wednesday. At the surface, a cold front is forecast to advance southeastward into the mid Mississippi Valley and Arklatex.
Thunderstorms appear likely to develop along and ahead of the front during the day due to weak destabilization and strong large-scale ascent. Moisture advection is forecast to continue during the day across the lower Mississippi Valley in the presence of a pronounced low-level jet. In spite of weak instability, very strong wind profiles associated with the low to mid-level jet structure, could enable thunderstorms that obtain a severe threat.
Cells that initiate well to the east of the front across the moist sector will have potential to become supercells. The main threat would be for a few tornadoes and isolated wind damage.
The potential appears great enough to add a 15 percent contour for parts of the lower Mississippi Valley.
On Thursday, an upper-level low is forecast to develop in the southern Plains. In response, the low-level jet in the central Gulf Coast states is forecast to strengthen. Thunderstorms will be possible in the Tennessee Valley and central Gulf Coast states along the axis of the low-level jet and further to the west, along the cold front. Instability is forecast to remain weak from Wednesday into Thursday.
However, strong wind profiles should offset this limitation, with the possibility of a severe threat continuing into Thursday. The main severe weather potential would be for an isolated tornado and wind damage threat with clusters that organize during the day. The wind damage threat could become more widespread if a squall-line can develop across the region.
A 15 percent contour has been added to parts of the central Gulf Coast for Thursday to account for this possibility.
SPC.NOAA.GOV
The SPC noted that while instability may be the limiting factor, the wind profiles will be more than sufficient to overcome surface instability. Plus, as we will see in the data, it looks like widespread ascent throughout each level of the atmosphere will be sufficient for ascent. In other words, while it may not show up in certain parameters at this time, the background environment will promote quickly rising air.
The Data
Data from the GFS and Euro operational models shows a difference in timing, and a slight difference in potency of the next system. The Euro is a bit slower and further north with the low at 500mb while the GFS is faster and a bit south.
The Ensembles show a similar story between the GEFS, EPS and CMCE.
You can see that since we are about 3-5 days out there is still a fair bit of uncertainty between the modeling. Because of this, the severe weather threat is not a complete “Slam Dunk” but there is sufficient evidence to support the threat for a few severe storms.
Between all of the available model data on Sunday morning, here is a look at the placement and breadth of the precipitation that will be falling Thursday evening.
Karrie Meter & CIPS Analogs
The Karrie Meter, run via the GFS, shows a wide area of modest numbers (between 1 and 3). That would convert back to a Marginal Risk to Slight Risk from the SPC.
Right now, though, because the Karrie Meter is tied to the available model data, it can’t pick up on things that aren’t there. And, as noted by the SPC, there are certain parameters that are coming in a bit lower than ‘needed’ for severe weather. Even though the background environment would be sufficient for those numbers to be higher.
The CIPS Analogs uses a similar pathway to asses the severe threat at the Karrie Meter. CIPS looks back in time and finds all of the situations where the atmosphere looked like the models show the atmosphere will potentially look like for any one event. And then it searched the databases for all of the weather that happened on days that looked similar.
And the CIPS shows a threat for severe weather is warranted.
Right now, the CIPS shows this as historically more of a wind event than a tornado threat. But keep in mind that straight-line winds from thunderstorms can sometimes do just as much damage as a tornado. So, I wouldn’t sleep on this threat just because at this point it doesn’t appear to be as much of a tornado risk.
The Bottom Line
a potentially multi-day severe weather event is looking possible for December 30th and December 31st. The threats may include very heavy rain, localized flooding, wind gusts up to 70mph, hail up to the size of quarters, and the potential for a few tornadoes. That threat will stretch from western Louisiana through Mississippi, Alabama and the Florida panhandle.
The specific timeline is still be nailed down. but for those in Louisiana this looks like a Wednesday event, for those in Mississippi this is looking like a Wednesday and Thursday event, and for those in Alabama and Florida, this is looking more like a Thursday event.
But that may change. As the shorter-range model data comes down, we will start to get a better idea of specifics. This storm system is just approaching the West Coast. Once it gets close enough to sample the storm with NWS weather balloons, then we will get a much better idea of what may occur – and when.
For now, double-check the batteries in your NOAA Weather Radio, make sure you have a good weather app downloaded to your phone, make sure your WEA alerts are turned on, and go over your severe weather plan.
I will continue to post updates as we get closer!
