Wrt the upcoming tornado season, it's honestly a little troubling how close both the low frequency ocean *and* atmosphere base states are this year to 2011, minus the fact that we have a much warmer Gulf this time around (yikes).
The deep-layer zonal wind/atmospheric angular momentum distribution mid-late winter this year & of course the global SSTs are honestly about as close as it gets.
The score so far in 2025 is 33 tornadoes and that is below the average of 76 as of Febuary 15. See the graphic that updates every day at first post. Hopefully it stays below average all year but I fear will be an active season as Webb points out.
Re: 2025 Severe Weather
Posted: Sun Feb 16, 2025 12:56 pm
by cycloneye
This is very interesting from Webb about location of most of activity and possible analog years.
These are Mr Webb's analogs.
Here is the message from first tweet.
I came up w/ list of analogs for this year's tornado season & this is what the 1°x1° tornado track density composite grid looks like over the CONUS using @NWSSPC database that goes back to 1950.
Note I used a 30-year sliding base period anomaly here to account for long-term non-stationary behavior in tornado data (due to better detection & increased spotting in recent years).
Although tornadoes will still certainly occur over the Great Plains, this analog composite is highlighting an *anomalous* eastward shift in tornado activity this year, with the epicenter of anomalously positive tornado activity closer to the mid-Mississippi Valley.
What really catches my eye w/ this anomaly composite is how closely it resembles the long-term trends in favorable tornado environments (left figure from @gensiniwx & Brooks (2018)).
This suggests that this year may reinforce some of the long-term observed trends in tornado activity over the CONUS.
From third tweet:
Fwiw, here's what the 2-week total tornado count looks like in this subset of years vs climatology.
Notice the peculiar "double" peak in activity near the peak of the season w/ one peak in late April into early May & another near the end of May.
This "double" peak in tornado activity actually also shows up in the 30-year mean climo data too, as far back as the 1960s & 70s, as well as the SPC watch counts
Below is the part of Webb's message about severe weather.
-NAO regimes also usually precede periods with big tornado outbreak potential in the spring by about 2 weeks & this year's low frequency base state is very conducive to that.
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0224 AM CST Sun Mar 02 2025
Valid 041200Z - 051200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS TUESDAY AFTERNOON AND EVENING ACROSS SOUTHERN ARKANSAS....MUCH OF NORTHERN AND CENTRAL LOUISIANA AND CENTRAL/SOUTHERN MISSISSIPPI...
...SUMMARY... One or two organized lines or clusters of thunderstorm, and perhaps a few supercells, will pose a risk for damaging wind gusts, a few tornadoes and hail, primarily across parts of the lower Mississippi Valley into Southeast, Tuesday through Tuesday night.
...Discussion... Latest model output remains a bit varied concerning the evolution and motion of a significant mid/upper trough, which is generally forecast to be in the process of shifting across and east of the southern Rockies Monday night into early Tuesday. However, guidance indicates that it will remain progressive, and likely to overspread much of the Mississippi Valley by the end of the period. In lower-levels a broad deep cyclone is likely to continue to evolve, with the center forecast to track from Kansas into the Upper Midwest by 12Z Wednesday.
In the wake of a recent intrusion of dry/potentially cool air, associated with surface ridging shifting east of the Atlantic Seaboard, models indicate that an influx of moisture off the western Gulf Basin will advect eastward ahead of the cold front trailing the cyclone. However, northeast of the southeastern Great Plains into lower Mississippi Valley, the moisture return may remain elevated above a residual cool/stable near surface layer. Still, large-scale forcing for ascent and destabilization will probably be sufficient to support extensive thunderstorm development across the interior U.S., and a fairly broad area with at least a conditional risk for severe storms, given the strength of flow/shear in the evolving warm sector.
...Lower Mississippi Valley into Southeast... An initially well-defined near-surface baroclinic zone may extend from the Arkansas/Oklahoma vicinity southeastward through the lower Mississippi Valley at the outset of the period. While it appears that this boundary may become more diffuse while shifting eastward during the day, it may still provide the primary focus for an organizing cluster and/or discrete supercell development, as forcing for ascent associated with a short wave perturbation within the larger-scale mid/upper troughing overspreads the region.
Of concern, models indicate that this feature will be accompanied by an intense jet core, which may include south-southwesterly winds of 70-100 kt in the 850-500 mb layer overspreading portions of Louisiana and Mississippi. These speeds appear generally forecast within the inflow layer of potential storm development, with speeds tending to weaken to 40-50 kt as they veer to a more westerly component in the potential downdraft source region. So uncertainty exists concerning the magnitude of potential downward mixing of momentum in convective development.
Even so, particularly along the remnant boundary, the environment probably will become conducive to potential for damaging wind gusts, a few tornadoes and some hail across southern Arkansas and northern/ central Louisiana into Mississippi. As this activity spreads eastward Tuesday night, the extent to which near-surface thermodynamic profiles support a risk for damaging surface gusts and tornadoes across Alabama into Georgia remains unclear, but it seems likely to diminish with eastward extent and time.
