Small Risk For Severe Storms Ahead Of Cold Front

Update 3:09 PM. Updated SPC graphic for Alabama, no other changes.

SUMMARY: Ahead of a strong cold front, showers and thunderstorms will occur late this evening into the overnight hours. Some of these storms could be strong to severe especially across northwest Alabama.

NWS Graphics:

NWS Huntsville Svr 10/15/21
A few strong/severe storms are expected later this evening/overnight as a cold front sweeps across the region. The main threats with the strongest storms will be damaging winds, but a tornado or two cannot be ruled out. Stay weather aware this evening

TIMING: Beginning around 9:00 PM this evening (10/15) and lasting through 2:00 AM across northwest Alabama.

Potential Hazards: Heavy rainfall and strong-locally damaging winds gusts from 40-60 MPH. A tornado or two cannot be ruled out.

Potential Impacts: Heavy rainfall along with gusty winds can knock down trees into power lines, causing power outages. Heavy rainfall could cause flooding in some areas. Damaging winds are winds of 58 MPH or stronger, which could damage roofs, outbuildings, sidings, gutters, sheds, and trees. Gusty winds are also possible outside of thunderstorms. Tornadoes – if any – will be brief and weak but is still enough to cause damage to mobile homes and roofs.

CONFIDENCE IN POTENTIAL HAZARDS: 9/10. Very confident.

Recommended Preparedness Actions: Stay weather aware this evening as the cold front gets closer. Stay inside, and have multiple ways to receive warnings should one be issued. Take the warning seriously. A Severe Thunderstorm Watch will likely be issued well ahead of the cold front as the storms get closer. If a Tornado Warning is issued – take the Warning seriously, do not wait to see or wait for confirmation because this will be a late-night event where tornadoes will be difficult to confirm.

DISCUSSION

SPC has placed a small corner of the state in a Slight Risk for severe thunderstorms this afternoon and evening, with a Marginal Risk going across the rest of Coverage Zone 1. Seeing no Slight Risk in Coverage Zone 2 will leave any discussions for Central Alabama out. HRRR model data shows storms coming in the form of a line expected to reach the AL/MS border around 03Z (9:00 pm). SBCAPE at the arrival will range from 500-1,000 J/KG and quickly dissipate with the arrival of the front. Updraft Helicity values are not overall impressive but are there nonetheless. This ties in with the STP values at about 2/10, which leaves a non-but-not-zero chance of a tornado as the cold front gets closer.

SCP however is favoring supercell development with the line, but again, it quickly dissipates with the arrival of the cold front. Hard to tie these parameters perfectly together. Graphics below. Stay safe, and get ready for fall after this cold front.

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