What is the MRGL severe probability?

A 5% severe probability within 25 miles of any point in the outlook area. That probability is the formal threshold that defines a Marginal Risk on the SPC categorical scale.

What Does MRGL Mean in Weather? — SPC Marginal Risk (Level 1)

What Does MRGL Mean in Weather? — SPC Marginal Risk (Level 1)MRGL (Marginal Risk) is level 1 of 5 on the SPC convective outlook scale. Isolated severe storms possible, short-lived. What MRGL means at the radio, how it differs from SLGT, and what spotter / EMA activity MRGL triggers.MRGL stands for Marginal Risk — the lowest of the five severe-weather risk levels on the Storm Prediction Center's categorical convective outlook (level 1 of 5). Isolated severe storms are possible, but generally limited in coverage and short-lived. A few storms may produce 1″ hail or 58 mph wind; a brief tornado is possible but not the primary concern.MRGL severe probabilityThe formal SPC threshold for Marginal Risk is a 5% severe probability within 25 miles of any point in the outlook area. That probability covers any combination of severe wind, severe hail, or tornado.MRGL vs. SLGTMRGL (level 1) means isolated severe storms possible — short-lived and few in number. SLGT (level 2) means scattered severe storms possible — multiple cells, some better-organized, with a higher tornado/hail/wind probability. SLGT is roughly twice as common as MRGL on active days and is the threshold at which most EMAs start coordinating proactively.Common MRGL scenarios

Disorganized afternoon convection with weak shear.

Pulse storms in the warm, humid southeast.

Isolated supercells in a sub-marginal environment (just enough shear to organize one cell out of a few hundred).

What MRGL triggers operationallyMRGL is typically the lowest tier that triggers active spotter networks in most regions. EMAs monitor but don't activate; broadcast meteorologists may break in during the most active part of the afternoon but rarely cut programming. Outdoor events with crowds (concerts, sports) move to a "ready to evacuate" posture.How MRGL verifiesA typical MRGL day produces one or two isolated severe reports across a several-state area — a quarter-sized-hail report from a pulse storm, a single 60 mph wind report from a downburst. Most MRGL days verify with no significant severe weather at all. On the calendar, MRGL is the most-issued risk level after TSTM.See the full SPC convective outlook guide for the complete scale and the supercell / MCS / QLCS glossary.

Frequently asked questions

What does MRGL mean in weather?: MRGL stands for Marginal Risk — SPC's level 1 of 5 severe categories. Isolated severe storms are possible, generally limited in coverage and short-lived. A few storms may produce 1″ hail or 58 mph wind; a brief tornado is possible but not the primary concern.
What is the difference between MRGL and SLGT?: MRGL (level 1) means isolated severe storms possible — short-lived and few in number. SLGT (level 2) means scattered severe storms possible — multiple cells, some better-organized, with a higher tornado/hail/wind probability. SLGT is roughly twice as common as MRGL on active days and is the threshold at which most EMAs start coordinating proactively.
What is the MRGL severe probability?: A 5% severe probability within 25 miles of any point in the outlook area. That probability is the formal threshold that defines a Marginal Risk on the SPC categorical scale.
What does MRGL trigger operationally?: MRGL is typically the lowest tier that triggers active spotter networks in most regions. EMAs monitor but don't activate; broadcast meteorologists may break in during the most active part of the afternoon but rarely cut programming. Outdoor events with crowds move to a "ready to evacuate" posture.
What types of weather happen during MRGL?: Isolated severe reports — typically a quarter-sized-hail report from a pulse storm, a single 60 mph wind report from a downburst. Most MRGL days verify with no significant severe weather at all; the few that do tend to produce one or two warned events in a several-state area.

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