April 16, 2026

With severe weather season in full swing, we've been pushing hard to make the SPC probability layers on NWSAlerts more informative and easier to read. Beta 1.5.3 is a focused update to how significant severe weather areas are displayed on the map — and it's a big improvement over what was there before.

What Changed: From "SIG" to CIG

If you've used the SPC probability layers before, you may have noticed a hatched overlay inside certain probability polygons. That hatching indicates a significant severe weather area — meaning the storms in that region are expected to be stronger or more impactful than the base probability alone suggests.

SPC recently updated how they classify these areas. Instead of a single generic "SIG" designation, they now use a tiered system called Conditional Intensity Groups (CIG). There are three levels:

• CIG 1 — Higher-end significant severe weather. For tornadoes, this means max intensity around EF2. For wind, gusts of 65+ knots (75+ mph). For hail, stones 2 inches or larger (tennis ball size).
• CIG 2 — More intense. EF3 tornado potential, 73+ knot wind gusts or MCS/derecho scenarios, hail 3.5 inches or larger (softball size).
• CIG 3 — Extreme potential. Violent EF4+ tornadoes, high-end derecho events, or extreme hail.

NWSAlerts now reads these CIG levels directly from the SPC GeoJSON and displays each one with a distinct hatch pattern on the map:

• CIG 1 — forward diagonal lines ( / )
• CIG 2 — backward diagonal lines ( \ )
• CIG 3 — crosshatch ( X )

At a glance, you can tell not just where significant weather is expected, but how significant.

Updated Map Popups

Click anywhere inside a CIG hatched area and the popup now tells you exactly what you're looking at. You'll see the CIG level for each hazard (tornado, wind, hail) along with a short plain-language description — no need to remember what CIG 2 means for wind gusts.

Separate Day 1 and Day 2 Probability Toggles

Previously, enabling the tornado probability layer showed both Day 1 and Day 2 together. A lot of you wanted to be able to look at just one day at a time — especially when comparing the two outlooks side by side.

Beta 1.5.3 splits these into 6 independent controls under the SPC dropdown: Tornado D1, Tornado D2, Wind D1, Wind D2, Hail D1, and Hail D2. Turn on exactly what you want to see.

SWCC Updated Too

The SPC probability card on the SWCC page now shows CIG chips alongside each hazard row when significant areas are present in the current outlook, with the intensity level and description displayed inline.