CPC proposes moving UVI forecasts 3 hours later as GCAFS replaces GEFS aerosols

On March 13, 2026, NOAA's Climate Prediction Center issued PNS 26-18, soliciting comments through April 20, 2026 on a proposed change to the daily Ultraviolet Index (UVI) forecast delivery time.

CPC would move the UVI forecast from 1830Z to 2130Z.

CPC says the UVI workflow depends on GEFS aerosol guidance to preserve realism in regions affected by wildfire smoke and haze. Under the proposed migration to GCAFS v1.0, those aerosol forecasts would arrive 3 hours later, so the downstream UVI product would shift by the same amount.

The notice also says CPC considers the UVI output quality with GCAFS aerosol input to be comparable to current operational products.

What to watch

If you use the UVI product operationally, the timing change is the main story:

• CPC says the change would show up on the main CPC UVI page
• it would also show up on NOMADS
• comments are open through April 20, 2026

If you poll these products on a fixed daily clock, update that schedule.

This matters if you:

• compare GEFS Chem or future GCAFS-style aerosol guidance against CPC UVI output
• have jobs or dashboards that assume UVI is ready around 1830Z
• care about smoke, haze, or UV-sensitive workflows and use UVI as a daily input

NOAA is explicitly warning that the proposed delivery time would become 2130Z.

Why this is tied to GCAFS

In the earlier NOAA proposal to replace GEFS aerosols with GCAFS v1.0, NOAA said the new system would provide:

• a 5-day forecast
• 3-hourly output
• forecast runs at 00 and 12 UTC
• a companion analysis system, GCDAS, at 00/06/12/18 UTC

This UVI notice is the downstream consequence of that upstream change.

Related reading

• NOAA proposes replacing GEFS aerosol products with GCAFS v1.0
• GEFS aerosol 06/18Z cycle discontinuation proposed for 2026
• GEFS Chem

Sources

• NWS PNS 26-18 / UVI delivery-time proposal (Mar 13, 2026): https://preview-forecast.weather.gov/product.php?format=TXT&glossary=1&issuedby=WSH&product=PNS&site=BYZ&version=17
• NWS PNS 26-07 / GCAFS v1.0 proposal: https://www.weather.gov/media/notification/pdf_2026/pns26-07_GCAFSv1.pdf
• GCAFS v1.0 products supplement: https://www.weather.gov/media/notification/ref/GCAFS_v1_Products_Supplemental.pdf
• CPC UVI page: https://www.cpc.ncep.noaa.gov/products/stratosphere/uv_index/uv_current.shtml