Blood Storm
Worrying clouds gather and roil above and the first drops reveal its sanguine nature: blood falls from the sky, soaking the ground in a charnel maelstrom and invigorating the local undead.
Disturbing. The unnatural blood weather soaks into both clothing and minds. While within the storm living creatures are rattled and are considered to be roughing it on any rests they make.
Slippery. The deluge turns the area into difficult terrain .
Undead Weather. The blood storm’s effects spread across the landscape in a 20-mile radius, filling the area with howling winds and blood. The maximum range of any sight or hearing-based senses is 30 feet (except for especially loud, booming noises).
In addition, undead creatures gain 5 (1d8) temporary hit points at the start of every turn while within the storm if they have at least 1 hit point.
The party can build and sanctify a shelter by combining a group Engineering check and an individual Religion check. Or they can simply press onwards and endure the downpour of blood by making Wisdom saving throws.
Critical Failure. A day soaked in blood douses both morale and equipment. Each party member suffers a level of strife and 4 (1d6) Supply are soaked in blood and destroyed.
Failure. Grossly soaked but still pressing on, 3 (1d4) Supply is soaked in blood and destroyed and each party member suffers a random short-term stress effect from the ordeal.
Success. The adventurers keep out of the worst of the storm and suffer no further effects as it passes.
Critical Success. Braving the storm fills the adventurers with confidence in tackling the supernatural. The party members make saving throws against the frightened condition with advantage for the next 24 hours.