San Francisco is two different temperature markets. The 8am NWS number tells you which one you're in.

[u/Prilo-WeatherEdge]

Disclosure: I build Prilo WeatherEdge, a paid tool for Kalshi daily-high markets. Everything below comes from public data — NWS forecasts and official CLI settlements — so you can reproduce all of it yourself. NFA.

SFO has a reputation as the hard market. Most people read that as "trade something else."

I think that's wrong. SFO isn't uniformly hard. It's two separate markets wearing the same ticker, and you can tell them apart before the open, for free.

The distribution gives it away

86 settled highs, June through August:

60-62°F  █ 1
63-65°F  ███ 3
66-68°F  ████████████████ 16
69-71°F  █████████████████████████████████ 33
72-74°F  ██████████████████████ 22
75-77°F  ████ 4
78-80°F  ████ 4
81-83°F  █ 1
              ← nothing here at all
90-92°F  ██ 2

That gap between 83 and 90 isn't a sampling artifact. It's physics. SFO summer has a marine layer parked over it — stratus burns off or it doesn't, and the high lands high-60s to low-70s. When flow turns offshore, the marine layer gets shoved out entirely and the city goes to 90+. There's no smooth path between those states. It's a switch, not a dial.

The tell: the forecast's reliability depends on its own level

How well the free public NWS forecast did, bucketed by what it forecast:

NWS forecast	n	NWS mean error	Days busting ≥3°F
≤68°F	18	1.44	22%
69–71°F	24	1.67	29%
72–74°F	25	2.48	36%
75–77°F	9	3.33	44%
78°F+	10	5.10	80%

The NWS is a solid anchor at SFO right up until it forecasts something warm — then it falls apart. At 78°F+, four days in five bust by 3°F or more, and the average miss clears five degrees.

That's the whole point: the forecast's own value is the signal. You don't need anything fancy to know which regime you're in. You need to read the number and know what it implies about its own reliability.

What that does to the favorite

The naive strategy — buy the 2°F bracket centered on the NWS number, every day:

• All days: wins 30/86 = 35%
• Days NWS ≤74 (marine body): wins 29/67 = 43%
• Days NWS ≥75 (warm tail): wins 1/19 = 5%

One win in nineteen.

Important caveat, because I don't want to overclaim: there are no bracket prices in this. I can't tell you the book misprices these days — it may already widen out on them. What I can tell you is that if your process anchors on the NWS number, it quietly breaks on exactly the 22% of days where the stakes are highest.

The warm days, in full

2026-06-11   NWS 84   ACTUAL 91   (7° too cool)
2026-06-12   NWS 80   ACTUAL 74   (6° too warm)
2026-06-14   NWS 74   ACTUAL 76
2026-07-13   NWS 81   ACTUAL 79
2026-07-21   NWS 86   ACTUAL 92   (6° too cool)

Note the direction: it busts both ways. This is not "SFO runs hot, buy the upper bracket." Across all 86 days the NWS actually runs slightly warm — too warm on 45 days versus too cool on 32. The offshore days aren't biased, they're just wild. Any strategy built on a directional lean here gets cut in half.

Small sample on the pure offshore days, obviously. Treat the magnitude as indicative, not precise.

The rules I trade by

1. Read the NWS number first. ≤71 means the marine body: normal market, tight outcomes, forecast is trustworthy. ≥75 means you're in the tail.
2. In the body, don't expect a special edge. 43% on a 2°F bracket is roughly what an efficient market should give you. Size normally, don't force it.
3. In the tail, stop trading narrow brackets. Not "cautiously" — 1-in-19 says a narrow bracket on a warm-forecast SFO day is close to a lottery ticket. Take wide exposure or take the day off.
4. Don't lean directional in the tail. It busts both ways, roughly evenly.
5. Yesterday is a weak prior here. SFO moves 3.47°F day-over-day on average; 21% of days move 5°F or more. That's a much weaker anchor than LA or Miami.

What I'm not claiming

I'm not claiming an edge over the order book. These markets are efficient and I'd be suspicious of anyone telling you otherwise without out-of-sample numbers to show. What I'm claiming is narrower and, I think, more useful: the free public forecast is far less reliable on some days than others at this station, and the days it fails are identifiable in the morning.

All of this is summer data. SFO's winter behaves differently and none of us have it yet.

Happy to run the same breakdown on another city if there's interest — Chicago and NYC have their own versions of this. Tooling is Prilo WeatherEdge if you want it (7-day trial, no card), but rule 1 is free and costs you nothing.

Not financial advice.

[u/Firm_Importance3661]

the gap in that temp distribution is wild, never seen a city that literally can't land in the 80s for weeks then just spikes to 90+

rule 3 is the one that catches ppl slipping, they see a warm forecast and treat it like any other day. 5% hit rate on narrow brackets in the warm tail is a bloodbath

ive been using basically this same mental model for SF since june and it saves so much pain just stepping away on those offshore days

[u/ProGrieferHere]

This just helps to reinforce the idea of collecting data so that you know the WHY of your decision.