Winter only scores 53-64% — is that rain, or something else?

It's snow, not rain — and that distinction matters because it changes what actually fixes it. January (53%), February (63%) and December (64%) are held back mostly by real observed snow depth at the 1,950-1,990m boulder fields, converted to water-equivalent and run through the site's snow accumulator. Unlike the summer heat problem below, an early start barely helps here: January's morning score is 54%, almost identical to its 53% afternoon score, because snow sitting on the boulders doesn't care what time you show up. If you're planning a winter trip, check the forecast for a clear weather window after a storm, not just the time of day.

Do summer mornings rescue the heat problem the way they do at Bishop or Hueco Tanks?

Yes, dramatically, and this is the opposite pattern from winter. Scored at each day's peak heat, June is 20% green, July collapses to 1%, and August to 6% — the site's dry-heat rule (AMBER from 27°C, RED from 38°C) doing exactly what it's meant to on a high-desert afternoon. Scored at the day's low instead, as a proxy for a dawn start, the same three months jump to 78%, 62% and 56%. That's a genuine rescue, not a rounding effect — climb before the sun hits the sandstone in summer and the numbers look like spring.

Why does Joe's Valley use a 24-hour rain wait instead of Indian Creek's 48 hours?

Joe's Valley boulders are Cretaceous Blackhawk Formation and Star Point Sandstone — a fluvial-deltaic sandstone that's measurably softer than the Wingate and Navajo sandstone at Indian Creek, Zion or Red Rock. climbingforecast models it in the plain soft-sandstone bucket (24h RED window, 72h AMBER subsurface caution) rather than the desert-sandstone bucket used for Wingate/Navajo (48h RED, up to 96-168h AMBER), because Joe's rock is more wet-fragile despite sitting in the same high-desert climate. The wet-rock ethic is identical either way: never climb damp sandstone, and treat the RED/AMBER windows as a floor, not a guarantee — this data doesn't change that rule, it just tells you how often the calendar hands you a clean window.

Where does the 30-year weather data come from?

Two real NOAA-tracked stations, both in Emery/Carbon County, Utah. Temperature, rain and snow come from the Ferron COOP station (USC00422798, 1,813.6m), 25km from the boulder fields and lapse-corrected (-6.5°C/km) for the ~150m altitude gap to Joe's Valley (1,965m average across the three sectors). Humidity and wind come from Price-Carbon County Regional Airport's ASOS record (USW00093141), 57km away via the Iowa Environmental Mesonet archive — NOAA's own daily-summaries dataset doesn't publish a humidity field for that station, so the Mesonet's METAR-derived daily averages fill that gap with real observations rather than a guess. Snow depth is real station data too: observed snow depth converts to water-equivalent (using the same settled-snow density assumption documented in the site's own snow model) and feeds the drying model's snow accumulator directly. Window: 1996-2025 (30 years), scored at each day's recorded maximum temperature for the afternoon numbers and its recorded minimum for the early-morning comparison.

Data 5 min read 23 September 2026

Best Time to Boulder at Joe's Valley: 30 Years of San Rafael Swell Weather Data

Q: When is the best time to boulder at Joe's Valley?

November is the numeric peak at 81% green days for a full afternoon session, with March (78%) and April (77%) close behind and October (69%) a solid fourth. That's the classic Utah high-desert shoulder-season pattern guidebooks already point to — but Joe's Valley has a wider gap between its best and worst months than most US bouldering destinations, because it gets squeezed from both ends of the calendar: real winter snow at altitude, and real desert heat in summer (see the next two questions).

Joe's Valley is one of American bouldering's great sandstone playgrounds — Left Fork and Right Fork's historic core, developed by Boone Speed, Jason Kehl and others through the early-to-mid 1990s, and New Joe's newer, steeper testpieces up Cottonwood Canyon, all set on the west flank of the San Rafael Swell in central Utah's high desert. The rock is Cretaceous Blackhawk Formation and Star Point Sandstone: golden-brown, pebbly-featured, and softer and more wet-fragile than the Wingate sandstone at Indian Creek a few hours south. We wanted to know what the calendar actually looks like here — including the part that makes Joe's Valley different from most other US desert bouldering: it isn't just a heat story.

We replayed 30 years of real daily observations from the NOAA NCEI Ferron station (temperature, rain, snow) and the Price-Carbon County Airport ASOS record (humidity, wind) through the climbingforecast drying model, run for Joe's Valley's soft-sandstone bucket. This piece uses the model's dry-heat climbability check and its real-snow-depth accumulator, so it can separate two things that guidebooks usually blur together: a genuine winter snow problem, and a genuine summer heat problem, with a wide, better-than-you'd-guess window between them.

Best months to boulder at Joe's Valley, scored at the day's peak heat — % green (climbable) days by month across all three sectors. March-April and October-November are reliable; winter is a snow story and summer afternoons collapse.

When is the best time to boulder at Joe's Valley?

The numeric peak is November — 81% green days for a full afternoon session — with March (78%) and April (77%) close behind and October (69%) a solid fourth. That's the reliable core of the season: two shoulder windows bracketing both the winter cold and the summer heat, exactly where you'd expect from a 1,950-1,990m high-desert boulder field.

What's less obvious is how different the two off-seasons are from each other. Winter (December-February, 53-64% green) is held back by real observed snow sitting on the boulders — a genuine accumulation problem that doesn't care what time of day you show up. Summer (June-August, 1-20% green in the afternoon) is a heat problem instead, and heat problems respond to an early alarm the way snow doesn't (see below). Treating "winter is bad" and "summer is bad" as the same kind of bad is the mistake this data corrects.

Month-by-month conditions (afternoon)

Month	Green Days	Amber Days	Red Days	% Green	Green + Amber
Jan	15.6	0.7	13.0	53%	56%
Feb	17.8	0.9	9.4	63%	66%
Mar	23.9	1.6	5.2	78%	83%
Apr	22.1	2.0	4.5	77%	84%
May	18.2	5.7	5.7	61%	81%
Jun	5.7	18.3	4.8	20%	83%
Jul	0.4	21.4	8.2	1%	73%
Aug	1.8	18.6	9.3	6%	69%
Sep	10.2	11.6	7.9	34%	73%
Oct	21.2	3.0	6.5	69%	79%
Nov ★	24.2	1.4	4.3	81%	86%
Dec	19.2	0.7	10.0	64%	67%

Winter's problem is snow, not rain — and an early start doesn't fix it

January, February and December sit in the 53-64% range, and the red days behind that number are overwhelmingly a snow story: real station-observed snow depth, converted to water-equivalent and run through the drying model's snow accumulator, not a "recent rain hasn't dried yet" story. That distinction matters for trip planning. Scored at dawn instead of the afternoon, January barely moves — 54% versus 53% green — because a boulder field under snow is under snow regardless of the hour. If you're planning a winter session, the lever that actually works is picking a clear stretch after a storm has cleared, not shifting your start time.

Summer afternoons collapse — but dawn patrol genuinely works

Scored at peak heat, June drops to 20% green, July to a near-total 1%, and August to 6%, with real RED "too hot to climb well" days appearing on top of the amber haze — the site's dry-heat rule (AMBER from 27°C, RED from 38°C) catching genuine high-desert afternoon heat on sun-baked sandstone. Scored at the day's low instead — a proxy for a first-light start — the same three months jump to 78%, 62% and 56% green. Unlike winter's snow problem, this is a heat problem, and heat problems respond to timing: climb before the sandstone has baked all morning and Joe's Valley's summer looks like its spring.