Southeast Arizona: Warm, Dry Week with Chilly Valley Mornings — Frost and Fair Weather Ahead

It's a week for desert clarity: mostly sunny skies, very little moisture, and a broad warm pattern carving through Southeast Arizona. The technical pieces are simple and useful for planning: a dry airmass with dewpoints in the upper 20s, light terrain-driven winds most days, and an amplifying ridge of high pressure that nudges temperatures into the mid‑80s — and produces a non‑zero chance of 90°F at the Tucson airport Sunday into Monday. But the story is twofold: cold, radiationally-driven mornings in sheltered valleys, and warm, dry afternoons across the region.

Early Thursday morning brings a sharp contrast that adventurers should respect. A weak backdoor cold front that filtered in from the east is washing out, leaving light winds and very clear skies. Where the ground drains cold air into bowl‑shaped valleys — most notably the Sulphur Springs Valley (northern Cochise and southern Graham counties) — radiational cooling is strong enough to produce freezing conditions. A Freeze Warning is in effect from 2 AM–9 AM Thursday for those valley pockets with expected lows of 30–34°F. Outside those deeper basins, most desert floor sites are chilly (40s) at dawn but will rebound quickly with sun.

The upper pattern is dominated by ridging off the California coast that briefly flattens as a weak dry shortwave slides southeast of southern Nevada. The ridge amplifies across Southern California Saturday, then shifts east into Arizona Sunday–Monday. Model guidance nudges the surface warmth quickly but not uniformly — probabilistic guidance at KTUS shows about a 28% chance of at least 90°F Sunday, rising to around 50% Monday, then backing off Tuesday. In practice that means warm afternoons for most recreationists without the abrupt heat spikes midweekers sometimes fear.

Winds are generally light and terrain-driven through most of the period, under 10 mph during the day with typical afternoon sea‑breeze/diurnal shifts. Expect afternoon westerly breezes 8–12 mph with occasional gusts to ~20 mph; a dry disturbance well north of the region will tighten the pressure gradients Friday and nudge 20‑foot winds into the 10–15 mph range with gusts to 25 mph — a detail that matters for ridge runners, exposed ridgelines, and lightweight wind setups.

Fire‑weather signals are clear: persistent dry conditions, minimum relative humidity values mostly in the 12–22% range, and the Friday gust potential are the main red flags. No precipitation is expected across the seven‑day window.

What that means for outdoor adventure:

• Morning trail starts in the desert valleys will be frosty in spots Thursday — expect icy vehicle surfaces, brittle plants, and a still‑cold air mass until full sun. Insulated mornings for overnight backpackers and early bird birders are mandatory. On the flip side, afternoons warm quickly and become excellent for long hikes, climbs and trail runs.

• For mountain outings (Catalinas, Rincons, Santa Ritas), mornings will be noticeably cooler than the valley. Elevated terrain moderates the top temperatures — you’ll feel strong sun but enjoy cooler air, making longer technical hikes and ridge scrambles comfortable midday. Nights on the high trails will be cool to cold; camp insulation matters.

• Desert foothills, Saguaro National Park, and low‑elevation multi‑use trails will be dry and firm — great for mountain biking and trail running. Watch for gusts Friday that can topple unsecured gear and make exposed ridge sections more challenging.

• Climbing and bouldering get a rare stretch of dry rock and stable temperatures. Early mornings will be chilly on shaded faces; midday offers excellent friction and moderate warmth.

• Water sports are again not a focus — surface water is limited, and dry conditions plus low humidity makes paddling and river travel mostly irrelevant in this coverage area this week.

Risks to keep in mind: frost in valley pockets Thursday morning, elevated fire danger all week with especially gusty winds Friday, and sunscreen/heat management needs during sunny afternoons. The aviation and fire‑weather outlooks line up: light winds most days, gustier afternoons, and sustained low humidities.

Plan for layering and for water: mornings can be in the 30s–40s in sheltered spots; afternoons can climb into the mid‑80s. That diurnal range is part of what makes Southeast Arizona so rewarding — and what requires you to pack both sun protection and an insulating layer.

In short: a photographer’s sky, a climber’s dry rock week, a backpacker’s crisp‑morning and warm‑afternoon mix — with elevated fire risk and a small but important frost hazard in specific valley pockets early Thursday. Match your timing to the valley/mountain differences, respect local burn and fire restrictions, and you’ll get some near‑ideal outdoor days.