October 9–13, 2026
IVT ≥ 250
Tropical cyclone nearby
Snow
Final
Network median 3.15 in (range 1.14–6.93 in); peak IVT 490 kg m⁻¹ s⁻¹ from the SSW; Rachel within 1,500 km
Summary
Across 39 gauges the event total ranged from 1.14 to 6.93 in (median 3.15 in). The central 80% of the network-mean rain fell between Oct 10 16:00 MST and Oct 12 21:00 MST (53 h). Moisture transport over Flagstaff reached atmospheric-river strength: ERA5 IVT was at or above 250 kg m⁻¹ s⁻¹ for 42 h and peaked at 490 kg m⁻¹ s⁻¹ from the SSW at Oct 11 05:00 MST. 73% of the network-mean rain fell while IVT was at or above 250. At the IVT peak, the region of IVT ≥ 250 over Flagstaff was continuous with the area around Rachel (remnant disturbance, 33.9°N 115.4°W, 373 km to the WSW). At the IVT peak, 500-hPa flow over Flagstaff was from the SSW at 35 m s⁻¹, and the 500-hPa trough axis along 35.25°N was at 122.2°W, 963 km west of Flagstaff (5,619 m, against 5,716 m over Flagstaff). A closed 500-hPa low (5,470 m) was centred 1,289 km to the NNW, at 45.2°N 119.2°W. The strongest 250-hPa wind within 1,000 km was 63 m s⁻¹, 958 km to the N. The 250-hPa wind over Flagstaff peaked at 62 m s⁻¹ (Oct 12 23:00 MST), 42 h after the IVT peak.
Rain across the network
- Network rain (39 gauges): median 3.15 in; 10th–90th percentile 2.31–4.18 in; lowest 1.14 in (Flagstaff Landfill), highest 6.93 in (Waterline Rd #1 (Lenox-Wupatki Trails)).
- Peak hour: network median 0.31 in (hour beginning Oct 11 16:00 MST); highest single-gauge hour 0.79 in.
- SNOTEL event precipitation: Fort Valley 3.8 in; Snowslide Canyon 7.8 in; Fry 5.5 in.
- ERA5 at Flagstaff: peak IVT 490 kg m⁻¹ s⁻¹; maximum 250-hPa wind 62 m s⁻¹; minimum 500-hPa height 5,675 m; maximum total column water vapour 23 mm.
- Rachel (NHC best track, peak 105 kt): closest approach 373 km at Oct 11 05:00 MST, 33.9°N 115.4°W (remnant disturbance, 30 kt).
Atmospheric setting
Oct 11 12 UTC · Oct 11 05:00 MST
ERA5 every 6 hours, from 12 h before to 12 h after the event window, opening at the time of peak IVT at Flagstaff. Shading: integrated vapour transport (IVT); blue contour and arrows: IVT ≥ 250 kg m⁻¹ s⁻¹. Black: 500-hPa height (60-m interval). Orange: 250-hPa wind 40, 55 and 70 m s⁻¹. ★ Flagstaff; ✕ NHC best-track position. Lower strip: network median hourly rain, with the event window shaded and the map time marked in orange. Step with the buttons, slider or ← → keys; space plays and pauses.
Climate context
- Airport precipitation: 3.55 in over 5 local days, against a 1991–2020 normal of 0.25 in for those days (14× normal).
- Rank: the 4th largest 5-day airport total in October among 129 years with data since 1898 (each year’s largest 5-day total ending in October).
- Airport temperature: highs averaged -5.2 °F and lows +10.6 °F relative to normal.
- Water year to date (Oct 1, 2026 – Oct 13, 2026): airport 3.55 in (normal 0.62 in); SNOTEL Fort Valley 4.30 in (median 0.40 in); Snowslide Canyon 7.90 in (median 0.70 in); Fry 5.60 in (median 0.40 in).
Station data
Flagstaff airport (local days; normals 1991–2020; M = not yet reported)
| Precip (in) | Normal (in) | Snow (in) | High (°F) | High vs normal | Low (°F) | Low vs normal | |
|---|---|---|---|---|---|---|---|
| Oct 9 | 0.26 | 0.05 | 0 | 74 | +8 | 41 | +7 |
| Oct 10 | 0.16 | 0.05 | 0 | 65 | -1 | 43 | +10 |
| Oct 11 | 1.98 | 0.05 | 0 | 58 | -7 | 49 | +16 |
| Oct 12 | 0.88 | 0.05 | 0 | 52 | -13 | 44 | +12 |
| Oct 13 | 0.27 | 0.05 | 0 | 52 | -13 | 40 | +8 |
| Total | 3.55 | 0.25 | 0 |
SNOTEL (water-year precipitation from Oct 1; medians 1991–2020)
| site | Event precip (in) | Water-year precip (in) | Median to date (in) | % of median | SWE at end (in) | Max snow depth (in) |
|---|---|---|---|---|---|---|
| Fort Valley | 3.8 | 4.3 | 0.4 | — | 0 | 0 |
| Snowslide Canyon | 7.8 | 7.9 | 0.7 | — | 0.2 | 1 |
| Fry | 5.5 | 5.6 | 0.4 | — | 0.2 | 1 |