Jerome County, ID — Water Intelligence Brief

August 17, 2026 | Free-Tier Edition

Situation Summary

Jerome County's 2026 irrigation season is defined by an early-melt year across the upper Snake River headwaters, with snowpack above Palisades Reservoir melting out 4–6 weeks ahead of the historical median meltout date — meaning the season's storage-fill window closed earlier than normal. For a county where 80% of irrigation supply comes from American Falls and Palisades reservoir storage, not from current streamflow, the critical supply question is how much carryover storage entered the irrigation season — data that is not available in this free-tier brief. Reservoir storage data, 7-day forecast details, and depletion trajectory analysis are available in the full brief.

Snowpack Conditions

Lewis Lake Divide (SNOTEL #577, Teton County WY, 7,880 ft — Upper Snake River Headwaters)

Current reading (August 16): SWE 0.0", Snow Depth 0.0"

Lewis Lake Divide is the upstream snowpack station most directly relevant to Jerome County's water supply — it monitors Continental Divide accumulation above the upper Snake River headwaters, the source that fills Jackson Lake, Palisades Reservoir, American Falls Reservoir, and ultimately supplies North Side Canal Company deliveries at Milner.

A reading of 0.0" SWE on August 16 is normal for this date — the median SWE for mid-August at this elevation is also 0.0", so this reading does not indicate below-normal conditions today. The relevant signal is timing: in 2026, Lewis Lake Divide melted out 4–6 weeks ahead of its historical median meltout date, driven by the anomalous March heat wave that accelerated snowmelt across the Mountain West. For Jerome County's storage-first supply system, early meltout means the Palisades fill window closed weeks earlier than normal — the practical consequence is lower-than-typical reservoir inflows during the critical spring accumulation period. Whether that translated into a meaningful storage deficit entering irrigation season depends on carryover storage figures not available in this tier.

Streamflow Conditions

No active USGS streamflow gauges with agricultural supply relevance are located within Jerome County's boundaries. Jerome County's in-county gauge (Devils Washbowl Spring) monitors a 0.22-square-mile spring vent drainage and is not a canal supply indicator. Jerome County agricultural water managers rely on two inherited Snake River reference points outside county boundaries: the Snake River at Milner Dam (USGS 13087995, pre-diversion supply indicator) and the Snake River near Twin Falls (USGS 13090500, basin integrator). No current gauge readings were available for inclusion in this brief.

During peak irrigation season, near-zero flow below Milner Dam is normal canal operations — the Milner Diversion Dam captures essentially the full Snake River flow for North Side Canal Company (north bank) and Twin Falls Canal Company (south bank) deliveries. This is not a crisis signal; it reflects the canal system functioning as designed. Supply anomalies for Jerome County should be interpreted through above-Milner flow levels and — most importantly — upstream reservoir storage status, not below-Milner readings.

Seasonal Guidance

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Data Sources: SNOTEL data through August 16, 2026; USGS streamflow data through August 17, 2026.

Data Current As Of: August 17, 2026.

Important Disclaimers: This brief provides automated analysis for informational purposes only. Specific numerical claims have not been independently verified. Consult official sources including IDWR Water District 36, Northside Canal Company, A&B Irrigation District (USBR Bureau of Reclamation project serving northern Magic Valley areas in Jerome and Lincoln counties), and USBR Pacific Northwest Region (Boise office) for current reservoir storage and operational data before making irrigation planning or herd management decisions.