Daily Analysis

PRE-ANALYSIS (per-gauge facts; gauge timestamps CDT. NOTE: QPE peak_1hr_time fields carry a "Z"/UTC suffix while gauge series are CDT(-05:00). Treating the QPE clock value as local produces physically impossible negative lags today, so for attribution I convert QPE peak times −5 hr to CDT and show both, e.g. "06:02 CDT (11:02Z)." Flagging this data-convention conflict explicitly.)

• Boxley: (a) 2.02 ft @00:00; (b) max 9.06 ft @09:30 — STUDY RECORD (prior 5.50 ft, Event 19 Day 100); (c) 4.42 @23:30; (d) low 2.00 @03:30–04:00; (e) low→peak +7.06 ft (2.00→9.06), ~5.75 hr (03:45→09:30). QPE: HUC 0201 1.3"/hr @06:02 CDT (11:02Z).
• Ponca: (a) 96.1 cfs @00:00; (b) max 8700 cfs @10:30 — STUDY RECORD (prior 2120, Event 2); (c) 1310 @23:30; (d) low 96.1 @00:00–04:45; (e) +8604 cfs, ~6.5 hr (04:00→10:30). QPE: zone 1.478"/hr @06:02 CDT (Smith Cr HUC 0203).
• Pruitt: (a) 3.89 ft / 166 cfs @00:00; (b) max 14.27 ft / 9710 cfs @15:45–16:00 — STUDY RECORD (prior 10.23 ft / 4290 cfs, Event 20); (c) 8.30 ft / 2390 cfs @23:30; (d) low 3.84 ft / 153 cfs @04:15; (e) +10.43 ft (+9557 cfs), low 04:15 → peak 15:45 ≈ 11.5 hr. Gauge precip 0.64".
• St. Joe: (a) 4.68 ft / 656 cfs @00:00; (b) max 7.97 ft / 3250 cfs @22:45 (still rising at cutoff); (c) = max; (d) low 4.56 ft / 598 cfs @04:45; (e) two pulses — early +2.16 ft (4.56→6.72 @09:00); late surge 5.55 (16:00) → 7.97 @22:45 ongoing. QPE own-zone 1.699" (Henson 1.06"/hr @06:02 CDT).
• Harriet: (a) 4.76 ft / 925 cfs @00:00; (b) max 6.13 ft / 2250 cfs @17:15–17:30; (c) 5.79 / 1890 @23:45; (d) low 4.73 / 901 @04:15; (e) +1.40 ft (4.73→6.13), ~13 hr (04:15→17:15). QPE zone 1.479" (Dry Cr 0.692"/hr @05:02 CDT).
• Richland: (a) 1.33 @00:00; (b) max 2.21 @14:00; (c) 1.87 @23:00; (d) low 1.31 @03:30; (e) +0.90 ft, ~10.5 hr (03:30→14:00). QPE zone 1.538" (Hdwtrs Richland 0.624"/hr @07:02 CDT (12:02Z)).
• Bear Cr: (a) 2.36 ft / 37.1 cfs @00:00; (b) max 4.19 ft / 875 cfs @07:00; (c) 3.19 / 208 @23:15; (d) low 2.35 / 36.2 @03:00; (e) +1.84 ft (+838.8 cfs), 4 hr (03:00→07:00); bimodal secondary 3.72 ft @11:45. QPE zone 1.583" (Outlet Bear 0.568"/hr @05:02 CDT).

1. PRECIPITATION SUMMARY

Major upper-basin-concentrated convective event (Event 21) — the Event-20 recession ended abruptly. Basin-max 3.377" (Boxley zone HUC 0201, 1.3"/hr). Upper-basin bullseye: Boxley zone 3.377", Ponca zone 3.114" (Smith Cr 3.807"/1.478"/hr, Whiteley 2.13", Beech 3.402"). Mid/lower basin moderate-uniform ~1.3–1.7": Pruitt 1.357", St. Joe 1.699" (Henson 2.574", Hdwtrs LB 2.508"), Richland 1.538", Bear 1.583", Harriet 1.479", ungauged 1.469". Peak 1-hr intensities study-class: 1.478" (Ponca), 1.3" (Boxley), 1.06" (Henson). Heavy core fell ~05:00–08:00 CDT (upper) shifting through midday. Antecedent DRY (7-day 0.1–0.32" basin-wide — Boxley 0.273", Richland 0.17–0.23", Bear 0.23–0.27") after the 9-day Event-20 recession drained the basin.

2. GAUGE RESPONSES

• Boxley → study-record 9.06 ft, far above Hailstone High (5.9). Direct extreme-intensity flash from HUC 0201.
• Ponca → study-record 8700 cfs (5.4× flood threshold 1600), near-instant step 202→4000 cfs @08:00. Directly forced by 3.1" Ponca-zone core (+ minor Boxley contribution).
• Pruitt → study-record 14.27 ft / 9710 cfs (4.85× flood 2000). Local zone only 1.357" and Pruitt height barely moved (3.89→4.06) until the 13:15 explosion — the Pruitt flood is the routed upper-basin flood, not local forcing.
• St. Joe two-stage: early Little-Buffalo pulse to 6.72 ft / 2050 cfs @09:00, then the trunk-integration surge beginning ~21:00, climbing to 7.97 ft / 3250 cfs @22:45 (~40% of flood, still rising — trunk peak pending Day 115).
• Harriet to 6.13 ft / 2250 cfs @17:15 (mid-basin + direct + Bear), ~24% of flood; main trunk surge not yet arrived.
• Richland +0.90 ft to 2.21 (below 3.2 floatable). Signal separation: Richland modest → St. Joe rise is Little Buffalo/Big Cr/mainstem + dominant upstream propagation, NOT Richland-driven.
• Bear Cr flashy +1.84 ft to 4.19 ft / 875 cfs @07:00, bimodal → Harriet compound source confirmed.

3. RAINFALL-RESPONSE PAIRS

• Boxley: lag QPE 06:02 CDT → peak 09:30 = 3.47 hr; transfer 7.06 ft / 3.377" = 2.09 ft/in. Antecedent DRY (0.273"). Prior dry high-intensity transfer 0.62–0.82 (Events 7/9/11) — today exceeds by >150%; deviation flagged. But today's 1.3"/hr is study-record intensity; the only comparable transfers are Event 19 Day 100 (2.28, very wet + 0.699"/hr) and Event 20 Day 106 (1.42, primed). Refined finding: at extreme intensity (>1.2"/hr) Boxley reaches ~2.0+ ft/in regardless of antecedent — intensity overruns pool storage. Lag 3.47 hr vs dry expectation 7–11 hr (Event 9: 7.2 hr) — >50% faster; intensity also shortens the dry pool-fill delay. Antecedent differs (dry today vs wet for the high-transfer analogs).
• Ponca: lag 06:02 → 10:30 = 4.47 hr; transfer 2763 cfs/in — out-of-regime (flood, far out of bank); NOT comparable to the in-bank wet 1000–1220 cfs/in. Flagged as flood-scale, not a refinement of the in-bank ratio.
• Richland: lag 07:02 → 14:00 ≈ 7 hr; transfer 0.90/1.538 = 0.585 ft/in. Dry (0.17–0.23"). Matches dry/dry: between Event 9 (0.25) and Event 11 event-scale (0.73); within ~20% of Event 11. Consistent — distributed, dry, no concentrated headwater bullseye.
• Bear Cr: lag 05:02 → 07:00 ≈ 2 hr; transfer 1.84/1.583 = 1.16 ft/in. DRY (0.23–0.27") but low pre-event stage 2.35 ft. Prior dry mid-stage Event 11 = 0.09–0.17 — deviation ~7–10×, flagged. This strongly confirms stage-dependence dominates antecedent: low pre-event stage (steep rating zone) + moderate forcing yields high ft/in even on dry soils (cf. Event 16 wet-low-stage 2.08, Event 20-onset moist-low 2.07). New data point: dry + low-stage + moderate forcing → ~1.16 ft/in.

4. DOWNSTREAM PROPAGATION

• Boxley 09:30 → Ponca 10:30 = 1 hr — implies ~15 km/hr if cascade (10.3 km ×1.5 sinuosity = 15.5 km), unrealistically fast → both gauges were directly forced (parallel-direct), not a true cascade. (Event-11/Event-20 parallel-direct signature.)
• Ponca 10:30 → Pruitt 15:45 = 5.25 hr at flood flow. Clean propagation pair (Pruitt local forcing negligible). 19.9 km ×1.5 sinuosity = 29.85 km / 5.25 hr = 5.69 km/hr ≈ 1.58 m/s — fastest mainstem propagation of study, consistent with ~9,700-cfs flood stage (vs 1.2 m/s at >1500 cfs). Matches the ~5.25-hr high-flow Ponca→Pruitt (Event 20).
• Pruitt 15:45 → St. Joe: St. Joe second surge began ~21:00, still climbing at 22:45 — trunk peak expected early Day 115 (~11–15 hr Pruitt→St. Joe at flood per prior events).
• St. Joe → Harriet: Harriet's 17:15 peak is the early/mid pulse + Bear + direct; the main trunk surge has NOT reached Harriet — expect overnight Day 115.

5. MULTI-DAY EVENTS

This is fresh rainfall (Event 21 onset), not Event-20 continuation. Event 20's deep-baseflow recession (Boxley 2.00, St. Joe 656, Harriet 925, Bear 37 cfs at the morning low) was the dry backdrop; the flood resets the system. Event 21 is incomplete at cutoff — upper basin (Boxley/Ponca/Pruitt) has peaked at study records; the trunk (St. Joe/Harriet) is still integrating and will peak Day 115. Total event magnitude TBD.

6. ANOMALIES OR SURPRISES

• DRY antecedent + extreme intensity produced study-record upper-basin flooding at Boxley (9.06 ft), Ponca (8700 cfs, 5.4× flood), and Pruitt (14.27 ft / 9710 cfs, 4.85× flood). This contradicts simple antecedent-damping — forcing intensity dominated antecedent moisture. Boxley's fast dry lag (3.47 hr) directly contradicts the "dry = slow 8–11 hr pool-fill" expectation; extreme intensity overran pool storage (local-knowledge pool-and-drop mechanism is overrun, not violated).
• Event 21 is the dry-antecedent, much-larger analog of Event 19 (upper-only flood). Event 19's upper flood (Ponca 1920, Pruitt 2130) attenuated to 30–36% of flood at the trunk. Today's upper volume is ~4–5× larger. Open test: will this far-larger upper-only flood drive a trunk flood at St. Joe/Harriet, or still attenuate? St. Joe at 3250 cfs and rising hard at cutoff — Day 115 decides.
• Pruitt flood from a modest 1.357" local zone is the strongest confirmation yet that Pruitt's high-flow response is dominated by upstream routing (Events 17/19/20 finding) — here in extreme form.
• High-stage rating curves at record flow (Pruitt 14.27/9710, Ponca 8700) tracked smoothly; the 202→4000-cfs Ponca step @08:00 is a genuine flash, not a rating artifact. Watch Days 115+ for post-record field-revision steps.