Today marks the first measurable precipitation across the watershed since March 8 — ending a 19-day zero-precipitation streak (the longest of the study). However, the amounts are very light:
Zone averages (24-hr totals): - Pruitt: 0.214" (highest zone average — driven by Cove Creek 0.283" and Flatrock Creek 0.402") - Harriet: 0.213" - Bear Creek: 0.203" - St. Joe: 0.173" (zone avg; but note Flatrock Creek HUC12 0.402" is assigned to St. Joe zone) - Ponca: 0.152" - Richland: 0.146" - Boxley: 0.101" - Ungauged: 0.197"
Spatial pattern: Broadly distributed, low-intensity rainfall. Most HUC12s received 0.10-0.20". A few localized peaks: - Flatrock Creek (0206): 0.402" with peak 1-hr intensity of 0.266"/hr — the only HUC12 exceeding 0.3". This is a St. Joe zone mainstem misc sub-watershed. - Water Creek (0408, Harriet zone): 0.303", peak 0.117"/hr - Cove Creek (0204, Pruitt zone): 0.283", peak 0.140"/hr - Tomahawk Creek (0407, Harriet zone): 0.241", peak 0.088"/hr
Timing: Nearly all precipitation fell in the afternoon/evening, peaking between 19:02-21:02 UTC (1-3 PM CDT). Duration was approximately 6-8 hours.
Gauge-measured precipitation: Pruitt 0.06", St. Joe 0.05", Harriet 0.05", Bear Creek 0.06" — consistent with the light, widespread pattern. These point measurements are lower than the HUC12 area-averages, suggesting the gauges were on the lighter side of the spatial distribution.
No significant responses detected at any gauge. All gauges continued their deep baseflow recession:
| Gauge | EOD Day 26 | EOD Day 27 | Change | Notes |
|---|---|---|---|---|
| Boxley | 1.92 ft | 1.88 ft | -0.04 ft | New study low. Dropped from 1.92 to 1.88 over the day. |
| Ponca | 96.4 cfs | 93.5 cfs | -2.9 cfs | New study low. Stepped to new quantization level (93.5). |
| Pruitt | 3.63 ft / 81.1 cfs | 3.59 ft / 69.0 cfs | -0.04 ft / -12.1 cfs | New study lows for both. CFS dropped sharply mid-day — likely rating curve artifact at low stage. |
| St. Joe | 3.62 ft / 225 cfs | 3.60 ft / 219 cfs | -0.02 ft / -6 cfs | New study lows. Height hit 3.58 ft intraday. |
| Harriet | 3.71 ft / 251 cfs | 3.68 ft / 237 cfs | -0.03 ft / -14 cfs | New study lows. Continued step-down from 270→251→237. |
| Richland | 0.99 ft | 0.97 ft | -0.02 ft | New study low at 0.97 ft. |
| Bear Creek | 2.30 ft / 5.5 cfs | 2.30 ft / 5.5 cfs | 0.00 ft / 0.0 cfs | At floor. |
Key observations: - All seven gauges set new study lows again — 3rd consecutive day of new lows across the entire network. - The 0.10-0.20" of precipitation produced zero detectable response at any gauge. This is the clearest "bone dry" non-detection data point in the study. - Pruitt CFS anomaly: CFS dropped from ~81 to ~69 during the day while height only declined ~0.03 ft. The CFS values at this stage (67.4-82.9 cfs) are highly quantized and unreliable per local knowledge about river-right scouring. Height is the reliable parameter here. - Harriet continued its step-down pattern: 270 (Day 25) → 251 (Day 26) → 237 (Day 27). This is a -33 cfs decline over 2 days, steeper than the prior days. The height data (3.75 → 3.71 → 3.68) also confirms real decline, not just CFS noise.
Critical calibration data point — non-detection under extreme dry conditions:
| Zone | Rain (24-hr) | Response | Antecedent (7-day) | Result |
|---|---|---|---|---|
| Boxley | 0.101" | No response | 0.0" (19 days dry) | Below threshold |
| Ponca | 0.152" | No response | 0.0" (19 days dry) | Below threshold |
| Pruitt | 0.214" | No response | 0.0" (19 days dry) | Below threshold |
| St. Joe | 0.173" | No response | 0.0" (19 days dry) | Below threshold |
| Richland | 0.146" | No response | 0.0" (19 days dry) | Below threshold |
| Bear Creek | 0.203" | No response | 0.0" (19 days dry) | Below threshold |
| Harriet | 0.213" | No response | 0.0" (19 days dry) | Below threshold |
Even Flatrock Creek's 0.402" (with 0.266"/hr peak intensity) produced nothing at St. Joe. This is strong evidence that under extreme dry antecedent conditions (19 days, 0.0" 7-day precip), even 0.4" with moderate intensity is below detection threshold for the St. Joe gauge.
Comparison with prior dry-state observation (Day 15): On Day 15, 0.41-0.48" with ~0.5" 7-day antecedent produced only marginal responses at Ponca/Pruitt. Today's 0.1-0.2" with 0.0" antecedent produced nothing — consistent with the hypothesis that dry antecedent conditions dramatically raise detection thresholds.
This supports revising the "bone dry" detection threshold upward — likely ≥0.5" zone average (and probably higher) is needed for any measurable response after 19+ days without precipitation.
No propagation to track — no rises detected.
Not applicable. The light rain fell mostly in the afternoon/evening of Day 27 and gauges showed no response by end of day. There is a slight possibility of a delayed response appearing tomorrow at downstream gauges from the Flatrock Creek 0.402", but given the extreme dry antecedent conditions, this is very unlikely.
Harriet's accelerating decline: The Harriet gauge has now dropped from 270 cfs (Day 25 EOD) to 237 cfs (Day 27 EOD) — a 33 cfs decline over 2 days. This is notably faster than its prior decline rate. The height data confirms this is real (3.75 → 3.68 ft, -0.07 ft in 2 days). The prior hypothesis suggested a "spring source exhausted" explanation for the Day 26 step from 270 to 251 — this continued rapid decline may indicate another source dropping out, or it could be that the 270 cfs "plateau" was itself a transient feature. The baseflow floor estimate needs further revision downward.
Pruitt CFS plummeting: Pruitt CFS hit 67.4 intraday (at 3.58 ft height) — the lowest CFS of the study. Given that Ponca is still reading ~94 cfs just upstream, a true 67 cfs at Pruitt would imply a ~27 cfs loss between gauges, which would be extraordinary. This almost certainly reflects the river-right scouring issue noted in local knowledge — the gauge is reading artificially low. The true Pruitt discharge is probably ~80-90 cfs. Height (3.58-3.59 ft) is the reliable measure here.
Boxley continuing to decline: Boxley dropped to 1.88 ft — down 0.04 ft from yesterday. This continued decline without any rain is consistent with the "pool and drop" nature described in local knowledge. The pools upstream continue to slowly drain, and the extended dry spell is depleting them.