Alta Collins precipitation and snow, MOS round 4

Issued Thu 10-29 10:42 MDT · cln_r4_20261030

= 2026-10-29 16:42 UTC −6 h−1 h+1 h+6 hnow

Models by hour: amount DA12 × 1, DA11 × 15, DA03 × 1; wet/dry DW12 × 1, DW11 × 15, DW03 × 1; SLR DS11 × 16, DS03 × 1

Hour to (MDT)ModelspIf wetCalled, p ≥ 0.5Called, p ≥ 0.4Called, p ≥ 0.3ExpectedLikely, p ≥ 0.5Phantom, p < 0.5CLN gaugeSLRExpected snowCLN boardHRRR wrfsubh lead (h)HRRR wrfsubh runsCLN lead (h)AGD lead (min)GFS lead (h)GEFS lead (h)AIFS lead (h)
10-29 11:00DA12 DW12 DS110.000.0130.0000.0000.0000.0000.0000.0000.004.80.000216140111111
10-29 12:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.70.0003152100121212
10-29 13:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.50.0004143160131313
10-29 14:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.40.0005134220141414
10-29 15:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.30.0006125280151515
10-29 16:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.10.0007116340161616
10-29 17:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.00.0008107400171717
10-29 18:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.00.000998460181818
10-29 19:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.00.0001089520191919
10-29 20:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.10.00011710580202020
10-29 21:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.20.00012611640212121
10-29 22:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.20.00013512700222222
10-29 23:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.30.00014413760232323
10-30 00:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.30.00015314820242424
10-30 01:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.30.00016215880252525
10-30 02:00DA11 DW11 DS110.000.0210.0000.0000.0000.0000.0000.0000.004.20.00017116940262626
10-30 03:00DA03 DW03 DS030.000.0260.0000.0000.0000.0000.0000.0000.005.80.000––171000272727
Total0.0000.0000.0000.0010.0000.0010.000.000

The weights: each source's share in each hour's amount and wet/dry models, the softmax weight ω over the sources in hand (mos/round-4/results_en.md), stacked to 100%. HRRR wrfsubh's share is spread over its runs by lead time. AIFS single has no share: it shifts the chance of a wet hour after the pool. DA12 and DW12 also add AGD's amount already measured in the hour, and HRRR wrfprs feeds only the SLR.

Totals from the start of the issue hour, each 15-minute step included at its end; inches of water, and in the main chart's bottom row inches of snow. Expected (p × the amount if wet) is the forecast total. Its areas split it into likely, from hours with p ≥ 0.5, and phantom, from hours with p < 0.5. Called is each hour as wet, max(amount if wet, 0.01) in, when p is at or above the cut-off, or dry, 0: what an hourly view shows. Its sum is not a total forecast: it counts each called hour as certain and the rest as 0, and in a storm of confident hours it runs above expected. The middle chart has each hour on its own: called at 0.5 against expected, and in replays the gauge. Expected snow is expected × the SLR, the inches of snow on CLN's board per inch of water; like expected, it adds up over hours. In replays the board is CLN's snow board by round 4's rules for it: glitches skipped, a clear counted whole, otherwise each hour's rise from the hour before, and a rise with no water at the gauge in that hour or the hours either side counted as 0. The gauge and the board count only the hours the forecast has. Models: DA for the amount, DW for wet/dry and DS for the SLR, picked for each hour by the sources in hand (mos/round-4/results_en.md); the last hours often take backups, as no HRRR wrfsubh run reaches them within 17 hours yet. HRRR wrfsubh runs: up to 10 runs in hand, up to the one picked, lighter the earlier, each the mean of its 4 points. Each MOS hour is split into 15 minutes as the HRRR wrfsubh run with the shortest lead time to it splits it, evenly without one. Each source lists its runs or readings in hand at the issue time that still reach a forecast hour, runs by their UTC start and readings by their local time; the forecast uses the source up to the one picked, and changing the issue time sets every source back to its default. In a replay, a source's default is its last run or reading at least this long before the issue time: the CLN gauge and AGD 15 minutes, HRRR wrfsubh and HRRR wrfprs 50 minutes (the whole run), GFS 5 hours, GEFS 6 hours and AIFS single 5 hours. Built in 1.24 s.