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Bug fix in UDM MP - #2365

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weiwangncar merged 2 commits into
wrf-model:release-v4.8.1from
Songyou184:WDM7-4.8.1
Sep 3, 2026
Merged

Bug fix in UDM MP#2365
weiwangncar merged 2 commits into
wrf-model:release-v4.8.1from
Songyou184:WDM7-4.8.1

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@Songyou184

@Songyou184 Songyou184 commented Jul 13, 2026 •
edited by weiwangncar
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TYPE: Bug fix

KEYWORDS: UDM, rain calculation

SOURCE: Songyou Hong

DESCRIPTION OF CHANGES:
Problem:
UDM MP occasionally produces unphysical rain rates.

Solution:
Allow tiny values of rain drops (qr < 1.e-9) to be sedimented

LIST OF MODIFIED FILES:
M module_mp_udm.F

TESTS CONDUCTED:

  1. This PR fixes the issue in 4.8 UDM MP testing.
  2. The Jenkins tests are all passing.

RELEASE NOTE: This PR fixes out-of-bound rainfall calculation in UDM microphysics which happens occasionally.

@Songyou184
Songyou184 requested a review from a team as a code owner July 13, 2026 22:19
@weiwangncar

weiwangncar commented Jul 15, 2026

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The regression results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None

@dudhia

dudhia commented Jul 27, 2026

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This should be targeted for develop.
The change in WDM7 includes the change for UDM, so it should go in after this one.

@weiwangncar
weiwangncar changed the base branch from master to develop July 27, 2026 17:27
@weiwangncar
weiwangncar changed the base branch from develop to release-v4.8.1 July 27, 2026 19:37
@weiwangncar

weiwangncar commented Jul 27, 2026

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This needs to be merged before PR-2366.

@weiwangncar
weiwangncar merged commit 26eb3b9 into wrf-model:release-v4.8.1 Sep 3, 2026
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@smileMchen smileMchen smileMchen approved these changes
@dudhia dudhia dudhia approved these changes

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@Songyou184 @weiwangncar @dudhia @smileMchen