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very little precip when cu_phys=0

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Good day,

I am a seasoned WRF user but never at high resolutions with cu physics turned off. I have performed a case study simulation over Nepal for a convective event. I'm using V3.9 and have 3 domains (12km/4km/1km) and I am using ndown to complete (also a new approach for me).

The issues I am having is relating the convective structures present in the model with the resulting precipitation. With cu_phys turned off, I am only looking at RAINNC for precip (although I confirmed RAINC contained zero fields).

Precipitation values are quite small (on the order of a few mm) for the intensity of convection as shown by max dbz fields and omega fields interpolated to various pressure levels. The spatial patterns just don't seem to match up and there are areas that see no precip despite an active and intense storm overhead.

I'm attaching both my namelist.input files (altered a bit to best represent the complete ndown process) and a pdf showing a snippet of output for a few hours of model time plotting max dbz (top), model accumulated precip (middle; mm), and 500-mb omega (bottom). In the dbz panel, there is a black dot representing Kathmandu's location for spatial context.

I'm hoping someone might be able to serve as a sanity check that there isn't some glaring issue with my namelist that would lead to the model's microphysics not translating into precipitation. I'm under the assumption that when cu_physics is off, the model's microphysics is responsible for all of the precip but maybe I'm missing another field in addition to RAINNC? The model produced the convective event just about perfectly so after my initial pleasure on that I need to make sure I didn't miss some small detail that is translating to poor precip performance (and all the subsequent model interactions).


  • namelist.input_wrfhelp.txt.txt
    5.1 KB · Views: 57
  • Spatial_Nepal_Precip_d03_1km.pdf
    8.1 MB · Views: 62
I have a few issues related to your namelist
(1) You specify time_step = 30, 4, 1, I don't think this will work. Did you get any error message when running WRF?
(2) Can you keep the options below consistent, i.e.,
parent_grid_ratio = 1, 3, 4,
parent_time_step_ratio = 1, 3, 4,
(3) Please keep radt the same for all domains
(4) Please tell me what forcing data you use and where you download them?
Reviving a thread here after not seeing the response. My apologies.

I'm using ndown on these simulations so they are being run separately as opposed to together. So the namelist won't line up with the usual ratios like if I was using two-way nesting.

WRF ran to completion just fine for all three domains, with no problems and no errors or warnings in any rsl files. Inner domain produced the storms I was hoping for in the place I was expecting at the time I was expecting so all seems fine with forcing data.

Forcing data is GDAS (~GFS). Downloaded from NOMADS. No problems in ungrib or metgrid steps.

My original concern is with precip fields. Specifically, where RAINNC+RAINC fields don't correspond to the reflectivity fields. So my question remains: Where does the convective precip go when cu physics is off. Is it entirely generated by the microphysics and would be contained entirely in RAINNC? If so, the model's storms are very intense (>50dBZ) but produce almost no precip.? Evaporation is possible to an extent under this scenario but not to the extent that I'm seeing. For example, many instances of a storm's core or periphery having zero impact on precip fields, not even those unreasonably small drizzle values that commonly seem to plague some simulations, so just wondering if precip is being sent to a different variable?