# Low temperature at 2m.

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#### figurski

##### New member
Hello to all WRF users.
I have a problem with very low temperatures in the WRF model recently. At extremely low temperatures in Poland, the model lowers the temperature at a height of 2 m by about 2 to 4 degrees Celsius.
Previously, the model worked correctly and the temperature differed from the observations at SYNOP stations by about 1 degree Celsius.
Can I ask you for help in solving this puzzle?

Best regards
Mariusz

My namelist.input: physics and Dynamics

&physics
mp_physics = 6, 6, 6, 6,
ra_lw_physics = 4, 4, 4, 4,
ra_sw_physics = 4, 4, 4, 4,
radt = 5, 5, 5, 5,
slope_rad = 1, 1, 1, 1,
topo_shading = 1, 1, 1, 1,
sf_sfclay_physics = 1, 1, 1, 1,
sf_surface_physics = 2, 2, 2, 2,
bl_pbl_physics = 1, 1, 1, 1,
bldt = 0, 0, 0, 0,
cu_physics = 5, 0, 0, 0,
cudt = 1, 1, 5, 5,
sf_lake_physics = 1, 1, 1, 1,
lakedepth_default = 50., 50., 50., 50., 50.,
lake_min_elev = 5., 5., 5., 5., 5.,
use_lakedepth = 1,
mp_zero_out = 0,
sst_update = 1,
levsiz = 59,
paerlev = 29,
cam_abs_dim1 = 4,
cam_abs_dim2 = 40,
isfflx = 1,
ifsnow = 0,
icloud = 1,
surface_input_source = 1,
num_soil_layers = 4,
num_land_cat = 21,
sf_urban_physics = 0, 0, 0, 0,
!num_urban_layers = 400,
maxiens = 1,
maxens = 3,
maxens2 = 3,
maxens3 = 16,
ensdim = 144,
cu_rad_feedback = .true., .false., .false., .false.,
cu_diag = 1, 0, 0, 0,
! nowa opracja modelowania gradu. tylko do testu
hail_opt = 0,
hailcast_opt = 0, 1, 0, 0,
haildt = 10,
prec_acc_dt = 60, 60, 60, 60,
bl_mynn_tkeadvect = .false., .false., .false., .false.,
bl_mynn_tkebudget = 0, 0, 0, 0,
/

&dynamics
w_damping = 1,
diff_opt = 1, 1, 1, 1,
km_opt = 4, 4, 4, 4,
diff_6th_opt = 0, 0, 0, 0,
diff_6th_factor = 0.12, 0.12, 0.12, 0.12,
base_temp = 290,
epssm = 0.3,
damp_opt = 0,
zdamp = 5000.0, 5000.0, 5000.0, 5000.0,
dampcoef = 0.2, 0.2, 0.2, 0.2,
khdif = 0, 0, 0, 0, 0,
kvdif = 0, 0, 0, 0, 0,
non_hydrostatic = .true., .true., .true., .true., .true.,
moist_adv_opt = 1, 1, 1, 1, 1,
scalar_adv_opt = 1, 1, 1, 1, 1,
/
&bdy_control
spec_bdy_width = 5,
spec_zone = 1,
relax_zone = 4,
specified = .true.,.false.,.false.,.false.,
nested = .false.,.true.,.true.,.true.,
/

Hi Mariusz,

I suggest that you check whether the snow depth values look good in the model output.
We had similar problems in regional climate simulations and found that the cold bias is caused by the overestimation of snow depth.
We resolved this by setting opt_snf=4 in the Noah-MP LSM (sf_surface_physics=4).

Akos

We are aware of the cold bias in WRF simulation, which is particularly severe over snow cover area. At present we don't have a solution yet to this issue.

Thank you very much for your answers. I made the changes proposed by Akos, but the change did not help.
I still count on help in solving the problem.

Mariusz

Mariusz,
This is an issue possibly related to soil physics, surface layer transfer and PBL parameterization. Our physics experts have discussed this issue but haven't reached a decision how to fix this problem. I am sorry.