Problems modeling CAPsClouds•Type (ice or liquid)•Extent•Duration

Winds•Too strong in surface layer•Over-dispersive, end CAP too soon

Proposed possible modeling ‘fixes’

Stability profile•Too weak/diffuse of capping inversion•Too deep of mixed layers

Further testing to determine best model parameterizations for CAP casesFurther edits to Microphysics code (more rapid ice nucleation)Possible edits to boundary-layer scheme or turn boundary-layer scheme offChanging model vertical and horizontal resolutionSnow physics model

Land surface•Snow cover and albedo mis-specified

Modeling PlansMeteorology.The Weather Research and Forecasting (WRF) model is the industry standard forSimulating the atmosphere, but it has only rarely been used to simulate winterInversion conditions. We will improve the model by:

• Improving simulation of snowfall, snow depth, melt rates, and snow albedo; and• Determining optimal model configuration for simulation of vertical atmosphericstructure, low cloud formation, and surface flow by performing detailed comparisonsof iterative model runs against available measurements.

Proposed WRF model refinement/testing procedure:

•Test existing WRF PBL/Microphysics schemes for both clear and cloudy CAP •Test impact of vertical and horizontal model resolution on CAP simulations •Further testing on appropriate snow cover /albedo treatment in WRF

Stability Profiles

• Test various vertical and horizontal resolutions for *several* cases (both cloudy and clear) CAPs to determine impact

• Test multiple PBL/Microphysics schemes

• Simulated stability profile inherently linked to land surface, PBL, and cloud parameterization schemes

Does Resolution Matter in Uintah Basin?

• In Salt Lake Valley, better results modeling CAPs using large-eddy simulation (ΔX ~ 200 m) than mesoscale model (ΔX ~ 1333 m).

• LES computationally expensive• Plan: Compare evolution of LES simulation of

1-6 Feb 2013 with Neemann et al. 2014 simulation.

LES ΔX 250 m

OBSERVATIONS

COARSE ΔX 1335 m

Parameterization Scheme Sensitivity Studies for Clouds

• Plan: Test sensitivity of cloud production/evolution in a CLEAR CAP and ICE CLOUD CAP to

• PBL/Microphysics schemes (two are nonlinearly coupled).

• Initial conditions• Examples: New Thompson microphysics with

prescribed aerosols, test new MYNN PBL fog scheme

Development of low clouds and fog… Nov25 2013 Nov 28 2103

AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND JUNCTION CO 944 PM MST SAT NOV 30 2013 .UPDATE... ISSUED AT 940 PM MST SAT NOV 30 2013

HAVE ADJUSTED AREAS OF FOG FOR TONIGHT THROUGH SUNDAY WITH FOG MAINLY IN THE VALLEY BOTTOMS AND ALONG THE SLOPES OF THE WESTERN MOUNTAINS. SOUNDINGS OVER THE LAST 36HRS AT GJT SHOW THE STRATUS LAYER NEAR 7500FT SO HAVE ADDED FOG TO THE SLOPES DEFINED BY 7-8KFT. THE NEW NAM IS NOT RECOGNIZING THE BOUNDARY LAYER FOG

SO ITS FORECAST TEMPS ARE TOO HIGH FOR THE WESTERN VALLEY SITES.

AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE ALBUQUERQUE NM325 PM MST SUN DEC 1 2013...

MAIN FORECAST CHALLENGE IN THE SHORT-TERM CONTINUES TO BE NAILING DOWN WHEN THE PERSISTENT LOW CLOUD DECK OVER NW AND WEST CENTRAL NM WILL SCOUR OUT OF

THE AREA. THE VAST MAJORITY OF MODEL GUIDANCE DID NOT SHOW THESE CLOUDS CONTINUING TO PLAGUE THE AREA TODAY BUT ALAS THEY ARE STILL HOLDING STRONG. THE

RUC13 WAS THE BEST TO HOLD ONTO SATURATION IN THE NEAR SURFACE LAYER AND INDICATIONS ARE THAT IT WILL CONTINUE TONIGHT AND EARLY MONDAY. WINDS ALOFT AND EVEN AT THE SURFACE ARE INCREASING HOWEVER IT IS POSSIBLE THE THICK/PERSISTENT LOW

CLOUD DECK IS FEEDING BACK TO STRENGTHEN LOW LEVEL INVERSIONS AND KEEP A VERY SHALLOW BOUNDARY LAYER DECOUPLED.

NAM 12Z 1 Dec F000 GJT GFS 12Z 1 Dec F000 GJT

University of Utah Task: Try to Get the Clouds Right!

• Neemann et al. 2014 looked at impact of cloud microphyics on 1-6 Feb 2013 CAP

• Ice clouds keep CAP colder with less mixing than liquid clouds

Microphysics Sensitivity

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Microphysics Sensitivity

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W m-2°C2-m Temperature Longwave Radiation from Clouds

- Mean temperature in basin ~1.5 °C higher in BASE simulation- Related to additional longwave radiation from clouds of 7-20 W m-2 - Greater coverage of stratus in BASE vs. ice fog in FULL leads to large

differences where stratus is present but ice fog isn’t

University of Utah Task: Snow physics evaluation

• For this study, implementation of Neemann et al. 2014 procedure.

• Idealized elevation-dependent relationship based on in-situ observations• USU has applied to Jan 2013 case with improved results.

• Plan to apply to 1-2 more cases (March 2013 high insolation case and entire Jan 2013 CAP)

• Initial work toward incorporating more sophisticated snow physics model

WRF Modifications- Idealized snow cover in Uintah Basin and mountains- Snow albedo changes- Edited VEGPARM.TBL

Allows model to achieve high albedos measured in basin

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Snow Depth Snow Water Equivalent

Photos: Erik Crosman

Albedo Changes

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Original Modified

0.62 - 0.65 0.81 - 0.82

- 0.82 is average albedo measured at Horsepool during 2013 Uintah Basin Winter Ozone Study

NAM and Prescribed Snow Cover

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‐ Snow cover difference in primary model simulations

‐ Depth/SWE prescribed by elevation

‐ Based on observations available in Uintah Basin and surrounding mountainsNAM

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