1. Chuliang Xiao 1 and Brent Lofgren 2 1 CILER, University of Michigan 2 NOAA GLERL A Study of Great Lakes Effects on Synoptic Processes by Using WRF Comparison Experiments The Great Lakes Operational Meteorology Workshop 2014 Ann Arbor, MI

2. Outline Synoptic Overviews Data and Model Results from Model Comparisons Conclusions

3. Outline Synoptic Overviews – Low Patterns – Low Tracks Data and Model Results from Model Comparisons Conclusions

4. Synoptic Map (Deep Low) 17Nov201318Nov2013 Midwest Tornados outbreak Courtesy http://www.hpc.ncep.noaa.gov/dailywxmap/http://www.hpc.ncep.noaa.gov/dailywxmap/

5. Synoptic Map (Shallow Low) 14Dec201315Dec2013 East-coast Snowstorm outbreak Courtesy http://www.hpc.ncep.noaa.gov/dailywxmap/http://www.hpc.ncep.noaa.gov/dailywxmap/

6. Outlines and Centers 992 hPa 1012 hPa

7. Outline Synoptic Overviews Data and Model – Datasets (NCEP Eta, FNL, SST, Station) – Model description – Experimental designs Results from Model Comparisons Conclusions

8. Datasets NCEP Eta (6 hourly, 40 km, North America) NCEP FNL (6 hourly, ~100 km, Global) (for comparison with NCEP Eta) NCEP RTG SST (Daily, HR, ~ 8 Km, Global) MODIS ( 20-cat. Land Use; 16-cat. Soil; Collected in 2001 ) Gauged Precipitation (Great Lake area)

9. Datasets (Cont.) DatasetNCEP EtaNCEP FNLRTG SST Resolution40 km1*1 degree1/12 degree 6 hourly Daily FormatGRIB 2 GRIB 1 ProviderNCEP Eta 212 gridNCEP GFSNCEP MMAB

10. WRF (Version 3.5.1) Domain ProjectionLambert True latitudes30°N, 60°N Reference Latitude45°N Reference Longitude85°W Analysis fieldNCEP Eta (40 km x 40 km) Domain Resolution15 km x 15 km Domain Mesh100 x 142 Land Surface ModelNoah LSM with MODIS 2001 (30”)

11. WRF Domain (Cont.) Lakes-mean: Only lake grids Area-mean: Red rectangle area Domain-mean: ALL model grids

12. Experiment Comparison CasesDeep LowShallow Low Experiment Integration Period (2013) 00Z16Nov~12Z19Nov00Z13Dec~12Z16Dec CONTROLMODIS, NCEP Eta NOLakesModifed Landuse+Vegetation+Soil, NCEP Eta SSTLakesMODIS, NCEP Eta, Updated RTG SST

13. Landuse Modification CONTROLNOLakes

14. Modification (Cont.) Variable Description Variable Name CONTROL- MODIS NOLakes- Modified SuperiorOthers Land useLU_INDEX Water Bodies (17) Mixed Forest (5) Cropland (12) Vegetation fraction VEGFRA0%20%25% Soil category fraction SOILCTOP Water (14) Sandy Loam (3) Silt Loam (4) SOILCBOT

15. Modification (Cont.) The land use, vegetation and soil categories were specified differently between Lake Superior and the other four lakes. This allows small surface fluxes of heat and moisture to develop, but prevents any mechanical effects from discontinuities in surface roughness. The lake surface and substrate temperature were also altered in Sousounis and Fritsch (1994).

16. Outline Synoptic Overviews Data and Model Results from Model Comparisons – Validation (Precipitation) – Storm Evolutions (SLP) – Surface process (Temperature, Moisture, Heat flux) – Vertical extent (local circulation) – Local circulation background flow Conclusions

17. Model Validation (Precipitation) NCEP Eta 40km NCEP FNL 100km CONTROL 15km Observation Deep LowShallow Low

18. Storm Evolutions (Area-mean SLP) Black: CONTRL RED: NOLakes Blue: SSTLakes local time (EST) The bottom bars are the differences Deep Low Shallow Low

19. Surface process (Temperature) Lakes-Mean Surface Temp (TSK) Area-Mean Air Temp at 2 m (T2) Lakes-Mean TSK-T2 Black: CONTROL RED: NOLakes Blue: SSTLakes local time (EST) Lake temperature is not changed in the initial time, but got quick equilibrium in WRF-Noah  ColdLakes

20. Surface process (Humidity) CONTROL CONTROL-NOLakes CONTROL-SSTLakes

21. Surface process (Sensible Heat)

22. Cross Sections 992 hPa 1012 hPa Dashed: Southwest-Northeast Dot: Northwest-Southeast

23. Cross-sections Shading: Temperature; Contour: Geopotential Height NW-SE SW-NE

24. Circulation Configuration Vector: U, V at 10 m Shading: T850 Contour: Z500 CONTROL CONTROL-NOLakes CONTROL-SSTLakes

25. Conclusions WRF performs well in simulating both the deep low and shallow low. Lake-air temperature gradient induces vertical heat flux; lake-land roughness contrast contributes to moisture convergence. The Great Lakes’ effect generally strengthens the low system near the surface but is sensitive to the background flow. This effect becomes much more significant for the development of the shallow low and extends to a higher level, tilting downwind. The remote influence of the Great Lakes tends to be subtle in both cases.