1. Mesoscale Circulations during VTMX John Horel Lacey Holland, Mike Splitt, Alex Reinecke jhorel@met.utah.edu

2. Overview Temporal and spatial context for VTMX IOPs Synoptic and mesoscale conditions during IOPs

3. October 1999 500 mb geopotential height

4. October 1999 500 mb geopotential height anomaly

5. October 2000 500 mb geopotential height

6. October 2000 500 mb geopotential height anomaly Cooler and wetter than normal PM-10 concentrations half those in October 1999

7. MesoWest Data available from January 1997 to present www.met.utah.edu/mesowest Paper describing MesoWest submitted to BAMS 9 Oct. 0900 UTC

8. Diurnal Temperature Range: Fall Alex Reinecke MesoWest Observations 1997-2000

9. Diurnal Temperature Range- Fall Latitude vs. Elevation SLC

10. Diurnal Temperature Range: October 2000 Rush Valley Tooele Valley Salt Lake Valley

11. October 2000: Salt Lake Valley SLC U42 Great Salt Lake: 21C- 10C

12. Surface Wind Convergence in Salt Lake Valley IOP 1 IOP 2 IOP 3IOP 4 IOP 5IOP 6IOP 7IOP 8IOP 9 IOP 10 Mike Splitt- Linear regression fit

13. Stability and Wind Surface-based inversions (greater than 5C in the lowest 100 mb) observed during 15 of the 31 morning (1200 UTC) soundings at the Salt Lake City International Airport Weak surface inversions with stable layers aloft below the crest of the Wasatch Mountains on 5 other mornings Well-mixed conditions present during the other 11 mornings Winds at 700 mb (near the crest of the Wasatch Mountains) were less than 10 m/s in 19 of the 31 morning soundings.

14. IOPs with Well-Developed Drainage Circulations 5 (14-15 October) 6 (15-16 October) 8 (19-20 October) Clear skies, weak winds aloft at crest level, strong nocturnal radiational inversions Limited moisture in the boundary layer Pronounced drainage flow into the Salt Lake Valley from the west, south, and east Surface based inversions and drainage circulations developed after sunset and persisted without significant interruption until sunrise

15. IOP-8: 9 UTC 20 October SLC 500 mb 700 mb

16. IOPs Modulated by Synoptic and Mesoscale Systems IOP 1 ( 2-3 October) Test operational procedures During evening: –clear skies with drainage flows developing as the evening progressed Synoptic-scale northerly pressure gradient developed overnight –Northerly winds penetrated into northern end of the Salt Lake Valley before midnight –Eventually reversed the down-valley (southerly) flow through the center of the valley –Drainage circulations down into the valley from the Oquirrh and Wasatch Mountains were largely unaffected

17. IOPs modulated by synoptic and mesoscale weather systems IOP 4 (8-9 October), IOP 7 (17-18 October) Similar boundary-layer structure to that in IOPs 5, 6, 8 until early morning Prior to that time, clear skies, weak winds aloft, and strong surface-based radiational inversions As a result of approaching upper-level troughs from the west, the nocturnal inversions eroded both by surface heating and by mixing due to the downward penetration of southerly winds

18. IOP-4 9 October SLC 500 mb 700 mb Wheeler

19. IOPs Modulated by Synoptic and Mesoscale Systems IOP 2 (6-7 October) and 3 (7-8 October) Split flow aloft with weak upper-level short waves to the southwest and northeast of Utah Strong outbreak of cold air to the east of the continental divide progressed westward after 0 UTC After 1000 UTC, the depth of the cold air to the east of the Wasatch Mountains built to sufficient height to spill over the lower terrain from Mill Creek Canyon to near the University of Utah in the northeast corner of the Salt Lake Valley IOP-3 began at 2200 UTC 7 October and was terminated before midnight Strong downslope conditions persisted into the evening in the northeastern corner of the Salt Lake Valley Winds in the western part of the valley were turbulent

20. IOPs Modulated by Synoptic and Mesoscale Systems IOP 9 (20-21 October ) and IOP 10 (25-26 October) Affected significantly by approaching upper-level troughs. weak short-wave ridge aloft initially Skies were broken to overcast Weak nocturnal surface inversion and drainage circulations Cold-front at 1200 UTC 21 October Southerly surface winds were enhanced during IOP 10

21. IOP 9- 3UTC 21 October 500 mb 700 mb

22. Summary Mountain/valley circulations and radiational inversions occurred on over half of the days Local circulations dominated several IOPs (5, 6, 8)- but each had unique characteristics Synoptic and mesoscale influenced IOPs: –IOP 1: interruption of drainage circulations in the north end of the Salt Lake Valley –IOPs 2, 3: downslope wind event –IOPs 4, 7: erosion of invesion from aloft –IOPs 9, 10: approaching weather systems

23. IOP-1 300 UTC 3 October 6UTC

24. IOP 2: 1200 UTC 7 October

25. IOP 3- 300 UTC 8 October 0Z

26. IOP-4 9 October SLC 500 mb 700 mb Wheeler

27. IOP 5 600 UTC 15 October

28. IOP 6 12 UTC 16 October

29. IOP 7 600 UTC 18 October

30. IOP-8: 9 UTC 20 October SLC 500 mb 700 mb

31. IOP 9- 3UTC 21 October 500 mb 700 mb 0Z

32. IOP-10 600 UTC 26 October