1. Winter Weather and Aviation
Mike Bardou
Meteorologist
National Weather Service Romeoville, IL
Jonathan Leffler
Center Weather Service Unit Aurora, IL

2. Summary
NWS Background
Weather Basics
Hazards
Planning

3. Weather Forecast Offices (WFO)

4. National Weather Service WFO Romeoville, IL
Located about 30 miles southwest of Downtown Chicago
27 full-time staff members
At least 2-3 per shift

5. WFO Aviation Weather Services
TAFs (every 2 hrs on weekdays/3 hrs on weekends)
- KORD
- KMDW
- KRFD
- KDPA
- KGYY
Aviation Forecast Discussion
Soaring Forecasts

6. TAF Sites
TAF sites around the region.

7. Center Weather Service Units (CWSU)

8. Center Weather Service Unit Aurora, IL
Located within the City of Aurora, IL about 40 miles west of Downtown Chicago
Staffed by 4 NWS meteorologists from 5:00 am – 9:00 pm, 7 days a week.

9. CWSU Aviation Weather Services
Provide Professional Meteorological Services to FAA Air Traffic System
Accomplished with:
Liaison to NWS Forecast Offices
In-person and telephone briefings to local FAA facilities
Center Weather Advisories (short-fuse “warnings”)
Collaborative Convective Forecast Products (CCFP)
Web-based products/decision aids

10. Weather Phenomena High Pressure Low Pressure Cold Front Warm Front
Occluded Front

11. High Pressure Overall sinking motion, stable conditions
Calm or near calm surface winds, except at far perimeter of high
Can have Cu growth, but normally little vertical extent to clouds
Favorable for fog development, esp. if ground is wet and skies are clear overnight
Snow covered ground can keep persistent IFR as airmass changes very little

12. Low Pressure Overall rising motion, unstable conditions
Moderate to very strong surface winds in cyclonic (counter-clockwise) motion
Great vertical extend of clouds (TSRA, SHRA)
Fog development typically not favorable due to stronger winds & mixing of drier air
Can help “scrub” atmosphere from stagnant high pressure

13. Warm Front Shallow sloping surface = less vertical extent
Winds usually SE shifting to SW after passage
Thickening & lowering of clouds ahead of front with widespread, layered precipitation
Warm and stable once warm front passes

14. Cold Front Steep sloping surface = greater vertical extent
Winds usually SW shifting NW after passage
Lines of TSRA/SHRA ahead/along front with residual -RA/DZ in some cases
Skies clearing and becoming stable

15. Occluded Front Acts similar to cold front, but normally not as strong
Can maintain SHRA and possible TSRA if atmosphere remains unstable (upper level low)
Wind direction varies based on position of low

16. Low Pressure Lifecycle

17. Weather Map Features

18. Tools

19. Average Snowfall

20. Weather Hazards Winds Ceilings Visibility Precipitation Icing
Turbulence

21. Wind Speed and Direction

22. Ceilings
Clouds typically develop as saturation occurs at a particular level
Cloud base is dependent on the level that saturation occurs
Thickness of cloud cover is dependent on depth of the saturated layer

23. Ceilings

24. Visibility Radiation Fog Advection Fog
Develops overnight with weak flow
Common under high pressure
Typical ahead of warm fronts
Can occur with weak movement of warmer air over snow cover…can be prolonged
Strong low level inversion develops (warm air moving over cold air)
South or east component to the wind is favorable

25. Precipitation Need upward motion and moisture to develop precipitation
Precipitation type (RA, SN, FZRA, PL…) is dependent on the vertical temperature structure through the atmosphere
Depth of cold/warm layers determines if freezing/melting occur as precipitation falls to the ground

26. Freezing Precipitation Frequency

28. Precipitation Intensity
Determines visibility reductions in falling precip
Strength of upward motion and amount of moisture in the atmosphere helps determine intensity
2 to 3 miles with light snow is common
1 mile or less is common in heavy bands of snow

29. Biggest TAF Challenges
Stratus or Fog?? Both?? Slight improvements/deterioration (eg. LIFR to IFR etc.)
Precipitation Type
Thunderstorm coverage
Thunderstorm timing

30. Icing

31. Areas Where Icing Occurs
Most non-convective icing occurs in late fall through early spring
Significant icing potential increased in areas of:
Cold air advection
Relative humidity greater than 85% (the higher, the more potential)
Enhanced upward vertical motion (trofs, fronts, orographic lift)
Icing can occur anywhere super cooled water droplets come in contact with an aircraft surface temperature below freezing
85% of all icing conditions occur in vicinity of frontal systems

32. Type is largely temperature dependent

34. Turbulence

35. Turbulence
Most common in cold season (fall-winter) as jet speeds increase
Associated with speed & directional shears (horizontal & vertical) - not just jet strength
Satellite clues and soundings can help

36. Satellite Clues

37. Sounding Example 1

38. Sounding Example 2

39. Sounding Example 3

40. Planning Ahead TAFs Forecast Discussion ADDS Tools
TAF Trends
Forecast Discussion
ADDS Tools
Icing/Turbulence
AIRMETs/SIGMETs
PIREPS
Winter Weather Headlines

41. Aviation Forecast Discussion
Issued by most local offices that issue TAFs
Explains the reasoning behind the TAF
May also indicate confidence in the forecast and potential deviations that may occur
Can also help provide info for conditions between the TAF sites

42. Winter Weather Headlines

43. Aviation Weather Resources
ADDS
Forecast Maps
NWS Chicago
CWSU (ZAU)

44. How You Can Help…PIREPs!!
-Limited observational data above the surface -They help us with the forecast -They also help other pilots

45. Questions??