DIFAX Maps

1. DIFAX Maps • Weather maps generated by the NWS • Before the Internet or AWIPS, these were the basic weather analysis and forecast charts used by meteorologists • They were only available through a fax machine connected to a dedicated landline

2. DIFAX maps are gradually being phased out; however, the most important ones are still produced • These maps are unique and contain information which is priceless for operational meteorologists • All meteorology students benefit from knowledge of these maps and their interpretation • If you understand how to interpret the black&white DIFAX chart, you should have no problem interpreting pretty colored charts from other sources

3. DIFAX Map Access National Weather Service: http://weather.noaa.gov/fax/nwsfax.html Colorado State Archive: http://ldm.atmos.colostate.edu/ SUNY Albany: http://www.atmos.albany.edu/weather/difax.html

4. Surface Charts • Analyzed charts issued every 3 hours (00Z – 21 Z) • Data includes • Hourly synoptic stations • Ship reports • Buoy reports • Maps can be found from the HPC: http://www.hpc.ncep.noaa.gov/html/sfc2.shtml

5. Surface Charts • Isobar analysis: • 4 mb increments labeled with tens and units digits • Lows and Highs labeled with L and H with the pressure value labeled nearby (in whole mb) • Frontal Analysis http://www.hpc.ncep.noaa.gov/html/fntcodes2.shtml • Used for current depiction of surface weather features (most valuable weather chart)

7. Upper Air Analysis • Generated every 12 hours with 00Z and 12Z data • Produced from the NAM Model analysis • The NAM Model uses a first guess from the previous model run 6 or 12 hours earlier as a basis for constructing the analysis fields • Data is incorporated into the first guess field and the analysis is created via Optimal Interpolation (OI) or 4-D Data Assimilation • Actual data is plotted on the chart, but may not agree with chart’s analysis field

8. 850 mb Chart • Isoheights (solid contours) • 30 m intervals with 1500 m (150 decameters) reference line • Contour labels in decameters • Plotted heights are in meters • Isotherms (dashed contours) • 5C intervals with 0C as reference line

9. 850 mb Chart • Uses: • Low level jets • Lower tropospheric temperature advection and thermal profile (thermal ridges and troughs) • Lower tropospheric moisture advection and profiles (moist and dry tongues)

12. 700 mb Chart • Isoheights (solid contours) • 30 m intervals with 3000 m (300 decameters) reference line • Contour labels in decameters • Plotted heights are in meters • Isotherms (dashed contours) • 5C intervals with 0C reference line

13. 700 mb Chart • Uses: • Mid-level jets • Mid-tropospheric temperature advection and thermal profile • Elevated tropospheric moisture advection and profiles • Height changes

16. 500 mb Chart (North America) • Isoheights (solid contours) • 60 m intervals with 5400 m (540 decameters) reference line • Contour labels in decameters • Plotted heights are in decameters • Isotherms (dashed contours) • 5C intervals with 0C reference line

17. 500 mb Chart (North America) • Uses: • Mid-tropospheric temperature advection and thermal profile • Mid-tropospheric moisture profile • Wave pattern in the westerlies • ID of longwaves and shortwaves • LND and approximate steering level for surface synoptic systems • Height changes and wave motion • Vertical and horizontal tilt of waves

20. 500 mb Chart (Hemispheric) • Contains same contours as the 500 mb North American analysis, except void of data plots • Additional Uses: • Circumpolar vortex • Planetary wave number and pattern • Wave ID

22. 300 mbChart • Isoheights (solid contours) • 120 m intervals with 9000 m (900 decameter) reference line • Contour labels in decameters • Plotted heights in decameters • Isotachs (light dashed contours) • 20 knot intervals with 10 knot reference line • Stippled regions represent: • 70-110 knot winds • 150-190 knot winds

23. 300 mb Chart • Uses: • Polar jet stream location/configuration/intensity • 4-quadrant jet/divergence relationship • Upper tropospheric wave pattern • Regions of difluence and confluence • Regions of upper-tropospheric vertical shear

26. 1000-500 Thickness / MSLP Chart • Thickness Values (usually dashed contours) • Vertical distance in m between 1000mb and 500mb pressure levels • Function of avg virtual temperature of 1000mb to 500mb layer • Increments of 60 gpm • MSLP (solid black contour)

27. 1000-500 Thickness / MSLP Chart • Uses • Temperature advection • Thickness is proportionally to temperature • Use MSLP contours as proxy for wind (assume geostrophic • 5400 (540) line generally divides polar air from mid-latitude air (rain-snow line)

29. General Rules For Drawing Contours (see handout for more detail) • Contour lines are drawn to identify constant values of an atmospheric variable • A contour is drawn through the station location only if the data for that station has the exact value of the contour; otherwise, the contour is drawn between stations • Higher values are on one side of the contour and lower values on the other side of the contour • Contours never cross or touch each other • More than one contour of a given value may appear on a given map • All contour lines must be clearly labeled • Often easiest to find the highest value or the lowest value and work from there • Keep the surface wind in mind when drawing pressure contours. • Relative to other stations, the stronger the wind, the stronger the pressure gradient, thus the closer the isobars.

31. 1016 mb H L

32. 1016 mb H L 1012 mb

33. 1016 mb H L 1012 mb 1008 mb

34. 1016 mb H L 996 mb 1012 mb 1008 mb

35. 1016 mb H L 996 mb 1012 mb 1000 mb 1008 mb

36. 1016 mb H L 996 mb 1012 mb 1000 mb 1008 mb 1004 mb

37. 1016 mb H L 996 mb 1012 mb 1000 mb 1008 mb 1004 mb