1. DIFAX Maps / Upper Air Charts
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: Colorado State Archive: SUNY Albany:

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:

5. Surface Charts Isobar analysis: Frontal 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
Used for current depiction of surface weather features (most valuable weather chart)

7. Today’s Sfc Chart (23 Sept 2014)

8. 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

9. 850 mb Chart Isoheights (solid contours) Isotherms (dashed contours)
30 m intervals with 1500 m (150 decameters) reference line
contour labels in decameters
plotted heights are in meters (generally add 1 in thousands digit)
Isotherms (dashed contours)
5oC intervals with 0oC reference line

10. 850 mb Chart Uses: Caution: Low Level Jets
Lower tropospheric temperature advection and thermal profile (thermal ridges and troughs)
Lower tropospheric moisture advection and profiles (moist and dry tongues)
Height changes
Caution:
Sometimes underground near high terrain

14. Today’s 850mb Chart (23 Sept 2014)

15. 700 mb Chart Isoheights (solid contours) Isotherms (dashed contours)
30 m intervals with 3000 m (300 decameters) reference line
contour labels in decameters
plotted heights are in meters (generally add 2 or 3 in thousands digit)
Isotherms (dashed contours)
5oC intervals with 0oC reference line

16. 700 mb Chart Uses: Caution:
Elevated tropospheric moisture advection and profiles (elevated dry intrusions; moist tongues)
Mid-tropospheric temperature advection and thermal profile (thermal ridges and troughs)
Mid-level jets
Height changes
Caution:
Sometimes near surface in higher terrain

20. Today’s 700mb Chart (23 Sept 2014)

21. 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

22. 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

26. Today’s 500mb Chart (23 Sept 2014)

27. 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

30. Today’s 500mb Hemis (23 Sept 2014)

31. 300 mb Chart 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:
knot winds
knot winds

32. 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

35. Today’s 300mb Chart (23 Sept 2014)

36. 250 mb Analysis Isoheights (solid contours)
120 m intervals with 10,000 m (1000 decameter) reference line
contour labels in decameters
plotted heights are in decameters (add 0 in ones digit for meters, and possibly a 1 for the ten-thousands digit [if first plotted number is a 0])
Isotherms (dashed heavy contours)
5oC intervals with -50oC reference line

37. 200/250 mb Analysis Isotachs (light dashed contours)
20 knot intervals with a 10 knot reference line
Stippled regions represent:
knot winds
knot winds

38. 200/250 mb Analysis
Uses:
Sub-tropical jet stream location/configuration/intensity
the 4-quadrant jet/divergence relationship
Upper-tropospheric wave pattern
Regions of Difluence and Confluence (convection/severe weather)
Regions of upper-tropospheric vertical shear (tropical cyclones)
Tropopause folds and breaks

41. Today’s 200mb Chart (23 Sept 2014)

42. 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)

43. 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 (first guess for the rain-snow line)