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
• 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
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
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
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)
Today’s Sfc Chart (23 Sept 2014)
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
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 (generally add 1 in
thousands digit)
• Isotherms (dashed contours)
– 5oC intervals with 0oC reference line
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)
– Height changes
• Caution:
– Sometimes underground near high terrain
Today’s 850mb Chart (23 Sept 2014)
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 (generally add 2 or 3
in thousands digit)
• Isotherms (dashed contours)
– 5oC intervals with 0oC reference line
700 mb Chart
• Uses:
– 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
Today’s 700mb Chart (23 Sept 2014)
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
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
Today’s 500mb Chart (23 Sept 2014)
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
Today’s 500mb Hemis (23 Sept 2014)
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:
• 70-110 knot winds
• 150-190 knot winds
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
Today’s 300mb Chart (23 Sept 2014)
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 tenthousands digit [if first plotted number is a 0])
• Isotherms (dashed heavy contours)
– 5oC intervals with -50oC reference line
200/250 mb Analysis
• Isotachs (light dashed contours)
– 20 knot intervals with a 10 knot reference line
– Stippled regions represent:
• 70-110 knot winds
• 150-190 knot winds
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
Today’s 200mb Chart (23 Sept 2014)
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)
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)