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: 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 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) 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

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

Today’s 850mb Chart (23 Sept 2014)

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

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

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 ten-thousands 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)