Map Wall Product Descriptions

The product descriptions below are included as an educational resource for the community. For each of the charts shown on the map wall website, we provide a short description of the products plotted and how the chart can be used for weather analysis and forecasting.

Jet-stream level: 200–300 mb Wind

What’s plotted:

  • Geopotential height (every 12 dam) contoured; wind speed shaded

What to look for:

  • Jet streaks (areas of maximum wind)
  • Entrance and exit regions of jet streaks
  • Straight jet streaks:
    • Right (equatorward) entrance and left (poleward) exit: Regions of upper-level divergence → ascent
    • Left (poleward) entrance and right (equatorward) exit: Regions of upper-level convergence → descent
  • Cyclonically curved jet streaks:
    • Entire entrance region → upper-level convergence → descent
    • Entire exit region → upper-level divergence → ascent
  • Anticyclonically curved jet streaks:
    • Entire entrance region → upper-level divergence → ascent
    • Entire exit region → upper-level convergence → descent
  • Jet streaks co-located with strong lower-tropospheric temperature gradients (baroclinic zones)
  • A jet streak upstream of a trough will tend to strengthen that trough (by injecting positive [cyclonic] shear vorticity into the trough)

Mid-troposphere: 500 mb

What’s plotted:

  • Geopotential height (every 6 dam) and temperature contoured
  • Relative vorticity shaded; vorticity advection contoured

What to look for:

  • Regions of both shear and curvature vorticity
  • Vorticity Advection:
    • Positive vorticity advection (PVA) → ascent
    • Negative vorticity advection (NVA) → descent
  • Troughs move towards regions of PVA; ridges move towards regions of NVA
  • PVA above a surface cyclone will intensify the surface cyclone (westward tilt of a cyclone with height)
  • NVA above a surface anticyclone will intensify the surface anticyclone (westward tilt of an anticyclone with height)

Lower-troposphere: 700 and 850 mb

What’s plotted:

  • Geopotential height and temperature contoured
  • Shaded: RH, temperature advection
  • Frontogenesis contoured

What to look for:

  • Evaluate horizontal temperature advection (except in the Rockies)
  • High relative humidity (>90%) → possible cloud cover
  • If 700 mb trough axis passes, skies may clear; if ridge axis passes, clouds may increase
  • Diagnosing temperature advection:
    • Warm-air advection (WAA) → ascent
    • Cold-air advection (CAA) → descent
  • Surface systems move towards areas of WAA (cyclones) or CAA (anticyclones)
  • CAA under 500 mb trough → 500 mb heights fall → trough intensifies
  • WAA under 500 mb ridge → 500 mb heights rise → ridge intensifies
  • 0°C line at 850 mb → rain/snow line indicator

Lower Troposphere: Sea-level pressure, 1000–500 mb thickness, Precipitation

What’s plotted:

  • Sea-level pressure (SLP) contoured; 1000–500 mb thickness dashed
  • 6-hour precipitation accumulation or precipitation rate

What to look for:

  • Thickness field shows upper-level troughs and ridges
  • Temperature advection diagnosis:
    • Warm-air advection (WAA) → ascent
    • Cold-air advection (CAA) → descent
  • Surface systems move towards WAA (cyclones) or CAA (anticyclones)
  • Critical thickness (rain/snow line):
    • East of Rockies: 540 dam
    • Rockies: 548-552 dam
    • West Coast: 522-528 dam
  • 0°C line at 850 mb + critical thickness line → mixed precipitation zone

Low-Level Lapse Rates

Products plotted:

  • Low Level Lapse Rates (Surface to 3km) - shaded
  • Low level flow (Surface to 3km mean wind) - streamlines

What to look for:

  • Destabilization in the boundary layer:
    • Great low-level lapse rates for convection: generally values >8
  • Low level flow:
    • Assessing the movement of greater low-level unstable air

Mid-Level Lapse Rates

Products plotted:

  • Mid Level Lapse Rates (700mb to 500mb) - shaded
  • Mid level flow (700mb to 500mb mean wind) - streamlines

What to look for:

  • Elevated mixed layer (EML)
  • Destabilization in the mid-levels:
    • Great mid-level lapse rates to persist convection: generally values >7.5

Surface-Based CAPE | CIN

Products plotted:

  • Surface-Based CAPE - shaded, colors
  • Surface-Based CIN - shaded, gray
  • 10m Wind - barbs

What to look for:

  • SBCAPE represents the total amount of potential energy available to a parcel of air originating at the surface and being lifted to its level of free convection (LFC). No parcel entrainment is considered.
  • SBCAPE Generalizations:
    • 0 : Stable
    • 0-1000: Marginally Unstable
    • 1000-2500: Moderately Unstable
    • 2500-3500: Very Unstable
    • 3500+: Extremely Unstable
  • SBCIN represents the potential energy to prevent surface-based parcels from rising
  • SBCIN Generalizations:
    • Greater than 0: Capped atmosphere. Other forcing mechanisms or CIN erosion needs to take place for convection to develop.

Mixed-Layer CAPE | CIN

Products plotted:

  • Mixed-Layer CAPE - shaded, colors
  • Mixed-Layer CIN - shaded, gray
  • MSLP - black contours
  • 10m Wind - barbs

What to look for:

  • MLCAPE represents the mean potential energy conditions available to parcels of air located in the lowest 100-mb when lifted to the level of free convection (LFC).
  • Better tool to assess a greater amount of instability compared to SBCAPE.
  • MLCAPE Generalizations:
    • 0 : Stable
    • 0-1000: Marginally Unstable
    • 1000-2500: Moderately Unstable
    • 2500-3500: Very Unstable
    • 3500+: Extremely Unstable
  • MLCIN represents the potential energy to prevent surface-based parcels from rising
  • MLCIN Generalizations:
    • Greater than 0: Capped atmosphere. Other forcing mechanisms or CIN erosion needs to take place for convection to develop.

Most Unstable CAPE

Products plotted:

  • Most Unstable CAPE - shaded, colors
  • MSLP - black contours
  • 10m Wind - barbs

What to look for:

  • MUCAPE is a measure of instability in the troposphere. This value represents the total amount of potential energy available to the most unstable parcel of air found within the lowest 300-mb of the atmosphere while being lifted to its level of free convection (LFC).
  • Better tool to assess the risk for elevated convection especially with strong inversions in place.
  • MUCAPE Generalizations:
    • 0 : Stable
    • 0-1000: Marginally Unstable
    • 1000-2500: Moderately Unstable
    • 2500-3500: Very Unstable
    • 3500+: Extremely Unstable

SBCAPE | 500-850-sfc Wind Crossover

Products plotted:

  • SBCAPE - shaded, colors
  • 10mb Wind - red barbs
  • 850mb Wind - orange barbs
  • 500mb - black barbs
  • MSLP - black contours

What to look for:

  • SBCAPE represents the total amount of potential energy available to a parcel of air originating at the surface and being lifted to its level of free convection (LFC). No parcel entrainment is considered.
  • SBCAPE Generalizations:
    • 0 : Stable
    • 0-1000: Marginally Unstable
    • 1000-2500: Moderately Unstable
    • 2500-3500: Very Unstable
    • 3500+: Extremely Unstable
  • Change in direction with height may indicate directional shear, favorable for severe thunderstorms and tornadoes. Assess other parameters before making conclusions.

0-1km Wind Shear | 500mb Heights

Products plotted:

  • 0-1km Bulk Wind Shear - shaded
  • 0-1km Bulk Wind Shear - black barbs
  • 500mb Heights - black contours

What to look for:

  • 0km-1km Bulk Wind Shear is the difference between the surface wind and the wind at 1-km above ground level. These data are plotted as vectors with shear magnitudes contoured. 0-1-km shear magnitudes greater than 15-20 knots tend to favor supercell tornadoes when favored with other severe weather parameters.

0-3km Wind Shear | 500mb Heights

Products plotted:

  • 0-3km Bulk Wind Shear - shaded
  • 0-3km Bulk Wind Shear - black barbs
  • 500mb Heights - black contours

What to look for:

  • 0km-3km Bulk Wind Shear is the difference between the surface wind and the wind at 3km above ground level. These data are plotted as vectors with shear magnitudes contoured.
  • 0-3km Wind Shear greater than 30-40 knots may be favorable for bowing thunderstorms.
  • May support dynamic, cool-season bow echoes with moderate to strong winds aloft, but little additional shear aloft.
  • Increased derecho risk with 0-3 km bulk shear > 30 kts and combined with 0-6 km bulk shear > 40 kts.

0-6km Wind Shear | 500mb Heights

Products plotted:

  • 0-6km Bulk Wind Shear - shaded
  • 0-6km Bulk Wind Shear - black barbs
  • 500mb Heights - black contours

What to look for:

  • 0km-6km Bulk Wind Shear is the difference between the surface wind and the wind at 6-km above ground level. These data are plotted as vectors with shear magnitudes contoured. 0-6-km shear magnitudes greater than 30-40 knots favor organized convection and supercells.
  • Will give you a clue as to how organized the convective mode will be.
  • Values > 40 kts support well-organized supercells, squall lines, and derechoes.