For information on interpreting analysis charts see: http://weather.unisys.com/upper_air/details.html and http://weather.unisys.com/surface/details.html Below are many common analysis charts used by meteorology. Most charts have an active link to a current online image of that chart. #1 PRESSURE CHANGE CHART *Millibars of pressure change in last 3 hours *Lows tend to migrate toward regions of greatest pressure falls *Pressure fall indicates low is moving toward a region or deepening over that region *Pressure rises indicate low is moving away or weakening (filling). Ridge could also be building #2 STREAMLINES *Shows regions of convergence and divergence *Often used in tropics due to a weak Coriolis and Pressure Gradient Force *Shows source region air is coming from #3 BOUNDARY LAYER WIND *Used for advection strength; air mass movement *Can locate frontal boundaries *Can be used to assess how uncomfortable people will be when going outside #4 THETA-E (EQUIVALENT POTENTIAL TEMPERATURE) *Found by combining temperature and dewpoint *Found on a Skew-T by raising parcel adiabatically from surface to upper atmosphere until all water vapor is condensed out then descending parcel to the 1000 mb level. *Higher theta-e indicates unstable air (look for intersection of highest dewpoints and temperature) *Theta-e ridge indicates possible burst point for convection. #5 850 MB WIND VECTORS *Strength of low level advection/convergence/air mass source regions *Low level jet/ pressure pattern/ general atmospheric circulation #6 WIND CHILL INDEX *Comfort level of outdoor activities *Wind chill advisories, brutalness of arctic outbreaks *Index found through a combination of wind speed and temperature #7 HEAT INDEX *Can assess stress on body during outdoor activities *Index found through a combination of temperature and dewpoint (relative humidity) *Direct sunlight and light winds adds to heat stress as well as heat build up in cars. #8 WEATHER DEPICTION CHART *Obstructions to vision if driving or flying. *Locate scale and magnitude of fog, haze, smoke, snowfall, rain, etc. *See how much obstruction to vision is lowering visibility. #9 24 HOUR PRECIPITATION *Regions with saturated soils (flood potential, scale of saturated soil) *Rainfall intensity #10 SNOW COVER *Snow covered areas tend to be lower in temperature. Often record lows occur on snow-covered nights with light winds and clear skies. *Polar/ Arctic fronts do not modify as quickly over snow covered regions. *Mesoscale snowfall cover *Can aid forecasting since forecast model snow cover is updated only weekly. #11 US DEWPOINT CONTOURS *Forecast CAA/ WAA/ moisture advection *Isentropic lifting and latitudinal convergence (gradual lifting of warm and humid air, usually over a warm front) *Warm/ cold/ dry sectors of mid-latitude cyclones (can locate drylines and the 4 other frontal types) #12 US TEMPERATURE CONTOURS *Frontal boundaries and advections *Mirror of trough and ridge pattern aloft (generally cool temperatures will be located underneath a trough due to cloudy skies and cold air advection) #13 COLUMN RELATIVE HUMIDITY *Closeness of air to saturation *Ascent/ subsidence in lower atmosphere *Drying power of the air (evaporation increases as relative humidity decreases); very important to agricultural forecasts #14 PRECIPITABLE WATER *Depth of liquid water if all water, ice and vapor in atmosphere were brought to the surface. *Higher Precipitable Water indicates regions where there is a larger depth of moisture and higher moisture content. Warm air can evaporate exponentially more water than can cold air. #15 1000-500 MB THICKNESS *Distance in geopotential meters between the 1000 and 500 mb level. *5,400 gpm line east of Rockies is used for rain/ snow line. 5,460 or 5,520 can be used in higher elevations as rain/snow line. *Gives clue to strength of warm air advection (higher thicknesses) and cold air advection (lower thicknesses) #16 LIFTED INDEX *(In)stability of the atmosphere (the more negative the value the more unstable) *LI is decreased (more unstable) by: warming the low levels of atmosphere, cooling mid and upper levels of atmosphere, adding moisture to low levels of atmosphere. #17 SURFACE CONVERGENCE CHART *Shows regions where air streams are coming together and rising *Used to locate regions which are most favorable for precipitation when moisture is available *Surface convergence can be caused by: fronts, outflow boundaries, topography, surface lows, friction #18 HELICITY *Regions with high speed shear and directional shear *High Helicity in the lower troposphere is caused by large changes in the wind direction in the low levels of the atmosphere and strong low level wind shear, especially when the PBL wind speeds are high *Helicity is important to tornadic environments #19 MOISTURE CONVERGENCE *Positive moisture advection occurs when a volume of water vapor is forced into a smaller volume *Areas with high moisture convergence will have higher dewpoint values. The buildup of low level moisture increases atmospheric instability #20 500 MB VORTICITY *Can assess upper level divergence #21 SURFACE TEMPERATURE ADVECTION *Atmosphere will become more unstable through moisture advection and low level warm air advection. |