Generically, a meteogram is a time-series graph that shows the actual or expected weather at a particular location (usually an airport) over a period of time. The meteogram found in the Airport Wx view in the EZWxBrief progressive web app includes winds and temperatures aloft, clouds, icing and turbulence.
Shown below is the 3-Day clouds (and temperature) depiction meteogram for Rock Hill, South Carolina (KUZA). This area is expecting a wintry mix of precipitation as an area of low pressure makes its way through the Southeast on January 10-11.
Time is located at the bottom of the diagram with time increasing from left to right. The weather icon row at the top of the meteogram depicts the weather (sky cover) and precipitation type (if any) at four-hour intervals (1-Day view is hourly). Notice how skies are clear at 17Z on the 9th and by 11Z on the 10th, clouds become broken then overcast before precipitation starts around 20Z. That precipitation begins as snow before transitioning to ice pellets (sleet) and then ending as freezing rain based on this forecast in EZWxBrief.
The cloud depiction in the main viewport area shown above describes this nicely. Notice that high clouds build in first around 05Z on the 10th. Clouds then "build down" to the surface throughout the day (red arrow). This is very typical as a major weather system moves into the area.
The meteogram view below depicts winds and temperatures aloft for Rock Hill. Temperature (isotherms) are shown as contours. Notice as the weather system approaches, the entire temperature profile is below freezing (all cyan isotherms) when the snow is expected to begin around 19Z on the 10th. However, as the weather system moves in through the day, warm air from 2,000 feet to 8,000 feet begins to overrun the cold, dense air just immediately above the surface. Isotherms that are yellow indicate a temperature above freezing. This creates a classic "warm nose" that will partially or completely melt snow into liquid.
As this transition occurs partially-melted snow will then freeze into ice pellets around 01Z on the 11th and then finally as the warmest air moves in around 04Z, the snow is completely melted to form rain and then falls into the subfreezing layer to form freezing rain at the surface.
This can also be confirmed by examining a forecast sounding. The HRRR model forecast sounding depicted below for Rock Hill at 04Z clearly shows the warm nose extending from near 2000 feet to 8,000 feet.
Lastly, we can compare this forecast at Rock Hill to a nearby (14 nm north) terminal aerodrome forecast (TAF) for Charlotte/Douglas International Airport (KCLT). The TAF clearly shows the "building down" of the clouds from clear skies, to scattered at 25,000 feet and then down to overcast at 1,000 feet at the end of the TAF period. The forecasters at the Greenville-Spartanburg (GSP) local weather forecast office are expecting the precipitation to start out as a mixture of light snow and ice pellets (-SNPL) with snow being the dominate precipitation type.
Below is the updated TAF for KCLT valid on the morning of the event. Notice the forecaster is more in line with the meteogram presented earlier for Rock Hill with snow arriving first, followed by a mixture of snow and ice pellets and ending with a mixture of freezing rain and ice pellets.
Most pilots are weatherwise, but some are otherwiseâ„¢Â
Dr. Scott Dennstaedt
Weather Systems Engineer
Founder, EZWxBriefâ„¢
CFI & former NWS meteorologist
