Winter returned with a vengeance on Friday, blanketing the region with several inches of snow. By the afternoon, reports of 3" up to 6" were common across the metro.
This is the biggest snowfall event for the entire season so far. And it follows a long stretch of mild weather.
The first 15 days of February recorded a high temperature warmer than average. And as recently as Thursday, temperatures were in the mid-50s.
Friday morning saw temperatures hovering in the mid to upper 30s as a storm system began developing west of the area. By mid-morning, a mix of snow and sleet was observed in most of the metro and temperatures began dropping into the mid-30s.
Everyone was close to the freezing mark by late morning and precipitation transitioned to all snow. The weather system strengthened over the region and heavy bursts of snow began overspreading the area.
Accompanying that heavy snow included flashes of lightning and thunder. Parts of the region experienced the phenomena of thundersnow. While not completely rare, it’s not something observed with every snow event.
Lead Meteorologist Matthew Beitscher at the National Weather Service in St. Louis explains, “Thundersnow is caused by convective elements within banded snow leading to similar processes to thunderstorms."
Like in a thunderstorm, ice crystals colliding in a cloud create a separation between positive and negative charges. If enough collisions occur, a static build-up will happen and discharge, thus producing lightning. The same happens when you rub your feet over the carpet, generating enough energy to create a shock or spark.
The snow muffles the sound of thunder, creating more of a low rumble rather than a loud crack. Thundersnow was reported in St. Louis, St. Charles and Jefferson counties. As well as parts of south St. Louis City early Friday afternoon.
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