After basking in the near 80 degree temperatures Sunday and Monday, residents of Blanco County woke up on Tuesday to the coldest temperatures by far of the season. The second of two frontal passages tore through south central Texas around 3am Tuesday morning, bringing frigid temperatures and wind chills with it.　

The first front Monday morning brought warmer temperatures with it due to the wind shift from the north to the south. Right before 11am Monday, weather data show a drop in barometric pressure, wind gusts of 10-15 mph, and a sharp shift in wind direction from the north to the south. Temperatures continued to rise into the high 70s and we experienced gusty winds throughout the rest of the day and evening. It was a beautiful preview day of the spring to come — even the trees and shrubs were fooled by the nice weather.

Around 3am Tuesday morning, another front ripped through the Hill Country. This was an extremely strong cold front. The Hill Country experienced a drop in atmospheric pressure up until the frontal passage, a sharp change in wind direction from south to north, wind gusts up to near 35 mph, and some rain. Blanco got about a quarter of an inch of rain overnight. During and after the frontal passage, temperatures dropped rapidly from the low 60s to the 30s, and they continued to drop throughout the day on Tuesday, hovering in the chilly mid- to high-20s. Wind chills dipped into the single digits at times. As is common with a cold front, the barometric pressure rose throughout the day as the front moved onward toward the coast. It also remained windy as the Earth balanced the change in pressure due to the frontal passage (wind is defined as air moving from an area of high pressure to an area of low pressure).　

Blanco County was in a wind advisory all day Tuesday as Northerly winds of 20-30 mph with gusts of 30-40 mph developed behind the cold front. A wind advisory means that sustained winds of 26-39 mph are expected. Winds this strong can make driving difficult, especially for high profile vehicles.　

A wind chill advisory was in effect overnight Tuesday night into Wednesday morning. The combination of gusty northerly winds and falling temperatures in the teens created low wind chills from minus five to zero degrees Fahrenheit across south central Texas. A wind chill advisory means that very cold air and strong winds will combine to generate low wind chills. This will result in frost bite and lead to hypothermia if precautions are not taken. If you must venture outdoors, make sure you wear a hat and gloves.　

One of the gravest dangers of winter weather is wind chill. The wind chill is based on the rate of heat loss from exposed skin by combined effects of wind and cold. As the wind increases, heat is carried away from the body at an accelerated rate, driving down the body temperature. Animals are also effected by wind chill. Check out the wind chill chart on the Internet at　www.weather.gov/er/iln/tables.htm#wind

A frontal passage is usually accompanied by a wind direction shift. This is because that fronts lie in troughs of low pressure. The isobars (lines of equal pressure) in a trough are curved cyclonically (counterclockwise) in the Northern Hemisphere. This means that as a trough, with its front, passes a particular location the wind direction shifts clockwise, up to 180 degrees. The wind behavior during the frontal passage depends upon the type of front, its speed, the contrast in temperature of the air masses involved, and upon local conditions of surface heating and topography.

The cold weather pattern will remain in place through Friday or longer. By Thursday, an upper-level disturbance will arrive in the area and bring a chance of light snow Thursday night into Friday. No accumulation is expected here in Blanco County, but some snow could stick since the ground is so cold. The areas east of I-35 have a better chance of accumulation than here in the Hill Country. Residents should protect plants, pipes, and outdoor animals. If you’re planning on traveling, keep an eye on the weather and be prepared for snow. Riders participating in the San Antonio stock show and rodeo trail this weekend should be prepared for the bitter cold the rest of the week, including hard freezes overnight.　

This weather system was part of an intense storm system that affected two dozen states and an estimated 100 million people. There was a 2,100-mile-long swath of the United States, extending from Oklahoma City to Chicago to Portland, Maine, where there was potential for over a foot of snow. Many of the Interstates in the midwest and the east were in "caution" mode, including much of I-70, I-35, I-44, I-80, and more.　

The weather for the rest of the week: Wednesday will be mostly cloudy with highs in the upper 20s. Winds will be from the north, 15-20 mph with the lowest wind chill readings flirting with zero degrees in the morning. Wednesday night will be cold with lows around 15 and north winds 10-15 mph.　

Thursday will be cloudy with highs in the lower 30s and north winds from 10-15 mph. Thursday night, there’s a chance of snow; otherwise, it will be cloudy with lows around 19.　

Friday will be mostly cloudy with a chance of snow, but a bit warmer with highs in the lower 40s. Friday night will be mostly clear with lows in the upper 20s.　

Saturday will be warmer with highs in the upper 50s and an overnight low in the mid 30s, and Sunday will be in the lower 60s with an overnight low in the upper 30s.