Month: February 2018

Houston is cooler today, but blink and you’ll miss it

The cold front that has been driving all of the precipitation finally pushed through the Houston area during the overnight hours, and so we’re generally seeing low temperatures in the 50s this morning—with 40s to the west and far north of Houston. The front lies just offshore, so this cold weather won’t last as the warmer air pushes back onshore.

Temperatures on Thursday morning show the cold front has pushed through almost all of Texas. (Weather Bell)

Thursday

High temperatures today will be in the 70s under cloudy skies. Rain chances remain, but we’re not going to see the prolonged, heavier showers the region experienced on Wednesday. About half of the area probably won’t see any rain at all today, especially along the coast. Lows tonight will be warmer, as the onshore flow resumes.

Friday and Saturday

Friday and Saturday will be warmer and muggier under mostly cloudy skies, as Houston falls back into a pattern we’ve experienced a lot of this month. Expect highs in the upper 70s, with southerly winds, and warm nighttime temperatures in the 60s. Rain chances will be lower on Friday, and a bit higher on Saturday as moisture levels ramp back up and a cold front approaches and moves through the area during the evening or overnight hours.

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Why are thunderstorms so common during spring months?

As most Southerners know, the arrival of spring also means the arrival of severe weather season. On Wednesday morning, many Houstonians heard the first rumblings of serious thunder for 2018, and if history tells us anything, this is just the beginning of a potential spring full of thunderstorms, flooding, lightning and tornadoes. What is it about the springtime that initiates this activity?

Hot, Hot Heat

Thunderstorm formation depends on atmospheric stability. We’ll forego talk about lapse rates and latent heat for now, and describe stability in simple terms. During the wintertime, our atmosphere is generally very stable. This means that conditions in the air prohibit any vertical motion. For thunderstorms to develop, they need warm air to rise from the surface, then to cool and condense into a tall, vertical column of clouds. In a stable atmosphere, this is nearly impossible.

As winter turns to spring, two things occur that make the atmosphere much more unstable. First, the air around us, especially if that air comes in from the Gulf, becomes much warmer and much more humid. Yesterday, February 20th, Bush Intercontinental Airport recorded a high of 80°F, with relative humidity values staying above 70%. This warm, moist air mass created a perfect environment of instability around us.

This diagram shows how air, heated at the surface, rises in the atmosphere until it condenses into a cloud. (Ahrens)

Second, as days become longer and the sun rises higher in the sky, the sun heats the ground, which, in turn, heats the air directly above the ground. This warm air will eventually rise in an unstable atmosphere, pushing cold air out of the way, as the diagram above shows. As it goes up, the air begins to cool, and as it cools, the water vapor in the air will condense–into clouds! If the atmosphere remains unstable, and these pockets of warm, condensing air rise rapidly, we have the recipe for a thunderstorm.

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Heavy rains overnight, but radar clearing for morning commute

A round of thunderstorms moved through Houston during the overnight hours, dropping as much as 2 inches of rainfall for some areas pretty quickly, but now the Houston region is seeing a break that should hold through at least sunrise and probably the morning commute.

Wednesday

The cold front that’s helping to drive these showers (along with some kinks in the atmosphere moving northward into the region) isn’t going away, so there’s the potential for redevelopment of heavy rain later this morning and throughout the day. To that end, the National Weather Service has issued a Flash Flood Watch through 3pm this afternoon for most of the region, excepting the coast.

A flash flood watch is in effect until 3pm CT. (National Weather Service)

With that said, I don’t things will get too bad today, and probably at most we are looking at the potential for some short-lived street flooding during heavier downpours. Bottom line—check the radar before heading out for any trips beyond the local grocery store. The front should eventually make its way through most of Houston, leading to a somewhat cooler night in the 50s for most of the area except for probably along the coast.

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Houston forecast turns wet, but how wet?

Conditions favorable for heavy rainfall will set up over Texas beginning later today, but for now we continue to think that the hardest hit areas will be north of Houston over the next two days. Regardless, we’ll be watching the system closely because of its potential for mischief.

Tuesday

After a warm morning, conditions will remain muggy throughout the day, with highs in the upper 70s and mostly cloudy skies. Winds will be gusty out of the south, and we may see some scattered rain showers this afternoon—but nothing to get too concerned about. We’ll have to wait until the overnight hours for heavier stuff.

Tuesday night, Wednesday, and Wednesday night

The combination of a very slow moving cold front (moving in from the northwest), very moist air, and a series of atmospheric disturbances moving north from Mexico will create conditions for bands of very heavy rainfall across Texas. As the map below from NOAA shows, the best chance for heavy rainfall appears to be north of the Houston metro area.

Seven-day rainfall accumulation forecast from NOAA. (Pivotal Weather)

As always, with these forecasts, they are a guide about general conditions rather than an exact prediction. Given the atmospheric conditions, we definitely will have the potential for heavy rainfall in Houston, too.

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