What the heck was up with last week’s hail in Houston?

Last week’s storm system was mostly about the heavy rain and flooding, as Eric summed up nicely here. But the story that I think was most fascinating, meteorologically, was the hailstorm that hit some parts of the Houston area on Thursday night. The National Weather Service Houston office collected over 20 hail reports from the event, more than half of which were golf ball size hail or larger.

https://twitter.com/VortexChasing/status/1126686637394518016

Houston doesn’t often get hail this big over this wide an area. So what happened here? Why did we have so much big hail last Thursday?

Houston doesn’t see a lot of hail

If you look at the map of annual average 1+ inch diameter hail days per year (this from 2003-2012), you’ll notice Houston is mostly on the outside looking in at significant hail reports.

Severe hail reports are most common from Missouri and Kansas into South Dakota. (NOAA)

Why is this the case? For one, thunderstorm updrafts are needed to allow for the water droplets that become hailstones to get above the freezing level. Houston is a warm place, and that freezing level is often too high and the storms not powerful enough to carry those droplets high enough for large hail to form. Our lower freezing levels occur in winter and spring, making hail more likely then. In fact, of the 62 hail reports of 2″ in diameter or larger in NOAA’s storm events database since 1950 in Harris County and adjacent counties, only 3 of those reports have occurred outside of January through May. The average hail maxima is also where it is because they simply get more powerful, supercell thunderstorms with violent updrafts in the Plains.

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Some storm chances this week, but a tricky forecast for Houston

It’s another clear and pleasant morning—low temperatures in the mid- to upper-60s are not to be taken for granted this time of year—and our forecast remains on track with May-like weather ahead. We’re still anticipating some rain, and the potential for storms later Saturday night and Sunday morning, but there is no guarantee this will happen.

Thursday

Overall, today will be similar to Wednesday, with mostly sunny skies and high temperatures in the mid-80s. Some high resolution models are showing the potential for some scattered storms that could pop up this afternoon, due to the combination of the sea breeze and daytime heating. The most likely window for these appears to be from 2pm to 6pm this afternoon, with areas along and west of Interstate 45 most favored. These shouldn’t pose too much of a problem unless they develop directly over freeways at rush hour.

The HRRR model shows the potential for at least isolated thunderstorms on Thursday. (Weather Bell)

Friday

This should be a partly sunny day, with highs in the mid-80s, and another chance of scattered to isolated showers and thunderstorms. More clouds will likely move in later on Friday and Friday night, leading to warmer overnight conditions for the region in the mid-70s.

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Storms likely to reach Houston Saturday night, hot thereafter

Good morning. We’re going to have a seasonable end of the work week, with a healthy chance of rain this weekend—the timing is most likely Saturday night, so don’t cancel those outdoor plans just yet—and then much warmer weather next week. It’s not June yet, but with high pressure moving in temperatures will go up and rain chances will go down.

Wednesday

Today’s forecast will feature partly to mostly sunny skies. We may see a very few scattered showers over the region, especially to the southwest of Houston, but mostly we’re going to see sunshine. Highs will be in the mid-80s and overnight lows will drop down to around 70 degrees. In short, this is pretty standard weather for May. And while it’s fairly warm, this is nothing like what’s coming.

Severe storms will affect West Texas on Friday. (NOAA)

Thursday and Friday

High pressure should keep a lid on all but scattered showers to end the work week, and allow partly to mostly sunny skies across Houston. Highs will likely reach into the mid- to upper-80s with southerly, humid winds. A reminder, if you’re traveling to West Texas or the Panhandle on Friday, check your travel plans closely, as a storm system will likely be moving across that part of the country with the potential to produce severe weather, including tornadoes.

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Expect a typical May week, with a chance for showers this weekend

After Monday’s superb weather—seriously, was that the nicest day of 2019 so far?—we’re going to return to a more May-like pattern with increasing humidity and warmer temperatures for the rest of the week. We still have some concerns about the potential for storms this weekend, but as for now it appears like the more severe weather will remain north and west of Houston.

Tuesday

It is warmer across the Houston area this morning, with lows generally down around 70 degrees in the city, and a few degrees cooler up north. With partly sunny skies later this afternoon, we can expect high temperatures to reach the mid-80s. We will see some slight rain chances in Houston, perhaps 20 percent or so, with the best potential to the southwest of the region over Matagorda, Wharton, and Colorado counties. Accumulations should be less than a tenth of an inch, or two.

Temperatures Tuesday will be typical of May in Houston. (National Weather Service)

Wednesday and Thursday

These should be a similar days to Tuesday, with low, but non-zero rain chances. Temperatures will be on the upswing, with highs in the mid, and possibly upper-80s by Thursday. Overnight lows will remain decent for mid-May, likely dropping to around 70 degrees in the city of Houston.

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