Matt Lanza

We managed the mid-80s yesterday with dew points sitting in the 50s all day, which is pretty comfortable. We get another day or two of that kind of weather before things go back to pre-summer and the details of the forecast get more complicated.

Today and Friday

Look for lots of sunshine and just a few clouds both today and tomorrow. A little low cloud cover or patchy fog is possible tomorrow morning southwest of Houston. We should manage mid-80s both afternoons and upper-50s to mid-60s tomorrow morning, similar to today. Galveston should bottom out near 70° tonight, however. No weather woes, but air quality may be poor. You may have seen the Ozone or Air Quality alerts on your phone or other sites you use for weather info. Having a lot of sunshine, warm temperatures, and light winds tends to help produce ground-level ozone in areas with pollution from heavy traffic and industry. Days like this in spring, summer, and early fall are not uncommon here unfortunately. Take it easy if you have any respiratory sensitivities.

Saturday

Humidity will still be low enough on Saturday morning to allow temperatures to drop perhaps into the low to mid-60s away from the bays and coast. But as Saturday progresses, the humidity will inch upward. Look for highs in the 80s, some sunshine and added clouds, and a very slight shower chance. Saturday night will see temperatures struggle to get below the low-70s, so “pre-summer” will be in full effect.

Mother’s Day

The forecast gets conveniently complicated beginning on Sunday unfortunately. The setup for Sunday and much of next week is going to be contingent on the exact placement of a cold front that is destined to stall out somewhere between the Gulf Coast and Dallas. This will likely lead to at least a couple rounds of thunderstorms, with the first occurring Sunday afternoon. Models still have some disagreements on coverage, intensity, and the exact location of Sunday’s storm chances, however.

The odds of more widespread showers and storms on Mother’s Day are still highest right now north of Houston. But there is little room for error in that current forecast, meaning any shift south will open the door to greater coverage of afternoon storms in and around Houston. The timing may allow for Mother’s Day brunch plans to go off successfully (though there will likely be at least a few showers around late Sunday morning into early afternoon). But those of you with Mother’s Day dinner plans, particularly outside, will want to keep tabs on the forecast.

Look for highs well into the 80s, though any thunderstorms will allow temperatures to briefly cool off.

Next week

As noted above, next week’s forecast will be highly contingent on exactly where that cold front orients and the timing of any disturbances rippling along the front. Expect at least a chance of storms Monday through Wednesday, but trying to hone in on exact details on timing and intensity this far in advance is very difficult. We will know more as we get closer. Look for highs in the 80s to near 90 degrees at times, lows in the 70s.

Another front?

By later next week, the European ensemble, which runs slightly tweaked versions of the European model 51 different times is showing about a 60 to 70 percent chance that the front responsible for next week’s unsettled start will slip through the region and offshore.

You can really only see this reflected in overnight lows, which noticeably drop back on the ensemble (boxed in above) beginning Thursday or Friday morning. It’s worth noting that the GFS model is somewhat less enthusiastic about this possibility. So, there is still some uncertainty here, but if we do see the front clear us next week, look for highs to drop back a few degrees into the low to mid-80s and morning lows to go from the 70s early in the week to mid to upper-60s perhaps, with some risk for slightly cooler. We will see!

With a fine, quiet stretch of weather beginning today for Houston, Eric and I thought it would be a good time to write a bit about the new climate normals released by NOAA on Monday night. When we compare weather to “normal” or “average,” these are the values we are comparing to, so it is useful to understand how they will be changing.

What are they? Every 10 years, NOAA and the National Weather Service, along with other government weather agencies around the globe recalculate what the typical weather has been like in the previous 30 years. Think of it like the Census, but for weather.

Why average 30 years of weather instead of, say, 50 or something? First off, the World Meteorological Organization (WMO), which is essentially the U.N. for meteorological agencies stipulates that member states use a 30 year standard. In general, 30 years is enough data to get you a good snapshot of what the current climate is, rather than a 50 or 100 year average. In other words, when we compare weather to a 30-year normal by saying something like, “Today was 15 degrees warmer than normal,” we’re comparing to the shorter-term climate we’re used to, not the one perhaps our grandparents lived through. And 30 values is generally when statistical averages become more reliable. Some users and industries prefer their “normal” to be calculated over a different timespan, so those calculations will be added to the mix from NOAA as well.

Why do they matter? When dealing with weather and making plans in business or designing buildings or planting crops, you need to have a baseline to anchor yourself to, some kind of “average” weather. Imperfect as they may be, the 30-year normals accomplish that. Having those allows us to explain weather in terms of how typical or atypical it is on a particular day or in a particular month. One thing we all know: Weather changes and can be wild, and “normal” is really just an average of a bunch of various extremes. But we need to have that anchor point to describe weather in a climatological context. I don’t know if this is originally attributable to him, but as Dr. J. Marshall Shepherd, former president of the American Meteorological Society likes to say: “Weather is your mood and climate is your personality.” It’s good to know a local area’s “personality!”

So what has changed? Let’s start big and then go small. Across the U.S., the new set of climatological normals is generally warmer, much warmer. The only areas cooler than the previous set of normals were in the Plains.

Officially, Houston’s annual average temperature (at IAH Bush Airport) rose by 0.7° versus the previous normal. At Hobby Airport that change was 1.0° warmer, and at Galveston it was 1.1° warmer.

The only months that showed cooling relative to the previous set of normals were November and December. Summers have warmed by a bit over a half-degree on average, and late winters have warmed by over 1 degree. Some other notes: Our first day with an “average” high of 90° has moved up to May 29th from June 3rd. Our last day of average highs of 90° or better is September 18th, up from the 14th. So, we’ve added roughly a week more of days with an average high of 90° in 1991-2020 versus 1981-2010. Additionally our hottest daily average maximum temperature (or “peak” of summer) is up to 95.7° compared to 95.0° in the previous set of normals. Not only that, that peak has moved up a bit to August 4-6 versus a longer, flatter peak from August 5-12 previously. I wouldn’t read too much into that last part, but it’s something to note at least.

You’ll also notice that rainfall has increased, thanks in part to average August rainfall being over 1 inch wetter than in the prior normals. This is almost certainly thanks mostly to Hurricane Harvey. Houston now sees rainfall of roughly 2 inches more than we used to each year.

Interestingly, but perhaps not surprisingly to some folks if they live there, Galveston actually saw annual average rainfall decrease in this latest set of normals. In fact, not only does Galveston see less rain now on average, it’s over 3 and a half inches less! This is likely both a function of randomness in the sporadic nature of daily thunderstorms here but also a notable change related to <waves hands> something with respect to the warming water temperatures of the Gulf of Mexico or more frequent ridging in the upper atmosphere over the Southeast. This feels like too big a change to me to be just random chance. In addition, Galveston was substantially warmer, especially during nighttime. Average lows are over 1.5° warmer now than they used to be.

Anyway, hopefully you find this interesting. How we describe weather “relative to normal” will change going forward, so we feel it’s notable to explain to you how that will change. On to the forecast.

Today through Friday

Step outside this morning, folks.

We have temperatures in the 50s inland to low or mid-60s in the city and along the coast. And the humidity has plummeted. Look for plenty of sunshine and highs around 80° or in the low-80s this afternoon. Tomorrow looks just as nice. Expect morning lows in the 50s north and west of Houston and low or mid-60s in the city and along the bay. Galveston should see upper-60s. Another day of sunshine will allow us to get into the mid-80s tomorrow. Friday looks like essentially a carbon copy of Thursday with a few added higher clouds at times.

Saturday and Sunday

Look for onshore flow to kick back in this weekend, driving our dew point temperatures back up to 70° or so, along with highs well into the 80s. Saturday morning will probably see 60s for lows, while Sunday should see 70s in the morning. Along with that, there is at least a chance of a shower or storm Saturday. For Mother’s Day, we expect a slightly better chance of showers, however despite being better, those chances still remain fairly low right now in most of the Houston area. As you go north of Highway 105, the chance for some more robust rain and storms may increase somewhat. We’ll hone in on details more tomorrow and Friday.

Next week

It’s too early to get too into the weeds next week, but with a cold front “in the neighborhood,” suffice to say it will probably be a somewhat unsettled period ahead. More on this for you tomorrow and Friday as well.

Today has worked out rather well so far for most of the area. South and east of Houston was minimally impacted as expected, with under an inch in most locales. North and west of Houston saw roughly 1 to 3 inches on average. The jackpot occurred in Waller County, as Eric discussed this morning. Threemile Creek at FM 362 just northeast of Prairie View was today’s champion with nearly 6.5 inches of rain.

While that’s certainly a lot of rain, thankfully flooding has so far been restricted to some sporadic street flooding and some lowland flooding in rural Waller County. If you do need to travel between Magnolia and Prairie View tonight, use caution.

So as of 8:30 PM the radar is quiet in our area. There are two clusters of rain right now: One is just moving east of I-35, east of Austin and San Antonio. The other is sitting offshore between Corpus Christi Bay and Matagorda Bay. Everything looks fairly innocuous now, but after midnight tonight, storms are likely going to explode to our southwest. Significant, widespread heavy rain is likely, well to the southwest of Houston. The area between Corpus Christi and Victoria seems to be the most likely to see significant 4 to 8 inch totals, well away from the Houston area. The HRRR model depiction of what radar could look like overnight is shown below.

Folks in Wharton or Matagorda Counties will want to pay attention to things overnight I think, but even they may be a bit far enough northeast to avoid the real heavy stuff. This area of rain is likely going to creep closer to the Houston area on Saturday morning. Thankfully, it should also begin weakening around the same time, so while I would plan on some rain for your Saturday morning activities, if everything goes according to forecast, we should see minimal issues on area roadways.

As always with upper lows, there is a tinge of uncertainty underlying everything. However, there is very good model agreement on the general theme of things tonight and tomorrow, so we aren’t especially worried. With that said, we will maintain a Stage 2 flood alert. But honestly, that’s mainly for areas that have already been hard hit, like Waller County, although the rains don’t look too serious there tonight and the first half of Saturday.

Also, folks near Galveston Bay have been removed from the NWS Flash Flood Watch as of late this afternoon. Depending on how things go tonight and early tomorrow, Eric and I will consider pulling back to a Stage 1 alert on Saturday. Fingers crossed.

Saturday afternoon and evening

As of this evening we think most Saturday afternoon plans should be fine. There may be a few showers or some light rain around, so have an umbrella handy. But you might be able to swing most plans without issue. Saturday evening may see conditions go downhill with a line of thunderstorms coming out of Central Texas and sweeping across Houston after 9-11 PM or so. Conditions would improve greatly on Sunday. We’ll update you on that tomorrow morning.

Here’s a quick breakdown of how Saturday looks:

6 AM-Noon: Heavy rain possible, especially west of I-45 and south of I-10. Scattered showers and storms possible elsewhere.

Noon-6 PM: Scattered showers or some light rain, but intensity and coverage of rainfall is expected to diminish.

6 PM-Midnight: Increasing chances of rain and thunderstorms as you get closer to midnight.

We will freshen things up for you again tomorrow morning. Have a good night!

The forecast situation across the Houston area is walking a fine line between very beneficial rainfall and “alright, you can stop now.” Based on model data this morning, it would seem most of the area will see the beneficial aspects, but there remain concerns that some parts of the area may get a bit more than hoped, and because of this, we are going to shift from stage 1 to stage 2 on our Space City Weather Flood Scale.

Flood watch

A flash flood watch was hoisted by the National Weather Service yesterday evening, right about the same time we posted about calling for a Stage 1 flood event on our Space City Weather Flood Scale. Our reasons for escalating to stage 2 are laid out here.

What does it all mean? You should interpret all of these things to mean that street flooding is a very good bet today and at times through Sunday. It would be a good idea to adjust your plans around the weather the next couple days.

Could it get worse than this? Thankfully, we are starting off with low water levels and dry ground. So it will take a little time for grounds to truly become saturated. Remember, flash flooding is less about how much rain falls and more about how quickly it falls. Rainfall rates are expected to be 1 to 3 inches per hour at times. Initially, that can produce street flooding, hence why the flash flood watch is in effect today. Rapid rises will likely occur within bayous today, but at this point, we would expect them to remain within their banks. After today, the ground will be more saturated, and if we were to see several hours of 1 to 3 inch per hour rain rates tomorrow or Sunday morning, then we could begin talking about something a little more serious. For now, expect street flooding to be the main issue, but we are going to watch things closely today and tomorrow in case this does escalate.

So, you’re bumping to a Stage 2 flood alert? Given that this looks to be a bit beyond just nuisance street flooding (Stage 1) and will likely have some more significant localized impacts (Stage 2), we are going to upgrade our flood alert to a Stage 2 this morning. For most folks, Stage 1 impacts of nuisance street flooding are all you will see. But given the “training” aspect of heavy rain rolling over some places again and again and the excessive rates (1-3″ per hour), we do believe a few locations may see a bit more than just nuisance street flooding, more akin to a Stage 2 event. In the interest of full transparency, the risk of this escalating to a Stage 3 type event, while not especially likely, is not zero, and this is something we will be watching closely this weekend.

So how much rain are we talking? On average, we expect most places to receive 2 to 4 inches of rain by the time we get to Sunday evening.

Some may receive a bit less. With 1 to 3 inch per hour rates, yes, others will receive a good bit more than this. Most models do indicate that the maximum total rainfall in very, very localized areas could reach 10 to 12 inches or even a little more. Given the setup today, I would expect the highest chance of those max totals to be north or west of Highway 59.

Today

Radar this morning shows heavy rain lined up mostly on the west side of the city stretching on an axis from Port Lavaca through Wharton, the Katy area, Cypress, up into The Woodlands and Conroe and northeast to Lake Livingston.

Notably, it’s around Lake Livingston where the heaviest rainfall is causing almost 3 inch per hour rates this morning. Closer to Houston, Kuykendahl at Spring Creek has seen over 1.3″ in an hour as of this writing. As I was about to press “post” here, a Flash Flood Warning was just issued for parts of Waller, Montgomery, and Walker Counties.

Flash Flood Warning including Willis TX, Prairie View TX, Waller TX until 9:00 AM CDT pic.twitter.com/mBgCOai4ZH

— NWS Houston (@NWSHouston) April 30, 2021

Over the next few hours, we expect this band of rain to stay mostly in place, though it may wiggle east or west a bit at times. This will allow for repeated rounds of rainfall on the west side of town, and totals could easily jump up to 2 to 5 inches or more in some spots before this evening. East of Houston? You’re fine for now. Expect at least some rain or showers and storms today, but places like Galveston or League City or Baytown will probably fare okay today with modest rain totals.

Tonight

We may see things taper off this evening for a time, or at least become more intermittent across much of the area. But the next round of rain seems likely to develop overnight, particularly to the southwest of Houston. This batch of rain is likely to try and work into parts of the Greater Houston metro toward Saturday morning. We’ll have more on this later today.

Saturday

Many folks have Saturday plans. Between crawfish boils, the MS 150 bike ride, and other post-vaccination life fun, there is a lot planned this weekend. While I want desperately to be an optimist and tell you it’s going to be fine, the reality is that you should have backup plans in place for outdoor events tomorrow. I will say that the afternoon *might* look better than the morning. We expect that area of rain and storms to weave through the area tomorrow morning and hopefully exit to the east or die off. But there are some models that keep periods of moderate to heavy rain going west and southwest of Houston in the afternoon as well. The reality with upper lows is that forecasts beyond 12-18 hours get sloppy, and we won’t have a great idea on what tomorrow looks like until tonight.

Saturday night & Sunday

One more slug of rain and storms is possibly going to move through later Saturday night and Sunday morning. By Sunday afternoon, the focus of rain should shift into far East Texas and Louisiana and Mississippi. Hopefully by Sunday afternoon we will see some sunshine.

Temperatures all weekend look tolerable, albeit with some humidity with highs in the 70s and lows in the 60s. Sunday could see temps surge past 80° with enough sunshine, however.

Next week

Monday looks like a fine day right now. There may be just enough of a trigger left behind after the weekend storm to allow a shower or storm to pop up, but as of today we would expect the vast majority of the region to stay dry on Monday. Heat and humidity will rule, with lows in the 70s and highs in the middle or upper-80s. A cold front still seems on track to hopefully clear the area on Tuesday. It will bring a chance of showers or storms, and then follow up with hopefully a little lower humidity for Wednesday and Thursday. Right now, this still looks promising, but as noted American philosopher Justin Timberlake once quipped, “It’s gonna be May.” May in Southeast Texas is often where cold fronts come to die. Here’s hoping that’s not the case next week.

We will have another update on today’s rain situation before Noon today.