In brief: In today’s update we discuss the ‘why’ behind today’s strong winds, and how cold it will get tonight. We also take a look at our sunny conditions into Saturday, when there is another chance of rain with a secondary front.

A gusty day

Houston will experience a very windy day today, with gusts this afternoon up to 40 mph or higher. This is the first time we have seen a really strong influx of colder and drier air this season, and you may be wondering why? The answer has to do with pressure systems, and particularly the circulation of air around a strong low pressure system bounded by a high pressure system.

In this case the low associated with Tuesday evening’s front has continued moving eastward. We are now effectively on the “back side” of this low, with strong high pressure building behind it. Today, therefore, we are seeing strong wrap around winds behind the low, with a tight pressure gradient (note the high over west Texas). This has created a superhighway for north-northwesterly winds that will peak this afternoon before finally ebbing late tonight. That sound you hear outside is fall blowing in.

Wednesday

Besides the wind, we are going to see much cooler temperatures today. In fact our highs in the mid- to upper-60s today will be cooler than about half of our nights so far this month. Gusty winds will build this morning and peak during the afternoon hours, with gusts up to 40 or possibly 45 mph possible.

With the setting sun this evening, lows tonight will quickly cool to around 50 degrees in the most urban parts of Houston, with outlying areas dropping into the 40s. It will be our coldest night in more than six months. Winds should begin to slacken this evening, and fall back toward more normal levels by Thursday morning.

Thursday

This will be a sunny and fine day, with lighter northerly winds and highs around 70 degrees. Thursday night’s lows may be a degree or so cooler than Wednesday night with ideal radiational cooling.

Friday

Halloween weather will be anything but spooky, with highs in the mid-70s and pure sunshine. Evening temperatures will be the 60s, with light winds. Overnight lows will drop into the 50s.

Saturday

The onshore flow resumes on Friday or Friday night, and so we’ll start to see the return of some moisture. The question is how much, because a weaker front is going to advance toward the area, and if there is enough moisture it is likely to produce some showers (and possibly a few thunderstorms). Given the uncertainty, there are corresponding questions about Saturday’s weather. For now I expect highs in the 70s, with mostly clear skies through the early afternoon. However I would say there is probably a 50 percent chance of showers later in the afternoon, evening, or overnight hours, and at this point I can’t rule out a few thunderstorms. We’ll keep an eye on things. Lows on Saturday night drop into the 50s.

Sunday, Monday, and Tuesday

These look like a trio of pleasant days in the wake of that secondary front, with highs in the 70s and lows in the 50s, with moderate levels of humidity. Sunshine should reign supreme.

Later next week

Temperatures may recover some later next week, with highs around 80 and lows in the vicinity of 60 degrees. We shall see.

In brief: Today’s update covers a lot of ground, from what a real fall front should feel like, to a chance of storms this evening, and just how cold it will get in the coming days. We also briefly discuss the catastrophic Hurricane Melissa.

What ‘real’ front should feel like

Houston has seen several cool fronts this fall, but we have always characterized them as weak. This is because they have mostly been ‘back door’ fronts in which a nose of drier air has pushed down into the region from the northeast, rather than the northwest. Typically these fronts have brought not abrupt change in winds or rapid drops in temperatures. This stands in contrast to the type of cold front that most of us think of, when a much cooler pool of air spills down from the north and northwest. If you happen to be standing outside when such a front passes you can feel it because there is an abrupt change in winds, and an almost immediate influx of cooler and drier air. Well, I am happy to report, that is the kind front we will experience today, along with a sustained stretch of cooler and drier weather in its wake.

Tuesday

Ahead of the front we are going to see a rather warm day, partly due to compressional heating as the front advances southward. Skies will be mostly sunny, with high temperatures reaching the upper 80s for much of the region. Winds will be generally light, from the south. The front itself will drop into the city this afternoon, and push off the coast this evening. I don’t think there will be too many showers or thunderstorms northwest of Houston, but as the front nears the coast it will find more moisture to work with, and this should result in a more robust line of storms in central Houston and for coastal areas.

The front will be moving quickly so flooding is not a concern, but there will be a brief period when damaging winds and potentially hail are a threat as the front pushes through. In terms of timing, I’m thinking 3 to 5 pm for a line from Katy to the Woodlands, an hour later for central Houston, with the front likely off the coast between 6 and 8 pm.

After this point we’ll see winds turn sharply from the northwest, with strong gusts tonight up to 35 mph. Lows will drop into the mid-50s by early Wednesday.

Wednesday

This will be a sunny and windy day. I expect winds to peak during the afternoon, when gusts could briefly reach about 40 mph, especially closer to the coast. Highs, otherwise, are likely to top out in the upper 60s. Lows on Wednesday night will drop to around 50 degrees in Houston, with cooler conditions for outlying areas. This will be our region’s coldest night in more than 200 days.

Thursday and Friday

These will be a pair of fine, fall days with lots of sunshine and high temperatures in the vicinity of 70 degrees. Friday morning should be the coldest of the week, with much of the area potentially dropping into the upper 40s. As for Halloween trick-or-treating we have precisely zero concerns, with clear skies expected along with moderate temperatures in the upper 60s, and light winds.

Saturday and Sunday

The weekend should see continued pleasant weather, with daily highs in the upper 70s, a touch more humidity, and nights in the 50s. There’s the potential for some rain on Saturday evening or Saturday night due to a passing disturbance, but I want to see more data before having confidence in such a forecast.

Next week

Most of next week will probably see something along the lines of high temperatures in the upper 70s to 80 degrees, with lows around 60, but I don’t have super high confidence in such a forecast yet.

Tropics

We haven’t said much here about the Atlantic tropics in the last month, when I wrote that the Texas hurricane season was probably over. (And indeed it was). However Hurricane Melissa bears a mention this morning, as this extremely powerful storm is poised to become the strongest tropical cyclone to ever hit Jamaica. We have ongoing, full coverage of Melissa at The Eyewall.

This storm is just about the worst imaginable hurricane: extremely strong and very slow moving. The only slightly positive note is that its core of strongest winds is relatively small. Nevertheless, Melissa is now bringing catastrophic damage to the Caribbean island of 3 million people, and compassion and help will be the order of the day in its wake.

In brief: In today’s update we discuss the season’s first real fall-like front, arriving Tuesday evening with the potential for some brief showers and thunderstorms. The city will then see its coldest weather in 200 days, along with ideal weather for Halloween. We’ve waited a long time for this, so enjoy!

Fall Day recap

Thank you to everyone who came out to see Matt, Lee, and myself on Fall Day Saturday at Midtown Park. I’ll be honest, it took a little faith to schedule an outdoor event on a day with a 100 percent chance of rain, but in the end the weather was exceptional. And we had a lot to celebrate. Not only did the region get the drenching rains it needed early on Saturday, we have the region’s first real fall front to look forward to this week (more below). Anyway, it was so nice to meet you all, and say hello. Thanks to Reliant for setting up, and Michael Chu for the great photos.

Monday

Temperatures this morning have a bit of a chill, having dropped to around 60 degrees for most of the area away from the coast. Temperatures will recover quickly into the mid-80s today, with mostly sunny skies, and a light south-southwest wind. Lows tonight will only drop into the upper 60s.

Tuesday

This will be a warm and humid day, with high temperatures reaching the mid- to upper-80s for most. However by late afternoon or early evening we should see a (broken, maybe?) line of showers and thunderstorms advance through the area ahead of a cold front. Some of our latest high resolution modeling is showing this line to be a little more robust than expected, but I want to see a little more atmospheric data before making this conclusion. Anyway, drier air will rapidly filter in on Tuesday night after the front, with lows dropping into the 50s.

Wednesday

What a change this day will bring. It will be windy, with gusts from the northwest up to 30 or even 35 mph. Highs are likely to only reach the upper 60s despite sunny skies. Lows on Wednesday night will drop to around 50 degrees in Houston, with cooler conditions for areas outside the urban core. The city will likely record its first sub-50 degree day since April 9 (which is 200 days ago, as of my writing this) at Bush Intercontinental Airport. So it has been a long time since the region has felt this chilly.

Thursday

Expect a sunny, pleasant day with light winds and highs around 70 degrees. I expect temperatures on Thursday night to even be a touch cooler than Wednesday night.

Halloween

This will be a sunny day, with highs in the low 70s and low humidity. Winds will be light, with trick-or-treating temperatures during the evening hours in the 60s. Overnight lows drop into the 50s.

Saturday and Sunday

It will be a partly to mostly sunny weekend with highs in the upper 70s to 80 degrees, and nights generally in the upper 50s. Humidity will be on the rise, but it still won’t feel particularly humid outside. In short, it should be fantastic weekend.

Next week

It’s possible that we could see another (weaker) front early next week to keep temperatures on the cooler side, but there is no definitive clear pattern yet.

In brief: After Saturday morning’s storms the atmosphere needed some time to recharge. It appears that is now happening, raising the possibility of more storms tonight. Here’s what we know, and what we don’t, about what to expect.

Fall Day

I’ll have some photos to share early next week, but I just wanted to thank the hundreds of people who came out to Midtown Park this morning to say hello, shake our hands, and share some kind words. It was wonderful to see everyone and share a few hours of lovely fall-like weather. Thank you also to Reliant for the hard work in setting it all up.

Saturday night

After this morning’s rollicking storms the atmosphere was pretty well worked over. This is why we had some confidence in several hours of calmer weather, and even some clear skies. However, factors such as atmospheric instability are now recovering, and by this evening the overall setup will become more conducive to the development of thunderstorms. With that said we still have some questions about how severe the storms will become. So what follows is our best guess, rather than a high confidence forecast.

Some time after sunset, perhaps in the range of 8 to 10 pm CT, a cluster of storms will develop northwest (near College Station) or north (along Highway 105). This line will then descend into Houston between 10 pm and early Sunday morning, bringing the threat of heavy rainfall, thunder and lightning, damaging winds, hail, and a very slight chance of a tornado. However, unlike the storms early on Saturday I think these will be less of a single line and more of a diffuse mass.

To that end I think these storms will be more hit or miss, but where they hit they could do so hard. Some areas may get less than 0.5 inch of rain, and some areas may get 3 inches or more. The higher totals are more likely south of Interstate 10. For the most part this should not be enough rainfall to cause significant flooding problems. The majority of the storms should have moved off the coast a couple of hours before sunrise.

In short there’s plenty of potential for storms to hit tonight, but unlike the guaranteed squall line on Saturday morning, there is a little more uncertainty.

Sunday and beyond

We could see a few isolated showers on Sunday, but for the most part I expect sunshine and a high near 80 degrees. With moderately drier air it should be a pleasant day, with lows Sunday night dropping to around 60 for much of the region. A stronger front arrives later on Tuesday, ushering in truly fall-like weather. We’ll talk about just how cold it’s going to get in Monday morning’s post. Until then, have a fine rest of the weekend.