After three sunny days gray skies and rain return to Houston.
TODAY
Dry air is moving off, and being replaced by moist, warmer air. A disturbance in the upper levels of the atmosphere will bring the impetus for rain. Light showers are possible this morning, with heavier stuff later this afternoon and especially tonight across the Houston area. Although I don’t expect any severe weather, much of the region should see a good 0.5 to 1.5 inches of rain.
Not much has changed since yesterday’s forecast. In about a week’s time, give or take, it appears that a large amount of Arctic air will spill into the Midwestern United States. What’s not clear is whether that air will be shunted off to the east, or whether much of it will continue moving southward into Texas. For the marathon’s purposes, it may not matter a whole lot.
After that feature, during the second half of next week, the models bring a somewhat warmer air mass into the eastern United States, including Texas. However by the weekend of the marathon it appears that air, too, has moved on, which would leave conditions cooler than normal.
Here’s how the GFS model suggests conditions will be between noon Saturday, January 16th, and Sunday, the 17th. The model is suggesting temperatures 3 to 5 degrees Fahrenheit below normal for Texas, including Houston.
Our forecast remains more or less the same, with a slow warming trend before cooler weather returns by the weekend.
TODAY
It’s a very cold morning, with freezing temperatures over parts of the northern half of the Houston metro area. As high pressure moves off we’ll see only partly sunny conditions today, with highs in the mid-50s and a slight chance of rain tonight. Lows in the 40s tonight.
WEDNESDAY
Wednesday, and especially Wednesday night, will see the best chance of rain as a low pressure system in the upper levels of the atmosphere moves through the area. I expect most areas to receive 0.5 to 1.5 inches of rain, with only scattered thunderstorms.
As promised, I’ll be providing daily weather outlooks for the Chevron Houston Marathon from now until race day, Jan. 17th.
At 13 days out there’s still not a whole lot we can say with confidence, especially because forecast accuracy after 7 to 10 days is pretty low even though forecast models run out to 16 days. With that said I’m feeling decent about not seeing abnormally warm conditions on race day, and we may very well see cooler than normal conditions. So let’s discuss what we know, and what we don’t.
Perhaps the best way to gauge conditions from this far out is to look at the ensemble runs of global forecast models. That is, the GFS and European models are each run about 50 different times with slightly different starting conditions. This gives a range of outcomes, and from looking at all of these ensemble runs we can get some probabilities on conditions. For example, do most of the ensemble runs show warmer or colder conditions?
The GFS model is colder than the European during the next two weeks as it predicts a major Arctic outbreak across Texas in about 11 days time. If this event occurs we could see very cold temperatures on marathon day, like in the low 30s on the morning of the run. (Is that too cold for most people?)
Anyway, the model forecasts the probability of a high temperature greater than 50 degrees Fahrenheit at noon to be 30 percent, or less. This is good, obviously, because anything warmer than 50 degrees can become uncomfortable after several hours of running.
