The weather is
getting more active in Texas for days 3 and 4 with greater uncertainty. The uncertainty
already begins tonight, with a slowly-moving cold front approaching from the
northwest. While most models have the cold front stalling just to the northwest
tonight, leaving San Antonio in the southerly winds and warm and moist air,
with low-level clouds preventing much radiational cooling, it is very close. If
it gets a little farther southeast, it would be southeast of San Antonio,
leading to a sharp temperature drop. The low clouds will likely break later
tomorrow, but with the front in the vicinity and uncertainty in how long it
takes for the clouds to break, the high temperatures are highly uncertain, with
the 12z HRRR being 25F warmer than the 12z NAM 3-km. Just about all models
agree on the front being just northwest of San Antonio for at least part of the
day tomorrow, perhaps retreating northwestward in the morning and early
afternoon, leading to a quick warmup once the clouds break. NAM 3-km is likely
too cool whereas HRRR appears slightly too hot, like today. USL or slightly
warmer seems like a good compromise.
The front could
also spark scattered showers and thunderstorms over the area tomorrow, though a
bit surprisingly, models are showing little or no convection initiation along
the front, again like today. Perhaps the best dynamics are off to the north, or
the wind field is confluent but not truly convergent along the front. The front
will advance slowly southeast again tomorrow evening, though there is even model
disagreement on whether the cold front will push through San Antonio at all, or
if it will just stall to the northwest and not pass San Antonio until Saturday.
This will make a big difference for the low. Again, I favor a slightly faster
cold frontal passage given model bias in not pushing low-level cold air quickly
enough in the Plains, leading to a low at the end (Saturday 06z) on the cold
side of the cold front, along with northerly. It’s not the type of really
strong low-level cold air that barges southward much faster than all models
show, and it’s a complicated and at times diffuse front with diabatic effects
(e.g. sunshine to the south on the warm side of the front and clouds to the
north on the cold side of the front, but mostly at a distance north of the
front) influencing the strength of the front and if any secondary cold fronts
develop. Today’s frontal passage appears to be in between HRRR and NAM 3-km. The
maximum wind is also uncertain, depending on which side of the front San Antonio
ends up on, but it will likely occur with any convective gust fronts, or with
the surge of northerly winds when the low-level cold air arrives tomorrow
evening. The cold advection and sunshine will contribute to a lot of vertical mixing in the afternoon and evening, helping bring the strong northerly winds down to the surface.
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| Source: PivotalWeather |
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