As expected, good
radiational cooling led to a quick cooldown to 30F last night. Almost no wind
so far today, with a maximum of 5 kt. Sunshine led to a warm up to 62F, but
then some cirrus appeared to stop the warmup at the critical time when the high
usually occurs. Cirrus will clear out tonight, and clear skies and light
southeasterly winds will lead to a decent cool down tonight, but likely not as
cool as last night with subtle warm advection aloft beginning. A warmer air
mass and strengthening downsloping westerly winds will lead to a much warmer
high tomorrow. While I am not sure it will get warmer than the already very
warm models given the surface nocturnal inversion to initially overcome and the
weaker sun angle in October, the winds do look stronger than on day 1 and
should more easily overcome the inversion. Some scattered mid-level clouds could
move in for late afternoon, perhaps cutting the warmup by ~1F.
A cold front tomorrow
evening will produce increased clouds and perhaps a little rain. There will be
rain falling aloft, but will be evaporated in the initially very dry lower
atmosphere, with most of the rain falling over the cooler higher terrain to the
west. The evaporation will also lead to a strong evaporative cooling cold pool
+ colder air behind the front to begin with combining to produce sharp spike in
wind speed, possibly >30 kt, especially with the winds aligning with the northwest-southeast
oriented valley going through Missoula. Most models aren’t resolving this well (even
the USL doesn’t!); only the NAM 3-km and HRRR models show it to some degree. The setup appears similar to but somewhat stronger than on the evening of September 25, 2024.
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| Source: PivotalWeather |
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| Source: weather.us |
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