Autumn is Coming

Autumn is Coming

There’s a lot I could talk about this week between severe weather potential, Colorado getting its first big snow event of the year, and Hurricane Michael, but I’m going to focus on the bigger picture of the forthcoming pattern shift. It may not feel like it, with forecast highs today in the mid to upper 80s across most of Texas, but autumn will soon be here. We have to get through a few almost spring like weather days first however. Without going into tremendous detail, SPC has hoisted a slight risk for severe weather for both Monday and Tuesday across parts of Texas. On Monday, the focus will be out west from the Panhandle down to the Big Bend. On Tuesday, the focus will move northeast into North Texas.

Day 1 Convective Outlook valid Monday, October 8, 2018 (source: SPC).
Day 2 Convective Outlook valid Tuesday, October 9, 2018 (source: SPC).

Walking outside here in Fort Worth this morning, it almost feels like May. Temperatures are in the 80s with dewpoints in the 70s. This air mass extends west towards the Caprock. While mid-level lapse rates are not particularly impressive, they should be sufficient that when combined with ample boundary layer moisture, there should be plenty of instability. An approaching deep longwave trough and associated jet streak should also enhance wind shear. The wind profiles are not super suggestive of a significant tornado threat, but damaging winds and some hail will certainly be possible.  On Tuesday, a Pacific cold front should drive through North and Central Texas, acting as a focus for shower and thunderstorm development. The air mass ahead of this front will be very unstable, and shear looks to be pretty impressive owing to the aforementioned jet streak. Usually when we have strong forcing along a cold front, convective development becomes very widespread, and thunderstorms will likely grow upscale into a squall line. This means that damaging winds will be the main hazard. This front will be moving pretty quickly, which should minimize the threat for widespread flooding (the story is different in Oklahoma), but given the ample moisture, 1-3 inches of rain will be pretty likely in North Texas, with locally higher amounts north of 4 inches possible. Don’t be surprised if some isolated flooding does develop, especially given the recent heavy rains in the region.

The Pacific cold front will bring cooler and drier air to the region, but we will get a strong shot beginning Wednesday morning as a Canadian cold front pushes through the region. Highs will likely struggle to get out of the 70s north of the cold front, with dewpoints likely to fall into the 50s, making for a spectacular day. This nice weather should stick around through the end of the week. Over the weekend, a fast moving upper-level trough could bring some rain chances, but the chances for widespread severe weather or heavy rain look low right now. By the end of the weekend, an even stronger cold front will blast through. It is entirely possible that by the beginning of next week, in North Texas, highs could struggle to get out of the mid 60s, with overnight lows falling into the 40s, with the coolest night likely to be next Monday Night (i.e. October 15th into the 16th). Perhaps most beautifully, dewpoints are likely to fall down into the 30s and even the 20s across much of North Texas, which will be some of the driest air in the region since at least April (when we had that late season Arctic blast), possibly earlier.

Forecast dewpoint temperatures valid the evening of Monday, October 19, 2018 (source: Pivotal Weather).

So far this fall, we’ve had a few cold fronts that have resulted in transient shots of cooler and drier air, but that cooler/drier air has typically only stuck around for a day or two before the tropical air moved back into the region. Based on the increasingly active pattern, and the fact that the long range guidance is now forecasting multiple shots of cool air, it appears that fall is finally coming to the Lone Star State.

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