South Valley, NM Weather

Key Messages

Issued at 525 AM MDT Tue Oct 20 2026

- Isolated to scattered showers and storms will focus over western and central New Mexico today. Brief gusty outflow winds and lightning are the main hazards.

- Flash flood risk increases in northwest New Mexico Wednesday, spreading eastward into central New Mexico late Thursday into Friday.

- A few strong to severe storms in western New Mexico Wednesday could produce damaging outflow wind gusts and large hail. The severe threat extends into central New Mexico Thursday.

Update

Issued at 525 AM MDT Tue Oct 20 2026

PoPs were updated based on current radar trends. In general, they were increased across central New Mexico where showers have increased in coverage over the past few hours.

Short Term

(Today through Wednesday Night) Issued at 131 AM MDT Tue Oct 20 2026

Water vapor imagery this morning shows a vort max over the Four Corners, with drier air making its way in from the southwest. Subsidence in the wake of this shortwave along with some dry air advection will slightly decrease the coverage of showers and storms today, with isolated convection favoring central New Mexico where a corridor of enhanced instability is progged to set up.

Meanwhile, the potent Pacific storm system that will impact the region later this week is starting to take shape off the California coast today. The trough will continue to dig southward today through tonight, with increasing southwest flow over the desert southwest as this storm begins to interact with the sub-tropical jet stream. Strong moisture advection will continue throughout the day Wednesday, with the strongest IVT (Integrated Vapor Transport) over central Arizona. Northwest NM will be on the eastern fringes of the main moisture plume. Large scale ascent will drive most of the rainfall (as opposed to destabilization) so light to moderate rainfall rates will be favored. This could change during the overnight period, depending on the evolution of convection over Arizona.

Long Term

(Thursday through Monday) Issued at 131 AM MDT Tue Oct 20 2026

The Pacific storm system off the California coast will eject inland into The Great Basin on Thursday, with very strong southerly moisture advection out ahead of it. Model consensus now keeps the main vort max well off to the northwest of New Mexico, which will focus the main bulk of precipitation over eastern Arizona early Thursday, eventually pushing into western New Mexico later in the day. PWATs will peak early Thursday across northwest NM at 4 to 5 standard deviations above normal for mid-October, shattering record levels for this time of year. Therefore, confidence is very high for soaking moderate rainfall across the Four Corners area, but instability remains a big question mark. Guidance has trended slightly more stable, keeping the steeper mid-level lapse rates off to the south and east over southern Arizona and central New Mexico. Even with the absence of robust instability, rounds of moderate rainfall over an extended period could create flooding issues for sensitive low-lying areas that cannot handle large volumes of water.

Strong vertical wind shear associated with a 700 mb jet max will promote the development of strong storms on Thursday afternoon and would not be surprised if there are a few supercells near the Arizona border as low-level winds shift around to the southeast and provide some directional shear as well. Given recent storm track shifts and the uncertainty with regard to exactly where corridors of elevated instability reside leave a big question mark around where the flash flood threat will be maximized. Furthermore, it should be noted that the flood threat will not necessarily follow the typical diurnal cycle with the threat peaking during the afternoon hours and diminishing through the night. Pockets of elevated nocturnal instability could keep moderate to heavy rates around through the overnight hours throughout this event.

While the energy from the main trough will exit off to the northeast Friday, deep Pacific moisture will remain entrenched over New Mexico. All 3 deterministic global models now favor the development of another Low over Arizona, which would keep large scale ascent and moisture over New Mexico through the weekend, with rounds of showers and storms night and day. Ensemble guidance is trending this way as well, although around 50% of models still favor an open wave trough moving over central NM this weekend. With either scenario, rain chances will focus over along and east of the central mountain chain, as a backdoor front and Gulf moisture interact over the area.