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Toltec, Arizona Weather Forecast Discussion

861
FXUS65 KPSR 201016
AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 316 AM MST Sat Sep 20 2025

.KEY MESSAGES...

- Near to slightly above normal temperatures will be common across the area through at least the middle of next week.

- Chances for showers and isolated thunderstorms will return on Sunday with the potential lasting through at least Monday.

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.SHORT TERM /TODAY THROUGH SUNDAY/... Upper level ridging and drier air has shifted over the region since yesterday providing mostly clear skies early this morning. An upper level trough remains situated off the West Coast with guidance showing this feature strengthening some over the next couple of days, while drifting more toward our region. However, the subtropical ridge will remain in charge for the rest of today with plenty of sunshine boosting daytime highs to around 100 degrees this afternoon.

As the trough to our west begins to shift toward the West Coast later today into Sunday, it should become cut off from the main flow and quickly pick up some moisture residing over Baja and western Mexico. A stream of mid-level moisture is forecast to reach southern California during the morning hours Sunday before spreading into Arizona in the afternoon and evening hours. This moisture should boost PWATs over much of our area to between 1.3-1.6" on Sunday with the moisture layer stretching from around 750-400mb. Over the past few days guidance has continued to trend wetter with this system, despite the lack of good instability. Modest mid and upper level forcing along with the moisture advection should be enough to get showers going mainly across southeast California starting Sunday morning before spreading into central and potentially southern Arizona during the afternoon and evening hours. This stream of good moisture is likely to persist through Sunday night providing even better chances for showers and maybe a few isolated thunderstorms.

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.LONG TERM /MONDAY THROUGH FRIDAY/... Monday morning is likely to be the peak of the rain chances with NBM PoPs of 30-40% fairly widespread across the area. These PoPs very well could be underdone as this may end up being a somewhat larger area of rainfall resulting in most locations receiving light amounts of a few hundredths of an inch to upwards of a 0.25". Lower forecast confidence is seen through the rest of Monday into Tuesday as guidance tries to mostly end rain chances, but keeps the cut-off low just off the southern California coast. This position may still allow for chances for isolated showers and thunderstorms, despite the NBM drastically lowering PoPs down to around 10%. Even if rain chances do continue into Tuesday, most locations may not see much if any rainfall as ensemble mean PWATs are forecast to lower to around 1.1-1.3" by later Tuesday. Given the higher than normal forecast uncertainty, don`t be surprised if the forecast shifts during this time.

Temperatures early this week are likely to start out near normal with highs mostly in the upper 90s across the lower deserts, but that may change going into the middle part of the week. Forecast temperature spread has improved enough to provide for fairly high confidence in warmer temperatures by next Tuesday or Wednesday. The latest NBM shows highs likely reaching 100 degrees by Tuesday with some potential for Phoenix to reach 105 degrees on Wednesday.

We are not likely to get rid of the cut-off low very quickly as guidance shows the low first drifting a bit to the north across southern/central California before potentially turning eastward at some point around next Thursday or Friday. It is unknown at this time if this shift will actually occur and how far it will venture to the east as the ensembles try to move it into western Arizona by next weekend. If the low does fully move into our region later next week it may bring a return of better rain chances and cooling temperatures, but that is a big if as cut-off lows are very hard for models to forecast.

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.AVIATION...Updated at 0515Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation concerns are anticipated through the forecast period. Winds will remain generally less than 7 kts and follow typical diurnal patterns. Light easterly flow will prevail overnight and gradually shift back to westerly at all terminals by 19Z-20Z tomorrow. Skies will remain mostly clear with the exception of a FEW cumulus developing over the region tomorrow afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are anticipated at the SE California terminals under mostly clear skies. Winds will remain predominantly W at KIPL and NW at KBLH overnight before transitioning to NW at KIPL and S at KBLH by Saturday afternoon. Speeds should remain aob 7 kts through the period.

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.FIRE WEATHER... Modest drying will occur today with better moisture returning to the region Sunday into Monday. Rain chances will also return on Sunday with the best chances likely Sunday night into early Monday with wetting rain chances between 20-30%. Minimum humidity levels will generally fall into a 25-30% range following good to excellent overnight recovery of 50-90%. Winds will remain rather light with limited upslope gusts. A slow moving weather system may impact portions of the region during the rest of next week keeping humidities a bit elevated and potentially additional rain chances.

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.PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. &&

$$

SHORT TERM...Kuhlman LONG TERM...Kuhlman AVIATION...Salerno FIRE WEATHER...Kuhlman

NWS PSR Office Area Forecast Discussion

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