Radar — KIWA
Surface Analysis — Western U.S. (Central)
Satellite
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Nearest monitored road: North Mesa Drive (Secondary)
Updated 18Z aviation discussion.
- scattered to widespread showers and storms are forecast to develop today across arizona, with potential for areas of high rainfall amounts leading to flash flooding.
- a flood watch is in effect through early tonight across much of southern arizona.
- shower and thunderstorm chances will greatly diminish by thursday and come to an end starting friday with much drier air moving in and lasting through at least this weekend.
- below normal temperatures are expected today across south- central arizona, before warming back to to slightly above normal levels by the weekend.
There is potential for a very active and highly impactful weather day across much of arizona today. Considerable and potentially deadly flash flooding is in the cards for today. Hi- res modeling continue to show scattered to widespread showers and thunderstorms eventually developing today across the region and leading to many areas receiving 1-3 inches of rain which will likely result in flash flooding. Where these hi-res cams have struggled so far is timing out initial convective development. Previous model runs suggested tuesday afternoon was going to be very active across south-central az, as well as early this morning, which has not quite come to fruition. While objective analysis shows moisture and instability have been favorable and continue to be favorable this morning, there has not been much in the way of forcing/lift. This is expected to change today though. A well defined low pressure circulation is seen on satellite along the west coast of sonora, mx. This feature is forecast to move straight north up through az likely this afternoon through tonight and help provide the lift that has been somewhat lacking. There will also be increased jet support with a strengthening of the 200mb jet and entrance region of the jet setting up over south- central az. So, the ingredients will all be there for strong showers and storms to develop, but there has still been a little bit of uncertainty with timing of greatest coverage and impact of showers and storms. Latest nbm pops are highest in the 5AM-11AM timeframe for the phoenix area and the 00Z hi-res models show highest QPF in this timeframe as well, but conceptually, based on the setup, the best timing for south- central az looks to be more from midday through this evening.
A flood watch is currently in effect for south-central az and will continue through 11 PM MST tonight. The watch was issued largely due to the synoptic and mesoscale setup being supportive of scattered to widespread showers and storms capable of producing 1-hr rain rates up around 1-2" and higher over shorter time frames. Hi-res modeling continues to show QPF upwards of 1-3" over a large portion of south-central az, and there are even high end amounts up to around 4" (10% chance). Rainfall amounts are still likely to vary widely, with some areas potentially missing out and receiving little to none. The flood watch has been expanded to include portions of la paz and yuma counties starting at 11AM and also going through 11 PM. Several of the latest hi-res models have supported training storms in this area. This area is also forecast to have higher instability and receive better daytime heating with more sunshine heading into the afternoon. Any storms that develop in this area may actually have the highest rain rates but be more isolated in coverage. Wpc's updated day 1 ero expanded the coverage of both slight and moderate risk areas. The moderate now includes all of gila and pinal counties and most of maricopa county. The last time a moderate risk covered this area was back in 2022.
The heavy rain threat looks like it will come to an end across south-central az later this evening and tonight, once the low circulation moves north of the area, the environment becomes overworked, and subsidence increases on the back side of the low. Still, a narrow axis of showers and storms may linger into the overnight hours, most likely toward eastern az. Drier air will begin moving in aloft through the day thursday with increased west-southwest flow, which will limit showers and storms mostly to northern az high terrain. Further drying of the entire column is expected through friday, with mixing ratios dropping to or below 8 g/kg and pwats falling below 1.00" by the end of the day which will hurt any chance at rain even in the high terrain.
Temperatures this afternoon may struggle to reach 90 degrees across south-central az, with ample cloud cover and rain around, while areas further west, with more sun, still warm into the middle 90S to around 100 degrees. Temperatures will warm back up by the end of the week, but only back to around seasonal levels, with highs around 100 degrees across the lower deserts, as broad troughing remain in place across much of the west.
The monsoon pattern may be done after today, shifting into the transitional season with more frequent troughs. Dry air will continue to spread across the region through this weekend with pwats forecast to drop below normal, as low as 0.4-0.7" across the lower deserts. The will inhibit any chance at rain. The broad trough moving through the west, helping drive the westerly flow and dry air, is expected to shift east into the plains by the start of next week. Global ensemble guidance then shows an upper low moving out of the pacific toward the socal coast by the end of the day monday. There is still plenty of uncertainty regarding this low this far out, but it may be what helps eventually drive moisture back up in the deserts and drive the next chance at rain. Average to slightly above average temperatures are forecast this weekend through the first half of next week with this forecast, with afternoon highs around to slightly above 100 degrees. With the drier air coming in, the morning lows will finally be more pleasant, consistently dropping into the 70S for most lower desert locations.
Updated at 1615Z.
South central arizona including kphx, kiwa, ksdl, and kdvt: forecast continues to remain on track with major operational impacts likely this afternoon through this evening. Clusters of thunderstorms are expected to develop within the vicinity in the next couple of hours with the current guidance indicating the highest direct impacts likely by the mid to late afternoon hours and possibly lingering into the evening hours. Overall wind direction should remain out of the southeast before activity materializes with the potential for gusty and erratic winds as thunderstorm activity increases in coverage within the vicinity. For most of the period, winds should generally maintain an easterly component.
In addition to direct thunderstorm impacts, instances of MVFR and possibly brief IFR flight categories are possible in the form of lowered cigs (as low as 4-5 kft with tsra) and visibilities. Shra activity will likely linger well into the evening and overnight hours with lower probabilities of tsra and thus have maintained a prob30 mention for this evening for tsra as there is high uncertainty. Vcsh look to linger through 10-12Z thursday morning with bkn cigs between 5-7 kft looking to linger before scattering out by the mid to late morning hours.
Southeast california/southwest arizona including kipl and kblh: no major weather issues will exist through the taf period under mostly clear skies, with few low (aoa 7-9 kft) and high clouds moving in at the end of the taf period. At kipl, winds will generally be out of the southeast with some gusts into the mid to upper teens later this afternoon through early this evening. At kblh, southerly winds are expected through the afternoon with periodic gusts between 20-25 KTS. There continues to be increasing confidence that an outflow from the convective complex in az will likely affect kblh by the early evening hours, shifting the winds more out of the east with potentially some gusts between 20-25 KTS and maybe some reduced visibilities due to some bldu, although confidence of bldu materializing is low at this time. Winds across both terminal sites should become mostly light and variable during the overnight and early morning hours.
Periods of scattered to widespread showers and thunderstorms are expected today, focusing mostly across the eastern districts this afternoon through this evening. There will be a heavy rainfall and flood threat with the activity. Moisture levels will be elevated most areas, highest across eastern districts, where minimum rh this afternoon will be around 50-60%. Minimum rhs will be lowest across southeast ca, with values around 20-30%. A drying trend will begin thursday with conditions becoming very dry by this weekend. Minimum rhs by saturday dip to 10-25% across the lower deserts (lowest across western districts). Overnight recoveries will still be good across eastern districts this weekend at 40-60%, while western districts hover around 25-45%. The drier air moving in will eliminate rain chances by friday, with low chances in gila county thursday afternoon. Winds will favor the south to southeast over much of the area through wednesday with gusts of 20-30 MPH at times across southwest az and southeast ca. In the following days winds will return to a more typical diurnal with modest afternoon upslope gustiness.