textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- A Flood Watch remain in effect for parts of the region through this evening, however most of the heaviest rain has exited the region.

- Below normal temperatures will be common through the end of the week across the eastern portion of the forecast area, while near normal readings will return to the western deserts starting Wednesday.

- Dry conditions will prevail from Thursday though early next week as high pressure takes hold across the region.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Areas of light to moderate rainfall will continue across portions of the region, mainly for Southern Gila, through this evening before the majority of the shower and thunderstorm activity begins to push of out of our forecast area. As expected, rainfall totals over the past few days have varied greatly, with the driest spots seeing only a few hundredths of an inch, while measurements upwards of 2-2.5" have been seen so far in parts of south-central Arizona. Accumulations will continue to rise for some areas, so it is not out of the question that areas of 3+", mainly confined to foothill and high terrain areas, will be seen once this is all said and done.

Even though most of the lower desert rainfall has moved on, it may not be the last of shower and thunderstorm activity seen over these areas. With drier air surging behind the main rain bands, noticeable clearing has taken place across most of the region. This dry air advection will not completely scour out boundary-layer moisture which, combined with day-time heating, should promote the presence of some decent CAPE upwards of 500-1000 J/kg. With the best ascent associated with the low removed from our area at this point, any convection that can pop will be heavily dependent on orographic influences. A sharp gradient of 0-6km shear will be located overhead, so maybe some longer lived cells are be observed, but the majority should be short-lived due to lack of mid and upper-level support/lift. Even with the environment, confidence in this round of activity is fairly low as CAMs have been inconsistent run-to-run on where it places these showers and storms, with some keeping them within the Flagstaff CWA, while others show the Phoenix metro and even areas as far south as the I-8 corridor seeing something form. Nonetheless, the main impacts will be brief heavy downpours, gusty winds, and perhaps some isolated instances of small hail if storms can become strong enough.

Today should feel a bit like fall across the portions of the region as high temperatures will run a good 15 degrees or so below normal across south-central Arizona. Readings for the lower elevations will run in the 70s and low 80s, while the higher elevations will struggle to get out of the 60s. The further west you go, the warmer it will be as Southwest Arizona and Southeast California will reach into the middle 80s and lower 90s, which is still a good 4-8 degrees below normal.

Wednesday will be a transition day as the Pacific low gradually exits the region. Some morning scattered showers are likely to still be across the far eastern Arizona high terrain, but any activity should quickly wind down in the afternoon. Elsewhere on Wednesday, sunny skies and warmer temperatures are forecast for southeast California and southwest Arizona while the south-central Arizona lower deserts will see some lingering clouds and a continuation of well below normal temperatures.

LONG TERM /THURSDAY THROUGH WEDNESDAY/

Model guidance shows upper level ridging fully moving into our region on Thursday and likely staying put through the upcoming weekend. This will lead to gradual drying and mostly clear skies while temperatures slowly rise closer to the normal range for the south-central Arizona lower deserts. The western lower deserts may reach 100 degrees again starting Friday, but for the eastern half of Arizona some reinforcing cooler air from the east Friday through Saturday should keep daytime highs at or just above 90 degrees through Saturday. This cooler easterly flow may even continue into early next week with temperatures in the Phoenix area staying right near seasonal normals for early October.

AVIATION

Updated at 2315Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Areas of lower cigs early this evening and uncertainty in wind shifts/directions will be the main weather concerns. Lower cigs with isold SHRA/TSRA will be common just east of the terminals this evening, though moving away from the metro. W/SW winds will prevail through early evening with decreasing confidence in timing of a shift to easterly component mid evening. Midlevel clouds and a few SHRA will sweep towards the Phoenix area overnight, though should have little to no impact. With a few mid/high cloud decks Wednesday, very low confidence exists regarding wind directions as a low pressure system may sit directly on the Phoenix metro creating a wide variety of directions through the afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: Gusty north winds with isold SHRA near KBLH early this evening will be the main weather concern before more tranquil conditions return Wednesday. Gusts 20-30kt under 8-10K ft AGL cigs will be common into the early evening before speeds weaken and cloud decks dissipate through mid evening. Confidence is very good that clear skies and near calm winds will prevail much of the day Wednesday.

FIRE WEATHER

Widespread showers and isolated thunderstorms will affect much of the area early today before mainly affecting the Arizona high terrain this afternoon and evening. Moderate to heavy rainfall is likely to impact the Arizona high terrain through at least early afternoon. Humidities will begin to trend lower across the western districts later today, but more so on Wednesday. Elevated humidities will persist across the eastern districts through at least Thursday. Winds will be breezy to locally windy at times today before becoming light again on Wednesday. Drier conditions and near to slightly above normal temperatures are forecast for later this week and through the weekend.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Flood Watch until 9 PM MST this evening for AZZ547-556>558- 560>563.

CA...None.