textproduct: NWS Phoenix

KEY MESSAGES

- Hotter temperatures this week will result in widespread Moderate Heat Risk and localized Major Heat Risk on Wednesday and Thursday.

- Extreme Heat Warnings have been issued for multiple locations across the area for today through Thursday with forecast highs between 107 and 114 degrees.

- Increasing moisture will lead to isolated to scattered showers and storms across the higher terrain areas with the best chances during the middle of the workweek.

- Drier conditions and increasing winds by the end of the week and this weekend will lead to high fire danger.

SHORT TERM /TODAY THROUGH THURSDAY/

Upper level water vapor and SPC Rap analysis reveal an elongated high pressure system centered over the El Paso and northern Mexico area. Additionally there is a trough off the coast of the Pacific NW that will come into play during the later half of the workweek.

The aforementioned high pressure is currently around 596 dm and will strengthen to around 597-598 dm by late tonight into early tomorrow before beginning a gradual weakening trend. As this high strengthens today it will shift slightly westward and become centered over southeast AZ, southern NM, eastern TX, and northern Mexico. This will lead to higher heights over our region, with H5 heights ranging from 594-598 dm over our CWA. On Wednesday the aforementioned trough will start to push onshore in the Pacific NW which will slightly weaken the high over our region. However, H5 heights will remain around 594 dm into Thursday. By Thursday the trough will push further inland with the high weakening even further (down to 590-592 dm) and propagating south and eastward.

As a result, temperatures will be on the rise through the middle of this week, peaking during the Wednesday-Thursday timeframe. Even though the high will be weakening on Wednesday and Thursday, there will be a delayed reaction seen in the surface temperatures. Which is why temperatures are expected to max out during the middle of the week. Temperatures will be around 5-7 degrees above normal today through Thursday. With afternoon high temperatures forecasted to be in the 108-114 degree range across the lower deserts and in the 100- 109 degree range across much of the higher terrain areas (the San Carlos area could see high temperatures up around 110-112 degrees today and Wednesday). Additionally morning low temperatures will be on the rise with the warmest mornings forecasted to be Wednesday and Thursday. Morning lows are forecasted to be in the 80s and upper 70s across the lower deserts and in the 70s across the higher terrain areas. These temperatures will result in widespread Moderate HeatRisk and localized areas of Major HeatRisk. Due to this Extreme Heat Warnings are in effect across portions of the area today through Thursday. These warnings are in effect for the San Carlos area today and Wednesday and the Phoenix Metro, Yuma area, Lower CO River Valley, SW Imperial County, and the Imperial Valley for Wednesday and Thursday. With the high positioned to the south and east of our area, the southerly and southeasterly flow will bring in moisture to our area. This increased moisture could lead to increased cloud cover that could allow us to fall short of reaching our forecasted afternoon high temperatures. However, the increased cloud cover over night would lead to higher morning low temperatures. EIther way, make sure to practice smart heat safety by limiting your time outside, especially during the afternoons, and drinking plenty of water and electrolytes.

As mentioned above, the southerly and southeasterly flow from the high will lead to increased moisture over our region. Models show PWATs going from 0.5-1.0" currently to 1.2-1.5" by the middle of the week. Hires models show isolated shower and storm activity over the western portion of the CWA for later tonight into Wednesday with PoPs (10-30%) focused over central Riverside County and Joshua Tree National Park. The increased moisture during the middle of the week will result in isolated to scattered shower and storm activity over the higher terrain areas of AZ, especially to the north and east of Phoenix.

LONG TERM /FRIDAY THROUGH MONDAY/

Global ensemble members remain in pretty good agreement on the overall synoptic patter for the end of the week and into the beginning of next week. The aforementioned upper level trough will push further into our region by the end of the workweek and this weekend. This trough will linger over our area into the beginning of next week. This trough feature will lead to lower heights aloft and as a result cooling temperatures. Temperatures will cool heading into the weekend before leveling out by the end of the weekend and beginning of next week. Temperatures on Friday and Saturday are still forecasted to be around 2-5 degrees above normal for this time of year. Then by the end of the weekend and beginning of next week temperatures are forecasted to fall slightly (2-4 degrees) below normal. Afternoon high temperatures are currently forecasted to be in upper 90s to around 105 degrees across the lower deserts and in the 90s across the higher terrain areas for the end of the weekend and beginning of next week. Morning low temperatures will also be decreasing and are forecasted to fall into the 70s to upper 60s across the lower deserts and in the 60s across the higher terrain areas. As a result of these decreasing temperatures, HeatRisk will also be decreasing across the region. In fact with temperatures forecasted to fall below normal, HeatRisk will fall into the Minor category across the entire region.

In addition to the cooler temperatures this trough will also bring in much drier conditions along with increasing winds. These drier conditions in combination with increasing winds will result in increasing fire fire danger. The breezy to locally windy conditions (especially Friday-Sunday) will lead to critical fire weather concerns.

AVIATION

Updated at 1115Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns expected throughout the TAF period. The overall wind pattern will follow the typical diurnal tendencies with speeds aob 10 kts along with some occasional afternoon/early evening gusts in the mid to upper teens. There is still a bit of uncertainty on whether or not an easterly shift materializes after sunrise at KPHX, but the potential does not look very good. Expect periods of FEW to SCT mid and high level clouds through the period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns can be expected throughout the TAF period. At KIPL, winds will generally be out of the southeast while at KBLH, winds will generally be out of the south. Some gusts between 20-25 kts can be expected at KBLH once again in the afternoon. Expect periods of FEW to SCT mid and high level clouds through the period.

FIRE WEATHER

Locally elevated fire weather conditions due to very low humidity and afternoon upslope/upvalley breeziness will continue through the middle of the week. Afternoon minimum humidities will improve slightly into a 10-15% range starting today due to increased moisture moving into the region. Slight improvement in overnight recoveries is also expected to around 25-40%. Temperatures will heat up into an above normal category for much of the week with lower desert highs topping 110 degrees at least on Wednesday and Thursday, and overnight lows will offer little relief as they rise into the 80s for much of the lower deserts. Winds will remain generally terrain driven through the middle of the week with upslope/upvalley gusts between 20-25 mph during the latter half of the afternoon into the early evening. Areas of critical fire weather conditions look likely by Friday and into this weekend as southwesterly winds increase across the region and slightly drier air (minRHs of 5-15%) moves back into the region.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Thursday for AZZ530-532-533-537-540-542>544-546-548-550-551.

Extreme Heat Warning from 11 AM this morning to 8 PM MST Wednesday for AZZ560.

CA...Extreme Heat Warning from 10 AM Wednesday to 8 PM PDT Thursday for CAZ562-566-567-569.