textproduct: NWS Phoenix

KEY MESSAGES

- Extreme heat conditions will persist through the weekend with temperatures hovering near to several degrees above normal while humidity values remain higher than normal.

- Shower and thunderstorm chances will favor high terrain areas and Southeast Arizona the remainder of the week with gusty outflow winds and blowing dust the most likely impacts for south-central Arizona.

- Shower and thunderstorm chances start to increase across the lower deserts late this weekend and into next week.

SHORT TERM /Today through Friday/

This afternoon, water vapor satellite imagery and objective analysis show that the subtropical high has shifted slightly to the north and is more centered over northern Arizona, but it is still elongated as it stretches from California to the Atlantic Coast. Visible satellite imagery revels a MCV centered over Yuma, AZ along with storms firing up along the Mogollon Rim. The MCV over Yuma, is the remnants from last night's complex of storms of Sonora Mexico that pushed an outflow boundary through the south- central AZ lower deserts that resulted in a large-scale dust event. Visibilities across the Phoenix Metro dropped below 1 mile from the blowing dust early this morning as the boundary moved through. Similar to Monday's large scale dust event, the dust and hazy conditions, and corresponding poor air quality, hung around through the majority of the morning. Early this afternoon, while it is still a little hazy out there, visibilities have improved across the Phoenix Metro with most locations seeing visibilities return to the normal 10 miles.

As for thunderstorm potential this afternoon and evening, similar to the past couple of days, thunderstorms are expected to remain in the higher terrain of eastern AZ. The environment in SE AZ is pretty worked over from all the activity they've seen over the past several days. Therefore, most of the activity today is expected in the higher terrain to the north and east of Phoenix. There is a 20-40% chance of showers and storms across southern Gila County this afternoon and evening. While there remains a large amount of MUCAPE across the lower deserts (1000-2000 J/kg) there is still an abundance of CIN (around 100 J/kg) that will likely inhibit and showers or storms to form across the lower deserts. Therefore there is less than a 10% chance of showers and storms across the lower deserts. Despite this low end chance CAMs continue to show the potential for a N/NE outflow moving off the Mogollon Rim and into the lower deserts. CAMs continue to back off on this potential and the outflow may wash out before reaching the Phoenix Metro or could only result in a wind shift, with little to no gusty conditions. The 12Z HREF does show 30% chance of wind gusts in excess of 35 mph in the Phoenix Metro and 50% chance of wind gusts in excess of 35 mph in the foothills. However, more recent runs of some of the CAMs show this potential decreasing. With limited activity across SE AZ expected this evening, a SE'rly outflow is not expected and therefore no blowing dust and reduced visibilities are expected either. A similar scenario is expected tomorrow as the high strengthens and moves north slightly.

As for temperatures, the Extreme Heat Warning remains in effect as hot and humid conditions continue. The thick cloud cover from this morning has mostly cleared out and cleared out sooner than the clouds did yesterday. As a result temperatures are similar to a few degrees warmer than they were at this time yesterday. Afternoon high temperatures are forecasted to be near to a few degrees above normal again today. Tomorrow however, temperatures will increase and go back to around 4-8 degrees above normal as the high pressure strengthens (goes from H5 heights of around 595 dm today to around 597 dm tomorrow). Regardless increased moisture in the are will keep dew points in the 60s to low 70s across the region resulting in even hotter apparent temperatures, with "feels like" temperatures ranging from 110 to even around 120 degrees for some locations out in SE CA.

LONG TERM /Saturday through Wednesday/

Heading into the weekend, the center of the anti-cyclone will shift eastward towards the Four Corners region. As it does this, it will actually pull in some slightly drier air off the Rockies, helping to add to what is already a relatively unfavorable environment for lower desert convection. It should not inhibit convection completely in the typically active spots, but coverage may be a bit more limited. This "drier' period should be short lived however as the center of the high will settle off to our north and east, inducing southeasterly flow once again and providing renewed moisture flux. Rain chances for Sunday bump back up, and the lower elevations may get in on some rain well as PoPs increase to around 20-30%, some of the better chances seen in a while. There still might be some recovery time from the drier air needed, so it would not be surprising that activity Sunday evening is not very robust for areas such as Maricopa and Pinal Counties, but it is a positive sign to see an uptrend in rain potential nonetheless.

For next week, the forecast appears that it will not change much in terms of convective activity as ensembles have the high parked over the Four Corners. Less subsidence aloft, and continued moisture flux bodes well for continued rainfall chances and that is reflected in current PoPs sit between 20-40% basically from Monday through Thursday. As typical with the monsoon, what days are active will have heavy influence on what occurs the day after, so day-to-day forecast changes should be expected once we get into this more active period.

Temperatures over the next seven days will be at their hottest on Saturday as current projections have widespread readings between 110- 116 degrees for the lower deserts. Add the humidity to that and it will not feel particularly great outside. Some more good news is that as that temperatures will begin to "cool" as the high shifts east and weakens slightly, we may be able to finally escape extreme heat criteria by the start of next week, at least for now.

AVIATION

Updated at 1745Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns for this TAF period will be lingering slantwise visibility issues through early this afternoon followed by another potential outflow boundary this evening. Visibilities around 5-6 SM due to lofted dust will continue through early this afternoon with a slow improvement anticipated into this evening. Winds will remain westerly for the next few hours with gusts into the teens to around 20 kts materializing. By early this evening, outflow emanating from storms over the higher terrain will descend into the Phoenix Metro. The strength of the outflow will highly depend upon storm coverage, however there is still moderate confidence of an abrupt N-NE wind shift occurring at most terminals by 02z-03z. The northerly winds shift may only persist for a few hours before returning to the W-NW overnight. SCT-BKN mid to high clouds will be common through early this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues under periods of mid/high cloud decks are expected throughout the forecast period. Winds will generally be southeasterly at KIPL and southerly at KBLH, with some modest afternoon/early evening gusts into the 20-25 kt range at KBLH.

FIRE WEATHER

Hot temperatures with relatively elevated humidity levels will continue through the weekend. Though afternoon RHs do trend downward for Friday, regional readings should remain at 15% or above into next week. Overnight recovery will offer modest to decent relief as MaxRHs range generally between 30-55%. Rain chances through Saturday will be confined mostly confined to high terrain areas and southeastern Arizona, with lower desert chances remaining 10% or below. By Sunday, increasing moisture will result in an uptrend in lower elevation shower and thunderstorm chances, which appears likely to persist into the following week. Outside of thunderstorm outflows, winds will follow familiar diurnal trends, with typical afternoon upslope breeziness around 20 mph.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Sunday for AZZ530>544-546- 548>551-553>555-559.

CA...Extreme Heat Warning until 8 PM PDT Sunday for CAZ560>570.