textproduct: NWS Phoenix

KEY MESSAGES

- Shower and thunderstorm chances will increase today and Tuesday, especially over the Arizona high terrain. Isolated storms can also be expected into the south-central Arizona lower deserts.

- Drier conditions during the latter half of the week will greatly curtail monsoon storm chances with at most slight chances by Thursday.

- Temperatures will remain near normal early this week before heating up during the latter half of the week.

- Areas of Major Heat Risk are expected beginning Thursday with a high likelihood of fairly widespread Major to Extreme Heat Risk by the weekend.

SHORT TERM /TODAY THROUGH TUESDAY/

Mid-lvl WV imagery and RAP-40 500mb analysis show the subtropical ridge expanding across most of the Desert SW and into the south- central Plains. Easterly to southeasterly winds aloft are still advecting decent moisture into the region, with PWATs from this morning's 12Z sounding 1.8". Current mesoscale analysis does show some drying has occurred over the Metro this afternoon, however PWATs are still hovering between 1.4-1.9" across the entire region. Heading into this afternoon/evening ensembles are in good agreement for storm development in the eastern high terrain with MUCAPEs forecasted between 500-1000 J/kg and mixing ratios remaining between 11-13 g/kg. Where the agreement falls apart in the models is whether any additional storms will be able to develop into the lower deserts as outflows push through. The latest HRRR is more optimistic for lower desert redevelopment, while other HREF members show very limited potential. Even with this uncertainty PoPs for the Phoenix Metro will remain between 20-30% while the eastern higher terrain will be between 50-70%. Otherwise, gusty winds up to around 35 mph and localized heavy rainfall will be the main weather concerns for the AZ higher terrain tonight. While gusty winds and patchy blowing dust will be the main concerns over the lower deserts with HREF members showing a 30-50% (mostly near 30%) chance of wind speeds above 35 mph this evening, however similar to PoPs, the HRRR is very optimistic of an outflow from the higher terrain moving through with speeds near 35-40 mph.

Similarly to the past few mornings lingering showers and a few storms will remain possible across south-central and eastern Arizona into Tuesday morning as the inverted trough moves into western New Mexico. Tuesday afternoon/evening is expected to be similar to today with HREF members again in great agreement of thunderstorm development in the eastern high terrain. This will bring localized heavy rainfall, with WPC putting a more expansive slight risk for excessive rainfall over eastern Arizona, with localized areas in Gila County may receive upwards of 1-2 inches of rainfall an hour. Due to this a Flash Flood Watch has been issued starting Tuesday afternoon through Tuesday evening for Eastern Gila County, when the peak rainfall is expected to occur. Otherwise, southerly drying flow into the lower deserts is likely to further inhibit chances in the Phoenix area, with even the HRRR showing limited chances of storm development.

Heat impacts early this week should be fairly limited with Minor to Moderate HeatRisk through Tuesday. Forecast highs are still below normal across central and eastern Arizona, but for southwest Arizona and southeast California highs will begin to push to above normal as early as Tuesday. Overnight temperatures are expected to fall within the normal range with lows in the low to mid 80s across the lower deserts.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Model guidance is now trending toward a noticeably less active monsoon period during the latter half of the week, largely in part due to the subtropical high strengthening and setting up over west Texas through our region. The main forecast concern will quickly shift from monsoon storms to extreme heat by Thursday. Ensembles show the high shifting southward starting Wednesday and then expanding into our region Thursday into Friday as H5 heights over our region quickly rise from 591-593dm Wednesday to 596-598dm by Friday. Southerly dry flow will pick up across our area on Wednesday, decreasing rain chances further before chances likely drop below 10-15% starting Thursday as strong subsidence spreads over the region.

Temperatures should quickly respond to the increasing heights and the decreasing monsoon activity later this week. NBM forecast highs show readings topping 110 degrees as early as Wednesday across southeast California and as early as Thursday across the Arizona lower deserts. Areas of Major HeatRisk are expected by Thursday, likely expanding in coverage Friday into the weekend as the heat reaches its peak. Overnight lows will also become an issue as surface moisture remains elevated enough to cause lows to only dip into the upper 80s to lower 90s by Thursday. Daytime highs of 113-116 degrees across the western deserts to 110-113 degrees in the Phoenix area are shown for this weekend, while heat indices of 115 degrees are likely to appear as early as Thursday for the western deserts. Due to this an Extreme Heat Watch has been issued for Southeast California Starting Wednesday and then expanding eastwards to include south central Arizona and the Phoenix Metro starting Thursday.

AVIATION

Updated at 1820Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

The primary aviation weather concerns will exist this evening as gusty outflow winds are expected to descend into the Valley. Guidance continue to suggest that convection across the higher terrain north and east of Phoenix will send outflows toward the terminals this evening with neighborhood probabilities suggesting ~50% chance of outflow gusts exceeding 30 kts. The exact timing of these outflows is uncertain with the best timing currently looking to be between 01Z-03Z. As this boundary pushes through the Phoenix area, there is the potential for new shower/thunderstorm activity to develop along it. However, confidence in this occurring is low with the HRRR remaining the most aggressive in suggesting this scenario. Have maintained a mention of VCSH in the TAFs with a higher likelihood of VCTS at KIWA. Any thunderstorms that do develop will be capable of producing gusty, erratic winds. Outside of this, winds will favor the west through the afternoon with a few gusts into the teens at times. SCT-BKN mid and high clouds will continue with bases generally aoa 8-10 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:

No significant aviation weather concerns are expected through the next 24 hours. Winds at KIPL will favor a SE component through the afternoon, switching around to the W early this evening. At KBLH, winds will predominantly favor a S to SW component through the period. Expect elevated wind speeds this afternoon/evening around 8-12 kts and a few gusts to around 20 kts. Can't rule out an isolated VCSH near KIPL this afternoon, however, chances of this occurring are less than 10%. FEW to SCT clouds aoa 10 kft will be common throughout the period.

FIRE WEATHER

Ample moisture will be available for additional rounds of showers and storms through at least Tuesday for the Arizona higher terrain. Much more limited chances are expected over the Arizona lower deserts. Humidities will remain elevated with MinRHs mostly ranging from 20-25% across the western districts to 25-40% across the eastern districts, while overnight recoveries remain good. Outside any influences from showers and thunderstorms, winds early this week will tend to favor the southwest with only short periods of downslope easterlies late at night for the eastern districts. Hotter temperatures with some slight drying is expected during the latter half of the week as a stronger high pressure system sets up over the region. Rain chances will be greatly diminished by Thursday, likely lasting through the upcoming weekend.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Watch from Wednesday morning through Monday evening for AZZ530-532.

Flood Watch from Tuesday morning through Tuesday evening for AZZ556-560-562-563.

Extreme Heat Watch from Thursday morning through Monday evening for AZZ531-533>555-559.

CA...Extreme Heat Watch from Wednesday morning through Monday evening for CAZ562>570.

Extreme Heat Watch from Thursday morning through Monday evening for CAZ560-561.