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/

The subtropical ridge remains quite expansive across the center part of the CONUS, but multiple inverted troughs continue to track westward under the high. One mesoscale circulation is currently tracking across southwest Arizona into southeast California, but most of the shower activity is south of the border. A larger circulation is slowly making westward progress across western Texas and New Mexico with this feature expected to help provide broad upper level ascent later today for convection over eastern and possibly central Arizona.

Moisture levels remain plenty adequate across the area with PWATs between 1.5-1.8" and low level mixing ratios of 11-13 g/kg, but some drying is ongoing. Current analysis shows very little MUCAPE across the lower deserts at the moment with forecast MUCAPE over the south-central Arizona lower deserts at most reaching 500 J/kg this afternoon. Higher moisture content and better instability will exist across the AZ high terrain with MUCAPEs this afternoon of 500-1000 J/kg. Hi-res CAMs mostly agree on good coverage of showers and storms over the high terrain this afternoon, but differ on 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 much more limited potential. A wildcard that could play a role in convective potential this evening is a Gulf moisture surge moving northeastward through southwest Arizona late this afternoon/early evening pushing into Maricopa/western Pinal Counties at some point early to mid evening. If the high terrain storms and/or outflows are late enough, they may interact with the Gulf surge causing better potential for storms to redevelop over or near the Phoenix metro. As of right now, we have 20-30 PoPs in Phoenix this evening. Gusty winds up to around 40 mph and localized heavy rainfall will be the main forecast concerns for the AZ higher terrain today, whereas gusty winds and patchy blowing dust will be the main concerns over the lower deserts.

Scattered showers and a few storms will remain possible across south-central and eastern Arizona tonight into Tuesday morning as the inverted trough moves into western New Mexico. The rest of Tuesday is of lower forecast confidence as models disagree on how fast the inverted trough moves northwestward into central and northern Arizona. Decent moisture and instability should still exist across eastern Arizona later Tuesday promoting similar shower and thunderstorm chances, but southerly drying flow into the lower deserts is likely to further inhibit chances in the Phoenix area. Similar to today, Tuesday should bring a localized heavy rainfall threat, while the gusty wind threat shifts more to the north into northern Arizona. Shower and storm chances Tuesday afternoon/evening over the south-central Arizona lower deserts are likely to be more limited compared to today with the threat for any impacts diminishing even further.

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. An Extreme Heat Watch is likely to be issued over the next day or so.

AVIATION

Updated at 0900Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Aviation concerns will remain relatively low through at least the first half of the TAF period before a potential outflow boundary brings an abrupt easterly wind shift later this evening. Until then, a fairly typical diurnal wind pattern will exist through this afternoon with winds veering back around to the W/SW by the late morning hours. Gusts up to 18-20 kts will be possible through this afternoon. After 00Z, convection over the higher terrain surrounding Phoenix will likely send an outflow into the lower deserts. Confidence in timing of this outflow is still low with guidance showing it arriving by 02Z at the earliest and around 05Z at the latest. When the boundary arrives, expect gusty easterly winds around 25-30 kts. There will be a low chance (30%) for isolated showers and storms to develop INVOF the area terminals this evening and thus VCTS/VCSH has been introduced to this package. SCT to at times BKN mid-to-high clouds will be common through the TAF period with lowest bases around 8-10 kft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather impacts are expected through tonight at the SE California terminals. Winds will remain predominately southerly at KBLH with speeds remaining elevated around 10-11 kts and gusts up to 20 kts materializing this afternoon. At KIPL, winds will follow typical diurnal trends with a return to S-SE winds by this afternoon followed by a westerly shift early this evening. Spotty VCSH may develop INVOF KBLH this morning, mainly between 12-18Z, but no impacts are anticipated. FEW to SCT clouds aoa 10K ft AGL 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...None. CA...None.