textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Above normal temperatures will continue through the forecast period with Extreme Heat Warnings in effect for portions of the area through mid week.

- Typical monsoon conditions will continue for the next few days with thunderstorm chances favoring Northern Arizona high terrain and portions of Southeast Arizona and low chances in the South Central Arizona lower deserts.

- High pressure will center itself over the region and strengthen late this week, resulting in hotter temperatures and another period of widespread Major to Extreme Heat Risk.

SHORT TERM /TODAY THROUGH THURSDAY/

The most prominent feature across the Southwest and Central US is a broad anticyclone centered approximately over NW/Western TX. In midlevel water vapor imagery, dry air aloft is evident punching into Eastern AZ as well as a vort max lifting northward through Central AZ. The combination of these factors with subsidence on the backside of the departing vort max has led to notable inhibition of thunderstorms so far this afternoon, especially compared to this same time over the last few days, with later timing of convective initiation over terrain features across the state and lower coverage of radar echoes. Despite this evolution so far, thermodynamics and low level moisture remain suitable for deep moist convection, with the 12Z PSR sounding (and PHX ACARS soundings in agreement) showing upwards of 1000 J/kg MUCAPE and near-surface mixing ratios near 10- 12 g/kg. Upslope convergence over the most prominent terrain features has been sufficient to trigger convection thus far today, and as capping/subsidence decreases through the remainder of the afternoon, an increase in thunderstorm coverage may be expected over Southeast and far Eastern AZ. Latest HREF remains pessimistic on development of thunderstorms over our CWA today, though better wind shear towards Southeast AZ could help storms move off terrain features, organize, and become more long-lived, pushing west northwestward towards South-Central AZ. A highly uncertain and conditional threat for an organized, long-lived outflow to push into South-Central AZ and trigger additional showers and storms exists. However, it is far more likely that the strongest storms will congeal closer to the international border or over Sonora, potentially forming an MCV this evening which will pass over Central AZ tonight/Tuesday morning. This would help to trigger isolated to scattered elevated convective showers over either South-Central or Southwest AZ Tuesday morning.

Tuesday, conditions will be fairly similar to that of today but with perhaps less inhibition late morning and early afternoon. HREF has begun to indicate a similar thunderstorm evolution, with the best coverage of strong thunderstorms over Southeast AZ near the international border, potentially forming yet another MCV that could spark showers over South-Central AZ late Tuesday night into Wednesday morning as it lifts north. By Wednesday, a downtrend in thunderstorm activity is anticipated, with drying conditions and winds aloft shifting southerly and even slightly southwesterly for a period. Latest GFS deterministic shows near-surface mixing ratios dropping below 10 g/kg across the forecast area, essentially ending lower desert storm chances. Ensemble mean PWATs will drop from current values between 1.2-1.7" across the forecast area (110-150% of normal) closer to 0.9-1.4" (80-100% of normal) by late Wednesday, with good agreement between that these lower moisture levels will persist through the remainder of the week and into the weekend.

Aside from the continued monsoon conditions the next few days, the primary concern through the entire forecast period and especially by late this week will be dangerously hot temperatures with little overnight relief. Temperatures will be fairly stable through midweek, especially across the western deserts, with afternoon highs in a 108F-114F range, between 2F-8F above daily normals for the typically hotter spots and Tuesday likely being the "coolest" of the next 7 days. While most of the region will fall out of the Extreme Heat Warning this evening, the Phoenix metro, Imperial Valley and the Lower Colorado River Valley will remain under the effect of the Warning through at least Wednesday evening. This is driven largely due to overnight lows remaining well above normal leading to very little relief in these areas. More expansive headlines will very likely be needed again by late week as the subtropical high moves closer and restrengthens. This is expected to drive temperatures back in the upper teens, with the lower deserts between 112F-118F, flirting with record highs yet again. H5 heights near the end of the work week will climb to between 595-597 dam, or in the 99th percentile to near max for climatology for this time of year.

LONG TERM /FRIDAY THROUGH MONDAY/

By the end of the of the week and heading into the weekend, most global ensembles continue to support the strengthening of the high pressure, with H5 heights up to 600dam and the center of the anticyclone shifting to over northern AZ/southern UT. These heights are near or at the max of NAEFS percentile for climatology for this time of year, which are quite frankly impressive. The peak of the extreme heat is expected to be Friday and Saturday, where the chances of Phoenix Sky Harbor at least tying the record high (116F) will be 65% on Friday and 50% Saturday. As mentioned previously, an additional widespread Extreme Heat Warning will be likely near the end of the workweek. Additionally, this setup will likely add more subsidence over the area and subdue afternoon convection. Global ensembles also show a slow downtrend in PWATs, falling under 1.5" by Thursday- Friday. So, this is not great for the prospects of seeing storms push into the lower deserts. However, the NBM keeps slight PoPs focused in the AZ high terrain.

AVIATION

Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Some minor uncertainty in wind direction will be the only forecast challenge through Tuesday evening under periods of thicker midlevel cloud decks with thunderstorms remaining over mountains of eastern Arizona. Confidence is good that west winds with modest gusts will prevail much longer into the evening/overnight than usual. Most evidence suggests KPHX never going easterly (variable, at best) overnight with only partial decoupling. While BKN midlevel cigs Tuesday morning may complicate wind trends, evolution should be similar to today.

Southeast California/Southwest Arizona including KIPL and KBLH: Occasionally gusty wind will be the only weather concern through Tuesday evening under passing mid/high clouds. Confidence is good that wind directions will oscillate between SE and SW at KIPL while a southerly component will be preferred at KBLH. Gusts around 20 kt will be common at KBLH during the afternoon.

FIRE WEATHER

Typical monsoon conditions are expected through much of the forecast, with thunderstorm activity mainly favoring the high terrain of northern AZ and southeastern AZ and low chances (<10%) in the lower deserts of south-central AZ. Above normal, temperatures will contribute to seasonally dry afternoon conditions each day through the first half of the week, before temperatures once again heat up during the second half of the week. Minimum RH values of 15- 30% will be common through the first half of the week before dropping into the 10-20% range late in the week as temperatures heat up again. Overnight recoveries will be fair most nights with RH values mostly in the 35-50% across lower deserts to 45-65% across southern Gila County. Wind speeds should be fairly light through the period with only local afternoon gusts 20-25 mph.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Wednesday for AZZ530-532-537- 540-542>544-546-548-550-551.

Extreme Heat Warning until 8 PM MST this evening for AZZ531- 533>536-538-539-541-545-547-549-552>555-559.

CA...Extreme Heat Warning until 8 PM PDT Wednesday for CAZ567-569-570.

Extreme Heat Warning until 8 PM PDT this evening for CAZ560>566- 568.