![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
991 FXUS65 KPSR 140530 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1030 PM MST Sat Jul 13 2024 .UPDATE...Updated 06z Aviation Discussion. && .SYNOPSIS... Above normal temperatures will persist across the region through next week, although weakening high pressure should allow readings to fall below excessive levels. Increasing moisture will support scattered thunderstorms the next couple days with the best chances for more widespread storms reaching south-central lower elevations occurring Sunday. Somewhat drier conditions will gradually spread into the area early next week, however will not preclude mountain storms and the potential for gusty outflow winds descending into lower desert communities. && .DISCUSSION... Early afternoon objective analysis and WV imagery depicts an expansive subtropical anti-cyclone with H5 heights near 597dm shifting to the central Utah/Colorado border resulting in deep E/SE flow across the forecast area. Concurrently, one subtle shortwave was ejecting westward through SE California with another more defined cyclonic circulation over the southern Gulf of California. These 2 features were combining to place much of eastern AZ under modest subsidence. If this were not enough to suppress widespread convection later today, a large slug of dry air from the high plains has rotated westward into eastern AZ where mixing ratios have dropped under 6 g/kg. Not surprisingly, HREF membership develops minimal deep convection over higher terrain focusing development within a plume of better quality moisture (>10 g/kg mixing ratios) from along the international border through the lower Colorado River valley and far western Arizona/SE California. Later this evening, confidence is moderate that a small northern Sonora convective complex combined with inland thermal low pressure will induce a modified Gulf surge. Forecast BUFR soundings are consistent in depicting shallow sfc-H8 mixing ratios spiking near 14 g/kg, albeit with notable dry air lingering within the upper half of the typical mixed boundary layer. As such, many models indicate partial erosion of this low level moisture throughout the day resulting in only 10-11 g/kg mixing ratios during peak heating and maintaining notable convective inhibition across lower elevations. This slight reduction in total available moisture should limit MLCape under about 1200 J/kg, however impressive DCape around 2000 J/kg will encourage deep, long traveling outflow boundaries. With strong evidence that low level CinH will exceed 50-75 J/kg, multiple outflow boundaries will likely be needed to spark additional deep convection over lower elevations. Recent HREF output (and subsequently NBM forecasts) has reduced the forecast storm coverage and probabilities given this evidence, however with such extreme DCape forecast, still feel enough colliding boundaries will materialize to invigorate isold/sct storms around the Phoenix metro. Thus, have made minor increases to the mandated NBM POP initialization though still lower than most previous forecasts. Regardless, these storms will be capable of producing strong, gusty winds, localizes dense blowing dust, and brief heavy downpours. Through the middle of next week, there will be a tendency for modest drying of the atmospheric column and more predominant subsidence as the center of the afomentioned subtropical high propagates back into central Arizona. This will not preclude diurnal mountain storms with outflows directed towards lower elevations, and cannot completely discount a isolated storm nearing population centers of south-central AZ. However, with mixing ratios likely dropping near 8 g/kg, chances are significantly reduced; although there is reasonable evidence of a few nocturnal/early morning elevated showers should pockets of enhanced midtropospheric moisture be thrust into a steeper lapse rate environment. Uncertainty regarding convective coverage increases during the latter half of the week as ensemble members diverge with respect to the position and magnitude of central H5 heights. Ensemble mean forecasts suggest the anti-cyclone center shifting more towards southern NV which would place the CWA in a more favorable location for moisture advection. However, if more moisture is scoured away from the region early in the week, it may take several rounds of outflows and moisture deepening to support more expansive storm coverage. Another aspect tied to the position and magnitude of the sub- tropical high is temperatures and the potential to return to excessive levels. While there is good agreement that H5 heights will relax near 594dm during the first part of next week, there is some growing evidence this will only be temporary with 598dm heights potentially returning to the central/northern part of the state. At this time, NBM forecasts cap levels well below record territory such that only expansive moderate HeatRisk exists with just very small pockets of major category precluding any headlines. However, if the 75th percentile of the full ensemble spread comes to fruition, a few days midweek could be flirting with excessive criteria. && .AVIATION...Updated at 0530Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Primarily westerly flow is expected to continue through the overnight hours. A period of enhanced winds are expected to move through the metro TAF`s over the next several hours, with periodic gusts up to 25 kts. Otherwise, the typical diurnal easterly wind is not expected to develop, hence the indicated light and variable directions for early tomorrow morning. Westerly winds will then quickly develop tomorrow morning and persist through the rest of the TAF period for the most part. Thunderstorm chances remain too low (10-20%) at this time to introduce any VCSH/VCTS, but outflow potential will increase towards the end of the TAF period. Current thinking is a favor towards either a northerly or southeasterly outflow, but currently only added TEMPO for a northerly component outflow for SDL and DVT. Outside of outflow potential, westerly winds will persist through the rest of the TAF period. Skies will remain SCT, with BKN possible that will be dependent on convective development across the region during the afternoon and evening hours. Southeast California/Southwest Arizona including KIPL and KBLH: Typical diurnal wind tendencies will continue for the most part through the TAF period at both sites. KIPL will favor a southeasterly wind, while KBLH will favor a south to southwesterly wind through the period. Thunderstorm activity remains very low (5-10%) in the immediate TAF areas, but higher terrain convection could result in outflows that could reach the terminals, especially KIPL where a TEMPO for southwesterly gusty winds are possible. Otherwise, periodic gustiness 20-25 kts are possible during the afternoon and early evening hours at both sites. && .FIRE WEATHER... Temperatures will cool slightly early next week, though remain in an above normal category as moisture increases over the region. Thunderstorms and wetting rainfall chances will be primarily concentrated over higher terrain of eastern districts through the week. however chances for lower elevation storm chances peak on Sunday. Gusty outflow winds will be possible on many days next week exacerbating issues on any ongoing wildfires and new starts. Otherwise, afternoon upslope gustiness of 20-25 mph will be periodically common. An increase in moisture will keep minimum afternoon humidity levels above 20% Sunday, however retreating to a 10-20% range by the middle of the week. Correspondingly, fair to good overnight recovery in a 40-60% range will fall into a 20-40% range midweek. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Sunday for AZZ530. CA...Excessive Heat Warning until 8 PM PDT Sunday for CAZ560>570. && $$ DISCUSSION...18/Smith AVIATION...Young FIRE WEATHER...18