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
833 FXUS65 KPSR 101133 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 433 AM MST Wed Jul 10 2024 .UPDATE...Updated 12Z Aviation Discussion. && .SYNOPSIS... Strong high pressure will allow extreme heat to persist across the region for another few days as many high temperature records will be threatened. Moisture will also slowly move back into the area providing modest chances for isolated thunderstorms over eastern Arizona high terrain. Over the weekend, far better moisture should be imported into lower elevations supporting improved rainfall chances, as well as pulling temperatures away from excessive levels and closer to seasonal normals. && .DISCUSSION... There was some improvement with atmospheric moisture yesterday as a patch of mid level moisture tracked southeastward out of Nevada into northern and central Arizona by the afternoon. This allowed for a bit more widespread and stronger convection than models advertised. However, the strong high pressure system remains intact over the region with the center now positioned over Nevada. The high has weakened slightly, but the expansive heat dome that it helped to create remains in place with daily highs still reaching near or even exceeding records. Guidance continues to support little overall change with heights and temperatures over our area through Friday as the high center very slowly drifts eastward into Utah. Excessive heat will remain the main forecast concern today through Friday with highs through Thursday ranging from 114-120 degrees across the western deserts to 112-117 degrees across the lower deserts of south-central Arizona. Convective activity today is expected to be less vigorous across the higher terrain east of Phoenix as some drier air will work southward into eastern Arizona. However, the HREF still indicates some modest convection developing in the mountains north of Phoenix this afternoon, likely sending gusty outflow winds into at least the northern portion of Phoenix early this evening. Moisture is then expected to increase again across southeast Arizona into the higher terrain east of Phoenix on Thursday leading to more widespread and stronger thunderstorm activity. Forecast soundings for Thursday afternoon show modest MUCAPE up to around 1000 J/kg along the Mogollon Rim extending into the foothills just east of Phoenix. This instability along with plenty of dry air in the boundary layer supporting high DCAPEs should result in good potential for strong to possibly a few severe thunderstorm wind gusts over the high terrain northeast and east of Phoenix. SPC has introduced a Marginal risk for severe storms on Thursday with the area encompassing much of area east of Phoenix and probably too optimistically westward into the Phoenix metro. Moisture levels over the south-central Arizona lower deserts are not likely to be high enough for additional redevelopment of storms into the Phoenix metro, but strong outflow winds from the east southeast are much more likely to occur. The 00Z HREF shows the threat for strong winds maximized over Gila County into eastern Pinal County, but it still shows upwards of a 50% probability of 30+ kt winds reaching Phoenix and a 10% probability of 50+ kt winds. However, just looking at the new 06Z HRRR, it barely shows any convection east of Phoenix Thursday afternoon and virtually no outflow winds getting near Phoenix. It will be something to monitor over the next day and a half. Friday still looks to be a transition day for our area as the high center is finally far enough to the north and east that easterly flow will overtake the area. Moisture advection will be much better starting Thursday night as a strong Gulf surge is expected to occur. Between the Gulf surge and easterly moist flow starting Friday morning, there should be a noticeable change in boundary layer moisture. Temperatures will react to the higher moisture, but Friday`s forecast highs are still expected to range from 112-116 degrees over the lower deserts. The higher moisture content air on Friday may allow for some convection over higher terrain areas south of Phoenix as well as over the eastern Arizona high terrain. However, convective potential into the south- central Arizona lower deserts should still be limited with PoPs generally at between 10-15%. An additional surge of moisture off Gulf of California is expected Friday night/Saturday morning along with the continued moist advection out of New Mexico. This is likely to increase PWATs across the lower deserts into a 1.2-1.5" range on Saturday, potentially allowing for lower desert convection developing off of any outflows from higher terrain areas. Temperatures Saturday are expected to continue to improve with readings dropping to between 107-111 degrees over most of the lower deserts. However, despite the lower air temperatures Saturday, the increased humidity is likely to still make it feel uncomfortably hot. The best potential for more widespread and potentially strong monsoon thunderstorm activity looks to be on Sunday when models continue to show upper level support from an upper level low that develops over New Mexico. This potential could carry over into early next week as the low is forecast to remain just east of Arizona, but as with active periods during the monsoon it is common to have a down day after a very active day due to convective overturning of the atmosphere. Starting Tuesday, an upper level trough is forecast to reach California, while the sub- tropical high center may shift back closer to or even into Arizona. This somewhat favored scenario would point toward some drier air working back into the region from the west during the middle of next week and thus pushing most of the monsoon activity back over the eastern Arizona high terrain. At least for now if this does occur, guidance generally supports the ridge not being nearly as strong as it currently is and keeping temperatures closer to normal readings through the rest of next week. && .AVIATION...Updated at 1130Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds will continue to follow their typical diurnal tendencies with extended periods of light and variable winds at times. Wind speeds will generally be aob 10 kt, with some occasional gusts up around 20 kt this afternoon and early evening. Hi-res guidance continues to show isolated storms to the north of Phoenix sending an outflow boundary south and into Phoenix. Have continued with the TEMPO groups at KDVT and KSDL, but pushed the time up to 00-02Z. Hi-res guidance shows the outflow reaching KPHX, but dying out before reaching KIWA. Because of this a TEMP group for KPHX from 01-03Z. The exact strength of the outflow is still uncertain, but have gone with gusts of around 20-25 kt for now. Hi-res guidance is indicating a westerly gulf surge late this evening, which could delay the easterly shift overnight, primarily for KPHX. Skies will be mostly clear with FEW mid and high clouds throughout the TAF period. Southeast California/Southwest Arizona including KIPL and KBLH: At KIPL, winds will favor the E to SE, whereas at KBLH, winds will favor the S. Wind speeds will generally be 8-12. A gulf surge from the south may cause winds to gust up near 20 kt for a few hours during the overnight hours tonight. Skies will remain mostly clear through the TAF period. && .FIRE WEATHER... Unusually hot weather will persist over the next few days with thunderstorm activity increasing over eastern districts starting Thursday. Today`s activity should be quite isolated with more widespread activity over the higher terrain Thursday followed by chances spreading into the lower deserts on Friday. However, chances of wetting rainfall will mainly stay confined to southern Gila Co. Minimum humidity values over the lower deserts will continue to fall into a 5-10% range through Thursday, improving to 10-15% Friday, with somewhat higher values over the Arizona higher terrain. Occasional upslope gusts near 20 mph will be common, and with increased thunderstorm activity, stronger outflow winds will gradually become more likely Thursday afternoon/evening. Far better chances for beneficial rainfall arrive over the weekend with activity moving into lower elevation locations. && .CLIMATE... Record Highs Phoenix Yuma El Centro --------- ------- ----------- July 10 115 (1958) 118 (1959) 116 (2021) July 11 118 (1958) 118 (1958) 117 (1975) July 12 116 (2020) 119 (1939) 118 (1964) && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ530>555-559. CA...Excessive Heat Warning until 8 PM PDT Friday for CAZ560>570. && $$ DISCUSSION...Kuhlman AVIATION...Berislavich FIRE WEATHER...Kuhlman CLIMATE...Berislavich/Kuhlman