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
039 FXUS65 KPSR 092145 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 245 PM MST Tue Jul 9 2024 .SYNOPSIS... Strong high pressure will allow extreme heat to persist across the region throughout the week as many high temperature records will be threatened. Moisture will slowly move back into the area over the next several days 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... Expansive ridging continues to dominate western North America this afternoon with objective analysis depicting the center of a 596dm H5 anti-cyclone situated over the lower Colorado River valley. Through the remainder of the week, the Conus synoptic pattern will be slow to advance, however progressive troughing entering the Pacific NW along with the movement of downstream remnant tropical wave action will allow the stubborn H5 center to constrict, shift east into the central Rockies, and eventually weaken. This process will back prevailing winds aloft from a northerly trajectory into an east/southeast heading far more supportive for higher quality moisture intrusion and thunderstorm sustenance. In the short term, excessive heat remains the greatest threat as temperatures continue to hover around 10F above normal and very near record levels (see Climate section below). Models depict very little variety in thermal profiles with H8-H7 forecasts solidly better than 2 normalized standard deviations above normal, or around +33C and +20C respectively. With readings of this magnitude only occasionally experienced, widespread major HeatRisk will continue through Friday before the introduction of thicker moisture profiles detracts from the extreme warming. Although deep moisture profiles are currently compromised, shallow moisture has been imported from outflow from northern Mexico/New Mexico as well as via a modified Gulf surge yielding around 8 g/kg mixing ratios. While insufficient towards supporting lower elevation convection, current moisture levels have been capable of sparking isolated storms from the Whites across the Rim. HREF members show northerly steering flow directing showers and decaying storms across Gila County with modest chances for minor rainfall accumulations and weak outflow boundaries. Upper level support appears to wane somewhat Wednesday with more notable convergence aloft and weaker updrafts reflected in limited storm coverage via HREF output. The latter half of the week will be characterized by gradually increasing moisture levels in both magnitude and depth, as well increasingly favorable synoptic flow. A more pronounced deep easterly/southeast flow will become established favoring northward and westward moving outflow boundaries initiating over higher terrain. Each outflow should progressively deepen moisture profiles such that Friday should be a pivotal transition day where values finally become sufficient for isolated storm surviving in lower elevations. Early in this evolution, strong outflow winds sweeping through lower elevations will be the greatest threat. In combination with an upper level cyclone propagating into central New Mexico, the position of the high pressure system shifting into Colorado will provide an excellent jet level wind field with a tremendous divergence field. Juxtaposed with more favorable moist flow and mixing ratios jumping near and over 10 g/kg, regional MLCape in excess of 1000 J/kg should be released over mountains with well defined outflows initiating additional storms downhill. Greater uncertainty exists whether atmospheric conditions will support more widespread lower elevation storms Saturday, however by Sunday, conditions look even more favorable for aggressive storm activity. While convective evolution on any given day starting this weekend may dictate the coverage and ability for thunderstorm formation the following day, the overall pattern will remain rather favorable for robust storm development and sustenance across much of the CWA. && .AVIATION...Updated at 1735Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation impacts are expected through the forecast period. Winds will follow typical diurnal tendencies with a westerly shift anticipated by 20Z-21Z across the Phoenix Metro. A brief period of light and variable winds will be possible before this westerly shift occurs. There could be gusts into the upper teens to 20 kts this afternoon, but speeds should diminish after sunset. Hi-res models do show convection developing over the higher terrain east of Phoenix this afternoon and evening. Therefore, there is a low chance (around 10%) for an outflow boundary emanating from distant storms reaching KIWA this evening, mainly between 00Z-03Z. Skies should remain mostly clear with the exception of a few high clouds. Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected through the forecast period. Winds should remain southeasterly at KIPL and southerly at KBLH through most of the period. Occasional gusts up to 15-20 kt will be possible at KBLH this afternoon. Skies will remain mostly clear over southeast California. && .FIRE WEATHER... Abnormally hot conditions will continue the next several days before increased moisture spreads into the area late in the week pushing readings much closer to the climatological normal. Minimum afternoon humidity levels will fall into a 5-15% range the next few days with moisture initially increasing over eastern districts by Friday. Corresponding overnight recovery will remain poor to fair in a 15- 40% range. Humidity levels should improve markedly over the weekend with minimum levels struggling to reach a 15-20% range as shower and thunderstorm activity becomes more expansive. Isolated storms will be possible over the higher terrain of eastern districts the next few days, however wetting rain chances are, at best, only 10%. Far better chances for beneficial rainfall arrive over the weekend with activity moving into lower elevation locations. In general, winds will be fairly light with occasional afternoon gusts around 20 mph. However, strong gusty outflow winds and abrupt wind shifts will become more prevalent through the week as storm activity increases over higher terrain. && .CLIMATE... Record Highs Phoenix Yuma El Centro --------- ------- ----------- July 9 116 (1958) 119 (1958) 117 (1958) 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...18/Kuhlman AVIATION...Salerno FIRE WEATHER...18/Kuhlman CLIMATE...Berislavich/Kuhlman