Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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623 FXUS65 KPSR 180927 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 227 AM MST Tue Jun 18 2024 .SYNOPSIS... Near normal temperatures are expected over the next couple of days before stronger high pressure moves over the region leading to another warm up later this week. Starting Thursday, temperatures will likely top 110 degrees across the south-central Arizona lower deserts with an Excessive Heat Watch in effect for the area on Thursday and Friday. Moisture will also increase across much of southern and central Arizona starting Thursday and this will provide for some shower and thunderstorm chances over the eastern Arizona high terrain into the coming weekend. && .DISCUSSION... A Pacific upper level trough has overtaken much of the Western U.S. since yesterday allowing heights across the Desert Southwest to fall. The near normal temperatures as the result of the lower heights will persist through Wednesday with highs today mostly between 101-104 degrees across the lower deserts. By tonight, the main energy from the larger scale trough will already be lifting to the northeast away from our region, while an unseasonably strong ridge centered over the Mid-Atlantic States into New England begins shift southwestward. Going through the middle part of this week, the trough to our north will continue to weaken and shift away from our region, while the ridge over the Eastern U.S. continues to migrate west southwestward closer to our region. At the same time, a tropical disturbance will be moving westward off the Gulf of Mexico into Mexico. This disturbance will quickly weaken as it progresses inland, but it will leave an inverted trough behind which should attempt to track west northwest across northern Mexico. Moist low to mid level flow in between the tropical disturbance and the upper level ridge across Texas will increase out of the east early on Wednesday reaching New Mexico Wednesday evening. This moisture is expected to continue to track westward Wednesday night reaching eastern Arizona Thursday morning. Guidance shows this moisture spreading westward through much of southern and central Arizona on Thursday increasing surface dew points over the eastern Arizona high terrain into the 50s and providing our first monsoon thunderstorm chances east of Phoenix starting Thursday afternoon. In addition to the moisture increasing later this week, the ridge will also be spreading westward into our region increasing H5 heights to around 590dm as early as Thursday. Temperatures are forecast to quickly heat up starting Thursday with highs between 110-114 degrees across the south-central Arizona lower deserts. Temperatures should increase further on Friday areawide with all of the lower deserts likely reaching or exceeding 110 degrees with 112-116 degrees forecast for the Phoenix area. Given the latest NBM forecast temperatures later this week, we have pushed up the timing of the Excessive Heat Watch to start on Thursday and going through Friday. The heat dome will continue to impact the region through the weekend with any daily monsoon higher terrain activity providing little relief from the heat over the lower deserts. In fact, guidance suggests the ridge may strengthen across the region and northern Mexico Sunday into early next week and this could result in additional Excessive Heat headlines over the lower deserts of southeast California. Our first chances of monsoon showers and thunderstorms are likely to mostly affect higher terrains as forecast moisture levels are not quite high enough to provide the lower deserts with much of a chance. Storm motion steering flow will also favor north northeastward progressing convection which is not favorable for activity making its way into the lower deserts. However, the south-central Arizona lower deserts, including the Phoenix area, may very well have to contend with gusty outflow winds and possibly some blowing dust. This first round of monsoon activity may only last through early next week as guidance favors the ridge sinking farther to the southwest by the middle of next week. This would shift the flow out of the southwest and gradually bring in drier conditions across the region later next week. && .AVIATION...Updated at 0543Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: W to SW winds will shift E by 8-9Z tonight with speeds aob 10 kts through Tuesday morning. A period of southerly winds, between 15-22Z, is expected before W to SW winds take hold. Afternoon wind speeds will peak upwards of 8-12 kts with gusts topping out around to 20 kts. Skies will remain mostly clear, with some passing cirrus around midday. Southeast California/Southwest Arizona including KIPL and KBLH: Breezy W winds will continue for another hour or two at KIPL before subsiding. Winds at KBLH will increase and shift N to NW as a dry front pushes through around 12Z. Sustained speeds up to around 12-15 kts are anticipated with potential for gusts as high as 25 kts. The N to NW winds at KBLH will prevail most of the day Tuesday, with speeds subsiding through the afternoon, while KIPL sees a period of NW winds followed by westerly sundowner winds in the evening. Skies will remain mostly clear aside from passing cirrus early Tuesday morning. && .FIRE WEATHER... Overall light winds are expected over the next couple days with near normal temperatures. The dry conditions will however persist with daily MinRHs around 10% and overnight MaxRHs between 20-40%. Starting Thursday, moisture will creep into much of southern and central Arizona providing daily shower and thunderstorm chances over the eastern Arizona high terrain. Humidities will also noticeably improve later this week over higher terrain areas, but CWR will stay low at mostly below 10%. Along with the increasing moisture, high pressure is also expected to build back over the region later this week resulting in very hot temperatures and lower desert highs between 110-115 degrees. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Watch from Thursday morning through Friday evening for AZZ534-537>555-559. CA...None. && $$ DISCUSSION...Kuhlman AVIATION...Benedict FIRE WEATHER...Kuhlman