Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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649 FXUS65 KPSR 251828 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1128 AM MST Tue Jun 25 2024 .UPDATE...Updated 18z Aviation Discussion. && .SYNOPSIS... Enhanced monsoonal moisture across the region will continue to allow thunderstorm chances to persist through most of this week, with greatest chances today and tomorrow. Temperatures will continue to run several degrees above normal, so hot and humid conditions will persist as well during this period. Drier and potentially hotter conditions possible heading into the weekend. && .DISCUSSION... Shower and thunderstorm activity have dissipated for the most part across the region, after a very active afternoon/evening/early overnight yesterday. The outlook for today will be dependent on an ongoing convective complex that is mainly across southern Arizona, as clearing skies will be necessary to improve shower/storm chances across the region today. That being said, higher terrain forecasted thunderstorm chances are still around 30-40%, as HREF ensembles continue to show decent instability in excess of 1000 J/kg. However, some low level inhibition will moderate surface-based convection, as model soundings would suggest surface parcels will need to rise several thousand feet to realize the available instability, at least in the higher terrain. Based on the mean SE-E flow across the region, outflow activity from convective activity along the Mogollon Rim looks less likely to traverse over the higher terrain areas today, with the consensus hi-res model analysis depicting most convective activity remaining north of the region across Yavapai County. Despite the mean flow being primarily easterly, the most noteworthy shower/storm activity across the region may be the low chance (15-25%) of southwesterly moving outflows that could spark convection late this afternoon and evening across central to western Maricopa County and eventually into La Paz and Yuma Counties late this evening according to a couple of the HREF members. Otherwise, temperatures are expected to run several degrees above normal today, as widespread Moderate HeatRisk persists. Heading through the middle of the week, peak ridging anomalies will begin to wane, as a troughing system begins to move into the Pacific Northwest. This change in weather pattern will usher in some dry westerly flow, which is the cause of lower moisture levels heading into the weekend. Despite there being height falls across the region through Thursday, temperatures will continue to hover several degrees above normal as slightly drier conditions settle into the region. Thunderstorm chances will wane as a result of this change in pattern as well, with daily chances dissipating below 15% for the higher terrain by Friday. Heading into the weekend, the troughing feature over western CONUS will slide off to the east, resulting in a rebound in mid-level heights and a return of southerly to southeasterly flow, which will enhance moisture levels once again. These trends are generally the ensemble consensus at this point, but handling of a secondary trough moving into the Pacific Northwest will dictate the magnitude of building heights and increasing moisture levels heading into next week. Due to these generalized trends, better daily shower and thunderstorm chances would be on the increase for eastern/southeastern regions of Arizona. Temperatures will continue to hover several degrees above normal with this pattern change, but no excessive heat is expected to develop over the extended period at this time. && .AVIATION...Updated at 1825Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: VFR conditions are anticipated through the TAF period under SCT- BKN mid and high level clouds. Some light showers/virga are passing through the metro area at this hour but are not expected to impact any of the terminals. Winds have begun to establish out of the SW/W, and a westerly component is expected to prevail through the remainder of the TAF period (aside from some very light speeds below 5 kt and variability early tomorrow morning). The greatest forecast uncertainty is the direction/timing of any outflow boundaries making their way into the Greater Phoenix Area. This will likely depend on where the strongest convection occurs today, but the current best timing for outflows would be as early as 00Z. Thunderstorms are expected to stay to the north of the terminals over the high terrain, which would lead to a gusty outflow boundary from the north, though some guidance indicates the potential for storms making their way into western Maricopa and eastern La Paz Counties this evening, which could send an outflow from the NW/W. A 10-20% chance of VCSH/VCTS remains for all the terminals this afternoon and this evening. Southeast California/Southwest Arizona including KIPL and KBLH: VFR conditions are expected at the SE California terminals through the period. Winds will continue to be southeasterly at KIPL and southerly at KBLH through most of the day. Expect some breeziness this afternoon with gusts up to 20-25 kts at KBLH. SCT mid to high lvl clouds will progress over the region, otherwise skies should remain mostly clear. && .FIRE WEATHER... Monsoonal moisture will continue to result in daily chances for shower and thunderstorm activity. The higher terrain areas will see the greatest potential with some locally heavy rainfall with any storms that develop. Best chances for storms are today, with a gradual decrease in chances/coverage through Friday, where chances drop around 15% or lower. Chances for wetting rains will generally remain around 10-20% for the higher terrain areas and 5-10% for the lower deserts of south-central Arizona today, before dropping below 10% across the region starting Thursday. With the elevated moisture in place, MinRH values through the middle of this week will range between 30-40% across the far eastern districts to between 15-25% across the western districts before slowly drying during the latter half of this week. Winds will follow their typical daily tendencies, with gusty outflows from any thunderstorm activity anticipated over the next several days. Temperatures average several degrees above normal through the forecast period. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Young AVIATION...Whittock/Salerno FIRE WEATHER...Young/Frieders