609 FXUS65 KPSR 162357 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 457 PM MST Wed Apr 16 2025 .UPDATE... 00Z Aviation Discussion. && .SYNOPSIS... Near to slightly above normal temperatures will be common this afternoon before noticeable cooling takes place through the remainder of the workweek as a weather disturbance traverses the region. This unsettled period will also result in periods of breezy to locally windy conditions along with chances for rain showers, with the best chances confined to the Arizona high terrain. Once this system exits, a quick warmup back to near and above seasonal temperatures will ensue. && .DISCUSSION... Current 500mb analysis reveals a myriad of weather regimes stretched out across the CONUS, with multiple areas of troughing over the coasts, and high pressure centered over the the Plains. Closer to home, we find ourselves in a bit of a transition zone, with the above-mentioned ridge beginning to push further east, while a closed upper-low spins just off the Southern California Coast. This cut-off will slowly inch closer toward the Desert Southwest over the course of the next few days but as it does, another shortwave, currently located over southern Canada, will dive south across the Great Basin. These disturbances will eventually merge right over Arizona and setup a somewhat unsettled, but noticeably cooler, end to the workweek. Before we get to that point however, one more day of near to above normal temperatures is in store as lower desert highs range from the mid 80s to lower 90s. The lower end of that range will favor the deserts of SE California and SW Arizona due to their closer proximity to the Eastern Pacific low. Regional pressure gradient enhancement will also result in breezy to locally windy conditions for portions of our forecast area this evening. Widespread gusts of 20-25 mph will be common, with higher gusts expected for the typical downsloping areas in SE California. Due to the high probabilities (>90%) of seeing gusts exceed 40 mph over the far southwest corner of Imperial County, a Wind Advisory has been posted for this area through tonight. It is not out of the question to see similar gusts further east toward the Imperial Valley even the Colorado River Valley, but any advisory level gusts are expected to be sporadic. As we approach the end of the workweek and the two aforementioned disturbances merge, a noticeable pattern shift will take place across the Desert Southwest. Noticeably cooler air will filter in starting Thursday when afternoon highs will remain below seasonal values, with highs generally in the middle 70s to lower 80s for a few spots. Due to the residence time of the newly amplified system, these cooler-than-normal temps will continue into Friday, when lower desert high are not expected to make it out of the 70s. Many spots will be a good 5-10 degrees below normal for this point in April during this timeframe. Something else that will need to be monitored will be the potential for rainfall during the period from Friday into early Saturday. The regional moisture profile will increase, which will likely be enough to produce some terrain induced shower activity for areas to the east of the Phoenix metro. One question that remains is will the cold core and associated dynamic ascent will reach far enough to spark some shower activity over lower desert areas of south-central Arizona. At this time, the global models do not seem to agree on this variable but hi-res data should provide some clarity over the next day or so. An enhanced regional pressure gradient will remain in place so more episodes of breezy to locally windy conditions will persist into at least Saturday. Once this system ejects toward the Plains by Saturday, a quick day- to-day warmup will ensure, with above-normal temperatures returning by the start of next week. The good news is, positive height anomalies are not expected to increase to the extent that they did last week, so triple digit heat is not expected to return during the next 7-10 days. Quasi-zonal flow will translate to lower desert highs in the upper 80s to lower 90s and dry conditions as when head into the latter portion of April. && .AVIATION...Updated at 2350Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns are anticipated through the forecast period. Winds have been slow to shift out of the W-SW at KPHX, but are expected to finally shift by the issuance of this forecast. There will also be intermittent gusts into the 20-25 kt range through this evening. Winds will attempt to switch back out of the E late tonight, but are more likely to remain out of the S-SE due to the presence of a low-level jet. Winds will return out of the WSW at all terminals late tomorrow morning. Around sunrise tomorrow morning, model guidance and forecast soundings continue to suggest a low cloud deck developing around 4-5 kft. There is a low chance that this deck will become BKN, but will only persist for a few hrs before scattering out. Southeast California/Southwest Arizona including KIPL and KBLH: The primary aviation concern through the TAF period will be gusty winds and temporary restrictions in vsby due to BLDU at KIPL this evening into the early overnight hours. Wind directions will generally favor S-SW at KBLH and W at KIPL with gusts between 20-25 kts at KBLH and 25-30 kts at KIPL. There will also likely be a period of stronger gusts as high as 35-40 kft at KIPL over the next few hours. Speeds will diminish slightly early tomorrow morning before picking back up again in the afternoon. Skies should remain clear && .FIRE WEATHER... Above normal temperatures will cool to below normal levels during the latter half of the week as a weather system moves through the region. Ahead of this system, gusty afternoon winds will be common today while seasonally low humidity values result in an elevated fire danger. Cooling temperatures and a modest increase in moisture will allow humidity levels to gradually increase the remainder of the week precluding widespread critical thresholds. In general, minimum afternoon humidity levels in the teens will be common today with values increasing closer to a 20-30% range during the latter half of the week. Early next week, warming temperatures and lowering RH values will return to the districts. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...Wind Advisory until 6 AM PDT Thursday for CAZ562. && $$ DISCUSSION...RW AVIATION...Salerno FIRE WEATHER...18