Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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193 FXUS65 KPSR 120810 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 110 AM MST Sun May 12 2024 .SYNOPSIS... Temperatures will warm into an above normal category this week with many lower desert communities nearing or exceeding 100 degrees most days. Dry springtime conditions will also persist with the usual late afternoon breeziness. In addition, occasional showers over the mountains of northern and eastern Arizona may support erratic, gusty winds descending into the lower deserts during the evening hours. && .DISCUSSION... East Pacific/western Conus omega blocking was in the process of breaking down early this morning with a four corners closed circulation center comprising the eastern footing of the block ejecting into the southern/central high plains. With the entire decaying pattern translating eastward, dampened high pressure ridging with modest height rises was edging into the Southwest resulting in an abbreviated warming trend. With H5 heights only peaking near 578dm over the next few days, guidance spread remains very narrow suggesting temperatures 4F-8F above normal. This should equate to only the warmest lower elevation communities reaching 100F, and merely localized moderate HeatRisk through Monday. Although the aforementioned four corners circulation was exiting the region, residual midlevel moisture juxtaposed with steep lapse rates and subtle subtropical jet energy may yield a few high based afternoon showers over the Mogollon Rim and mountains of eastern Gila County. Granted measurable rainfall would be isolated, however NBM POPs appear too low given a large subset of HREF members suggest a few cells leaking into the eastern CWA. Regardless, the greatest impact from any activity would be erratic, gusty outflow winds affecting any of the ongoing wildfires, and even potentially surviving into lower desert communities. During the middle of the week, ensemble members remain in good agreement depicting the southern extension of the wave responsible for dislodging the blocking pattern propagating into the Southwest. This evolution will reintroduce modest height falls back across the forecast area as H5 heights retreat closer to 572dm yielding a brief respite in temperatures closer to the seasonal normal. While not really importing any additional moisture, this shortwave looks to be the next feature to support high based mountain showers, and eventually the prevailing northerly flow on the backside of this low center would be favorable towards more robust propagation of gusty outflow winds into lower desert locations. Towards the end of the week, forecast uncertainty grows as a weakness in the midtropospheric height field may linger over the SW Conus prohibiting stronger ridging from building into the region. Ensemble means indicate H5 heights rebounding back near 580dm with high temperatures returning 4F-8F above normal, however the more extreme ensemble members hint at H5 heights closer to 585dm. Thus, the upper 25th percentile bounds of NBM output indicates some of the warmest locations over the weekend could be flirting with the 105F threshold and more expansive moderate HeatRisk should the stronger ridge solution comes to fruition. && .AVIATION...Updated at 0529Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: There is uncertainty in wind directions tonight, especially at KPHX. Northerly winds now may shift back west for a few hours with some variability. Confidence in the east shift at KPHX is low and may occur as late as 14-15Z. The other terminals will see more typical diurnal tendencies. Light variability is expected at all terminals through Sunday morning followed by westerlies prevailing by noon local time. West winds will increase up to 7-10 kts with afternoon gusts up to 15-20 kts. SKC will prevail with the exception of a few cumulus to the north Sunday afternoon. Southeast California/Southwest Arizona including KIPL and KBLH: Light winds will prevail through the night at both terminals with W to NW component favored at KBLH, and W at KIPL. Light variability is expected at both terminals Sunday morning. Winds shift back N at KBLH and W at KIPL Sunday afternoon with sustained speeds up to 10 kts. Sundowner winds at KIPL Sunday evening may lead to occasional gusts up to 20 kts. SKC will prevail. && .FIRE WEATHER... Periodically gusty winds, dry fine fuels, and low humidity levels will yield a locally elevated fire danger this week. Temperatures will maintain an above normal level with seasonably dry weather persisting across the districts. Minimum afternoon humidity levels around 10% will be common across lower desert elevations with values in the teens over higher terrain areas. Overnight recovery will range widely from poor to fair in a 20-50% range. Afternoon breeziness with gusts 20-25 mph will be common over most areas with some enhancement possible in far eastern districts due to high based showers over mountains during the first half of the week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...18 AVIATION...Benedict FIRE WEATHER...18