Sunrise 5:23 AM   Sunset 7:26 PM Moonrise 4:03 PM   Moonset 3:09 AM

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FXUS65 KPSR 190955 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 255 AM MST Sun May 19 2024

SYNOPSIS
A weather disturbance will slide primarily north of the region early this week, but it will allow temperatures to retreat closer to the seasonal normal. This system will also bring an increase in winds, especially during the afternoon and evening hours with Monday having the strongest winds and greatest impacts. Very tranquil weather with near normal temperatures will prevail during the second half of the week.

DISCUSSION
A Pacific upper level trough is gradually shifting southward across Pacific Northwest into the Great Basin with a much weaker southern branch shortwave trough now tracking through the Desert Southwest. The disturbance moving across our region will help to lower temperatures today several degrees from yesterday's highs in the lower 100s, while winds will become breezier over much of the area. The main forecast concern over the next couple days will be the increased winds combining with low humidities to create elevated to near critical fire weather conditions. Wind gusts this afternoon and early evening are expected to easily reach into the mid 20s areawide to 30-35 mph across portions of southeast California. As the trough to our north continues to shift farther south, the gradient over our region will increase into Monday while another shortwave trough currently well west of southern California tracks through our region. Both of these features will enhance winds further with wind gusts Monday afternoon and early evening likely reaching 25-35 mph across south-central Arizona to 30-45 mph across the western deserts of southeast California through the the Lower CO River Valley. Near critical fire weather conditions are expected over much of the area Monday afternoon.

Temperatures will continue to trend downward on Monday with afternoon highs mostly in the lower 90s, or a couple degrees below normal. The broad troughing over the Western U.S.,including our region, should then persist through the rest of the week as several progressive shortwaves are forecast to track across the Northwestern U.S before sliding just to the north of our region.
This should keep upper level heights fairly stable over our region at between 574-578dm, or right around climatological normal for this time of year. This will keep seasonably dry conditions in place through the coming week with temperatures right around normal. Guidance is still suggesting we will eventually see a warming trend, but as of now that should hold off until around Memorial Day.

AVIATION
Updated at 0550Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns will exist through the TAF period under clear skies. Wind directions will exhibit their typical diurnal tendencies, with afternoon and early evening breeziness out of the SW-W. The SE switch will take hold between 08-10Z at KPHX, with sustained speeds overnight remaining mostly aob 8 kt across all the terminals. Confidence is low in a weak surge of SW winds reaching the terminals over the next few hours, which would act to temporarily increase speeds and slightly delay the SE switch. Speeds are expected to be slightly lower (i.e., gusts peaking around 20 kt) tomorrow afternoon than what was observed today.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns, aside from gusty winds, are anticipated over the next 24 hours under clear skies. Wind directions will remain WSW at KIPL through the period, whereas directions will favor SW to S at KBLH through much of the period.
Gusts to around 20 kt will persist through the early morning at KIPL before calming to aob 12 kt sustained, and winds will soon establish out of the south at KBLH and remain aob 8 kt through tomorrow morning, albeit with some periods of very light speeds and variability. Gusts are expected to redevelop tomorrow afternoon at both terminals, again peaking around 25-30 kt at KIPL and slightly lower at KBLH.

FIRE WEATHER
A disturbance moving mostly north of the districts early this week will force temperatures to cool closer to the seasonal normal while also producing a period of strong, gusty winds. Throughout the week, minimum afternoon humidity levels will fall into the single digits at lower elevations and the teens across higher terrain areas. This will follow poor to fair overnight recovery of 20-40%. Widespread wind gusts as high as 30-35 mph may be common Monday afternoon yielding an extended period of near critical thresholds when combined with low RH and dry fine fuels. Land managers should be cautious for rapid, uncontrolled spread of any ongoing fires or new starts Monday. Otherwise, afternoon gusts of 20-25 mph should be more representative the remainder of the week resulting in a slightly elevated fire danger.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...None.
CA...None.

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