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FXUS65 KPSR 181733 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 1033 AM MST Sat May 18 2024

UPDATE
18Z Aviation Discussion.

SYNOPSIS
High pressure will persist over the region this weekend resulting in many more lower desert communities exceeding 100 degrees. A dry weather disturbance will then move north of the region early next week with temperatures retreating closer to the seasonal normal. Occasionally breezier conditions are likely during the afternoon and evenings early next week under mostly clear skies.

DISCUSSION
The shortwave ridge is slowly progressing east across the region with the ridge axis now positioned across eastern Arizona. To the west of the region, an elongated weak upper level trough is beginning to edge into southern California while a closed low hangs back another 800 miles to the west. These features are all part of the southern branch of a split flow regime with the stronger northern branch temporarily staying put across the northern tier states. With H5 heights hovering around 579dm across southern California to 581-584dm across southern Arizona today, high temperatures will again top out around or just over 100 degrees for much of the lower deserts, or 5-8 degrees above normal.

Going into Sunday, the elongated trough to our west along with increasing influence from the trough to our north will begin to knock down our heights aloft. Temperatures Sunday will only drop 2-3 degrees from today's highs, but eventually the current closed low well off the southern California coast is expected to move through our region during the daytime hours Monday bringing further cooling.

The main forecast concern this weekend into Monday will be the increased winds due to the passing shortwave trough and increased pressure gradient with the help of the northern stream trough. Winds will begin to increase already late this afternoon across southeast California with gusts of 30-35 mph possible in some locations through this evening. Similar breezy conditions are likely on Sunday with afternoon gusts commonly reaching 25 mph across the majority of the lower deserts to up to 35 mph across southeast California. Guidance is calling for the strongest winds to occur during Monday afternoon with gusts of 30-40 mph across southeast California to 25-35 mph possible across much of southern Arizona.

The cooling trend will become more noticeable by Monday as H5 heights fall back to between 572-576dm, or right around climatological normal for the period. Temperatures are expected to drop back to around or just below normal starting Monday with highs in the low to mid 90s. These near normal temperatures will persist through at least midweek and likely longer as broad troughing should continue to dominate across the region. NBM forecast temperatures do show a slight warming trend and a bit higher temperature spread later next week into next weekend, but with the bulk of ensemble members keeping at least some troughing over our region our temperatures should easily stay in the 90s.

AVIATION
Updated at 1730Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

VFR conditions with no aviation concerns expected through the forecast period. Winds are beginning to shift out of the WSW, but there could still be an hr or two of southerly crosswinds before ultimately becoming westerly. There will be an increase in breeziness this afternoon with speeds up to 15 kts and gusts in the 20-25 kt range. Winds will diminish after sunset and return to east again after midnight. High clouds will exit the region, with skies becoming clear through the rest of today.

Southeast California/Southwest Arizona including KIPL and KBLH:

VFR conditions and no aviation concerns besides breezy winds are anticipated through the forecast period. Winds will remain WSW at KIPL and S-SW at BLH, becoming elevated and gusty this afternoon.
Both terminals will see speeds up to 15-20 kts with gusts up to 25-30 kts. Gusts could linger past sunset at KIPL. Skies will remain clear.

FIRE WEATHER
High pressure will hover over the region through the weekend with dry conditions and temperatures reaching much above normal. Only a disturbance moving north of the districts early next week will allow temperatures to cool closer to the seasonal normal. Throughout next 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%.
Breezy afternoon/early evening conditions with gusts around 20 mph will be common, though somewhat stronger winds will occasionally be possible in far western districts. The greatest weather concern will occur Monday afternoon where frequent, widespread wind gusts closer to 30-35 mph may be common yielding near critical thresholds when combined with low RH and dry fine fuels.

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

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