Sunrise 5:50 AM   Sunset 7:03 PM Moonrise 3:26 PM   Moonset 3:56 AM

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FXUS65 KPSR 200535 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 1035 PM MST Fri Apr 19 2024

UPDATE
Updated 06z Aviation Discussion.

SYNOPSIS
Hot, above normal, temperatures and mostly sunny skies will persist through early next week. Daily high temperatures in the 90s are expected across the lower deserts, with the hottest days on Sunday and Monday, will lead to widespread minor heat-related health risks. A weak passing disturbance this evening will lead to breezy to locally windy conditions in southern California.
Otherwise, winds will be light through this weekend. A weather system later next week is forecast to regionally cool temperatures back down and increase breezes.

DISCUSSION
Above normal temperatures, leading to widespread Minor HeatRisk, will continue daily through early next week, with lower desert high temperatures reaching into the 90s most days. There is a weak, low- amplitude, shortwave trough seen in WV satellite this afternoon, pushing eastward into SoCal. Given the low amplitude, little if any change to the temperatures are expected. High temperatures today will be very similar to yesterday, with most areas reaching the upper-80s to lower-90s, as there has been very little change in the lower tropospheric thermal profile over the past 24 hours. Saturday will also be similar, despite the passage of the shortwave.
Following the shortwave, heading into late this weekend and early next week, stronger positive height anomalies will build over the Southwest with a transient ridge of high pressure passing through the region. This will allow temperatures to warm another few degrees, with lower desert highs pushing into the middle to upper 90s Sunday and Monday. The NBM spread continues to support a ~10-30% probability for 100+ F highs in many of the lower desert valley locations Sunday-Monday, including Phoenix, with very localized higher probabilities in some of the typical hottest spots, like Phoenix Sky Harbor and on the west side of Salton Sea.

The one sensible weather impact the weak shortwave moving in today will bring is an increase in winds in Southern CA, primarily late this afternoon through at least early tonight. Sundowner winds into the Imperial Valley could briefly peak up to 30-35 mph, with a 10% probability of exceeding 35 mph. Winds will be highest in the southwest corner of Imperial County, along I-8, where wind gusts are expected to exceed 40 mph (100% HRRR probability) and could briefly exceed 50 mph. As a result, a Wind Advisory has been issued for that southwest corner.

Model ensemble guidance is supporting a Pacific trough, digging south in the eastern Pacific early next week before slowly transitioning inland into the Western CONUS during the latter half of next week. There is still a decent amount of uncertainty with this next weather system, especially with the depth of the trough, but it should at least lead to a gradual cool down next week. The latest NBM suggests highs will fall back into the 80s by the end of next week. The negative height anomalies across the West may then persist for several days with reinforcing shortwaves. Any potential for rain still looks very low at this time, less than 10% across the southern lower deserts.
The Desert Southwest is heading into the dry season and fire weather season. Climatologically it becomes difficult to see much rainfall, even if the NBM may be suggesting chances in the forecast. As with any spring weather system, breezy conditions can typically be counted on.

AVIATION
Updated at 1750Z.

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

Virga or sprinkles currently moving through the metro will subside over the next few hours. Otherwise, winds will follow their typical diurnal patterns. Wind speeds will generally be aob 10 kt through the period. SCT to BKN skies will become mostly clear by daybreak tomorrow morning.

Southeast California/Southwest Arizona including KIPL and KBLH:

Wind speeds 10-15 kts will calm to aob 6 kt by the early morning hours and through the remainder of the period. Skies will remain most clear.

FIRE WEATHER
Dry conditions and above normal temperatures will persist through the coming weekend as lower desert highs top out each day mostly in the low to mid 90s. Winds today will pick up during the afternoon with gusts to around 20 mph in most locations. Winds Saturday will continue to follow diurnal daily trends with any afternoon breeziness in the mid teens. Min RHs will continue to fall into the 5-15% range each day, while overnight Max RHs mostly stay in a 25-45% range for most places. A cooling trend is forecast by the latter half of next week eventually bringing temperatures back down to normal or below normal late next week.
Breezy to locally windy conditions are also expected for much of next week with daily afternoon gusts commonly reaching to between 20-30 mph. Humidities are likely to stay quite low next week with daily Minors of 10-15% through the middle of the week before some improvement is forecast to around 20-25% late week as temperatures cool down.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...None.
CA...Wind Advisory until 5 AM PDT Saturday for CAZ562.

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