textproduct: NWS Phoenix

KEY MESSAGES

- Relatively stable temperatures with afternoon highs 4 to 8 degrees above normal will prevail through Saturday, then cool closer to the daily normals Sunday into early next week.

- Breezy conditions will return to the area over the weekend with the strongest gusts across Southeast California and the Arizona high terrain.

- Critical fire weather conditions will be possible this weekend, particularly on Sunday for the Eastern Arizona higher terrain.

SHORT TERM /TODAY THROUGH FRIDAY/

Early morning midlevel water vapor imagery reveals southwesterly flow still entrenched over AZ, with some lingering moisture over the eastern half of the state scouring out, resulting in clearing skies. The bulk of subtropical jet energy has shifted east of the forecast area, and so expect a return to lighter winds with only marginal afternoon breeziness. To the west of the area, 500 mb RAP analysis indicates the presence of a SW-NE oriented, elongated weak trough stretching from off the SoCal coast northwards towards a more potent system progressing eastward along the Canada/US border over Montana. While the elongated disturbance to our west appears connected with the more progressive northern stream, ensembles remain in excellent agreement that it will remain largely in place through the end of the work week, helping to hold H5 heights steady near 582 dam over the forecast area. This should result in a near persistence temperature forecast, with afternoon highs around 4F-8F above daily normals and only fluctuating a few degrees day to day into the weekend, near 100F for the typically warmer lower desert communities. However, the dry airmass in place coupled with clear skies will promote effective overnight radiative cooling resulting in comfortable morning lows, near their normal values for mid May.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

The main concern in the long term will be increased winds across the region this weekend leading to elevated to locally critical fire weather conditions. Ensembles show good agreement that a trough in the northern stream will move onshore along the Pacific Northwest Coast early Saturday, followed by a period of amplification and strongly negative midlevel height anomalies becoming established over the Interior West. However, WPC cluster analysis does still show discrepancies in how strong this trough will be and the precise timing, resulting in some uncertainty in how much regional pressure gradients will tighten, and thus the timing and peak magnitude of winds. Several disturbances are likely to rotate about this larger scale troughing feature, affecting the Desert Southwest this weekend into early next week. The current timing of the stronger winds (and associated areas of fire weather concerns) favors southeast California and southwest Arizona Saturday, the Eastern AZ higher terrain Sunday, and potentially the Lower CO River Valley on Monday. Wind and/or fire weather headlines will likely need to be considered in future updates.

Aside from winds and fire weather concerns, the pattern this weekend will promote cooler temperatures by Sunday. Latest NBM probabilistic temperature guidance shows spread increasing, with IQRs of at least 5F Sunday onward. However, Monday is shaping up to be the coolest of the next 7 days, with many lower desert areas struggling to reach the middle 90s. Negative midlevel height anomalies appear to depart to the north and east during the middle of next week, allowing H5 heights to rebound closer to 580 dam. Anticipate afternoon highs to warm in response through the middle of the week, likely nearing 100F once again for the typically warmer spots across the lower desert. However, the overall pattern/flow aloft does not substantially change, with ensembles generally showing ridging off the West coast and broad anticyclonic flow over the Western/Central CONUS.

AVIATION

Updated at 1045Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns under generally clear skies can be expected throughout the TAF period. The overall wind pattern will follow the typical diurnal tendencies with speeds generally aob 10 kts, with occasional afternoon gusts into the mid to upper teens.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns under generally clear skies can be expected throughout the TAF period. At KIPL, winds will generally be out of the west while at KBLH, winds will generally fluctuate out of the south to southwest. Wind speeds will generally be between 8-12 kts throughout the period. Another round of peak gusts upwards of 20-25 kts will be possible at KIPL during the late afternoon/evening hours.

FIRE WEATHER

Slightly above normal temperatures, dry conditions, and lighter winds with typical afternoon upslope/upvalley breeziness will prevail through Friday. A weather system will move onshore along the Pacific Northwest early Saturday and deepen over the Western US resulting in increased winds across the area this weekend. The strongest winds are anticipate in Southeast CA into Southwest AZ on Saturday, then over the Eastern AZ high terrain Sunday, and this will likely result in elevated to locally critical fire weather conditions. Afternoon minRHs will commonly fall in an 8-15% range through early next week, with overnight recoveries ranging from 25-45% across the area and improving only slightly from there on Saturday and Sunday nights.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.