textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion.

KEY MESSAGES

- Breezy conditions will linger as a weather system moves southwest of the area and settles off the Baja California Coast on Sunday.

- The weather system will then pass just south of the area early next week, increasing chances for showers and potentially some thunderstorms.

- High pressure returns midweek, allowing temperatures to warm back up into a well above normal category, with lower desert highs likely reaching the nineties by Thursday.

SHORT TERM /TODAY THROUGH SUNDAY/

Midlevel water vapor imagery and 500 mb RAP analysis place the center of an upper low just off the West Coast of the northern Baja. Height falls to the southwest have lessened, and so surface winds have already begun to relax across the area. Gusts this morning to between 25-40 mph were common across Southeast California, with lighter, yet still gusty winds across portions of South-Central AZ in a 15-30 mph range observed at times. Ensembles remain in good agreement that the upper low will stay far enough to the southwest on Sunday that positive midlevel height anomalies will fill back in over the region, allowing for a quick warmup into the 80s across the lower deserts. GFS bufr soundings also indicate at least a weak midtropospheric inversion, perhaps indicative of subsidence on the backside of this upper low and aiding in warming thermal profiles. Regardless, the spread shown in the probabilistic NBM guidance is incredibly narrow for KPHX, yielding excellent confidence in afternoon high temperatures achieving near 10-13F above normal for South-Central AZ and 6-10F above normal across the western deserts (closer to the low).

LONG TERM /MONDAY THROUGH FRIDAY/

The cut-off low will be fairly stationary over the weekend but come Monday afternoon will begin its journey eastwards over Northern Mexico/Southern Arizona. Moisture advection into the region associated with this system will begin early Monday morning and will peak Monday evening into Tuesday morning, with PWATs around 180-220% of normal. PoPs and QPF have once again increased since the previous forecast package, however, this high run-to-run variation could be a result of the global model's poor handling of this cut-off low. Despite this uncertainty, this recent shift in guidance has resulted in a more credible thunderstorm potential across the area. Ahead of the low, upper level diffluence and vorticity advection may be sufficient to realize upwards of 250-500 J/kg of MLCAPE (as indicated in KYUM GFS bufr soundings) across Southwest AZ on Monday afternoon. The eastward progression of the low will push the thunderstorm threat over South-Central AZ later in the afternoon into Monday evening. With these thunderstorms, small hail will possible, with 500 mb temperatures in a -20C to -23C range and decent instability in the hail growth zone. Bulk shear between 30-50 kts ahead of the upper will also be sufficient to organize a few storms. Coverage of showers/storms is still expected to be scattered at best, and not all will see rainfall. Locally higher totals will be possible in t-storms, but average totals across South-Central AZ will range from 0.05-0.25", with higher totals focused east/southeast of the Phoenix area.

As the core of the cut-off low progresses eastwards over Northern Mexico/ Southern Arizona, temperatures will cool into the upper 70s for Monday afternoon. Afterwards, by Tuesday evening the cut-off low will be ejecting into Western Texas and into the Plains. Once the low is to the region's east, upper level ridging will take place over the Desert SW. With strong ridging moving in, temperatures by mid to late next week will climb to 10-15 degrees above normal, with H5 heights above the 90th percentile of climatological normal.

AVIATION

Updated at 2350Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Periods of elevated easterly winds will be the primary aviation weather concern under some passing mid to high-level clouds throughout the period. Easterly winds have subsided to around 8 kts or less this afternoon and guidance is still indicating a brief 3-4 hour period of W-NW flow developing around sunset. Winds will then revert back out of the east late tonight with speeds generally aob 10 kts, although KSDL may see periodic gusts near 20 kts through the overnight hours. All terminals will likely see gusts into the teens to around 20 kts early Sunday morning until the gradient subsides and winds relax in the afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: Periods of gusty N-NE winds under a FEW mid to high-level clouds will be the primary aviation weather concern throughout the TAF period. Gusts upwards of 20-25 kts out of the north will continue over the next couple of hrs before diminishing at both terminals early this evening. Winds at KIPL will shift out of west during the overnight hours and return to the E-SE by tomorrow afternoon. Winds should remain N-NE at KBLH through the period.

FIRE WEATHER

Lingering breezy winds out of a northerly to easterly direction will continue across portions of the area as a weather system settles west of Baja California this weekend. Dry conditions will persist across the region with minimum relative humidity values staying entrenched between 10-15% through Sunday, while overnight recoveries will only reach the 30-45% range. Lingering breezy conditions across southeast California and over higher elevations will continue, leading to locally elevated fire weather concerns before slight increase in moisture arrives Monday. Monday's weather system will help increase MinRHs to between 30-40% with good overnight recoveries before returning to drier conditions by the middle of the week.

PSR WATCHES/WARNINGS/ADVISORIES

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