textproduct: NWS Phoenix

UPDATE...Updated 18z Aviation Discussion

KEY MESSAGES

- Lingering low pressure will help keep breezy to locally windy conditions in the forecast for today.

- A weather system continues to meander near the region through the start of next week allowing for an increase in rain potential for Monday.

- High pressure, along with consistent above normal temperatures make their return by the middle portion of next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Current RAP40 analysis of H5 heights shows the core of the trough beginning to split, and starting to develop into the cut-off low models have been hinting at the past few days. This low will continue to break off, tightening into a well developed cut-off low throughout today. By this afternoon the center of the low will be over the Northern Baja Peninsula. The negative height anomalies associated with the cut-off will mildly effect todays afternoon highs with temperatures expected in the mid to high 70s across the lower deserts. By tomorrow the cut off low will be just off the NW coast the Baja Peninsula, allowing for H5 heights over the Desert SW to climb near 570-573 dam. High temperatures for sunday in response will be in the upper 80s, with some areas across the lower deserts having 15-25% chance of reaching 90 degrees.

A relatively enhanced pressure gradient will also be present this afternoon, bringing breezy to locally windy conditions especially around the Lower Colorado River Valley and westward. Gusts 25- 35 mph will be common across these areas, with locally higher gusts focused over enhanced terrain features. Given the high likelihood of achieving gusts greater than 40 mph, a Wind Advisory has been posted for portions of SE California for Saturday morning hours.

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 PWAT anomalies around 180-200% of normal. Monday evening into early Tuesday morning will also be the best chances for precipitation across mainly South Central Arizona (25-35%), and Eastern Arizona into the higher terrain areas (45-55%). QPF totals over the past 24 hours have trended upwards with SC AZ now between 0.05-0.15" and the higher terrain areas between 0.15-0.25".

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 1735Z.

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 with gusts upwards of 20-25 kts will be common through the early/mid-afternoon hours before subsiding aob 10 kts late afternoon/early this evening with a northwesterly directional shift anticipated for a few hours after sunset. Winds will then revert back out of the east by the mid- evening hours with speeds generally aob 10 kts, although KSDL may see periodic gusts near 20-25 kts through the overnight hours.

Southeast California/Southwest Arizona including KIPL and KBLH: Periods of gusty northerly winds under a FEW mid to high-level clouds will be the primary aviation weather concern throughout the TAF period. Gusts upwards of 25 kts out of the north will be common through this afternoon before speeds subside early this evening with the wind direction shifting out of west at KIPL during the overnight hours.

FIRE WEATHER

The current passing system continues to bring mostly diurnal winds across the region, and will begin to strengthen bringing breezy to windy conditions this afternoon, mainly in the western districts. 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. Peak wind gusts of 25-35 mph across southeast California and into the high elevations will continue, leading to elevated fire weather concerns before a potential slight increase in moisture arrives Monday. Monday's weather system will help shortly increase MinRHs to between 30-40% with good overnight recoveries before returning to drier conditions by mid next week.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory until noon PST today for CAZ560-561-564-568>570.