textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion

KEY MESSAGES

- Chances for light rain will persist over Arizona higher terrain locations east of Phoenix the next couple days with minimal accumulation.

- Temperatures will gradually warm closer to the seasonal normal through the middle of the week before abruptly cooling later this week. - A Pacific low pressure system moving into the Southwest later this week will result in much better rainfall chances with the possibility of a few embedded thunderstorms.

SHORT TERM /Today through Tuesday/

Early afternoon WV imagery and objective analysis depicts an upper level trough becoming elongated across the SW Conus with one vorticity center ejecting through the four corners, while a secondary circulation slowly moves into SW Arizona. A plume of higher, anomalous PWATs around 1" continues to hover over southern Arizona within the southwest flow on the leading edge of the trough axis, though the majority of this moisture was relegated to the H7 layer and above. Ascent will continue to be maximized ahead of the SW Arizona vorticity center through this evening, with some measure of subsidence and drier midtropospheric air moving into the CWA in its wake. However, enough moisture will remain in the midlevels coincident with favorable cyclonic flow, sheared vorticity, and another subtropical jet streak to support bands of light showers through Monday afternoon. Orographic areas will be primarily favored for accumulating light rain, but even a few isolated showers could affect lower desert locations in south-central Arizona. With the trough finally absorbed into the mean flow by Tuesday, precipitation chances dwindle while modest height/thermal increases briefly spread into the forecast area. As a result, forecast confidence is excellent that temperatures will rebound near, or even a couple degrees above the daily normals.

LONG TERM /Wednesday through Saturday/

By Wednesday, deep troughing and strong negative height anomalies will be established off the central/southern California coast, and poised to move inland the remainder of the week. Ensemble and deterministic modeling have come into much better agreement over the past 24 hours with EPS members largely abandoning the idea of a deeper, slower troughing driving eastward through the CWA. Instead, the preponderance of ensemble output now support previous GEFS solutions showing shortwave energy and the main cold core lifting from southern California into southern Utah in response to anomalous high amplitude, strong ridging stationed over the central/southern plains. However, ECMWF forecasts continue to highlight more robust moisture advection via deep, meridional flow ahead of the trough passage into Arizona, though differences among ensemble members are now becoming much smaller.

Regardless, Wednesday and Thursday continue to have the best window for rainfall potential with the synoptic pattern strongly favoring persistent moist upslope and orographically focused moderate rainfall north and east of Phoenix. Occasional bands of showers will undoubtedly extend into lower desert communities of south-central Arizona with much of SE California/SW Arizona remaining dry. The adjusted northerly track lifting away from the CWA also decreases the potential for strong thunderstorm development, though a few embedded storms would still be likely before rapid drying behind a frontal passage sweeps through the region Friday. With better ensemble agreement, the full suite of the NBM temperature spread has narrowed slightly during this time frame with the expectation of additional forecast confidence in future iterations showing a rapid descent towards readings around 10F below normal by the end of the week.

AVIATION

Updated at 2320Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected during the TAF period. There will be a break from persistent E'rly flow this evening as diurnal trends try to gain the advantage once again, but a familiar full W'rly shift is not likely to emerge. Winds will once again contain an E'rly component overnight, but speeds should be noticeably lower than the past few days. There is a signal that isolated SHRA may move within the vicinity of the terminals tonight into Monday morning, but chances of that occurring currently stand at 10% or less as most rainfall should remain over the eastern portion of the airspace. After some brief clearing, SCT low and mid-level cloud decks will be common with the lowest bases around 6-8 kft.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected over the next 24 hours under mostly clear skies. Outside of some light W'rly and and oscillations between NE and NW at KIPL and KBLH respectively, winds will be generally light and variable.

FIRE WEATHER

Wind speeds over the next few days will be much weaker than this past weekend with minimal gustiness, however speeds and gust frequency will increase again towards the middle of the week ahead of an incoming weather disturbance. Occasional light showers may continue to impact eastern districts, though wetting rainfall potential is under 20%. Much better rainfall chances will arrive during the middle of the week with amounts greater than 0.50" likely east of Phoenix. Minimum humidity levels in a 30-50% range will be common throughout the week with even higher readings likely across eastern districts. Overnight recovery should be good to excellent resulting in little to no fire weather concerns for at least the next week.

PSR WATCHES/WARNINGS/ADVISORIES

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