textproduct: NWS Phoenix

KEY MESSAGES

- Temperatures will cool a few more degrees the rest of the week, however remain in a slightly above normal range.

- Breezy conditions will develop along the Lower Colorado River valley and Arizona high terrain on Wednesday, then return to area over the weekend.

SHORT TERM /Today through Thursday/

Early afternoon objective analysis depicts a 590dm H5 anti-cyclone centered over western New Mexico slowly being dislodged and de- amplified by the combined effort of subtropical energy lifting north from the Baja into the SW Conus and stronger troughing entering the Pacific NW. As such, H5 heights within the forecast area have eroded into a 584-588dm range providing slight cooling versus yesterday, and most pronounced over the western CWA. Otherwise, only a narrow midlevel moisture band associated with Baja shortwave will pass through the region with some virga (and possible erratic winds) as a result.

Over the next couple days, high pressure aloft will further be displaced eastward with a progressive flow pattern resulting in additional modest heights falls across the SW Conus. Some measure of weak troughing/quasi-zonal flow will prevail over the region with H5 heights generally hovering in a 580-584dm range. Ensemble guidance spread is rather narrow leading to excellent forecast confidence of high temperatures mostly 6F-8F above normal, while clear skies and a dry airmass promote efficient nocturnal cooling and lows not far from climatology. This pattern of weak troughing/height falls will support deep mechanical mixing and gusty afternoon winds, though nothing unusually strong for mid May.

LONG TERM /Friday through Tuesday/

The weather pattern later this week is expected shift to a more zonal westerly dry flow pattern, but with some influence from passing troughs to our north. The drying flow will result in clear to mostly clear skies Friday-Saturday with temperatures remaining quite stable averaging 5-7 degrees above normal. Ensembles are currently favoring a larger Pacific trough moving through the Pacific Northwest this weekend bringing lower heights as far south as the Southwestern U.S. NBM/WPC temperature guidance suggests daytime highs falling back more into the upper 90s by around Sunday. Otherwise, daytime gusty winds will return to the region over the weekend in association with the aforementioned trough passage.

AVIATION

Updated at 1705Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds will be the primary weather issue through Wednesday afternoon under periods of mid/high cloud decks. Confidence is good that a westerly component will develop by early afternoon, then obtain enhanced gustiness early/mid evening. There is some uncertainty in the magnitude of wind gusts, and virga may create some erratic directions and speeds for a few hours. Otherwise, the switch to the nocturnal easterly component should be delayed again tonight. A period of 8-12kt southerly cross runway winds are likely Wednesday late morning/early afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: Periods of gusty winds will be the main weather issue through Wednesday afternoon under occasional mid/high cloud decks. A S/SE component will be favored across the area through the afternoon with directions at KIPL likely abruptly shifting to SW early evening. Confidence is excellent that gusts 20-30kt will become common through the afternoon and early evening before decoupling and weakening overnight.

FIRE WEATHER

Hot, dry, and locally breezy to windy conditions will result in elevated fire weather potential this afternoon across the Lower CO River Valley. Wind gusts of 20-30 mph along with RHs 7-10% are expected across the Lower CO River Valley. Elsewhere today, winds will be lighter but with afternoon gusts of 15-20 mph possible. Wednesday will bring another round of breezy winds over southeast California and the Arizona high terrain with elevated fire weather conditions again a possibility. Temperatures today will be 10-15 degrees above normal dropping to 5-8 degrees above normal starting Wednesday. Winds will diminish starting Thursday, but very dry conditions will continue to prevail.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST this evening for AZZ537-540- 542>544-546-548-550-551.

CA...None.