textproduct: NWS Phoenix

KEY MESSAGES

- Residual moisture may spark a few showers and storms this afternoon, mainly south and east of Phoenix.

- The moisture axis and corresponding rain chances will shift west into southeast California and southwest Arizona during the weekend.

- Temperatures will remain near to slightly below normal through this weekend before warming to slightly above normal by early next week.

SHORT TERM /TODAY THROUGH SUNDAY/

The overall synoptic pattern continues to be defined by an elongated ridge of high pressure extending from the Southern Plains into the southeastern U.S. while a broad trough encompasses much of the Pacific Northwest and west coast. Due to this pattern configuration, the Desert Southwest remains under dry southwesterly flow aloft. Residual low-level moisture from Hurricane Marie, centered well to the west of the southern tip of the Baja Peninsula, remains across much south-central and southeast AZ with dewpoints in the 60s while much drier air with dewpoints in the 30s and 40s encompasses much of southeast CA and southwest AZ. The residual moisture will still combine with strong daytime heating to cause cumulus buildups heading into this afternoon across south-central AZ with the potential for a few showers and storms to develop, mainly across the terrain escarpments. However, as the afternoon progresses, drier air will be filtering in from the west, which will erode the low-level moisture somewhat and thus reduce instability significantly with the latest forecast soundings from Phoenix showing CAPE values dropping from over 1000 J/KG earlier today to less than 100-200 J/KG by this afternoon. Therefore, any convective cells that attempt to develop this afternoon will be very short-lived.

As Hurricane Marie continues to move northwestward well offshore from the Baja Peninsula over the weekend, some additional moisture will be transported northward but this time towards southern CA and southwest AZ as PWATs rise to around 1.6-1.8". Therefore, rain chances heading into this weekend will be mainly confined across these areas with PoPs only topping out between 10-20%. An abundance of mid to upper-level moisture will result in extensive mid-high clouds across much of the area so as a result mid-level lapse rates and thus instability will be very poor with forecast soundings showing little to no CAPE. As a result, any rainfall activity that materializes will be on the light side with little to no impacts. In fact, much of the activity that falls on Saturday across southeast CA and southwest AZ may actually be virga given that the low- levels will remain very dry as dewpoints will still be in the 30s and 40s. Better low-level moisture is expected heading into Sunday, however, the better forcing for ascent from an upper- level jet streak is likely to shift northward towards the Mohave Desert Region, where the best rain chances will be located. Fairly quiet weather is expected this weekend across much of south- central AZ as the lack of instability and forcing for ascent will hinder storm activity.

The continued presence of troughing to our west will continue to maintain temperatures near to slightly below normal levels through the weekend with highs generally in the upper 90s to low 100s, with Saturday expected to be the coolest day. In fact, due to the presence of abundant mid to high clouds across much of the western deserts on Saturday, temperatures may struggle to reach the triple digits. The associated height falls from the troughing to our west will also result in another round of afternoon/early evening breeziness today across much of southeast CA and southwest AZ with peak gusts around 20-30 mph, potentially reaching up to 40 mph in the typical wind prone areas of far southwest Imperial County. Slightly weaker winds are anticipated during the weekend.

LONG TERM /MONDAY THROUGH THURSDAY/

Deterministic and ensemble guidance continue to differ on the magnitude and positioning of the subtropical ridge early next week which will dictate how hot temperatures get and how soon rain chances will return to our area. Both the EPS and GEFS show the ridge strengthening over the Southern Plains through the middle of the week which will allow hghts aloft to increase across much of the Desert Southwest. In turn, temperatures will also increase from near normal Monday to slightly above normal on Tuesday. The temperature forecast becomes much more unclear heading into the middle of next week with large spreads in the NBM interquartile range. This is likely due to differences in the magnitude of the ridge with many EPS members showing a stronger ridge with 500 mb hghts approaching 596-598 dam while the GEFS shows slightly lower overall hghts. For now NBM temperatures show a cooling trend after Tuesday which is likely due to an increase in moisture as southeasterly flow aloft returns to the lower deserts.

PWATs are expected to increase back to around 1.5-1.8" by the middle of next week which will bring rain chances back into the picture by the Wednesday-Thursday timeframe when PoPs increase to around 20-40% areawide. The GFS is even showing an easterly wave/inverted trough arriving into southern AZ along with additional tropical Pacific moisture on Wednesday which could boost rain chances significantly, but we will likely have to wait for more run to run consistency as these features are always difficult to resolve at longer time scales. Either way, most of the GEFS and EPS members are showing measurable precipitation across portions of the area by the middle of next week.

AVIATION

Updated at 1826Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds will follow a similar pattern to yesterday, with a SSE-SSW direction for most of the day and a veering trend to W-SW this evening. Wind speeds will mostly be in the 5-10 kt range with occasional gusts into the teens. Scattered cumulus, based around 10K ft AGL, will develop through this afternoon with a very low chance (5-10%) for a brief isolated shower or storm late this afternoon and evening. Light E'rly winds will eventually develop after midnight tonight and then a S'rly component will develop again by midday Saturday, but a quicker more pronounced W'rly shift is anticipated Saturday afternoon. SCT high clouds will overspread the area Saturday.

Southeast California/Southwest Arizona including KIPL and KBLH: Afternoon through early evening gusty winds will be the main weather impact through the TAF period. Gusts 20-25kt will be common at both terminals, from the S-SW at KBLH this afternoon and from the W-SW at KIPL this evening. Speeds will relax overnight and early morning where brief periods of nearly calm conditions will exist. Mostly clear skies will prevail though this evening before mid and high clouds overspread the area heading into Saturday.

FIRE WEATHER

Residual moisture may spark a few showers and storms this afternoon across south-central AZ. Rain chances will expand westward through this weekend, becoming focused over the western districts Saturday and Sunday. However, the chances for wetting rains will remain very low at less than 10%. Afternoon minimum humidities will range from 7-15% across southeast CA and between 20-35% for the the AZ deserts today and will likely increase above 20-25% areawide starting this weekend. Overnight recoveries will range from poor across the western deserts to good across the eastern districts tonight and increase to good areawide this weekend. Winds will remain elevated out of the south to southwest, with the strongest gusts in Southeast CA and along the Lower Colorado River Valley peaking between 20-30 mph this afternoon/early evening. Lighter winds, generally around 15 mph or less will transpire this weekend.

PSR WATCHES/WARNINGS/ADVISORIES

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