textproduct: NWS Phoenix

UPDATE

Updated 00Z Aviation Discussion.

KEY MESSAGES

- High pressure lingering over the area will result in dry and tranquil conditions and above normal temperatures for today.

- A more unsettled pattern develops starting Friday and persist well into next week as a series of weather disturbances will bring occasional rain chances and cooling temperatures.

SHORT TERM /TODAY THROUGH SATURDAY/

Latest objective analysis shows upper-level ridging persisting over the Desert Southwest. This will result in another day of dry and tranquil conditions with mostly clear skies. Temperatures will once again be above normal with afternoon highs topping out in the middle 80s across much of the lower desert locations.

By late tonight through early Friday, the overall synoptic pattern is expected to shift as an upper-level shortwave trough moves in from the eastern Pacific. This troughing feature will result in increasing moisture levels through Friday morning and afternoon as PWATs rise close to 200% of normal. With the increasing moisture, rain chances will also be on the increase. Given that much of the energy associated with this shortwave will remain sequestered across far southern AZ into northern Mexico, the greatest shower coverage is expected to remain mostly confined across southeastern AZ with some isolated to widely scattered showers extending into central AZ. While most of the shower activity will remain relatively light, a few isolated thunderstorms resulting in briefly heavier rainfall rates cannot be ruled out given that there will be a least a few hundredths J/KG of CAPE present. Nevertheless, the activity should be inconsequential with average total rainfall accumulations expected to range between a few hundredths of an inch across the lower deserts to at most 0.10" across the higher terrain areas.

On the heels of this initial shortwave bypassing to the south, another shortwave will quickly move in from the northwest from early Saturday morning through Saturday afternoon. This shortwave, however, will mostly be bypassing to the north. As a result, the greater shower coverage will be mostly confined across the AZ High Country with some of the activity affecting mainly the foothills and higher terrain areas north and east of Phoenix metro, with the lower deserts expected to remain mostly dry with rain chances limited to less than 20%. Similar to the Friday system, rainfall amounts for the most part will remain light with average amounts ranging between 0.10-0.25". As the shortwave quickly exits to the east by Saturday evening, rain chances will come to an end.

With these disturbances moving through the Desert Southwest, temperatures Friday and Saturday will be on a cooling trend. Afternoon highs on Friday will top out in the mid to upper 70s across much of the lower deserts, with a few areas potentially reaching 80 degrees across the western deserts. Even cooler temperatures in the low to mid 70s are expected on Saturday with some areas reaching into upper 70s across the western deserts.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

Sunday is slotted to be a down day for shower activity with a brief period of shortwave ridging and some slight dry air advection from the northwest. This will lead to considerably less clouds and virtually no rain chances. Models continue to forecast one after another northern Pacific waves being ejected southeastward toward the U.S. West Coast with the next potential system reaching the California coast early Monday before reaching our region Monday night into Tuesday. This may even be followed by another system during the second half of next week. However, it is too early to have any good sense on the track of these systems as they could move directly through the Desert Southwest or mostly miss us to the north, so continued monitoring will be needed. NBM/WPC PoPs of 30-70% are still in the forecast for the Tuesday disturbance, but that could easily change depending on the eventual track. So far, any system that may move through is not expected to carry anything more than average moisture, so any rainfall amounts are likely to be on the lighter side with no flooding concerns expected at this time.

With the aforementioned shortwave ridging briefly moving in Sunday, temperatures will slightly warm into the middle to upper 70s through Monday. A more significant cooling trend is then expected by the middle of the week as the series of weather systems moving in from the northwest will likely usher in a cooler air mass with afternoon highs trending more towards the upper 60s to low 70s.

AVIATION

Updated at 2355Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: A period of VCSH/SHRA with gusty erratic winds and CIGs as low as 6-8K ft AGL is anticipated Friday afternoon, mainly between 20-03Z. An isolated storm or two may also develop, but chances are too low (10%) for inclusion in the 00Z TAF package. Light easterly winds are favored through Friday morning, although a brief period of light VRB is expected this evening and directions may briefly (1-2 hrs) veer S-SW. There is low to moderate confidence winds will veer SSW-SSE by Friday afternoon. SCT to BKN mid and high clouds will be common through most of the TAF period. Lower clouds, with bases around 4-6K ft AGL, are expected Friday night into Saturday morning.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are expected over the next 24 hours. Winds at KIPL will favor a W'rly component through most of the TAF period. KBLH will see VRB through much of tonight and Friday morning before an increase in S'rly winds develops. Wind speeds at both terminals will remain light through Friday morning and then increase up to 8-12 kts in the afternoon and evening with occasional gusts up to 20 kts. Mostly clear skies will continue over the area through tonight and then clouds will increase Friday morning, with lowest bases down to around 7K ft AGL.

FIRE WEATHER

The dry conditions and above normal temperatures will persist through the rest of today. A more unsettled weather pattern is expected to develop starting on Friday and persist well into next week as a series of weather disturbances moving through the region will bring occasional rain chances and cooler temperatures. Minimum humidity values through today will range between 20-30% for the lower deserts to 30-40% for higher terrain areas, while overnight recoveries stay good to excellent at 40-70%. Higher minimum humidity values above 30% are expected area wide starting Friday and are expected to remain elevated through much of next week. Expect overall light winds today before increasing Friday through early Saturday, mainly across the western districts, with peak gusts mostly staying under 25-30 mph.

HYDROLOGY

Gila: A Flood Warning remains in effect from Painted Rock Dam through the Dateland area through at least early next week due to water released from the dam. Water release levels have now risen to 3000 cfs and are expected to remain at this release level through the next several days. This will have the potential to flood farm fields and low-water crossings along the river downstream from the dam.

PSR WATCHES/WARNINGS/ADVISORIES

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