textproduct: NWS Phoenix

KEY MESSAGES

- Dry weather will return to the region through the weekend with temperatures hovering a few degrees above normal.

- An unsettled pattern is forecast to set up over the Desert Southwest by the middle of next week, resulting in much cooler and wetter conditions.

SHORT TERM /Today through Saturday/

Latest mid-lvl wv imagery and 500 mb streamline analysis reveals a trough of low pressure situated several hundred miles off the coast of California while shortwave ridging is now building inland over the Desert Southwest. The upper-lvl ridge will be the predominant feature over the region through this weekend, which will promote dry and tranquil weather. Early morning fog has burned off, leaving partly cloudy skies across the lower deserts. Skies may not fully clear until late this afternoon as abundant moisture remains trapped in the boundary layer. Since this low-lvl moisture will be slow to erode, we could see another round of patchy fog overnight, particularly in the same locations as this morning including the Lower Colorado and Gila River valleys. The main caveat will be abundant high clouds which will begin to overspread western portions of the forecast area early Saturday morning which could inhibit fog development. Temperatures are expected to remain around 5 to 7 degrees above normal through Saturday with highs again ranging from the mid 60s to lower 70s and lows mainly in the upper 40s to low 50s across the lower deserts.

LONG TERM /Sunday through Thursday/

The hemispheric longwave pattern will only be slow to advance through the middle of next week owing to stubborn downstream North Atlantic blocking. Ensemble membership remains in excellent agreement indicating low amplitude ridging prevail across the SW and central Conus while East Pacific troughing only slowly edges towards the West Coast. A series of lead shortwaves will almost certainly eject from the longwave trough position early in the week, however only de-amplify and lift into the Great Basin bringing a cold front onshore into cntrl/srn California, but no further. A more defined cold core should drop towards a developing weakness in the midlevel height field into the Southwest during the middle of the week. While a handful of ensemble members still depict an earlier arrival (particularly in the CMC suite), the trend among the preponderance of membership suggests a slower PV passage sometime in the Wednesday time frame.

While low level moisture will not completely be eliminated early in the week, warmer air aloft and rain shadow effects from prevailing W/SW flow will limit any inland deep saturation and rain chances. As usual, NBM POP bias in SE California becomes evident bleeding higher chances off mountains to the west, and have trimmed values back appropriately. It would not be uncommon for thicker cirrus decks to impact daily highs at some point early in the week, however numerical guidance remains consistent in advertising readings a few degrees above the daily normals into the middle of the week. Uncertainty in the precise track and intensity of the PV anomaly moving into the region midweek limits a larger POP mention in the official forecast with the majority of model output leaning towards another weakening wave and limited ascent/precipitation potential.

AVIATION

Updated at 0500Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

VFR conditions and very light winds are expected through the TAF period with SCT to BKN mid and high clouds. Any fog development Saturday morning is expected to stay south of the Phoenix area and is not expected to spread to any of the terminals. Winds will favor a light east through Saturday morning hours followed by a light west Saturday afternoon and evening, with speeds at or below 6 kts.

Southeast California/Southwest Arizona including KIPL and KBLH:

Potential reductions in visibility in fog Saturday morning will be the primary aviation weather concern through the TAF period. Odds of fog at the terminals are lower than Friday morning, with increased mid and high clouds over the area. Wind directions will favor a westerly component, but with extended periods of calm winds and light variability.

FIRE WEATHER

Moisture levels will remain elevated through much of next week with minimum afternoon humidity only falling into a 40-60% range. This will follow excellent overnight recovery greater than 75% region- wide. Very light winds with speeds aob 10 mph will be common over the next several days and directions should follow normal diurnal trends. A dry weather pattern through the first part of next week will likely become more unsettled pattern during the middle of the week with increased chances for wetting rain.

PSR WATCHES/WARNINGS/ADVISORIES

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