textproduct: NWS Phoenix

UPDATE

Updated 12Z Aviation Discussion.

KEY MESSAGES

- Departing high pressure will keep temperatures across the region around 5 to 8 degrees above daily normals today.

- A weather system will approach from the west this afternoon, resulting in gusty winds across portions of Riverside and Imperial Counties where a Wind Advisory is in effect.

- Temperatures will cool back to near normal in the wake of the passing weather system with continued breezy conditions for the remainder of this week and into this weekend.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Latest mid-lvl wv imagery and 500 mb streamline analysis reveals a broad ridge of high pressure currently centered over the Southern Rockies while a closed low sits off the coast of N California and the Pac NW. Today, our forecast region will be located between both of these features resulting in increasing southwesterly flow aloft. Southcentral AZ will still be under the influence of the departing upper-lvl ridge this afternoon where 500 mb hghts will range from 577-579 dam, keeping high temps around 5 to 8 degrees above normal. Farther west in SE California, lowering hghts from the approaching low pressure system will result in slightly cooler temperatures, although most lower desert communities will still reach up to 90 degrees which is a few degrees above normal. The main weather concerns this afternoon and evening will be a corridor of stronger winds, especially across western portions Imperial and Riverside Counties. A Wind Advisory is in effect starting at 3 PM PST for the far SW corner of Imperial County where gusts up to 50-55 mph can be expected. The western portion of Joshua Tree NP has also been included in the Wind Advisory this afternoon where gusts could reach 35-40 mph at times. The main impacts from these gusty winds will be potential blowing/lofted dust and stronger crosswinds along I-8 and I-10 in SE California heading into this evening. Winds will not be as strong today in southcentral AZ, however it will still be breezy this afternoon with gusts reaching 20-25 mph.

Late tonight into Wednesday, the closed low off the coast of N California will begin to progress inland and transition to an open trough as it moves through the Intermountain West. At the base of the resulting trough, a compact 700-500 mb hght gradient will result in another bout of breezy conditions on Wednesday afternoon. However, the focus of the strongest winds will shift into N Arizona and the high terrain areas NE of Phoenix where gusts could reach 25-35 mph. Negative 500 mb hght anomalies associated with the main trough axis will overspread the forecast area on Wednesday, resulting in temperatures cooling back down to seasonal levels in the mid to upper 80s across the lower deserts and mid to upper 70s in the high terrain areas.

LONG TERM /THURSDAY THROUGH MONDAY/

Ensemble members and deterministic guidance continues to indicate quasi-zonal flow returning to the Desert Southwest Thursday and Friday which will result in temperatures remaining near to slightly above normal. A compressed 500 mb hght gradient will prevail over the Desert Southwest resulting in continued breezy to locally windy conditions through the end of this week with afternoon gusts reaching 20-30 mph. A progressive pattern will continue into this weekend as a series of mostly dry weather systems passes north of the region. The strongest shortwave looks to arrive on Sunday which will cool temperatures to around 3 to 5 degrees below normal across the region. Both the mean of the GEFS and EPS show negative hght anomalies persisting over the Desert Southwest well into next week which will keep temperatures at least near normal to slightly below normal to finish off the month.

AVIATION

Updated at 1120Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: An extended period of a southerly cross runway winds early Tuesday afternoon, then locally gusty winds late afternoon/evening will be the main weather concerns as thicker cirrus decks gradually clear. East winds winds early this morning will become southerly cross winds by late this morning, with speeds in excess of 10 kt before veering SW mid/late afternoon. Gusts near 20kt will be locally possible around sunset Tuesday with the preponderance of model output suggesting winds not completing the nocturnal easterly switch until closer to sunrise Wednesday morning, if at all.

Southeast California/Southwest Arizona including KIPL and KBLH: Strong, gusty winds Tuesday late afternoon/evening will be the primary weather concern as thicker high cirrus decks gradually clear. Confidence is good that westerly winds at KIPL will remain in place while southerly/southwesterly winds will be preferred at KBLH. Gusts 20-25kt will materialize Tuesday afternoon with gusts likely strengthening above 30kt at KIPL during the evening.

FIRE WEATHER

A progressive pattern with multiple dry weather systems passing north of the region will result in breezy conditions and periods of elevated fire weather throughout this week. Relative humidity is not expected to fluctuate much, bottoming out around 8-15% each afternoon. Overnight recoveries will remain poor to fair over the next several nights. The strongest winds will reside in SE California this afternoon and evening where gusts up to 25-35 mph (locally higher) will be possible. These stronger winds coupled with very dry conditions (RH as low as 10%) will result in a brief period of near critical fire weather conditions this afternoon. Widespread breezy conditions with gusts around 20-30 mph will continue each afternoon through the remainder of this week, resulting in persistent elevated fire weather.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory from 3 PM this afternoon to midnight PDT tonight for CAZ560.

Wind Advisory from 3 PM this afternoon to 8 AM PDT Wednesday for CAZ562.