textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Spotty showers with an isolated thunderstorm are expected across portions of south-central Arizona this afternoon through this evening.

- Breezy conditions will materialize along the Lower Colorado River including portions of Southeast California and Southwest Arizona this afternoon and linger through tonight into tomorrow.

- Much drier conditions return tomorrow along with slightly below normal temperatures and localized freezes in the morning, then expect gradually warming temperatures and continued dry conditions during the upcoming work week.

SHORT TERM /TODAY THROUGH SUNDAY/

So far, over the past couple of days, not much rain has fallen across south-central AZ, despite PWAT levels up to 150-200% of normal. There have been a few areas in Phoenix with a few hundredths to one tenth. Even most of the high terrain east of Phoenix has only received less than a tenth, and only a couple spots have received one to 3 tenths. However, this is not surprising as the synoptic and mesoscale setup has not been favorable for south-central AZ, with an upper low staying south of the region, plus most of the abnormal moisture has been above the boundary layer.

While the weather conditions have been pretty tranquil so far today, there will still be one more chance for showers, and even a thunderstorm, this afternoon through early tonight with a shortwave trough still yet to move through. This shortwave can easily be picked out on wv satellite just pushing into northwest AZ early this afternoon. Scattered showers have already been developing just ahead of the shortwave axis and as the shortwave continues east- southeastward it will bring the scattered showers through south- central AZ over the next 12 hours. The best chance at a thunderstorm this afternoon and evening will be from Phoenix's longitude eastward, where limited surface instability - up to a couple hundred Joules of SBCAPE - has developed. Any storm will be capable of producing very brief downpours, small hail, and strong gusty winds around 20-30 mph. Rain totals, where rain actually falls, will remain on the light side, with HREF probability only at 5-10% of >0.10" in Phoenix and around 20-40% of >0.25" in southern Gila County.

There will be a relatively strong cold front associated with the passing shortwave trough later today tonight that will act as a pallet cleanser for the current abnormal moisture, with significant drying post-front. PWAT anomalies are forecast to go from 100-150% of normal now to 25-50% of normal by noon Sunday. A strong northerly gradient wind will also develop today in response to strong pressure rises in the Great Basin. Winds will be highest down the Lower Colorado River where station observations are already showing gusts up to 20-30 mph. The elevated winds out west will continue through tonight and may gust locally as high as 35-40 mph.

Colder air will also follow in the wake of the shortwave trough, with some higher terrain and lower desert valley locations dipping down to or slightly below freezing the next few mornings. No freeze products are planned at this time as most of the spots that will experience a freeze have already seen a freeze this winter. Afternoon highs Sunday will be around 2-5 degrees below normal, in the 60s across the lower deserts.

LONG TERM /MONDAY THROUGH FRIDAY/

A somewhat complex upper level pattern takes shape next week with global ensembles in good agreement that the North Pacific jet will extend well into the east Pacific, and a split jet regime will evolve downstream over the Western CONUS. Despite the complexity, midlevel heights paint a quiescent picture, with ridging sliding east off the Pacific and building over the Western US (especially over the Northwest). This will result in a warming trend beginning Monday and lasting through at least the middle of the upcoming work week. Some breeziness out of the NE/E will be possible into early next week as suggested by the large-scale MSLP gradient, but this should not be impactful.

By the latter half of the upcoming work week, WPC cluster analysis reveals disagreement on the impacts of a possible weather disturbance undercutting the ridge and influencing the area by Thursday-Friday. Slight rain chances may re-enter the picture for the AZ high terrain or Southeast AZ, though this will rely on the exact trajectory, residence time, and strength of the disturbance. At this time, the main impact looks to be a temporary pause on the warming trend and perhaps another period of increased breeziness. QPF amounts this far out, even at the 90th percentile of the NBM, are very light and confined to E/SE AZ high terrain.

AVIATION

Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Isolated showers with the potential for erratic, gusty northwest winds this evening will be the primary weather concern as cloud decks 060-080 may briefly impact terminals. Confidence is low regarding any direct SHRA impact or cigs falling below 080, but isolated activity may allow some wind gusts 20-25kt to develop along with a brief cigs near 060. Forecast confidence is also low regarding the evolution of wind directions through Sunday morning with a general trend from NW towards NE, however significant variability may occur. Clearing skies and light winds will become more common by early Sunday afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: Locally breezy north winds this evening and overnight will be the greatest weather issue through Sunday afternoon with 8K-12K cloud decks clearing by the morning. KBLH will be most at risk for gusts 20-25kt this evening with some question when decoupling will begin. Gusts may resume Sunday afternoon with mixing. Gusts at KIPL will be weaker, far more brief or even absent with moderate confidence of directions temporarily reverting to westerly by sunrise.

FIRE WEATHER

Spotty showers with an isolated storm is expected this afternoon through early tonight across south-central AZ. CWR remains best across southern Gila County. The convective showers and any storm today will be capable of producing localized wind gusts up to 20-30 mph and small hail. A northerly wind gradient has developed already, and is strongest across western districts, resulting in breezy conditions primarily along the Lower Colorado River Valley and the adjacent typically prone areas of Southwest AZ and Southeast CA. Breezy conditions will linger through tonight and tomorrow morning before gradually subsiding. Localized wind gusts may peak as high as 35-40 mph. MinRHs will be in a 30-60% range today, increasing from west to east, and then dry considerably heading into tomorrow, with MinRHs dropping into a 10-25% range. Near normal temperatures today will drop to slightly below normal tomorrow before a warming trend commences early next week.

PSR WATCHES/WARNINGS/ADVISORIES

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