textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- High pressure over the Southern Plains will cause breezy to windy conditions for portions of south-central Arizona Sunday morning, with the strongest gusts over higher terrain east of Phoenix.

- Temperatures will warm through the beginning of next week, reaching 5 to 10 degrees above daily normals, which translates to widespread lower desert highs in the nineties.

- Periods of breezy to locally windy conditions and cooler temperatures are expected by the middle of next week.

SHORT TERM /TODAY THROUGH MONDAY/

It is a crisp sunny start to the weekend across much of the Desert Southwest with shortwave ridging progressing across the area. The sunshine and high pressure has already contributed to a 24-hr surface temperature change of around +4-7F. The warming today will lead to afternoon high temperatures reaching the lower 90s across most lower desert communities, which is around 5 degrees above normal. Winds are much lighter today across SE CA and SW AZ, as the surface pressure along the Lower Colorado River weakened with the shifting eastward of the Great Basin surface high. Winds are also fairly light across south- central AZ following some morning northeasterly breezes.

A strengthening surface high in the Southern Plains tonight will set up a strong pressure gradient across parts of southern NM and AZ and lead to enhanced easterly winds. Comparatively, ensemble guidance is predicting a weaker gradient than the very strong one that set up back on March 28th, which saw wind gusts measure up to around 40-45 mph in the high terrain east of Phoenix in the morning, with 25-35 mph measured in the lower deserts of South- Central AZ. The March 28th gradient wind event also produced a lot of lofted dust that became apparent after sunrise. Similar conditions are a reasonable expectation with tonight/tomorrow morning's gradient wind event although it is expected to be a degree of magnitude weaker than the March 28th event. Hi-res models and the NBM support localized mountaintop wind gusts up to 45-50 mph, with up to 35-45 in some higher terrain communities, like San Carlos and Globe/Miami, while lower elevations of South-Central AZ can reasonably anticipate up to 25-35 mph gusts after sunrise tomorrow. A Wind Advisory has been issued for most high terrain areas east of Phoenix from 3 AM - 11 AM MST tomorrow. Wind gusts should abate through the afternoon as the gradient relaxes.

As is common with elevated breezes during the overnight and morning hours, morning low temperatures will likely be warmer than the NBM deterministic forecast. As a result, lows were boosted up a few degrees across south-central AZ and bring record warm low into the picture for Phoenix (current record: 73F). Afternoon high temperatures tomorrow are expected to warm another few degrees compared to today, under continued high pressure and southerly mid- level flow. Lower desert highs will push into the mid-90s, which is around 10 degrees above normal for this time of year. There will also be an increase in high clouds and some high-based cumulus downstream of a very weak shortwave trough. A few echoes of virga and a brief light sprinkle shower cannot be ruled tomorrow evening, with weak mid-level ascent, in parts of south- central and southeast AZ.

While a pronounced Eastern Pacific cutoff low will near the northern CA coast Monday, higher pressure and warm southerly flow will persist across AZ and southeast CA. As a result, temperatures will again warm into the middle 90s across the lower deserts and the clouds will clear up as the very weak shortwave departs. Although, some lingering midlevel moisture may be enough for a few afternoon convective shower across the eastern AZ high terrain, mainly in the White Mountain. The easterly gradient wind will be much weaker tomorrow night into Monday, as the Southern Plains surface high shifts further east, with no impactful wind gusts expected.

LONG TERM /TUESDAY THROUGH FRIDAY/

By the middle of the upcoming work week, the pattern will begin to shift. The upper low off the West Coast will push inland over the Western US, albeit in a weakening phase. Ensembles are in good agreement on this evolution, but details such as the N/S displacement of the low and the exact timing/speed of its eastward progression remain unclear. On a large scale, a broad area of positive midlevel height anomalies looks to establish off the Pacific Northwest/British Columbia with negative height anomalies to its south and east. This is in response to a split jet regime, where much of the Western and Central CONUS falls under the broad cyclonic flow of the poorly defined southern stream. As a result, we can expect cooler temperatures (likely closer to seasonal levels, in the 80s across the lower deserts) Wednesday onward across the forecast area, and periods of breezy to locally windy conditions as shortwaves progress through the Desert Southwest. The first period of increased winds will likely be Tuesday into Wednesday, especially for the Western CWA, as the initial, broad upper low moves inland and packs heights fields over the Southwest U.S..

AVIATION

Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Gusty winds and uncertainty in timing of wind shifts will be the main weather forecast issues through Sunday afternoon under increasing high cirrus decks. Confidence in exact wind directions through the evening is low as variability mixes with a light westerly component. Confidence is much better than east winds will resume overnight with stronger gusts materializing near or after sunrise. Conditions may flirt with LLWS criteria, as well as becoming conducive towards importing lofted dust and creating slantwise vsby issues around sunrise Sunday. After an extended periods of 20-30kt gusts, speeds should relax mid/late afternoon with moderate odds of becoming variable or light westerly around sunset.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through Sunday evening under periods of increasing high cirrus decks. Confidence in wind forecasts is moderate with a W/NW component favored at KIPL and varying between NW and S at KBLH. Extended periods of nearly calm conditions may be common.

FIRE WEATHER

Dry and occasionally breezy conditions will prevail through the next week. Winds will be light today, generally below 15 mph, and then a strong easterly wind will develop across south-central AZ tomorrow morning. The strongest winds will be over the higher terrain of the eastern districts, with wind gusts pushing up to 35-45 mph, but shortly after sunrise, gusts up to 25-35 mph are likely to become common across the lower elevations. Given the time of day of strongest winds, RH values will be above critical levels. Still, some locally elevated fire weather conditions may exist across south- central AZ midday through early afternoon tomorrow. Afternoon MinRHs below 15% and at times in the single digits will be common through the next 7 days, with minor day to day variations. Overnight recoveries will also vary through the next week, but fall mostly in the 30-50% range.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Wind Advisory from 3 AM to 11 AM MST Sunday for AZZ547-552-555- 557-558-560>563.

CA...None.