textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- A Wind Advisory remains in effect through 11 AM for portions of Southeast California for strong northerly post-frontal winds.

- Coolest temperatures over the next week and beyond are expected today, with high temperatures 4 to 7 degrees below normal, before slowly warming back up and nearing 100 degree highs again this weekend.

- Daily dry conditions, with no threat of rain, and seasonal afternoon breeziness are expected through the next 7 days.

SHORT TERM /TODAY THROUGH TUESDAY/

A potent shortwave trough was seen moving eastward through UT early this morning with a southward and southeastward moving cold front through AZ and SoCal. Strong northerly winds and widespread lofted dust were observed post-front in San Bernardino County. The cold front will continue dropping south through southeast CA and southwest AZ early this morning, with strong northerly post- frontal winds expected through mid-morning. A Wind Advisory is in effect for eastern Riverside and northeast Imperial Counties through 11 AM PDT/MST this morning with northerly gusts up to 35-50 mph expected. Latest HREF shows strongest 850mb winds (>40 mph) occurring through around 3-5 AM PDT/MST this morning. During this time is when the greatest impacts - primarily northerly crosswinds across I-10 and localized blowing dust - are anticipated. While the gradient wind is expected to weaken around the sunrise hours, some areas may see northerly wind gusts pick back up for a few hours after sunrise due to mixing. Otherwise, winds should gradually subside across southeast CA and southwest AZ heading into late-morning and the afternoon. Hazy skies should become evident after sunrise this morning, with all the lofted dust across CA and NV, especially across southeast CA and southwest AZ.

Hi-res models depict the cold front stalling out across south- central AZ toward sunrise and mid-morning. So, south-central AZ is not expected to experience any of the strong northerly and northwesterly post-frontal winds. There will still be some breezy southwest winds though late morning and this afternoon, mostly gusting up to 15-30 mph. A narrow band of low level moisture and forcing along and ahead of the front will lead to some lower clouds this morning across south-central AZ, including the Phoenix area, and a few hi-res models still support a brief sprinkle shower. So, a few drops falling in the morning, after sunrise cannot be ruled out, but do not expect any measurable rain.

The dip in 500mb heights over the area and push of cooler air from the north will result in cooler surface temperatures today, with below normal high temperatures expected across the region. Highs this afternoon are forecast to mostly be in the 80s across the lower deserts, with only 10-20% chances of reaching 90F in places like Phoenix and Yuma.

Heading into tomorrow, the potent trough will have left the region, ejecting through the Plains, but another trailing weak shortwave will follow and keep a large-scale trough pattern in place across the Desert Southwest. This will keep temperatures from rapidly warming back up and while they will warm up from today, highs tomorrow are still forecast to come up shy of daily normals. Most lower deserts will top out with highs in the lower 90s. Winds tomorrow will be even lighter than today for most areas. Although, with the trailing shortwave there will be another enhancement to northerly winds down the Colorado River and southeast CA, with peak wind gusts as high as 20-30 mph in the morning through midday. The lagging shortwave will also help draw scattered high clouds into the Desert Southwest through the day.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Through the rest of the week, global ensembles depict a lasting weak longwave trough pattern across the Desert South, with neutral height anomalies and no significant shortwaves rolling through the region. This will translate to rather seasonal weather conditions, but with a slow day-to-day warming trend. High temperatures are forecast to be near normal through the end of the work week - highs in the middle to upper 90s. Meanwhile morning lows are expected to be near to slightly below normal, largely due to dry air/low humidity and limited cloud cover. It is not until the weekend when odds of high temperatures reaching the 100 degree mark spikes back up to around 30-60%, as the longwave trough across the Desert Southwest breaks down. Conditions will remain dry through this weekend, with no threat of rain, and seasonal wind patterns are expected, with light winds through the overnight and morning hours and afternoon upslope breezes up to 15-25 mph.

AVIATION

Updated at 1120Z.

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

Low confidence on wind directions early this morning and the potential for a FEW-SCT deck as low as 4 kft AGL between now and 17Z are the main concerns through the TAF period under otherwise mostly clear skies. There is a low probability of slantwise VIS restrictions around sunrise and 20-40% probability of brief CIGs around 040-050 only for KDVT (just north of the Phoenix airspace). S- SW winds may persist through the morning, though a brief period of variability or relatively light SE winds for a few hours around sunrise cannot be ruled out. SW winds will establish and increase late morning to around 10 kts, with gusts into the mid to upper teens likely to develop this afternoon. A more typical nocturnal SE wind shift is anticipated tonight.

Southeast California/Southwest Arizona including KIPL and KBLH:

Gusty north northwest winds and slantwise VIS restrictions around sunrise due to lofted dust/haze will be the only weather issues through the next 24 hours under mostly clear skies. A period with stronger gusts (25-30 kts) will be possible at KBLH between 14-18Z, but otherwise gusts will mostly peak around 20-25 kts and subside by the evening. Occasional gusts to around 20 kts may be observed at KIPL this morning. Speeds will diminish at both site through the afternoon, with directions backing out of the W-NW this evening.

FIRE WEATHER

Elevated and marginally critical fire weather conditions are expected early this morning across portions of southeast CA as a result of strong northerly winds and dry air following a frontal passage. Conditions will improve by late-morning/early-afternoon as northerly winds subside. Elsewhere today, winds will be lighter, but still with peak southwesterly gusts up to 15-30 mph across south-central AZ. Minimum RH values today will be around 5-10% across western districts to 15-25% across eastern districts. Temperatures will be coolest, and below normal, today, which will result lower max mixing heights (up to 6-8K ft above ground level). Temperatures will slowly warm through the end of the week, but remain near seasonal level, and conditions will remain dry. Daily minimum RH values will be around 5-15% each day after today with poor to fair overnight recoveries at 25-50%. After today seasonal wind patterns are expected through the rest of the week, with afternoon upslope breezes up to 15-25 mph and the only exception being another brief enhanced northerly wind down the Colorado River tomorrow morning. There is no rain in the forecast through this weekend.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory until 11 AM PDT this morning for CAZ560-561-564- 568>570.