textproduct: NWS Phoenix

UPDATE

06Z Aviation Discussion

KEY MESSAGES

- A quick moving system tonight into Friday morning will reinforce cooler temperatures with additional chances for light showers across central Arizona.

- Breezy to locally windy conditions return this afternoon into tonight, particularly across portions of Southeast California, and so a Wind Advisory has been issued for some areas. - Drier weather returns this weekend, with temperatures warming back into an above normal category by Sunday.

SHORT TERM /Today through Friday/

Midlevel water vapor imagery shows the next troughing feature starting to move down California, and zonal flow positioned over the Desert SW. Even with the core of the trough currently in Northern California, our region will still be under the influence of negative height anomalies, with H5 heights today between 555-561 dam. This will result in today's afternoon highs in the mid to high 60s across the lower desert areas, about 4-6 degrees below normal for this time of year. The core of this troughing feature is expected to progress mostly W to E across the Four Corners region late tonight through early Friday morning. Simultaneously as this trough passes, a cold front will bring a swath of moisture into Central AZ, with PWATs around 100-130% of normal. This will lead to additional chances of light showery activity starting tonight into Friday morning across the lower deserts, similar to yesterday. However, most of the activity will be confined to the foothills and eastern higher terrain. Total QPF associated with this frontal passage will be between 0.01"-0.04" in the Northern Phoenix Metro/foothills, and 0.05"-0.10" in the higher terrain, while many areas may not see any precipitation at all.

For the western portions of our CWA, winds will be the main concern starting this afternoon through Friday morning. The NAEFS mean 850 and 700 mb wind speeds are in the upper 90th percentile of climatology starting tonight through early Friday morning. As pressure gradients increase ahead of this incoming system, wind gusts to 25-40 mph will become common across the SE CA and SW AZ lower deserts. However, some periods of higher gusts can be common in the SW corner on Imperial County, with speeds near 60-65 mph. A Wind Advisory has been issued for the higher terrain areas of Riverside County, Imperial county and for Joshua Tree National Park, starting this afternoon (3PM PST). This can lead to localized areas of blowing dust and reduced visibilities, take care while driving along roads in these areas.

Friday will continue to experience below normal temperatures. Across the lower deserts morning low temperatures will be in the low to mid 40 and afternoon highs will be in the low to mid 60s across most of the lower deserts. Other than gutsy conditions early Friday morning in the SW portion of Imperial County, winds will subside considerably by late tomorrow morning into the afternoon, leading to much calmer conditions as we head into the weekend.

LONG TERM /Saturday through Wednesday/

An abrupt pattern change will occur this weekend, with Western CONUS troughing weakening and shifting into the Plains and ridging rapidly building in its wake. Before the effects of increasing heights/temperatures aloft can be felt, we are in for a chilly morning on Saturday. Clearing skies, much lighter winds, and a cool, dry post-fronal airmass should result in efficient radiative cooling and thus some of the coldest temperatures we've seen in well over a month. Communities in higher elevation valleys east of Phoenix, such as Globe, San Carlos, and the Tonto Basin may flirt with freezing (32F or lower) temperatures. Latest NBM gives 20-80% probabilities for freezing temperatures Saturday morning for the typical cold prone valleys across the area.

Ensembles are in decent agreement that heights aloft will peak Monday-Tuesday, with mean H5 heights between 583-586 dam, in excess of the 98th percentile of CFSR climatology. Ensemble mean 850 mb temperatures in a 14C-17C range during the first half of the upcoming work week support temperatures between 8F-14F above normal for latter half of February, i.e., afternoon highs in the middle 80s for the typically warmer lower desert locales. Heights aloft decrease somewhat midweek as a series of troughs are advertised to skim the northern tier states and begin to flatten western CONUS ridging. This shift will also allow an IVT plume to penetrate inland but remain mostly north of the forecast area, bringing slight precipitation chances to the AZ high country. However, this shift in the upper level pattern is not likely to dislodge/diminish the warmer airmass in place over the Desert Southwest, and so NBM highs look relatively stable through the middle of the upcoming workweek. The primary uncertainty in temperatures will be the extent of mid to high level cloud cover with the inland penetrating IVT plume.

AVIATION

Updated at 0445Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns during the period will be focused during the overnight/early morning hours with low CIGs, breezy conditions, and iso -SHRA. Cloud bases should bottom out between 09-12Z at 3-4k ft, with the lowest CIGs closer to the 4k ft mark. Some brief windows of MVFR conditions, but forecast confidence is too low to warrant anything sub-VFR in the TAFs at this time. During this similar timeframe will be the best chance to see VCSH/-SHRA before they quickly exit the region after 12Z. Breezy conditions will be present through a good portion of the night, gusting to between 20-25 kts. Conditions should improve markedly prior to sunrise as CIGs should quickly scatter out and breeziness relaxes. Daylight hours should be accompanied by some light W'rly winds, with perhaps some residual breezes, and passing high cirrus.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to windy conditions will remain the main aviation concern, but only through this evening as much calmer winds should make up the majority of the forecast period. W/NW winds will be favored through Friday morning with some periods of VRB to calm conditions, especially at KBLH. High cirrus will stream over the region with bases remaining above 15k ft.

FIRE WEATHER

Wind speeds will increase again today, particularly later this afternoon across western districts with gusts 25-40 mph common. A cold front will sweep the area tonight, bringing a focus for a few showers mostly over foothills and mountains of Central Arizona and the eastern districts. Minimum humidity values will generally range between 25-45% this afternoon, then decrease slightly to 20-35% Friday. This will follow good to excellent overnight recovery of 60-100% tonight. Drying and warming conditions are expected for the weekend with MinRHs dropping into the teens for the lower deserts and temperatures rising to above normal.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory until midnight PST tonight for CAZ560-564-568.

Wind Advisory until 5 AM PST Friday for CAZ562.