textproduct: NWS Phoenix

UPDATE...Updated 00z Aviation Discussion

KEY MESSAGES

- A cold front is sweeping the area this afternoon bringing chances for showers and isolated thunderstorms, some potentially strong, as well as breezy to locally windy conditions.

- Below normal temperatures are forecast into this weekend with freezing temperatures in some rural and low lying areas Friday and Saturday mornings.

- Temperatures will warm near to above normal by Sunday and remain in an above normal category during the upcoming work week.

- After today, dry conditions will prevail across the region through at least the middle of next week.

SHORT TERM /TODAY THROUGH FRIDAY/

Satellite and radar imagery from late this morning showed a couple well defined lines of clouds/showers with a few embedded thunderstorms occasionally popping up, moving into the CWA from the north northwest. These features are associated with a cold front along the base of a shortwave trough, which has followed an inland trajectory and dived southward over the West Coast states overnight into this morning. As this front moves into the forecast area, anticipate there to be a window of time, between approx. 1-4 PM MST, where the potential for a few strong thunderstorms will be maximized across South-Central AZ. This timing coincides with the highest instability, with most guidance indicating MUCAPEs peaking just upwards of 500 J/kg, as well as modest to good shear (EBWD around 20-30 kts.) Remain weather aware this afternoon! Thunderstorms will be capable of producing locally gusty winds, small to marginally severe hail, and brief heavy rainfall.

The other impact of this front sweeping the area will be regionally breezy conditions and cooler temperatures. Winds will be stronger out west, with most guidance honing in on the evening/overnight/early Friday morning hours for wind gusts locally in excess of 40 mph. Overnight, these stronger gusts will be confined to the SE CA higher terrain. However, once the surface inversion begins to break down after sunrise tomorrow morning, the higher momentum air above the surface layer will be able to mix down to the surface and cause a surge in winds along the lower elevations in the vicinity of the Lower Colorado River Valley. Wind Advisories have been issued for these areas. Elsewhere, winds will likely peak with the frontal passage this afternoon, with gusts between 20-35 mph and some lingering breeziness Friday that will decrease over the afternoon as regional temperature/pressure gradients relax.

Temperatures will remain below normal through the end of the work week and into this weekend. The upper level low moving over the region today has significantly cooler temperatures aloft at its center than recent systems, with NAEFS mean 700 mb temperatures below the 10th percentile of CFSR climatology. In fact, some rural and low-lying areas will see sub-freezing temperatures Friday and Saturday mornings, and so Freeze Warnings have now replaced the previous Watches. Lighter winds and clear skies Friday night will allow for a more widespread freeze than what is expected tonight. Snow levels will have dropped to between 5000-6000 feet thanks to the cooler air mass moving into the area, and so lingering showers during the latter half of the afternoon into this evening will fall as snow over the peaks east of Phoenix. Anywhere from a dusting to a few inches may be expected along the peaks above 6000 ft.

Behind the cold front, very dry air will filter into the region from the north tonight through Friday, with NAEFS mean PWATs dropping below the 10th percentile of climatology for this time of year (0.10- 0.15"). This will bring rain chances to an end Friday onward.

LONG TERM /Saturday through Wednesday/

Saturday morning will be another day of cold temperatures. Winds will be light to calm and paired with clear skies will result in the coldest morning of the winter season so far. Rural and low lying areas will see temperatures near or below the freezing mark. Due to this a Freeze Warning is now in effect for portions of the CWA Saturday morning.

Heading into the rest of the weekend, ensembles continue to be in pretty good agreement on the overall synoptic pattern through the middle of next week. A blocking pattern will develop this weekend with high pressure returning to Western CONUS. The center of this high will initially be off the coast of central CA, and will eventually migrate over northern CA during the beginning of next week. This blocking pattern will continue through at least the beginning of next week, with the high pressure strengthening through the first half of next week. H5 heights will be in the 576-582 dm range Sunday-Wednesday. With the high pressure strengthening through the middle of next week, temperatures will gradually warm as a result. On Sunday and Monday afternoon high temperatures are forecasted to be in the upper 60s to low 70s across the lower deserts and in the upper 50s to low 60s across the higher terrain. Then on Tuesday, afternoon high temperatures will warm to the low to mid 70s across the lower deserts and in the low to mid 60s across the higher terrain. Temperatures will warm even more on Wednesday, with afternoon high temperatures in the mid to upper 70s across the lower deserts and in the mid 60s to around 70 degrees across the higher terrain. Morning low temperatures will also warm, going from the upper 30s to low 40s (low to mid 30s) across the lower deserts (higher terrain) on Sunday to the mid to upper 40s (upper 30s to low 40s) across the lower deserts (higher terrain) on Wednesday. Additionally, with high pressure building back into the region, dry conditions dry and tranquil weather conditions return this weekend and continue through at least the middle of next week.

AVIATION

Updated at 2352Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through the TAF period. CIGs have already started to improve and will be returning to the status quo of mostly clear to clear skies as early as 06Z. Wind directions will generally be out of the west through late this evening before shifting out of the east during the overnight period, with the exception of KPHX, where directions may become highly variable. Winds speeds are expected to remain aob 10kts.

Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation weather concern throughout the TAF period will be strong winds out of the northwest to north through Friday. Wind speeds are expected to mostly be aoa 10kts, with gusts upwards of 25 kts at KIPL and near 30 kts at KBLH. Winds at KIPL will diminish to aob 10 kts through this evening but will remain elevated at KBLH, with a high likelihood of gusts near to potentially exceeding 35 kts during the overnight hours tonight through early Friday evening. Skies will remain mostly clear throughout the period.

FIRE WEATHER

Moisture levels will remain elevated today across the central and eastern districts with heightened wetting rainfall chances as a cold front moves through the region. This cold front will have isolated to scattered showers and some isolated thunderstorms possible. Much drier conditions will return on Friday and continue into next week. MinRHs today will be in the 50-80% range across the central and eastern districts, with excellent overnight recovery. In the western districts, minRHs today will be in the 20-40% range, with fair overnight recovery. Tomorrow, minRH will fall into a 15-40% range, with good overnight recovery, region wide and will continue through the first half of next week. Strong northerly wind gusts in excess of 30 mph will likely surge into the lower Colorado River valley this afternoon through Friday morning yielding an elevated fire danger. Additionally, wind gusts in excess of 30 mph are also anticipated across SE CA, mainly across ridgetops. Elsewhere, gusts should be somewhat weaker (15-25 mph) with lesser impacts before returning to more seasonal levels over the weekend.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Freeze Warning from midnight Friday night to 9 AM MST Saturday for AZZ530-533-534-551>554-556-560>562.

Freeze Warning from midnight tonight to 9 AM MST Friday for AZZ534-552-556-560-562.

CA...Freeze Warning from 11 PM Friday to 8 AM PST Saturday for CAZ560.

Freeze Warning from 11 PM this evening to 8 AM PST Friday for CAZ560.

Wind Advisory from 7 PM this evening to noon PST Friday for CAZ560-564-565-568.

Wind Advisory from 5 AM to noon PST Friday for CAZ569-570.