Marine Weather and Tide Forecast for Rillito, AZ

KEY MESSAGES

-Scattered to numerous showers and isolated thunderstorms expected on Friday. Rain may be moderate to locally heavy at times resulting in minor to moderate impacts.

-Snow showers expected in the mountains above 7500 feet on Friday into early Saturday. Snow may be moderate to heavy at times resulting in minor impacts. Snow levels will drop to around 7000 feet by early Saturday morning.

-Additional precipitation chances continue Monday thru Wednesday along with breezy to windy conditons. Although, confidence is low on timing, there is potential for minor to moderate impacts from winds, valley rain, and mountain snow.

DISCUSSION
This afternoon water vapor imagery depicted two low pressure systems that we have been tracking over the past couple days. One of the lows is located just off the coast of California and the other is located not too far behind it to the southwest hanging out over the Pacific. The two lows will finally come into phase tomorrow and drive our upcoming chances for precipitation and cooler temperatures across southeast Arizona.

By late tomorrow, the mean trough axis will begin to shift eastward toward the Desert Southwest. Concurrently, a substantial but short lived plume of moisture will be sipped up by and wrapped into the low. Scattered to numerous showers with isolated thunderstorms are expected through the day Friday as the center of the low moves over southern Arizona. Mountain snow will also be occurring above 7500 feet and could be moderate to heavy at times. Use caution when traveling in the snow on mountain roads.

By early Saturday morning, snow levels will drop to around 7000 feet and most of the activity will be shifting into New Mexico. However, a few lingering light valley rain showers and mountain snow showers will be possible east of Tucson. Overall, 3-6 inches of snow is expected above 7000 feet with locally higher amounts possible on southwest facing ranges resulting from locally enhanced southwest upslope flow with the trough passage. As far as valley rain goes, latest forecast amounts of 0.20 to 0.50 inches. For the mountains, expect 0.60-0.90 inches of liquid equivalent with locally higher amounts up to 1 inch. Rainfall runoff may result in significant ponding of water in normally dry washes, roadway dips, and low-lying areas. Additionally, anticipating the potential for locally heavier rainfall rates in thunderstorms, isolated instances of street flooding cannot be ruled out resulting in minor to moderate impacts across the Tucson Metro Area Friday into Friday night.

By Saturday afternoon, the mean trough axis will be to our east with shortwave ridging moving in and high temperatures warming to near normal. Sunday, temperatures will rise to 4-6 degrees above normal. Monday through Wednesday another trough will impact the Desert Southwest, but there is noticeable uncertainty in the timing and trajectory of the storm system. However, minor impacts from precipitation and wind will be possible during this timeframe. Stay tuned.

AVIATION
Valid through 13/00Z.
SCT clouds AOA 8k-11k ft AGL through 12/03Z. Thereafter, SCT-BKN cirrus around 18-20k ft AGL thru the remainder of the period. SFC wind SWLY to WLY at 8-12 kts through 12/03Z becoming VRBL and below 8 kts through 12/17Z. Thereafter, SFC winds pick up again becoming SWLY to WLY at 8-12 kts.

FIRE WEATHER
A cold and wet winter weather system is expected to make its way into Southeast Arizona Friday resulting in valley rain and high elevation snowfall. Isolated thunderstorms will also be possible with this system. Min RH levels will be 25-35 percent in the valleys and 35 to 45 percent in the mountains today, lowering by 5-10 percent Thursday, then increasing significantly Friday to 35-45 percent in the valleys and 45-65 percent in the mountains with the arrival of that weather system. Although quiet weather will briefly return this weekend, unsettled weather returns the first half of next week with valley rain and mountain snow. Strong and gusty southwest winds are possible Monday.

TWC WATCHES/WARNINGS/ADVISORIES
None.