Flagstaff, Arizona

After isolated to scattered rain showers today, a significant storm system arrives tonight, lasting through early Monday. This second storm will produce prolific rainfall totals across the region and a Flash Flood Watch is in effect for all of northern and central Arizona. This is a serious situation. Stay tuned to your favorite weather source and find a way to receive warnings. Stay away from waterways. Turn around, don`t drown.

A low-level jet continues early this morning through the Gulf of Mexico and northern Sonora, pumping moisture into the deserts of western and southern Arizona. Shallow instability and upslope have enabled light to moderate showers to continue, with isolated to scattered coverage. This pattern will continue through the day today, as 700mb flow and the upslope component continues to strengthen. The moisture profiles are quite robust, initially the thinking was that showers activity would largely pause today, but now it looks like we will be a bit more active. The upslope regions south of the Mogollon Rim will continue to see scattered coverage throughout the day.

By late this afternoon and into the evening, the aforementioned components ramp up even further, along with the arrival of a deeply saturated sub-tropical plume and associated jet. This will quickly increase the coverage and strength of rainfall, with large areas of the state seeing nearly continuous moderate to heavy rain heading into Sunday. Even as the plume begins to get shunted southward, the arrival of a strong cold front from the north will further enhance rainfall Sunday evening and overnight. The FROPA will also feature a localized severe threat as it moves southeast Sunday night.

Mesoscale models now have peaks within the upslope regions ranging from 4 to 6+ inches of rain, with at least 1 to 3, locally 4 inches in most other areas. This will cause major and serious hydrological issues, especially since we are already saturated in many locations. A second FFA is in effect for the entire CWA during this time frame.

Behind the final trough passage Monday morning, we quickly dry out with strong ridging developing for a few days. Long-range ensembles are hinting at yet another cut-off low forming near the end of next week, potentially bringing more showers and thunderstorms.

This is a dangerous situation, especially pertaining to flooding. Both flash flooding and then longer term river flooding will be a problem. Larger stem waterways may be flooding for days after the event, especially the Little Colorado River and the Verde River.

Again, we cannot stress enough, THIS IS A SERIOUS SITUATION. Stay tuned to your favorite weather source and find a way to receive warnings. STAY AWAY FROM WATERWAYS, TURN AROUND, DON`T DROWN!

Saturday 31/18Z through Sunday 01/18Z...Areas MVFR/IFR over higher terrain and south of the Mogollon Rim, otherwise VFR through 01Z. ISOLD-SCT -SHRA through the day, mainly along the I-17 corridor and north to terminal KGCN. Deteriorating conditions after 01Z-03Z Sunday, with MVFR/IFR and LIFR spreading SW to NE across the area. Most flight restriction due to rain, low clouds and some fog. Winds generally light, but turning S10-20kts after 12Z over higher terrain.

OUTLOOK...Sunday 01/18Z through Tuesday 03/18Z...WDSPRD MVFR/IFR and some LIFR in RA/+RA ISOLD TSRA through 12Z-16Z Monday, then VFR expected late Monday morning and continuing into Tuesday. Sfc winds SW 15-25g30kts through late Sunday night, then W-NW10-20g25kts Monday, then NW- NE 5-15kts Monday night.

Saturday and Sunday...Isolated to scattered showers for most of Saturday. By tonight, a major rainfall event will begin. Expect an extended period of moderate to heavy rainfall, along with embedded thunderstorms. lasting through Monday morning. Southerly winds today, 10 to 20 mph. Winds increase Sunday, especially over the eastern zones, with southwest winds 15 to 25 mph and gusts as high as 30 to 35 mph.

Monday through Wednesday...A cold front will push most precipitation out the region by late morning Monday. Expect dry and warmer weather for Tuesday and Wednesday. Winds shift west through northwest 10 to 20 mph Monday, with gusts to 25 mph over the eastern zones. Easterly winds 5 to 15 mph Tuesday, turning back southwesterly 5 to 15 mph for Wednesday.

Flood Watch from this evening through late Sunday night for AZZ004>018-037>040.