St. Johns, AZ 85936 Weather

Synopsis

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.

Discussion

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!

Aviation

Saturday 31/06Z through Sunday 01/06Z: MVFR expected in SCT SHRA/TSRA expected through 08Z, with MVFR/IFR CIGS remaining over the higher terrain through 15Z-17Z. VFR expected thereafter, before MVFR conditions set in after 03Z Sunday. Winds S/SE 4-8 kts overnight, becoming SE-SW 5-10 kts after 17Z.

OUTLOOK: Sunday 01/06Z through Tuesday 03/06Z: MVFR/IFR conditions develop after 06Z Sunday as WDSPRD SHRA/TSRA develops from south to north. Occasional LIFR possible over the higher terrain in +RA and low CIGS. VFR conditions return after 12Z Monday. Winds S/SW 10-20 kts with gusts 25-35 kts on Sunday, shifting to the W/NW Sunday night, becoming NW-NE 5-15 kts on Monday.

Fire weather

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.

Watches, warnings and advisories

Flood Watch from 11 PM MST Saturday evening through 5 AM MST Monday morning for AZZ004>018-037>040.