textproduct: NWS Flagstaff

SYNOPSIS

Drier weather continues today, with isolated showers and thunderstorms possible, mainly near the White Mountains. There will be a gradual increase in coverage Friday into the weekend, as moisture starts to push northward. Expect breezy southwest winds to start easing this weekend, along with slightly below normal temperatures continuing into early next week.

DISCUSSION

Radar and satellite imagery shows a few light showers near the White mountains in portions of eastern Gila county early this afternoon, with additional showers and thunderstorms developing further south in southeastern AZ. Otherwise, breezy southwest winds with gusts up to 35 mph, especially in western Arizona, and dry pattern extends across northern AZ as the trough continues to be centered over the Pacific Northwest. Hi-res models still to show the potential for overnight convection tonight into early Friday morning in Gila, southern and central Apache and Navajo, and southeastern Yavapai counties, but this will be highly dependent on how showers and thunderstorms activity develops in southeastern AZ, so the chance for showers for showers and thunderstorms for most areas were kept around 40% or less.

Still expecting a gradual increase in shower and thunderstorm coverage Friday and into the weekend as moisture associated with Hurricane Marie is siphoned by the large trough and lifted northeastward toward northwestern AZ, and a strengthening of the ridge in the central US continues to support southerly flow in southeast AZ and pushing moisture northward into eastern AZ. The biggest challenges however, are: 1) Timing of this moisture being siphoned and being pushed into AZ. 2) How much moisture will be siphoned and where the greatest concentration will set up. 3) What kind synoptic profile will be in place. For the moisture, models show a gradual increase in moisture Friday and Saturday and have delayed the bulk of the moisture to Sunday and have shifted it northeastward into NV, UT, and far NW AZ. This is based on Marie's current track and speed and when the peak interaction between Marie and the trough will occur. For how much moisture, a PWAT around 0.92 inches is the 90th percentile of PWAT values for Flagstaff this time of year and the NBM shows a 30-40% chance exceeding this PWAT value by Saturday and a 50-65% chance Sunday, then decreasing to around 40-50% by Monday evening. For the synoptic profile, forecast ensembles have a the strongest 500 mb winds setting up over NV and UT, with 25-35 kts winds over NW AZ and decreasing to 15-25 kts over eastern AZ as the large trough moves northeast across the Pacific NW. The placement of the moisture and synoptic pattern currently places the greatest risk for storms and flooding somewhere around or north of the NV, UT, AZ border, but this pattern may shift over the next few days, and does not mean showers and thunderstorms will not develop across central or eastern AZ as dirnual-monsoonal showers and thunderstorms along the higher terrain are possible, especially if the tropical moisture does not create a mid or upper-level cloud deck over the state during the daytime hours. For now, the greatest potential for showers and thunderstorms on Sunday will be near and north of the Kaibab Plateau and the White Mountains, with day time temperatures staying near or slightly below normal into early next week.

AVIATION...Friday 04/00Z through Saturday 05/00Z

Expect mainly VFR conditions. ISOLD-SCT SHRA/TSRA east of a KPAN-KRQE line, ISOLD or no cells elsewhere. Some nocturnal activity may form this evening and overnight from the I-17 corridor up to the Four Corners, but confidence is low. Daytime sfc winds SW15-25g30kts.

OUTLOOK...Saturday 05/00Z through Monday 07/00Z...Expect mainly VFR conditions. SCT activity continues mainly for the eastern portions for early Friday evening, possibly becoming more widespread heading into Saturday and Sunday. Daytime sfc winds are not anticipated to affect flight operations over the weekend.

FIRE WEATHER...Friday and Saturday

Friday will see generally dry and breezy conditions west of a Show Low to Four Corner line with scattered showers and thunderstorms along and east of this line. On Saturday, isolated to scattered activity spreads area wide. Winds southwest 10-20 mph with gusts up to 35 mph, strongest across northwest Arizona. Little change in temperatures.

Sunday through Tuesday...Increasing moisture will cause shower and thunderstorm coverage to expand. Highest chances for rainfall will be seen on Sunday. Winds south through southwest 5-15 mph each day, then generally light and variable overnight. Little change in temperatures.

FGZ WATCHES/WARNINGS/ADVISORIES

None.