textproduct: NWS Flagstaff

SYNOPSIS

Deep monsoonal moisture will remain over the area through at least mid week, with a slight decrease later in the week. With this moisture comes the daily threat of thunderstorms, along with the risk for locally heavy rainfall and flooding. Daytime temperatures will remain at or below normal much of the week, with hotter temperatures toward the weekend.

DISCUSSION

It was a very active day on Monday, with numerous thunderstorms, some severe with flash flooding. This continued well into the night, especially in far northern Arizona where a large cluster of storms brought strong winds to the Page area (measured 58 mph) around midnight. Things have quieted down as of 3 AM, with the last remaining cluster of rain over NW Coconino County where a widespread 0.50-1.00" has fallen since midnight. With such a large scale rainfall event, often the following day will be more subdued with the rain-cooled air mass. However, an upper level disturbance currently located in SW New Mexico is forecast to move up into east central Arizona later today and then into northern Arizona tonight. The latest model guidance does indicate a slower start to convection over much of our area today, but with such deep moisture in place and an approaching disturbance we still expect numerous storms to develop. The greatest coverage by early to mid afternoon looks to be over eastern Arizona, but these will spread westward and impact the rest of northern Arizona later in the afternoon and evening. The primary threat continues to be heavy rainfall and flash flooding, especially considering the wet ground conditions and many streams/rivers are already flowing and elevated. For this reason, there is a Flash Flood Watch in effect through late this evening for all of our forecast area excluding the far northeast corner. There is also a localized strong wind/hail threat today though wind shear is weaker than Monday. As the disturbance moves northward Wednesday, scattered thunderstorms are expected in the afternoon, especially over the higher terrain with a somewhat lower threat of heavy rainfall. Thursday into the weekend - the center of high pressure to our east is forecast to shift toward Arizona. While moisture levels will drop, there will still be enough for daily scattered storms over the higher terrain, but more isolated for the valleys. Temperatures will also begin to heat up to above normal levels. Temperatures by the weekend may approach warning levels for the lowest elevations of the Grand Canyon so we'll keep an eye on that.

AVIATION...Tuesday 21/12Z through Wednesday 22/12Z

Isolated -SHRA this morning. After 18-20Z, scattered to numerous SHRA/TSRA developing once again and moving westward. Stronger storms will be capable of producing hail, wind gusts to 45 kts and brief MVFR and IFR conditions. Activity decreasing in coverage after 03-06Z Outside of storms, winds light and variable.

OUTLOOK...Wednesday 22/12Z through Friday 24/12Z...Look for SHRA/TSRA activity through the period, most numerous during the afternoon/evening hours. Coverage of SHRA/TSRA decreasing a bit by Thursday and mainly focused over higher terrain. Stronger storms will produce brief MVFR and IFR conditions, gusty winds to 40 kts and hail. Localized IFR conditions due to low clouds and fog possible during the overnight hours Wednesday. Outside of storms, surface winds light and variable.

FIRE WEATHER...Today and Wednesday

A medium to high grade monsoon environment continues, with generally light winds outside of outflow and thunderstorm activity. Most storms will produce wetting rain and any stronger storms may produce flash flooding, hail, and wind gusts to 50 mph especially through this evening.

Thursday through Saturday...Chances for showers and thunderstorms continue, though coverage will decrease somewhat. Generally light winds outside of outflow and thunderstorm activity. Most storms will produce wetting rain and any stronger storms may produce localized flash flooding. Expect a warming trend and minimum RH back to around 20% for the lowest elevations.

FGZ WATCHES/WARNINGS/ADVISORIES

Flood Watch from 11 AM MST /noon MDT/ this morning through this evening for AZZ004>009-012>018-037>040.