788 FXUS65 KSLC 300939 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 339 AM MDT Tue Jul 30 2019 .SYNOPSIS... High pressure will begin to drift eastward Tuesday but not before providing another hot day across the region. The high will be centered over New Mexico by Wednesday which will open up a monsoonal surge to invade most of the state. A drier southwesterly flow will develop for the end of the week. && .SHORT TERM (Through 00Z Saturday)... High pressure centered near southern Colorado will continue to slowly amplify in place today and Wednesday, maintaining southwesterly flow aloft across the forecast area. A robust subtropical wave seen in satellite imagery over northwest Mexico, and its accompanying moisture, will get caught up in the southwesterly flow on the western periphery of the ridge, and track north across Utah on Wednesday and Wednesday night. While some modest monsoonal moisture and limited cloud cover is slowly working its way into Utah today, the amplifying ridge, mainly clear skies and southerly flow will maintain warm to hot temperatures across the region today with mainly dry conditions. The exception will be isolated to widely scattered showers and thunderstorms that develop over the southern mountains this afternoon where just enough monsoonal moisture will support some high-based convection. The Salt Lake Valley will remain especially warm with downslope southerly flow in place overnight keeping temperatures in the 80s as of writing this discussion. Temperatures will quickly rebound today with afternoon high temperatures running very close to yesterdays values. By tonight, cloud cover will increase and thicken overnight, and when combined with the persistent southerly winds will keep overnight temperatures quite warm. By Wednesday, a plume of impressive moisture advection accompanying the aforementioned subtropical shortwave will surge northward across the forecast area. This will support numerous showers and moving northward across the region on the nose of the deep layer moisture advection and ahead PV max. Ample cloud cover will likely limit instability, producing more light to moderate rainfall rates despite the impressive PW anomalies of 2-3 standard deviations above normal. However, there is some early indication from available high resolution models of a possible break in cloud cover behind the shortwave passage across southern Utah in the afternoon that could support better late day destabilization. If this can occur, the ingredients for heavy rainfall are certainly in place, with BUFKIT profiles showing a deeply saturated sounding, tall-skinny CAPE with a deep warm cloud layer. Continue to mention heavy rainfall in the forecast across southern Utah, and WPC has upgraded the day 2 outlook to a slight risk of excessive rainfall across southern Utah. Temperatures will run a fair bit cooler, albeit muggier, on Wednesday given the thicker cloud cover and precipitation moving across the region. By Thursday, the wave will have departed, rejoining the northern jet stream. However, monsoonal moisture will remain entrenched across the forecast area. A slight westerly/drier trajectory into northwest Utah behind the wave passage will limit the axis of better moisture to eastern and southern Utah. Sparser cloud cover on Thursday will help with afternoon instability, thus expect scattered showers and thunderstorms will develop in a more typical diurnal pattern tied to the terrain given the overall lack of synoptic forcing. Expect thunderstorms that develop to remain quite capable of producing heavy rainfall, and continue to mention that threat in the forecast. By Friday, moisture axis will be shunted farther east, however expected enough lingering moisture for isolated to widely scattered coverage in the typical diurnal/terrain induced cycle. Temperatures will moderate to more typical seasonal values for Thursday and Friday. .LONG TERM (After 00Z Saturday)... Mid level ridging will remain centered near the Four Corners region through the long term period. Lingering moisture across the forecast area will continue to support a threat for diurnally driven terrain based convection, primarily over the central and southern mountains. This ridge is forecast to expand through the period, with associated height rises allowing for a warming trend over the weekend into early next week. Leaned toward the somewhat drier ECMWF Monday, as the GFS brings a rather robust vorticity maxima northward across the forecast area. These features are difficult to predict this far out, and thus leaned toward the drier EC. && .AVIATION... VFR conditions will prevail at KSLC through the TAF period. Northwest wind shift is expected to occur 20Z, but has a 30 percent chance of being delayed until 22Z with conditions similar to previous TAF period. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ SHORT TERM...Church LONG TERM...Seaman AVIATION...McNamee/Seaman For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php