Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 201625

Area Forecast Discussion
National Weather Service Salt Lake City UT
1025 AM MDT Thu Jul 20 2017

.SYNOPSIS...Monsoon moisture will persist over most of Utah
through today. Drier air will spread back into the area from the
northwest Friday into Saturday.


.DISCUSSION...The forecast area remains on the back side of a
ridge this morning, and the resultant southerly flow has allowed
deep moisture to spread across Utah and southwest Wyoming.
Satellite derived PWs are in excess of 1.0 inch across the entire
area, with many locations in the 1.2 to 1.4 inch range, near the
maximum observed for this time of year.

Overall forcing is less than yesterday, with the shortwave of the
day expected to rotate around far southwest Utah instead of
spreading across a larger portion of the state. Still think that
daytime heating will provide more than enough instability for
convection, especially with much less cloud cover than yesterday,
and the flow will allow showers to move off the terrain. With such
a moist airmass in place, any storms that do develop will have
the potential to produce heavy rain, especially where the best
moisture is over southern Utah. Going Flash Flood Watch covers
this threat well.

A trough moving over the ridge will flatten the ridge tomorrow,
moving the flow aloft in a more westerly direction and allowing
drier air to move in from the northwest. Drying will be most
noticeable over northern Utah and southwest Wyoming but the drier
airmass should spread south over the weekend.

Updated the forecast earlier to adjust POPs and sky today and
tonight. No additional updates planned.


.AVIATION...VFR conditions are expected at the SLC terminal
throughout the day. Southerly winds, gusty at times, should
prevail during the daytime hours, but there is a 20 percent chance
of a late shift to the northwest between 21Z and 23Z. There is a
40 percent chance that showers and thunderstorms in the vicinity
of the terminal will result in periods of erratic winds.


.FIRE WEATHER...Monsoonal moisture remains over most of Utah this
morning, and is expected to bring another round of showers and
thunderstorms to the state through this afternoon and evening.
Most of these storms will be wet, with a good chance of wetting
rain across most of the area, except perhaps the far northern
portions of Utah. South-southwesterly winds will increase across
the state today, with the strongest gusts expected in western
Utah, but relative humidities will remain relatively high in most

A drying trend from the northwest will begin late today and
continue Friday through Sunday, slowly but surely bringing a drier
airmass to the entire state by Sunday afternoon. Moisture will
hang on longer in southern and eastern Utah, where decent coverage
of showers and thunderstorms will continue through Friday and
Saturday. This drying will likely be short-lived, as moisture
will likely return for the beginning of next week.


UT...Flash Flood Watch through this evening for UTZ010-012>016-




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