Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 202145
Area Forecast Discussion
National Weather Service Salt Lake City UT
345 PM MDT WED JUL 20 2016
.SYNOPSIS...A warm southwest flow will remain over the forecast
area through Thursday, keeping a moist airmass over southern and
eastern Utah. Drier air will move into much of Utah and southwest
Wyoming beginning late Friday.
.SHORT TERM (Through 06Z Sunday)...Southwest flow remains over the
forecast area this afternoon in between the high over the central
United States and the low over the Pacific Northwest. This has
allowed deep moisture to move into southern and eastern
Utah with satellite derived PWs in excess of 1.0 inch. Meanwhile,
the airmass remains quite dry over northwest Utah, with PWs in the
0.3 to 0.4 inch range.
In this moist airmass, a few showers and thunderstorms have
developed over the higher terrain. However, overall instability is
quite limited apart from what is being induced by the terrain,
limiting overall coverage. Temperatures remain on the warm side
over northern Utah, with maxes in excess of 5F above seasonal
norms while southern Utah maxes stay closer to climo.
Little change in the overall pattern is expected tomorrow.
However, weak vorticity moving up from Arizona will increase
instability somewhat, so that afternoon/evening coverage of
convection over southern and eastern Utah should be more scattered
in nature. Going POP grids reflected this trend well so only made
a few changes.
The Pacific Northwest trough is progged to move onshore Thursday
night before moving across Washington, Idaho, and Montana Friday
and Saturday. This will shift the flow over the forecast area to a
more westerly direction, allowing the moisture pooled over
southeast Utah to spread westward before a drier airmass moves
into all but far southeastern Utah late Friday into Saturday. As
the trough passes north of the area, it will bring a weak front
into northern Utah late Friday. As a result, temperatures will
trend downward for Friday and Saturday over northern Utah and
southwest Wyoming while southern Utah sees a bit of a warming
.LONG TERM (After 06Z Sunday)...Dry westerly flow will prevail
across the region through the extended period as a ridge of high
pressure bridges across the Great Basin this weekend. This ridge
will center over California/Nevada next week which will then turn
the flow slightly northwest which will suppress the monsoonal
moisture well south into Mexico. Temperatures will remain above
normal through this period.
.AVIATION...Gusty southerly winds at the SLC terminal are expected
to shift to the northwest by 2230Z. There is a 40 percent chance
winds will remain southerly through the day and into the evening. At
this time...any impact from convection to the terminal is unlikely
through Thursday morning.
.FIRE WEATHER...Moisture that has been over the southeast half of
Utah will filter northwestward into western Utah Thursday into early
Friday. This will occur in response to the trough off the Pacific
Northwest coast moving to the coast and turning the flow aloft
across the eastern Great Basin more southerly. Although this
moisture will increase at mid levels there will be limited
instability associated with this plume along the western periphery.
Can not rule out isolated dry thunderstorms over western valleys
Thursday into Thursday night. Farther east the moisture will remain
rather deep so scattered mountain thunderstorms with locally
wetting rains more likely.
By Saturday the flow will become mainly westerly across the Great
Basin bringing in a dry air mass. While temperatures will cool a few
degrees Saturday across northern Utah, temperatures will warm again
to more than 5 degrees above normal next week. Single digit minimum
RH values are expected across most valleys.
LONG TERM/FIRE WEATHER...Struthwolf
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