Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 260359
Area Forecast Discussion
National Weather Service Salt Lake City UT
959 PM MDT WED MAY 25 2016
.SYNOPSIS...The elongated upper level trough over the western
Great Basin will shift east across the region through Thursday.
Unsettled conditions associated with this trough will persist
through the balance of the week.
.SHORT TERM (Through 12z Saturday)...The upper level trough axis
extends from a low centered over north-central Montana south to a
second low over southern California this evening. This trough axis
will slowly shift east into western Utah late tonight...then
continue east through the state Thursday.
Showers and isolated thunderstorms once again formed along and
east of the trough axis across west-central through northern Utah
this afternoon. This activity has largely ended with the loss of
daytime heating...though a few cells still persist across far
northwest Utah and over extreme southwest Wyoming.
A second organized band of convection has developed across central
through northeast Utah. This band appears to be associated with a
newly developed deformation axis which has formed on the north
through northeast flank of the upper low over far southern
California. South of the deformation light showers close to the
upper low center are beginning to stretch into far southern Utah
this evening. Suspect that these showers will remain isolated in
areal coverage across the south through the remainder of the
Looking at an increasing trend in convective precip along and
south of the deformation axis Thursday morning as the upper low
shifts into central Arizona. Areas to the north will see limited
convection as dynamic forcing will be weak at best. Most
convection will be tied to the terrain and should dissipated
fairly quickly with loss of heating Thursday evening.
Convection should wind down early Thursday evening across the
south as the upper low moves east of the four corners region.
Various model guidance are indicating that a trailing vorticity
lobe will sweep southeast across Nevada and southwest Utah
Thursday evening. This feature could generate additional
convection...though suspect much of this will skirt far western
and southern Utah during the early evening.
A shortwave ridge will build into Utah Friday ahead of the next
weather disturbance settling into the Pacific Northwest. Residual
moisture will fuel some terrain-based convection underneath the
ridge Friday afternoon/early evening. Could see a weak shortwave
eject out ahead of the Pacific Northwest system Friday night. Can
not rule out some light precip associated any shortwave late
.PREVIOUS LONG TERM (After 12Z Saturday)...A broad upper trough
remains to the north of the CWA at the start of the long term
period with latest GFS showing a short wave lifting out of the nrn
Rockies and subsidence spreading into the northern CWA in its
wake. The EC roughly agrees so have lowered pops for the north Sat
into Sat eve and raised them over the south.
A weaker trough splits south into CA on Sat as well and this
feature is forecast to bring a return of convection to much of the
CWA starting later Saturday night and continuing through Sunday
night. The EC phases a nrn branch trough with this weak wave and
shifts the main trough axis into the eastern CWA Monday afternoon
with drying for the west. Meanwhile the GFS follows a similar
solution but does not shift the main trough axis east of the CWA
until almost midday Tuesday. This solution keeps convection
fairly active on Monday and maintains a threat of rain for
Memorial Day activities.
Have leaned towards the GFS solution here and kept a mention of
rain through Monday as just a slight slowing of the trough in the
EC would bring it in line with the GFS.
Both models bring a ridge into the Great Basin by midweek for a
break in the cooler wetter pattern.
.AVIATION...Showers have ended over the terminal area with the
loss of daytime heating. Lingering ceilings near 8 kft this
evening will dissipate around midnight...with the remaining
ceilings generally above 10 kft. Light west to north winds will
turn to the southeast around 05z.
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