Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 181053
Area Forecast Discussion
National Weather Service Salt Lake City UT
453 AM MDT MON JUL 18 2016
.SYNOPSIS...High pressure over the southern plains with an upper
level trough settling into the Pacific Northwest will leave the
Great Basin under a southwest flow through much of the week.
Moisture will spread across southern and eastern utah today, and
remain in place through much of the week before a drying trend
ensues late in the week.
.SHORT TERM (Through 06z Thursday)...A subtropical ridge axis
extending across much of the southern US westward into the
southern Rockies, coupled with an upper low situated along the
Pacific Northwest coast, is inducing a deep layer southerly to
southwesterly flow across the Desert Southwest/Colorado Plateau
and far eastern Great Basin early this morning. After a fairly
prolonged dry spell this flow is finally allowing moisture to be
advected northward through AZ and into southern UT early this
morning. Showers associated with this moisture advection have
already spread across south central and southeast UT, although a
deep and dry sub cloud layer is likely resulting in much of this
evaporating before reaching the surface.
As the day progresses this moisture will continue to increase
from south to north across the eastern half of the forecast area.
Model BUFR soundings suggest instability will remain quite limited
owing to a combination of poor mid level lapse rates and the fact
the moisture is largely confined to the mid levels. As such
convection will likely remain rather weak but given the deep sub
cloud layer should be capable of strong microburst winds
initially. As the airmass across southern and central UT gradually
moistens measurable rainfall will become increasingly likely
although heavy rain is not expected today owing to a combination
of storm motions in excess of 20 kts and limited instability.
Anticipate isolated convection to reach portions of the Wasatch
Front by mid to late afternoon with strong microburst winds
Little change in the overall pattern is expected through the
remainder of the short term period, as moisture remains in place
across the eastern two thirds of the forecast area, which should
allow for daily convection to fire from the Uintas southward along
the central spine and into the terrain of southern UT. Storms
along and east of the terrain should be capable of producing
measurable rain with a gradual upward trend in the potential for
locally heavy rain, while along and west of I-15 storms which are
able to form will tend to be drier with a threat for microburst
.LONG TERM (After 06z Thursday)...The persistent PacNW trough
will begin to shear and split Thursday with the downstream lobe
transitioning east through northern Rockies, and the upstream lobe
retrograding west towards 140W by 12z Friday. Coincident, the low
amplitude high over the southern conus will bulge further west
with the western periphery extending into SoCal. Although
streamlines within the return flow environment will continue to
favor modestly deep moisture advection and associated convection
across the central/eastern mtn spines and eastern Utah Thursday
afternoon, a much drier near westerly flow aloft suggested by
models looks to cut off the deeper moisture residing over the area
by Friday. Have reduced PoPs Fri afternoon to isolated coverage
over the central/eastern mtns as such, with any convection driven
by the remnant low level moisture in place.
Thereafter the high is forecast to reorient south and west of the
eastern Great Basin, with an anticyclonic northwesterly flow
parking over the area for the weekend, and into early next week.
With said trajectories favoring a dry flow with limited if any
instability, have trended the forecast dry those periods, with
seasonal to slightly above average temps each day.
.AVIATION...Gusty southerly winds will be the name of the game
for the KSLC terminal through the valid TAF period. Periodic gusts
above 30 mph remain possible through 11z this morning, then likely
after 16z this morning. Additionally, a 20 percent chance exists
convection will develop over the Oquirrhs this afternoon,
maintaining a slight chance that erratic and gusty outflow will
impact the terminal in the 20z-02z window.
.FIRE WEATHER...Southwesterly flow will prevail across the region
through much of the upcoming week. Moisture within this flow will
spread northward from Arizona today bringing an increased threat
for thunderstorms. Along the northern and western edge of this
moisture surge thunderstorms may initially be dry today with
lightning and gusty microburst winds possible, however as moisture
continues to increase storms should transition to wet across most
areas. Given the recent dry spell lightning associated with these
storms will pose a significant risk for new starts prompting a red
flag warning across much of central and eastern Utah. Meanwhile
dry and breezy conditions will continue across northwest and west
central Utah resulting in critical fire weather conditions.
Moisture will remain in place across the eastern half of the area
through much of the remainder of the week maintaining a threat for
showers and thunderstorms each day. These storms will be capable
of producing wetting rains given the moisture in place.
UT...Red Flag Warning from 10 AM this morning to 9 PM MDT this
evening for UTZ479-483-489-493-498.
Red Flag Warning until 9 PM MDT this evening for UTZ478-492.
Red Flag Warning from noon today to 9 PM MDT this evening for
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