Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 172222
Area Forecast Discussion
National Weather Service Salt Lake City UT
422 PM MDT SUN JUL 17 2016
.SYNOPSIS...High pressure over the southern Rockies will shift
to the east ahead of the next upper level trough settling into
the Pacific Northwest. Moisture pooled to the south over Arizona
will begin to spread north across southern Utah today, then over
most of southern and eastern Utah early in the upcoming week.
.SHORT TERM (Through 12z Wednesday)...A ridge of high pressure
remains centered over New Mexico this afternoon with a breezy
southwest flow in place over Utah. Moisture has begun to spread into
the area from Arizona, with GOES-estimated PWATs now in the 0.7-0.9
inch range over southeast Utah. The leading edge of this moisture
surge currently extends from St. George to around Green River UT.
Weak high-based showers have developed within this moisture surge,
but so far little if any rainfall and no cloud to ground lightning
have been observed.
Moisture will continue to increase and spread farther north tonight
into tomorrow, but substantial moisture is not expected to really
make it to the northwestern quadrant of the forecast area. However,
for much of the spine of Utah and points south and east, showers and
thunderstorms will increase in coverage tomorrow. With the moisture
becoming deeper, the chance of measurable rain should increase.
However, some of the storms initially will likely be dry and/or
produce strong gusty outflow winds. In conjunction with the moisture
and associated cloud cover, max temperatures tomorrow should fall a
few degrees across the southeastern half of the forecast area.
A storm system over the Pacific northwest will eject across across
the northern Rockies and flatten the ridge slightly tomorrow night
and Tuesday. This will turn the flow westerly enough to weaken the
moisture surge and as a result shower activity should decrease a bit
.LONG TERM (After 12Z Wednesday)...Under broad southwest flow
aloft and a nearly stationary upper level low positioned over the
Pacific Northwest, Monsoon moisture continues to stream
northwards from Arizona and the Desert Southwest through the
week. With high pressure centered off to the east and several
short waves rotating up through New Mexico and Arizona, unsettled
afternoon convection is possible each afternoon through Thursday.
Made some tweaks to PoP chances in the extended, highlighting the
eastern half of the forecast area where the better available
moisture and instability should reside.
From Friday into the weekend, the upper level trough finally
pushes eastward through the Northern Rockies, thus shifting the
flow across the Great Basin to more westerly and drawing in some
drier air. This should lower precipitation chances into the
weekend ahead. Through the period, winds do not look to be much
of an issue, outside of convective induced storms, and
temperatures don`t seem to change much from day to day.
.AVIATION...Winds are expected to remain northwesterly at the SLC
terminal but there is a 40 percent chance winds may occasionally
shift back to the south due to the proximity of the lake breeze. If
winds remain northwesterly, expect the typical diurnal wind shift to
the south between 02-04Z.
.FIRE WEATHER...A dry and breezy southwest flow will continue across
much of the fire district through this evening. Moisture has started
to work its way into the area from the south and a few weak showers
producing little rainfall have developed across portions of
southeast Utah. The moisture will continue to increase tonight into
tomorrow and result in greater coverage of thunderstorms for southern
and eastern Utah tomorrow. Although the thunderstorms will become
increasingly wet tomorrow...they may be dry during the early part of
the afternoon and produce gusty outflow winds. The onset of
thunderstorm activity after a prolonged dry period has led to the
issuance of Red Flag Warnings for much of the spine of Utah and some
southern and eastern zones where fuels are critically dry. A sharp
moisture gradient is expected to be in place across west-central
through northwest Utah and as a result...a dry and breezy southwest
flow will remain in place northwest of this gradient tomorrow so Red
Flag warnings remain in place for winds and low RH for zones 478 and
492 for tomorrow.
The moisture will decrease a bit for Tuesday but will increase again
for the middle to latter part of the week. The moisture plume is
expected to be cut off for next weekend leading to drier conditions.
UT...Red Flag Warning until 8 PM MDT this evening for UTZ479-483-484-
Red Flag Warning from 10 AM to 9 PM MDT Monday for UTZ479-483-
Red Flag Warning until 9 PM MDT Monday for UTZ478-492.
Red Flag Warning from noon to 9 PM MDT Monday for UTZ480-482-484.
SHORT TERM/FIRE WEATHER...Cheng
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