Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 160907

Area Forecast Discussion
National Weather Service Salt Lake City UT
307 AM MDT Mon May 16 2022

.SYNOPSIS...Another warm day is in store across the region. A weak
cold front will cross into northern Utah, with isolated high based
convection expected mainly north of I-80 this afternoon and
evening. The front will settle into central Utah Tuesday, with
additional convection possible along the boundary. A strong cold
front will cross the state Thursday into Friday, bringing a much
cooler airmass to the region.


.SHORT TERM (Through 12Z Thursday)...Another very warm day is
expected across the CWA, with temperatures approaching or
potentially exceeding Sunday`s highs.

Morning satellite and upper air analysis indicates the center of
the upper level ridge is currently across northern Mexico and the
adjacent southern Rockies/High Plains region. A weak disturbance
embedded in the southerly jet is noted on satellite imagery
across the Desert Southwest, though this is mainly a cloud storm
for Utah.

Meanwhile, a persistent upper level low remains in the Gulf of
Alaska to coastal BC. A shortwave trough ejecting ahead of this
upper level low will help to drive a weak cold front into northern
Utah today.

There should be sufficient forcing for convection near this
boundary, mainly north of I-80 this afternoon and evening. Model
soundings indicate inverted-V type profiles with cloud bases
between 10,000 and 12,000 feet above the surface. 00Z HREF mean
SBCAPE values near 1000 J/kg near the Utah/Idaho border with
values closer to 500 J/kg near I-80. Deep layer shear is around
25-30 kts. This environment will be supportive of convection, with
the attendant threat of dry microbursts. Looking at the 00 and
06Z CAMs, as expected, isolated to widely scattered convection
develops near the Raft Rivers and across northeast Nevada and then
shifts eastward with time near and north of I-80. HREF 4 hour max
10m AGL wind speeds indicate a 50 percent probability of wind
gusts in excess of 30 kts, which is usually a sound microburst
signature on the HREF.

Added gusty wind with thunderstorms to the forecast...and those
with outdoor plans near and north of I-80 should keep a careful
eye on the forecast this afternoon and evening.

As another shortwave trough ejects across the region Tuesday
afternoon and evening, expect another round of convection across
portions of central Utah. SBCAPE values will again approach
500-750 J/kg per the HREF mean SBCAPE. Deep layer shear may be a
bit stronger Tuesday near the boundary. The FV3 core CAMs are
quite bullish, with widespread strong convection across central
Utah Tuesday afternoon and evening. Notably, the HRRR isn`t quite
as bullish and is rather conservative with more high-based and
isolated convection. Expect a threat of convection, potentially
somewhat organized Tuesday afternoon and evening across portions
of central Utah.

By Wednesday, the longwave trough is expected to begin shifting
south and east into the PACNW. This will gradually shift mid-level
flow to the west then southwest, with a bit of a warm up across
many locations Wednesday.

.LONG TERM (After 12Z Thursday)...A broad trough will deepen into
the Great Basin ahead of a 140+ kt jet streak over the PacNW
early Thursday, with the most rapid mid-level height falls
expected over central Utah. A tightening H7 temperature gradient
will accompany the arrival of the trough, and will help boost
gradient driven winds along the boundary. Exposed terrain will be
most impacted by the gusty winds, though widespread gusts to 35
mph are possible. Ahead of the boundary, modest amounts of
moisture will be present, aiding the convective potential for
Thursday evening out ahead of the front as it pushes south through
the forecast area. Any showers or thunderstorms will likely
produce gusty winds in excess of those already occurring with the
cold front.

Winds should die down somewhat behind the front and with an
increasingly stable environment Friday, though will linger near
fire weather thresholds. Relative humidity is expected to trend
sharply downward behind the front, with many areas of southern and
central Utah falling below 15% and perhaps into the high single
digits. Across northern Utah and southwest Wyoming, some showers
are possible, and should colder solutions play out, there is
potential for some light mountain snow as well as mid-elevation
areas with snow levels falling just below 5kft.

While daytime highs are expected to be much cooler Friday in the
post-frontal environment, overnight minimum temperatures will be
the factor to watch, which will run far below seasonal norms
through the weekend. Northern valleys such as the Cache could see
temperatures fall to or below freezing during this period.

Spread in the ensembles increases greatly towards the end of the
extended, with the potential for a shortwave trough to dive down
the western edge of the departing longwave trough. That said, this
is a minority solution, with more than 75% of the ensemble
membership supporting the return of strong ridging or at least
more zonal flow.


.AVIATION...KSLC...VFR conditions are expected to persist through
the TAF period. Expecting increasing mid-level cloud cover as a
weak wave moves in from the south early Monday, with the potential
for some convective showers and isolated thunderstorms in the
afternoon and evening. Some storms are expected to be capable of
producing gusty outflow winds that could lead to sudden and
erratic shifts. Currently, winds are forecast to remain out of the
north through at least the first half of Monday night, bolstered
by outflow boundaries moving in across the lake, finally shifting
back out of the southeast by 09Z if at all.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions are expected
across the forecast area throughout the TAF period. Increasing
high and mid-level clouds are expected through the morning, with
isolated convection developing in the afternoon and evening,
especially across northern and central Utah. Any showers or
thunderstorms could produce strong outflow or microburst winds.
Some cells could produce locally heavy rain that may temporarily
reduce visibility at impacted terminals. Convection is expected to
die down by 05Z Tuesday.


.FIRE WEATHER...Very dry conditions persist across southern Utah
early this morning, with RH recovery in the single digits. High
pressure remains in place across the region, with a very warm
airmass residing across the state. A weak cold front will sag into
northern Utah this afternoon, with at least a few dry
thunderstorms along the boundary near and north of a Salt Lake
City to Wendover line. This front will shift south to central Utah
by this evening, with another disturbance helping to develop
mainly dry thunderstorms near the boundary across central Utah
Tuesday afternoon and evening. South of this boundary through
Tuesday evening, expect gusty winds and low to very low humidity.
Critical fire weather conditions are expected in southern Utah
zones with critical fuels (currently mainly fire weather zone 496)
through Tuesday evening.

By Tuesday morning, humidities will start to creep upward across
southern Utah, though remaining at or below critical levels.
Wednesday may be a break in critical weather conditions. By
Thursday, a much stronger system will approach the area. Strong,
gusty winds in excess of 40 mph are expected ahead of this system
across southern Utah. Areas with critical fuels will see another
round of critical fire weather conditions Thursday afternoon and
evening and a fire weather watch for Thursday may be necessary
later today.


UT...Red Flag Warning from noon today to 10 PM MDT Tuesday for UTZ496.




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