Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 172248

Area Forecast Discussion
National Weather Service Salt Lake City UT
448 PM MDT Mon Jul 17 2017

.SYNOPSIS...A ridge of high pressure will remain in place across
the region through mid week, resulting in a continuation of hot
temperatures. Lingering moisture will continue to bring scattered showers
and thunderstorms to the area today, followed by a drying trend on
Tuesday. Monsoon moisture will spread into the area Wednesday and
Thursday and may bring the potential for heavy rain to central
and southern Utah.


.SHORT TERM (Through 12Z Thursday)...Upper level ridge centered
over the southern plains will shift slowly east through mid week.
Residual moisture in place across much of Utah this afternoon
resulting in scattered showers and storms across much of the
state. SBCAPE and precipitable water values are highest across
southern Utah although limited shear there lends storms more to
producing heavy rain than severe weather. Further north, near the
northern extent of the convection deep layer shear values of
30-40 knots indicate that a little more storm organization is
possible. Anticipate that convection will diminish after sunset in
most areas, although isolated showers may longer through the
night across southern Utah.

A drying trend will occur across northern Utah on Tuesday as the
upper high elongates bringing drier air into Utah. Anticipate
that storms will largely be confined to the southern half of Utah
and the Uinta mountains on Tuesday. On Wednesday, the models are
in good agreement that a strong monsoon surge brings deep moisture
into central and southern Utah and then into northern Utah
Wednesday night. Precipitable water values in excess are expected
for much of the state with values in excess of 1.25" across
southern Utah. GFS also indicates a a mid level shortwave moving
north out of Arizona on wednesday which would provide support for
more widespread convection. Certainly see the potential for flash
flooding across central and southern Utah with very deep moisture,
deep warm cloud layers, and the possibility of larger scale
forcing. As is always the case with such events timing of any
shortwave forcing is critical.

Temperatures will remain above normal across the area with
overnight lows remaining well above normal. Temperatures will
drop back a bit on Wednesday, especially across southern Utah,
with the increased coverage of showers and storms.

.LONG TERM...(After 12Z Thursday)...Deep moisture will continue to
stream into Utah Thursday, with PW values of 1.2-1.4" across
southern Utah and 1.0-1.2" across northern Utah. Thursday will
likely be another active convective day across Utah, though
extensive cloud cover could limit activity across central and
southern Utah. A shortwave trough moving slowly across central Utah
into SW Wyoming and upper level diffluence associated with the right
entrance region of a jet streak positioned across ID, should allow
for an increase in convective coverage across northern Utah Thursday
afternoon. A few organized storms could be possible across far
northern Utah near the UT/ID/WY border as 0-6 km bulk wind shear
increases to around 40 knots.

A mid-level trough pushing across the Montana/Canadian border will
act to flattened the ridge and bring in drier air into northern Utah
Friday. A slow drying trend will take place through the weekend
across central and southern Utah, with isolated convection expected
across the higher terrain of southern Utah Sunday and Monday, while
northern and central Utah remain mainly dry.

Forecast highs Thursday, Friday, and Saturday will remain near
average across Utah, before warming a few degrees above normal
Sunday into early next week as an upper level ridge begins to
amplify across the Western U.S.


.AVIATION...Southerly winds are expected at the SLC terminal
through 00Z, then a band of thunderstorms will likely bring erratic
winds in excess of 30 mph with a 30 percent chance of exceeding 45
mph. Thunderstorms should impact the terminal for about 1 hr from
00z until 01Z. Winds will likely return southeast about 03Z.


.FIRE WEATHER...Upper level ridge remains in place over the southern
plains today with southwest flow aloft over Utah. Scattered
showers and thunderstorms this afternoon will decrease in
coverage by late evening. Drier air overspreads much of northern
Utah on Tuesday limiting the coverage of shower and storms to
central and southern Utah and in the Uinta Mountains. As the
upper level ridge shifts east by mid week, much deeper moisture
will lift north into Utah greatly expanding the coverage of
showers and storms on Wednesday and Thursday and also bring the
potential for flash flooding to southern Utah. It is not out the
question that there may be some dry thunderstorms on the leading
edge of the moisture across northwest Utah on Wednesday.

Relative humidity values will be lower on Tuesday, especially
across northern and central Utah where drier overspreads the
region. Much higher afternoon relative humidity readings can be
expected on Wednesday and Thursday for much of the state as
monsoon moisture spreads through the region.




LONG TERM...Lukinbeal

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