Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 240234

Area Forecast Discussion
National Weather Service Salt Lake City UT
834 PM MDT Fri Jun 23 2017

.SYNOPSIS...A generally dry west to northwest flow aloft will exist
across Utah tonight and tomorrow. Strong high pressure aloft will
return to the region late in the weekend. A brief surge of
moisture will move through the area Monday.


Water Vapor Satellite shows ridging from California into New
Mexico and northern Mexico, while northwesterly flow aloft
resides from the Pacific Northwest into the Northern Rockies.
400-200mb MDCARS wind observations place a cyclonic 75-105kt jet
from British Columbia into the north central Plains. GOES/SLC 00Z
RAOB/HRRR indicate that precipitable water values vary from
0.10"-0.25" mountains to 0.33"-0.60" valleys.

With high pressure in place, benign weather once again tonight.
Going forecast in fantastic shape. Just tweaked the hourly diurnal
T/RH curve based on latest observations and forecast data. Also
massaged the winds due to the northerly pressure gradient with
high pressure building in. Winds outside of St George will be
lighter than last night though.


Mountain cumulus clouds have developed across far southern Utah
this afternoon, in and around the Brian Head fire. The smoke plume
from the fire remains visible on satellite as the plume drifts to
the southeast. As the atmosphere has become destabilized, the
smoke plume appears to be growing. Winds statewide largely remain
northwesterly this afternoon and some locally breezy conditions
are observed.

Going in to the weekend, the flow remains mostly unchanged under a
building ridge and northwest flow aloft. Moisture fields are pretty
meager, with mixing ratio values 3 g/kg or less. Temperatures also
change very little day to day, as 700mb temps across the north range
from 10-12C and across the south 16-17C. As the heat continues
across the south, the going excessive heat warning remains in effect
for the Dixie area in the southwest.

The ridge slowly shifts over Utah and southwest Wyoming on Sunday
night and Monday, as a shortwave trough pushes into northern
California. Southwesterly flow will increase over the forecast
area ahead of this trough, and Monday will bring a considerable
warming trend for many locations, particularly across the northern
half of the CWA.

This increased southerly flow will help bring in some additional
mid-level moisture to the area, and isolated showers and
thunderstorms could initiate over the higher terrain of Utah and
eastern Nevada on Monday, with the latter storms potentially
drifting into northwest Utah Monday afternoon/evening. Have
increased POPs slightly for this possibility, particularly across
the far northwest. That said, any storms that do develop Monday
will be high based, and the dry low level airmass will make gusty
winds much more likely than significant rainfall.

The weak shortwave passes through Idaho and northern Utah late
Monday into Tuesday. This is just the beginning of a pattern
change, with a mean trough setting up over the Pacific Northwest.
While most of the moisture and instability generally remains north
of the area through Tuesday and early Wednesday, enough low level
cool air does look to filter into Utah to drop temps a bit,
including ending the long string of very hot temperatures in far
southern Utah. (That said, temperatures Tuesday generally
decrease from "very hot" to simply "hot".)

Timing differences in the global models begin to become more
evident Wednesday through Friday, though the general idea is that
a series of weak waves and surface cold fronts could push through
the northern half of the CWA through the latter half of the week.
Have generally decreased temps a bit and raised POPs for the north
Wednesday and Thursday. Leaned a bit more toward the GFS timing
for now, which has a cold front with decent moisture associated
with it on Wednesday afternoon.


.AVIATION...VFR with clear skies overnight at the SLC terminal.
North winds will become light and variable as the night progresses.


.FIRE WEATHER...Northwest winds will continue to weaken across the
south and east this evening, becoming much lighter Saturday. Hot and
dry conditions remain in place area wide and will continue into the
weekend. A more stable air mass across northern Utah will create
poor mixing and clearing indices while the south remains good to
excellent for clearing.

High pressure is building back across the region which will result
in more widespread Haines values of 6 as the airmass becomes warmer
into next week. A weak system has the potential to bring isolated
showers and thunderstorms mainly across the north Monday into
Tuesday, and lightning is possible as well with these storms.


UT...Excessive Heat Warning until 10 PM MDT Sunday for UTZ019.



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