Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 270944

Area Forecast Discussion
National Weather Service Salt Lake City UT
344 AM MDT Tue Jun 27 2017

.SYNOPSIS...A weak upper trough will cross the region tonight and
Tuesday. Additional weak troughs will clip northern Utah through


Water Vapor Satellite shows a shortwave trough crossing Idaho.
400-200mb MDCARS wind observations place a 60-90kt subtropical
westerly jet was nosing into Utah from California. GOES/SLC 00Z
RAOB/HRRR indicate that precipitable water values vary from
0.10"-0.20" central and southern mountains to 0.40"-0.60" northern

Passage of a cold front will take the edge off of temperatures
across the north and central areas, with the boundary stalling
near Interstate 70 late day. Left exit of aforementioned jet will
continue to support high-based showers and thunderstorms into the
morning hours. Despite developing strong instability this
afternoon, the passage of this feature should limit convective
chances. For valleys played as dry thunderstorms with gusty

Westerly flow will mix down from aloft as the day progresses today
and tomorrow, bringing a dry breeze to the region.

Northern stream wave currently over British Columbia should near
northern Utah tomorrow, touching off isolated to scattered high-
based shower and thunderstorms across the north. Given the
cooling aloft and jet dynamics from the associated jet, elected
not to use the dry thunderstorm wording for the northern valleys.

The shortwave trough continues to slide southeast across the area
through the day Thursday. With continued cold advection northwest
flow, Thursday will likely be the coolest day of the week in many
locations. The airmass behind the cold front looks fairly dry,
but cannot currently rule out isolated mountain convection
Thursday and Friday, primarily in the Uintas.

A relatively flat ridge looks to build over the west coast Thursday
night, then shift over Utah on Friday and early Saturday, bringing a
warming trend for those two days. Southwesterly flow increases a bit
Saturday afternoon, as a weak trough slides into the Great Basin
from the west. Models are still struggling a bit with this wave,
including whether to cut it off over Nevada or push it across
northern Utah as an open wave. For now, have kept some slight chance
POPs in the higher terrain of Utah and across the far northwest on
Saturday afternoon, to account for the possibility of increased
instability with/ahead of the shortwave.

Despite different fates for this disturbance, global models re-
converge on Sunday and Monday, building a ridge over the forecast
area heading into early next week. Have maintained above normal
temperatures and mostly dry conditions for days 5-7.


West winds at the SLC terminal as of 0930Z are expected
to switch back to the south or become light and variable around 11-
13Z. Northwesterlies will eventually pick up a bit again through the
afternoon hours. VFR conditions should prevail under mostly clear


ERC values have risen to between the 80th and 96th percentile
across southern and central Utah. Far northeast Utah remains
below 50th percentile, but the remainder of northern Utah is
climbing above the 50th percentile.

Multiple concerns regarding fire weather. The Haines index will
be a 6 today and tomorrow across central and southern Utah. Haines
index will increase back to a 6 across the entire region next

Some of the driest RH values the region sees will continue to
occur today and tomorrow while it remains warm despite the passage
of a shallow cold front this morning. West southwest winds will
respond by increasing. A Red Flag Warning is in place for much of
the state of Utah today and tomorrow. Isolated high-based showers
and thunderstorms primarily across the north and east early this
morning may exaggerate the hazard bringing potential for
lightning and gusty/erratic dry microburts. Luckily this threat
should end this morning.

Another round of isolated to scattered high-based showers and
thunderstorms primarily across the north re-develop tomorrow
afternoon and evening, again bringing the hazard of lightning
potential and gusty/erratic dry microburts.

Northwest flow remains for the remainder of the work week and
weekend. It will remain warm, though RH should rise a bit.
Saturday appears to be the day with the highest probability of
isolated showers and thunderstorms. No strong wind events are
anticipated during this period.


UT...Red Flag Warning until 10 PM MDT Wednesday for UTZ493-495-496-

     Red Flag Warning from 10 AM this morning to 10 PM MDT Wednesday
     for UTZ479-482-484-488-489-494.




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