Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 172149
Area Forecast Discussion
National Weather Service Salt Lake City UT
349 PM MDT WED AUG 17 2016
.SYNOPSIS...A weak low pressure system over northern Nevada will
drift east into extreme northwest Utah by late this evening. This
low pressure will weaken as it slowly tracks east across Utah
Thursday. A dry cold front will settle into extreme northern Utah
and southwest Wyoming for Friday night through Saturday.
.SHORT TERM (THROUGH 06Z SATURDAY)...Water vapor loop shows a
closed low making its way across northern Nevada, with a trailing
wave along the Pacific Northwest coast. MDCARS wind observations
place a 50-60kt northwesterly jet from northern California into
central Nevada. GOES/HRRR/12Z KSLC RAOB indicate the precipitable
water value ranges from 0.35"-0.50" far west central Utah and
mountains to 0.70"-0.90" most valleys.
Forecast soundings indicate the increase in precipitable water
values is being realized in the mid levels, with high-based
activity expected. Due to amount of dry sub-cloud layer and high
DCAPE values, expecting dry microbursts to be an issue. Most
locations will see little to no rainfall, with the best chance for
measurable rain in the higher terrain.
Dynamics remain supportive through the evening hours, and with
heating of the day convective activity will tend to deepen,
enhancing the microburst threat.
The shearing upper level trough will propagate from a line from
about Delta to Evanston. Believe convective focus will be along
and south of this line. Still high-based activity.
By Friday the upper level trough makes its way to southern Utah,
likely suppressing much activity across northern and central Utah.
.LONG TERM (AFTER 06Z SATURDAY)... The forecast area is expected
to be under west to northwest flow on Saturday in high pressure
behind the cold front, which should make it into central and
possibly southern Utah by Saturday afternoon. Drier air is progged
to move in with this flow, with PWs progged to drop below 0.4 inch
over all but southern Utah by Sunday afternoon. A bit of lingering
shortwave instability will keep the possibility of a few showers
in place, primarily over the higher terrain, but most of the
forecast area will remain dry over the upcoming weekend with
temperatures near to slightly below seasonal normals.
Global models continue to be in good agreement in showing moisture
returning to the forecast area from the south beginning Monday, with
the ridge axis shifting east of the area, allowing southerly flow to
develop. EC is a bit more bullish with the amount of moisture, but
even the GFS indicates PWs in excess of 0.75 inch spreading across
the entire forecast area by Tuesday, with moisture remaining in
place through day 7. Have increased POPs a bit with increased
confidence in this moisture surge.
South winds will likely prevail through the evening at KSLC,
although there is a 30 percent chance winds will shift to the
northwest between 22-02z. VFR conditions are expected to prevail
through the TAF period.
Yesterday`s ERC values were above the 90th percentile across
northern Utah, while stations across far southern Utah remain
near the 50th percentile, with values creeping higher.
A Red Flag Warning for much of Northeast and central Utah
continues through this evening for dry thunderstorms and dry
microbursts. The Red Flag Warning for central Utah will continue
through tomorrow evening.
Gusty southwest winds and low RH are possible this afternoon
across southwest Utah where fuels are getting closer to becoming
Through the week it appears as high temperatures will cool
slightly with an increase in RH particularly far Southern Utah and
east of I-15. This is due to the best mid instability for
convection being across these areas. Lightning and gusty/erratic
winds are the primary threats.
A strong cold front may move into northern and central Utah from
Wyoming Friday night and Saturday, providing cooler conditions
while stabilizing these areas from convective development.
UT...Red Flag Warning until midnight MDT tonight for UTZ479>484.
Red Flag Warning until midnight MDT Thursday night for UTZ488-
SHORT TERM/FIRE WEATHER...Rogowski
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