Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
405 PM MDT Friday Jul 29 2016
Synopsis...high pressure aloft across the southern rockies into
Southern California will remain in place over the next several
days. Moisture rotating around this ridge will increase across
the region this weekend, then remain in place through early next
Short term (until 06z tuesday)...the upper ridge axis across the
southern rockies through Southern California will remain
relatively unchanged in position through the short term forecast
period. Deep layer moisture concentrated across Arizona through
southern Nevada has worked into southwest Utah this afternoon.
Will see this moisture continue to wrap around upper ridge and
eventually cover the state by late Saturday afternoon or early
For this evening will maintain the greatest concentration of
showers/storms near the best moisture over west-central through
south-central Utah. Isolated showers/storms will continue over the
northeast mountains until loss of heating around mid-evening.
A possible vorticity Max over north-central Nevada could bring
isolated thunderstorms into northwest Utah later tonight. Suspect
this activity will at best generate isolated dry storms over the
far north, with little support to move into northeast Utah and
southwest Wyoming late tonight/early Saturday.
Looking at a significant increase in convection as moisture expand
over the remainder of the state Saturday. Most of this convection
will generate minimal rainfall outside of southwest Utah where the
moisture profile should be more supportive for locally heavy
rainfall. Winds and lightning look to be the main impact from
convection on Saturday afternoon.
The upper level trough settling into the Pacific northwest
through the northern rockies Saturday night/Sunday could bring
strong convection to the northern for the latter half of the
weekend. Embedded shortwaves associated with the main trough will
graze far northern Utah Saturday evening, then again on Sunday,
this dynamic support along with a favorable moisture profile
should be sufficient for organized, and possibly strong,
convection with these passing features.
Drier air will begin to move northern Utah/southwest Wyoming early
next week. For the remainder of the state the bulk of the weekend
moisture will remain in place, leading to mostly terrain-based
convection to begin the week.
Long term (after 06z tuesday)...moisture is forecast to reside
across much of the forecast area at the beginning of the long term
period, as mid level ridging is forecast to reside near The Four
Corners region. An upper low is forecast to quickly translate
eastward through the Pacific northwest/northern rockies region
Tuesday through Tuesday night. The models differ a bit with respect
to how much drying occurs across northern Utah in the wake of this
wave during the midweek period, with the ec more aggressively pushing
drier air southward into Utah, while the GFS is more stubborn in
keeping deeper moisture across a good portion of the County Warning Area.
Regardless, moisture looks to remain in place across southern Utah
throughout the upcoming week. Temperatures at the beginning of the
long term period will remain above normal, but with slightly cooler
air behind the passing wave, should see a slight cooling trend
during the latter half of the week.
Fire weather...moisture circulating around the upper high over
the southern rockies remains concentrated over the southern two-
thirds of Utah this afternoon. This moisture will work north
across the remainder of the state Saturday, leading to scattered
convection across all fire districts this weekend.
For tonight convection will likely not generate more than isolated
wetting rains across southern Utah. The threat for mostly dry
thunderstorms and the associated gusty/erratic winds will keep the
fire danger on the high side down south overnight and well into
Saturday afternoon. Wetting rains may finally become a bit more
common for the south as the air mass continues to moisten down
south late Saturday afternoon and evening. For the north could see
a few dry thunderstorms over the northeast mountains and near the
Nevada border this evening. The increase in moisture Saturday will
lead to increased areal coverage of showers/storms, though the
threat of wetting rains will remain low. Will expand the red flag
warning to cover all zones with critical fuel conditions.
A weather disturbance moving east across the northern rockies
late Sunday/Monday will draw somewhat drier air into the far
north heading into early next week. For the remainder of the
region moisture will remain in place, leading to the potential of
showers and thunderstorms, mainly terrain-based, into early next
Aviation...winds at the slc terminal are expected to Switch Back to
the southeast around 03-05z. Clouds will likely increase overnight,
but any ceilings should remain above 7000 feet.
Utah...red flag warning until 10 PM MDT Saturday for utz492-493-495-497-
Red flag warning from 10 am Saturday to 3 am MDT Sunday for
Excessive heat warning until 9 PM MDT this evening for utz019.
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