Scientific Forecaster Discussion
fxus65 kslc 240935
Area forecast discussion
National Weather Service Salt Lake City Utah
335 am MDT Wed may 24 2017
Synopsis...high pressure aloft will shift east of the region
this morning. This exiting high pressure will be followed by a
series of weather disturbances which will impact Utah late
Wednesday through the first half of the upcoming weekend.
Short term (through 12z friday)...
water vapor loop shows a low amplitude ridge overhead, with a cold
and deep closed low over southern British Columbia. Amdar 400mb-
200mb wind observations reveal a 130kt-155kt cyclonic jet over the
Pacific northwest, which translates to a 110-130kt anticyclonic
jet east of The Rockies. GOES/hrrr/00z kslc radiosonde observation indicate
precipitable water values range from 0.15"-0.25" mountains to
The warming and drying trend will peak today with a ridge overhead
this morning. The ridge shifts to the east as the day progresses
allowing strong westerlies to develop. Gusty westerly flow will
mix down to the surface, though values are sub-advisory.
The other threat late this afternoon and early this evening are
strong/erratic winds associated with dry microbursts. Heights fall
this afternoon as the subtropical jet noses in from the Desert
Southwest. This should increase mid level moisture enough that we
see modest destabilization by late afternoon. Any activity that
develops will be high-based, with an inverted-v sounding yielding
a good bit of dcape. Simulated reflectivity from NCEP and our
local convective allowing models indicate convection initiating
in northern and central Utah late day ahead of the approaching
cold front. The last several runs of our local convective allowing
models indicate wind gusts of 40-60kt associated with this
convection for several hours on either side of 01z 25 may. Would
however be more concerned about severe wind gusts if the mid level
flow was greater across central Utah, but its increases
significantly further north toward the Idaho border.
Coverage of rainfall looks to increase this evening as the cold
front sweeps across northern Utah. Convection is expected to last
well into the night given dynamics and instability in place,
though will be on the decline late tonight as the boundary
becomes more diffuse and stalls across central Utah.
This boundary should remain across central Utah tomorrow with the
instability axis remaining in the warm sector across south central
Utah where isolated showers and thunderstorms are possible
tomorrow afternoon and evening. The boundary lifts northward as a
warm front tomorrow night, ahead of a cold front which makes its
way across northwest and west central Utah by Friday morning.
Focused shower activity along the Idaho border region late
tomorrow night as the right entrance region of the polar jet
propagates into northern Utah in advance of the next storm system.
Pops were increased a little bit this evening, and focused south
of Ogden to near Provo from north of Delta across southwest
Wyoming. This activity shifts east and a bit south overnight. Area
of pops reduced Thursday to just along the frontal zone and
Thursday night just along the Idaho border.
Went on the high side of guidance for today's high temperatures
everywhere, and in the warm sector tomorrow. Tomorrow will be much
cooler across the north where I leaned more heavily on the cooler
Long term (after 12z friday)...
the last wave from the trough is expected to cross northern Utah
and southwest Wyoming during the day Friday, likely resulting in
at least scattered convection over much of the northern half of
the forecast area. Most convection will tend to dissipate Friday
evening/overnight as the trough weakens and pulls away from the
area. However, enough instability will remain for isolated
convection into Saturday.
Behind the exiting wave, high pressure is expected to move back into
the forecast area, resulting in a warming and drying trend for the
latter portion of the Memorial Day weekend. Maxes by Monday are
expected to run at least 5f above seasonal normals with a bit more
warming through the middle of next week. Conditions remain mostly
dry for the majority of the extended period, though ec/GFS show the
ridge shifting east Wednesday with some instability moving in from
an approaching trough, so have added climo pops for day seven.
the slc terminal will see VFR conditions through the morning with
clear skies. Southeast winds are expected to increase during the
morning before shifting to the northwest between 20z and 22z.
There is a 30 percent chance that the shift will hold off until
the passage of a cold front during the early evening.
excellent clearing is expected most areas through the end of the
work week. The exception is some northern valleys may see clearing
reduced to fair to the good category tomorrow and Friday.
The warming and drying trend will peak today. A cooler and more
moist trough will impact the area during the second half of the
work week. A cold front will cross into northern Utah tonight,
stalling across the central part of the state Thursday, before
finally passing into Arizona late Friday. This will spark isolated
to scattered showers and thunderstorms each day. Showers and
storms late this afternoon and evening will likely contain
Short term/fire weather...rogowski
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