Scientific Forecaster Discussion
fxus65 kslc 231624
Area forecast discussion
National Weather Service Salt Lake City Utah
1024 am MDT sun Jul 23 2017
Synopsis...moisture in place across Utah will spawn another round
of showers and thunderstorms today. A new northward surge of
moisture into the area early in the upcoming week will bring an
increase in shower and thunderstorm activity through midweek.
Discussion...the vorticity Max entering southwest Montana
has a lobe extending back into extreme northern Utah late this
morning. This lobe has generated organized convection across
eastern Idaho through extreme northern Utah this morning, and will
likely continue to generate convection until it exits the forecast
area early this afternoon.
Current GOES precipitable water imagery places the best moisture (pwat values
between 1.00" and 1.25") near the Arizona border and across
extreme western Utah. Strong surface heating across southern and
eastern Utah will lead to early convective development over the
mountains late this morning, with scattered showers/storms during
the afternoon/early evening hours. Generally weak mean layer flow
should keep much of this activity tied to the higher terrain, and
also promote locally heavy precipitation due to slow movement of
the individual cells.
West-central through northern Utah will likely see a slower start
to deep convection due to somewhat inhibited surface heating from
high clouds, and from dynamic subsidence across far northern Utah
behind the exiting vorticity lobe. Convection should finally pick
up later this afternoon and early evening as surface heating
peaks. Also looking at the possibility of some dynamic support for
lift as GOES 16 water vapor imagery does indicate a weak dynamic
feature lifting slowly north through southwest Utah late this
Model guidance still showing a moisture surge from the south
developing early this week. Current GOES imagery indicates a
rather impressive moisture pool to tap into across Arizona through
northwest Mexico. The surge should get legs late Monday/Tuesday
as a deep layer southerly flow develops over the Great Basin.
Looking at scattered or better areal coverage of convection by
Tuesday as weak dynamic features embedded in the mean southerly
flow supply the necessary lift to this well primed air mass.
Issued an earlier update to address convection across the far
north this morning through early afternoon. Remainder of the
forecast package looks good at this time.
Aviation...a weather disturbance moving through far northern Utah
has spawned convection near the Idaho border this morning. Outflow
from this convection could bring an early return to northerly
surface winds by late this morning.
Showers and storms forming over the surrounding higher terrain
will likely drift into the valleys mid to late afternoon. Any
impacts from this convection should hold off until late afternoon
or early evening. Gusty/erratic winds and lightning will be the
main issue late this afternoon and evening.
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