Scientific Forecaster Discussion
fxus65 kslc 201056
Area forecast discussion
National Weather Service Salt Lake City Utah
456 am MDT sun Aug 20 2017
Synopsis...southerly flow aloft next week will bring an increase
in mid-level moisture, leading to increasing showers and
thunderstorm chances by midweek. Eclipse viewing will likely be
hampered by clouds in southern Utah.
Short term (through 12z tuesday)...mid level ridging, centered
across the southern rockies, is currently expanding northwestward
across the forecast area, while an upper low is noted spinning
along the Southern California coast. This is resulting in a light
southerly flow aloft across central/southern Utah with a lingering
deformation axis extending across the north. A few showers are
noted in 88-d imagery from the southern Wasatch front southward,
however with a fairly deep and dry sub-cloud layer most of this is
likely not reaching the surface.
Moisture is expected to gradually increase across the south today
through tonight and into Monday, as the flow around the Southern
California low gradually pulls moisture across the Lower Desert
southwest northward into southern Utah. This will result in an
increasing threat for showers and thunderstorms later today
through tonight and into Monday, although precipitable water values remain less
than an inch. With the increase in moisture cloud cover will
likely obscure monday's eclipse across portions of central and
Further north, northern Utah will remain on the far southern
periphery of a belt of westerlies extending across the Pacific
northwest/northern rockies, with lingering moisture maintaining a
small threat for convection over the uintas today. A shortwave
trough passing well north of the area tonight is expected to
bring a wedge of drier mid level air into southern ID, and the
models suggest only a limited amount of mid level moisture
extending across northern Utah Monday morning, which it seems
likely will burn off by mid morning. As such conditions for
viewing the eclipse Monday are looking more favorable across the
northern third of the state.
Long term (after 12z tuesday)...not much change in the long term
forecast with this morning's package. A relatively weak upper level
low off the California coast will gradually move eastward through
Thursday. A jet streak associated with this low will provide
favorable jet dynamics to the area Tuesday into early Wednesday.
Unfortunately, due to southwesterly flow and net drying...moisture
will be fairly anemic. Expect convection will be able to overcome
this but will remain on the low end of coverage Tuesday and
An upper level low crossing the US/Canadian border near Washington
Thursday into Friday will bring a boundary across the area Friday.
This will put an end to the any precipitation into the weekend.
Aviation...southerly winds will continue at the slc terminal,
shifting to the northwest between 18-20z.
Fire weather...southerly flow aloft will gradually pull moisture
northward across the region through the remainder of the weekend
and into early next week. The best moisture will initially remain
across southern Utah through Monday before gradually spreading
northward Tuesday. With this moisture returning northward, the
chance for wetting rains will increase across the area. A drier
westerly flow is expected to develop late in the week into next
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