Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 160300
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
900 PM MDT Tue Aug 15 2017

.SYNOPSIS...A weak weather disturbance will exit the state
tonight. Another weak feature will cross Utah late Wednesday
through Thursday. Limited moisture will linger Friday then will
start to increase from the south over the weekend.

&&

.DISCUSSION...A shearing upper trof is moving out of UT and into
the central Rockies this evening with a portion of it hanging
back across the central part of the state.

Convection developed along and south of the axis of this feature
this aftn with storms firing over the Uintas wwd thru Utah Co and
across the west deserts south of Delta, altho the far south stayed
quiet. A few of these cells became strong mainly over Duchesne Co
but one over western Utah Co became very tall.

Showers a isolated weak tstms are still active at this time across
nern thru w-central UT but these should die out pretty quickly by
midnight or shortly after across the far northeast.

The next weak trof will begin to impact western UT tomorrow aftn
the slowly shear out across the CWA thru Thu. Weak forcing with
this wave will bring a threat of convection back into the CWA Wed
eve thru Thu.

.PREVIOUS LONG TERM (After 00z Friday)...An upper level ridge
centered near 40N and 130W with an upper level trough positioned
across the high plains and Great Lakes regions will keep a dry and
warm northwest flow in place across Utah Friday and Saturday. Just
enough moisture will linger around (PW values of 0.3-0.5" over
the mountains and 0.50-0.75" across the valleys) in the mid levels
to keep minor instability in place, allowing afternoon and
evening convection over the higher terrain. Overall, expect a
drying and minor warming trend heading into the weekend as high
temperatures push near or slightly above seasonal normals.

Looking ahead to late this weekend and early next week, the likely
question on many minds is what the weather will be like for
northern UT, southwest WY, and surrounding areas near the
eclipse path, especially Monday around noon. The short answer is
the current forecast is not optimistic for completely clear skies,
although forecast confidence remains limited this far out in
time.

The consensus of today`s 12Z model runs for late next Sunday
through Tuesday is to develop a closed low off the California
coast. Southwest flow ahead of this feature would bring increased
mid-level moisture to much of our area, which combined with some
weak synoptic lift aloft (a weak jet aloft approaches our area and
diffluence develops overhead) would bring a threat of showers and
thunderstorms. Looking at model ensembles in addition to
deterministic runs, there is moderate confidence in the closed low
forming around that time, but there is limited confidence in its
position and magnitude. Those attributes will ultimately determine
how far north the enhanced moisture and synoptic support reaches,
which greatly affects the forecast near the eclipse path. For
example, the deterministic ECMWF has the low much weaker and
farther south, such that northern UT and southeast ID would more
than likely remain dry and clear. Our current forecast remains
largely unchanged and trends towards climatology, which translates
to a chance of showers/thunderstorms over our higher terrain,
especially the mountains of southern Utah and in the Uintas. Stay
tuned as the eclipse forecast details should become clearer in the
coming days.

&&

.AVIATION...Northwesterly winds at the SLC terminal will shift to
the southeast around 04Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

SHORT TERM/AVIATION...Wilensky
LONG TERM...VAN CLEAVE/LUKINBEAL

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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