Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 221512

Area Forecast Discussion
National Weather Service Salt Lake City UT
912 AM MDT Sat Oct 22 2016

.SYNOPSIS...An unseasonably warm southwest flow will exist across
the area this weekend. Moisture will spread north into Utah late
Sunday, and will continue to increase into early next week. Drier
conditions will return for the middle of the week.


Water vapor loop shows southwest flow aloft between a cold closed
low over the Gulf of Alaska and a strong ridge over Texas. Several
disturbances are shown embedded within the southwest flow aloftto
our northwest, with the strongest off the Pacific Northwest coast.
Another disturbance was over southeast Pacific Ocean near 25N
125W. MDCARS wind observations show a 125-140kt anticyclonic jet
from the Pacific Northwest into south central Canada and down the
western Great Lakes. GOES/HRRR/12Z KSLC RAOB indicate the
precipitable water value ranges from 0.15"-0.25" mountains to
0.30"-0.40" valleys. Blended Precipitable Water product shows a
moisture plume beginning to surge north from the Gulf of
California. A second plume of moisture was off the Pacific
Northwest coast extending back into the central Pacific where it
is substantially greater in magnitude.

HRRR 850-700mb Thickness/Saturated Equivalent Potential
Temperature/streamlines indicate a shallow cool front over south
central Idaho and northeast Nevada this morning will lay out just
south of Interstate 80 this afternoon. This will reinforce a 9C
inversion evident on the 12Z KSLC RAOB keeping temperatures in the
60s most locations.

To the south of this boundary it will be well mixed up to 700mb with
temperatures well into the 70s to mid 80s Dixie. Gusty southwest
winds with 700mb flow expected to near 35kts by late afternoon.

Updated to refine the Sky forecast today. Satellite trends
indicate increasing high clouds for much of the area today. Added
mention of mostly cloudy conditions to far northwest Utah this
afternoon closer to the aforementioned upper level jet.

Otherwise tweaked the temperature/rh curve today based on
observations and latest guidance. Rest unchanged.


The axis of the upper ridge to the east of Utah has left the
forecast area under an unseasonably warm and dry southwest flow
aloft. A moderately strong near 700mb flow along with adequate
mixing should generate fairly strong southerly winds across the
southern and western valleys the next couple of days.

GOES Pwat imagery shows a decent amount of moisture pooled over
southwest Arizona/northwest Mexico this morning. This moisture
will remain well south of the state through early Sunday, then
quickly move north into southwest Utah as the mean layer flow
backs and strengthens ahead of the upper trough advancing on the
west coast.

A few terrain-based showers could show up along the leading edge
of the moisture surge over southwest Utah late Sunday afternoon
through early evening. Model guidance does show a weak embedded
shortwave lift northeast into southern/central Utah Sunday night.
This feature will bring some expansion in areal coverage to
showers, though with lift still on the weak side would think that
precip amounts will remain on the light side.

A more substantial shortwave rotating out of the west coast trough
looks to bring more widespread and somewhat heavier precip to the
forecast area Monday through early Tuesday. This dynamic feature
will encounter rather substantial amounts of moisture by the time
it arrives in Utah. Convection could strengthen across western
and northern Utah Monday night as cooler mid-level air arrives and
the nose of the Pacific jet punches into the western Great Basin.

Showers will continue into Tuesday morning, with most of the
activity along the passing remnant of the shortwave across
northern and eastern Utah. Increasing dynamic subsidence and
building heights Tuesday afternoon should bring a rapid decreasing
trend to showers by late in the day.

Ridging will be present at the start of the long term portion of
the forecast. A fairly robust trough is expected to be approaching
the Pacific Coast, helping to shift the ridge eastward, and
bringing increasing southwesterly flow to the area Wednesday.

Given the ridge remains in place across the southern Rockies and
southern Plains, the trough is expected to split across the West
Friday. Right now, the split occurs in a position to still bring a
fairly robust system through Utah Friday.

Global models continue to have timing differences in the evolution
of this trough as well as when/if the trough will split. With a
significant disparity between various global model solutions,
started increasing pops in the extended, particularly Friday, though
did not raise pops nearly as high as the GFS in particular would
indicate. If model to model and run to run consistency increases
with the evolution of this pattern and the split occurs in a favored
location, Utah may be in store for a fairly significant precipitation
event. Confidence is low at this time, however.


Operational weather concerns will remain minimal at the KSLC
terminal through the valid TAF period. Light and variable winds
currently in place will become a prevailing light southerly by
16z, remaining in place through 19-20z, before switching to the
northwest per norm. VFR conditions under largely clear skies will





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