Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 120925

Area Forecast Discussion
National Weather Service Salt Lake City UT
325 AM MDT Mon Mar 12 2018

.SYNOPSIS...Strong high pressure aloft will develop over the
region early this week, followed by a major eastern Pacific trough
moving inland by midweek.


Antecedent Conditions...
Severe Drought is occurring from Salt Lake City south and east,
with a pocket of Extreme Drought in south central Utah. Most other
areas are in Moderate Drought except just Abnormally Dry along
the Idaho and Wyoming borders.

Big Picture...
During the past 5 days, the pattern across the Pacific has re-

Water Vapor Satellite shows a ridge over the central Pacific and
a closed low over the eastern Pacific now being picked up by the
strong jet. A weak wave is nearing western Wyoming from southwest

400-250 MDCARS wind observations show a 100-125kt westerly sub-
tropical jet extends from southern California into Texas.
Meanwhile a 125-175kt jet is carving a trough over the far western
Pacific and a ridge over the central Pacific and trough over the
eastern Pacific.

Blended Precipitable Water Product shows a significant Atmospheric
River extends from the equator at 150W into Baja California.
Abnormally high values extend across the Southwest CONUS.

Local Observations and Trends...
12Z KSLC RAOB shows a dry column except some trapped moisture
under a subsidence inversion near 600mb with moderate westerly
flow aloft.

A 1027mb anticyclone is centered over northwest Wyoming, creating
a moderate northerly pressure gradient over the north. Meanwhile a
southeasterly pressure gradient is in place over southwest Utah.

Precipitable Water values range from 0.15"-0.25" mountains to
0.35"-0.55" most valleys.

During the past 24 hours, temperatures are 5-10F warmer across
northeast Utah and southwest Wyoming, except 5-10F cooler
southwest Utah. Dewpoints are 5-15F higher across northeast Utah,
while dewpoints are 5F drier across southwest Utah.

Shortwave traversing areas to our northwest today will provide
for a chance of snow showers across northeast Utah and southwest
Wyoming this morning, with limited to no impact.

Once this feature goes by, heights will build allowing the ridge
to recenter itself from Nevada to Utah tomorrow. A few high clouds
will be possible with the arrival of this feature.

As the Pacific bowling ball enters the Pacific Northwest and
Western Great Basin Tuesday night and Wednesday, expect strong
gusty southerly winds to develop, with potentially many areas
seeing gusts near 45mph while southwest valleys may near 60 mph.

While there will be good forcing for strong gusty winds, one
limiting factor will be increasing cloud cover and chances for
showers as SREF indicates a good chance for destabilizing.

Decided to time best chance of precipitation with the European
depiction of the first ejecting lobe Wednesday and Wendesday

In the short term went at the high end of guidance for
temperatures and low end for RH, transiting to to the reverse
scheme Wednesday with the arrival of the next system.

Global models remain out of sync through the long term portion of
the forecast, with relatively small differences Thursday morning
magnifying by Friday and Saturday. The general idea remains
similar...a large and relatively cold upper level trough is
expected to be located across the PACNW into the western Great
Basin Thursday morning. Earlier in the short term forecast period,
a shortwave ejected from the parent trough. The differences in
the models begin with the evolution of this ejecting shortwave
Thursday into Friday.

The GFS takes this shortwave and strengthens it over the
Montana/Canadian border.  The shortwave then gets caught up with a
northern jet trough moving across interior Canada.  The EC, on the
other hand, ejects this trough into the Plains States. These
differences play a big role in where the upper low eventually ends
up, the timing of precipitation for Utah and the location of
heaviest precipitation.

For now, kept a blend of the global model solutions for the majority
of the long term forecast. Confidence in the exact timing/location
of precipitation from Friday onward is lower than average. Also
decreased temperatures state-wide to below normal levels given the
active pattern anticipated through much of the longer term forecast


Light and variable winds at the SLC Terminal are expected to
continue through 14-16Z. Expect a period of southerly winds this
morning before a shift back to the northwest between 18- 20Z.





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