Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 200931

Area Forecast Discussion
National Weather Service Salt Lake City UT
331 AM MDT Sat May 20 2017

.SYNOPSIS...High pressure will temporarily build into the area
today, before a weak trough crosses northern Utah on Sunday. A
ridge will build into the west next week bringing a warming/drying
trend through the middle of the week.


Water vapor loop shows an eastern Pacific ridge with the next
disturbance over the Pacific Northwest. AMDAR 400mb-200mb wind
observations reveal a 75kt-115kt cyclonic jet over the Pacific
Northwest becomes northwesterly over the Rockies into the upper
level trough shown over Colorado and New Mexico. GOES/HRRR/00Z
KSLC RAOB indicate precipitable water values range from
0.15"-0.25" mountains to 0.40"-0.50" valleys.

SREF indicates weak instability develops today well ahead of the
approaching disturbance. Simulated Reflectivity from the Convective
Allowing Models suggests isolated shower and thunderstorm activity
develops in the mountains of northern Utah and northeast Nevada,
drifting southeast across the adjacent valleys.

As the disturbance begins to reach southern Idaho tonight,
expecting coverage of showers and perhaps a thunderstorm to
increase across the north with SREF indicating maintenance of
some instability overnight. This convection should begin to ease
south into central Utah tomorrow afternoon, lingering through the
evening before dissipating. Northwest Utah will be drying out due
to subsidence behind the wave by tomorrow evening.

The warming and drying trend behind last weeks storm continues
through the weekend.

Could see some enhanced easterly canyon winds along the Wasatch
Front late tonight into early tomorrow due to a building
northeasterly pressure gradient. Winds at 700mb though are
west/northwest supporting the thought that this will be a minor
and shallow event.

Sunday`s shortwave fully exits the region on Monday, kicking off
a warming and drying trend as a ridge amplifies over the west
coast. One last shortwave trough moving through Colorado late
Monday through Tuesday could affect the eastern portions of the
CWA, but the only real impact looks to be some shallow low-level
cold advection, which could keep Tuesday temperatures in the east
similar to Monday (while the rest of the CWA continues to warm).
Otherwise, pretty much all of the moisture and instability with
this wave looks to remain east of the forecast area.

The ridge axis slides east and moves overhead on Wednesday,
providing for what will probably be the warmest day of the week in
most locations. Thursday could also be fairly warm, but a trough
approaching from the Pacific Northwest looks to start impacting the
area, with increased cloud cover and convection ahead of the trough.
With a little better agreement in the development and progression of
this trough, have increased POPs for Wednesday night and Thursday,
primarily across the northern half of the CWA.

Considering how jumpy the models have been for the end of the week,
confidence remains relatively low for Friday and Saturday. That
said, the current solution that models have latched onto involves
lingering the aforementioned trough just to our north for most of
Friday, then swinging at least a piece of it through the area late
Friday into Saturday. For now, have moved the forecast toward this
idea, which would include a continued chance of showers across at
least the north, and a cooling trend heading into the weekend.


Surface winds at the SLC terminal are expected to switch
to the northwest around 17-19Z, with a slight chance that
southerlies persist through 20Z. Otherwise, mostly sunny to partly
cloudy skies should prevail, though significant cloud cover will
likely return after 00Z.


Weak transport winds will limit clearing to the fair to good
categories across many valleys during the next several days.
Mixing also becomes limited across the western valleys Monday.

Isolated showers and storms across the far north this afternoon,
ahead of a disturbance dropping south from Idaho tonight and
tomorrow. The arrival of the disturbance will increase the shower
and thunderstorm threat.

The warming and drying trend this weekend will accelerate for the
first half of the work week as a ridge builds over the region.





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