Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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744
FXUS65 KSLC 221517
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
917 AM MDT Mon Apr 22 2019

.SYNOPSIS...
A low pressure system over southwest Utah will drift south into
Arizona today. High pressure aloft will build in behind the
exiting low pressure beginning tonight. This high pressure will
remain across the Great Basin through the middle of the week.

&&

.DISCUSSION...
Water Vapor Satellite clearly shows the circulation of our Spring
storm, west of Cedar City drifting toward the southwest into
Nevada. As the day progresses, this feature is expected to shift
southward along the Arizona/California border. This will position
the spine of our mountains along the mid/upper level deformation
axis that stretches northeast from the circulation. Wrap-around
precipitation is occurring from southwest Wyoming across northern
Utah.

The combination of cold air aloft and diurnal heating will lead to
modest instability along the spine of the mountains this
afternoon. Forcing, in addition to the usual terrain circulations
will also include the aforementioned deformation axis. This
should result in widespread showers and thunderstorms, which drift
southwest. Valleys such as from Provo to Cedar City, along with
the central valleys, are most likely to see shower and
thunderstorm activity that moves off the terrain today. Snow level
should be around 9,500 today, with spotty snow accumulations
likely above that level.

Given relatively low LCL, dry microbursts are less of a concern
today, and forecast soundings also don`t point to heavy
precipitation given drying aloft and in the boundary layer.

Northern Utah should see the start of a warming trend this
afternoon, with the airmass stabilizing as the storm shifts
southward.

Locally gusty northwest/north winds are expected along and west
of the I-15 corridor due to the tightening pressure gradient.

&&

.PREVIOUS DISCUSSION...
The upper low currently centered over southwest Utah will
continue to work south into western Arizona later today. Building
in behind the exiting upper low will be high pressure aloft nosing
into the western/northern Great Basin beginning late this
afternoon and evening. This high pressure will expand across much
of the western CONUS for the middle of the week.

Warm advection wrap around in the northern flank of the upper low
extends across southwest Wyoming through far northern Utah early
this morning. This thermally-driven lift has been gradually
weakening overnight, with only residual light precip across
southwest Wyoming and far northern Utah at this time. Precip
remains convective near the Utah/Nevada border, though this
activity will likely rotate west into Nevada over the next couple
of hours.

One other area of active convection exists in the eastern flank
of the upper low across south-central through east-central Utah.
The driving force for this convection is likely a vorticity lobe
rotating north around the upper low. Not anticipating any further
strengthening or expansion in areal coverage of the convection as
the dynamic and thermal forcing are weak, as is the upper
divergence in the absence of any significant jet support.

The deformation axis associated with the exiting upper low will
align southwest through northeast across Utah this afternoon.
Increasing instability along with abundant moisture will allow
convection to expand along the deformation late this morning and
afternoon. This convection will dissipate quickly this evening as
the upper low continues south and with the loss of daytime
heating.

High pressure aloft building into the area from the west will
bring mostly dry and increasingly warm conditions to the forecast
area through Thursday.

Globals more in line regarding the future presence of short wave
energy crossing the northern Rockies region beginning Friday
night, each delving a bit further south in latitude thereafter
through the weekend (than in days previous). Although still
remaining north in the northern Rockies, passage of these waves
thereafter through the weekend does look to lower heights in the
north, with a slight cyclonic nature of the flow aloft aiding to
pin the ridge further south of the area. Ample moisture and
diurnal instability within this cyclonic flow looks to promote
daily convection in the north, though the south looks to remain
more stable/dry tied closer to the remnant ridge. Have maintained
generally chance/slight chance PoPs each day through the weekend
in the northern third as such, and with a slight diurnal trend in
likelihood.

Coincident with this will be a closed low slowly churning east off
the SoCal coast, a feature that looks to become absorbed and
translated inland within the northern branch flow early next week.
Model inconsistencies in how this absorption evolves vary in detail
(and resultant timing), but the big picture points towards a
maintenance of unsettled conditions early next week as well. Its a
continuation of spring, but remaining mild if not a bit above normal
at its coolest.

&&

.AVIATION...
A band of light precipitation will bring vicinity showers and
ceilings below 7,000` AGL to the SLC terminal through the early
afternoon. While light NW winds are most likely, there is a 30%
chance of light easterly winds through about 19Z. Meanwhile, there
is high confidence in NW winds for the afternoon period.
Showers/thunderstorms in the afternoon should be displaced to the
south and east of the terminal, but may impact S/E approach gates
through about 01Z. Clearing skies are on the way for the evening
and overnight hours.

&&

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

$$

PUBLIC...10/Conger/Merrill
AVIATION...Van Cleave

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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