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Area forecast discussion
National Weather Service Salt Lake City Utah
332 am MDT sun Apr 20 2014
Synopsis...a weak storm system will move slowly out of the
region late today. A warm southwest flow will develop Monday. A
Cold Spring storm will impact the area Tuesday and Wednesday.
Short term (through 12z wednesday)...
water vapor loop shows a disturbance exiting The Four Corners
region as another crosses the far northern rockies. Amdar
400-250mb wind observations reveal a 90-110kt westerly jet over
the Pacific northwest. GOES/GPS/rap/00z radiosonde observation indicate the
precipitable water value ranges between 0.15" and 0.70".
700-850mb rap saturated equivalent potential temperature and
streamlines indicate a cool front will be through northern Utah by
12z...but weaken as it makes its way into southern Utah this
afternoon. Short range ensemble guidance suggests plenty of
instability ahead of the boundary due to the sampled precipitable
water values alluded to earlier. Kept mention of isolated to
scattered convection along and ahead of the boundary through the
afternoon hours...decaying quickly around sunset. Downslope winds
will likely be somewhat enhanced this afternoon and evening across
favored locations of east central and southern Utah.
Return flow sets up quickly Monday with a broad significant storm
developing over the eastern Pacific. Guidance has trended more
supportive of convection mainly in the higher terrain as the warm
front lifts through the area.
Warm south winds develop Monday afternoon and increase Monday night.
Could see our first 80 degree day at slc Monday. Continued to trend
temperatures further above guidance Monday night ahead of a sharp
cold front owing to gusty south winds and cloud cover.
Strong pressure gradient...pressure falls to the north...and 40-
55kts of 700mb flow all supportive of a high wind event Tuesday.
Guidance is a bit faster with the cold front crashing through
northern Utah Tuesday afternoon...with timing still fairly uncertain
at this point. Nevertheless...tight thermal gradient continues to
strongly support a high wind event Post frontal as well...especially
considering the time of day.
Much colder Tuesday night with instability and orographic showers
forecast for the north. Bumped probability of precipitation higher especially north of
Interstate 80. Snow levels fall below 5000 feet Tuesday night with
snow accumulations expected for the northern mountains and benches.
Have issued a Special Weather Statement addressing the highlights
for the upcoming storm. Next shift may need to Ponder a high wind
watch for many of the western zones Tuesday.
Long term (after 12z wednesday)...
by Wednesday morning...the trough is centered over the area with
the associated cold front down into central/southern Utah. Tight
pressure gradient continues to weaken during the daytime
hours...allowing gusty winds to wane. The GFS keeps lingering
moisture and instability over northern and central Utah through
Thursday morning due to its farther south track of the trough.
With its farther south solution...the latest European model (ecmwf) is already
bringing drier air into much of the County Warning Area by Wednesday evening. Have
more closely followed the GFS solution during this period as it
has been the more consistent of the two models.
High pressure is expected to return Thursday as the trough
exits...remaining in place through Friday morning. This will allow
for a quick warming trend over the County Warning Area. The ec warms things a bit
more quickly than the GFS...particularly over the south...due to
Global models continue to indicate another Pacific storm system
moving over the area for the weekend. Latest ec is a bit faster with
the system...bringing it through in pieces Friday night through
Monday. The system appears to be significantly better organized in
the GFS but it really does not begin to impact the area until
Saturday afternoon/evening and exits by Monday morning.
Regardless...all models are indicating moist and unsettled weather
during this period and have moved probability of precipitation above climatology in the
Aviation...the slc terminal will see VFR conditions throughout the
day with some scattered clouds. Southeast winds are expected to
shift to the northwest a bit earlier than usual with the passage of
a weak front...sometime between 15z and 17z.
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