Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Salt Lake City Utah
245 am MDT Friday Apr 18 2014
Synopsis...a pair of storm systems will impact the region through
the weekend. A stronger storm will impact the area during the
middle of next week.
Short term (through 12z monday)...
water vapor loop shows a ridge over The Rockies with the next
trough along the West Coast. Amdar 400-250mb wind observations
reveal a 100- 135kt cyclonically curved jet off the northwest
Pacific coast...translating to an anticyclonically curved jet over
the northern rockies. GOES/GPS/rap/00z radiosonde observation indicate the
precipitable water value ranges between 0.17" and 0.54".
Best chance for showers today will be in the cool sector across
northern Utah...though enough moisture from a Southern California
closed low will allow convection in the central and southern
mountains during the afternoon. Copious clouds develop and thicken
through tonight. High temperatures will be earlier in the day across
the north owing to a morning cold frontal passage. Gusty southwest
winds ahead of the cold front given strengthening pressure
gradient and 30kt of southwest flow at 700mb.
Frontal boundary settles into central Utah tonight...with further
moisture advection occurring across southeast Utah. Bumped up probability of precipitation
ahead of slow-moving weakening Arizona low through Saturday
morning...with divergence aloft spreading northward over southern
While the remnant of the Arizona low continues to weaken and lift
through southeast Utah Saturday afternoon...ridging begins to build
across western Utah. With thinning clouds and not a lot of
subsidence yet...believe fairly widespread convection will develop
especially south of Interstate 80 during the afternoon and evening
hours...given the ambient moisture in place. Depending how slowly
the southern feature moves through...deformation zone could be in
the vicinity of our eastern zones during peak heating...thus raised
probability of precipitation once again.
Next northern rockies wave Saturday night will prompt a shallow cold
front across northern and into central Utah Sunday. With remnant
moisture in place...kept mention of convection along and ahead of
this feature...with plenty of drying expected across the far north.
Storm Prediction Center thunder guidance from short range ensembles indicate potential
each afternoon through Sunday.
Long term (after 12z monday)...
a fairly strong ridge will begin the long range forecast
period...with temperatures above normal levels Monday into
Tuesday. By Tuesday...it is not out of the realm of possibilities
that the Wasatch front will see temperatures maximum out around 80f.
These warm temperatures will come to a rather abrupt end on
For several days...global models have been advertising a
large...cold Pacific trough that would impact the western United
States...though the details have been somewhat inconsistent. Model
to model consistency has improved with the 00z model runs.
Differences remain in the specific details as is typical for the middle
to long range portion of the forecast.
The 00z GFS brings a cold...negatively tilted trough through the
Great Basin Tuesday into Wednesday...keeping the system largely in
place until an upstream wave dislodges the trough and finally moves
the system out of the northern rockies Thursday. The 00z ec favors
a more consolidated...negatively tilted solution that is far more
progressive than the GFS. Thus...confidence in specific timing of
various features is a bit on the low side. Decreased probability of precipitation across
southern Utah as it is looking more and more likely that any
precipitation will be mainly across the northern half of Utah.
The main takeaways regarding the impact of this system will be
temperatures and wind. Very warm temperatures can be expected Monday
and Tuesday ahead of this system...approaching record levels for
some parts of the Wasatch front by Tuesday. Much colder
temperatures will be felt in many locations by Wednesday and the
cool temperatures will likely remain in place through the
remainder of the forecast period.
The biggest impact will likely be a period of very strong
winds...with gusts in excess of 60 miles per hour possible Tuesday morning into
Tuesday night. Anyone traveling or impacted by strong winds should
continue to monitor future forecasts as this event looks like it has
the potential to be a high end wind event.
Another large cold Pacific trough is forecast by both the 00z ec and
00z GFS toward the end of the model run...impacting the area next
weekend. Definitely something to keep an eye on...but confidence is
quite low at this time.
Aviation...gusty southerly winds will continue at the slc terminal
through the morning hours. A cold front is expected to cross the
terminal between 16-18z...shifting winds to the northwest. Winds
will remain gusty through much of the afternoon. A few showers will
be possible in the vicinity of the terminal near and behind the cold
front. These could bring gusty and erratic winds to the terminal.
For more information from National oceanic and atmospheric administration/S National Weather Service visit...
http://weather.Gov/saltlakecity (all lower case)
For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)