Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
932 am MDT Tuesday Jul 28 2015
Synopsis...below normal temperatures early this week will give
way to a warming trend for the latter half of the week as a strong
ridge of high pressure builds over the Great Basin. Moisture will
begin to return to southern Utah late this week and then spread
slowly north through Utah over the weekend.
Discussion...heights are beginning to rebound in wake of
yesterdays trough passage and associated cold front...but
unseasonably cool temperatures will remain the norm today. 700 mb
temperatures per 12z kslc radiosonde observation near +4c this am indicative of the cool
airmass in place. Although warm advection will coincide with
building heights today...will struggle to reach the upper 70s to
low 80s most valley locales during peak heating this afternoon.
High pressure will bulge northwest across the eastern Great Basin
middle/late week allowing a continuation of building heights and warm
advection through that time...this allowing a significant warming
trend to ensue. 700 mb temperatures at kslc prognosticated to climb back up to near
+15c by Friday allowing a return to near normal temperatures late
The high pressure axis will remain generally south and west of
the forecast area through late week pinning the bulk of higher
precipitable water south and west as such. Will likely see a gradual infusion of
middle level moisture across the far south beginning tomorrow...but
lack of substantial instability should limit convective potential
to generally terrain based cumulus. A northeast shift of this axis late
week through the weekend will allow for a net increase of middle
level moisture/convective potential during that time...and this
remains the primary forecast problem to focus on this shift.
No updates made or planned. Previous long term discussion below...
Long term (after 0000 UTC thursday)...medium range models in good
agreement on the evolution of the large scale pattern for the
latter half of the week through the weekend. Upper level ridge
amplifies late this week extending from the Southern Plains
through the Pacific northwest. Beneath the strengthening ridge
temperatures will climb through the end of the week to near
normal before leveling off for the weekend.
Models continue to vacillate on the return of higher precipitable
water values late this week into the weekend...especially with
respect to how quickly the deeper moisture lifts north through Utah.
European model (ecmwf) and GFS continue to indicate that middle level moisture begins
to return to far southern Utah on Thursday and with elevated
instability in place slight chance storms for the southern
mountains still looks good. Friday through early next week the
threat of convection slowly expands north each day until slight
chance...or chance probability of precipitation...are needed statewide by Monday
The slow return occurs since deep southerly flow never really
develops over Arizona and Utah. Instead moisture seeps northwest into California
and Nevada and then eventually fills in the eastern Great Basin.
Models continue to struggle pinning down the timing of the
moisture return and plenty of uncertainty still remains. If the
center of the upper high shifts a little further east over The Four
Corners region....setting up southerly flow over Utah...the
moisture could return north much more quickly. Given the
uncertainty associated with the moisture return...have continued
idea of slow northward expansion from late this week into early
Aviation...no operational weather concerns to note for kslc
through the valid taf period. Northwest winds will remain in place
through this evening...with a return to light southeast winds
Fire weather...the airmass in the wake of mondays cold front will
bring unseasonably cool temperatures to the district Tuesday.
Gradual warming can be expected through Wednesday. As high pressure
shifts...moisture will gradually increase across southern Utah
Thursday into Friday. This moisture increase will gradually
transition northward...reaching portions of northern Utah by Sunday
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