Scientific Forecaster Discussion
fxus65 kslc 252156
Area forecast discussion
National Weather Service Salt Lake City Utah
356 PM MDT Thu may 25 2017
Synopsis...a cold front will stall over central Utah today. The
next upper trough will move across the area Friday. A cool
northerly flow will follow the trough on Saturday. A warming
trend starts Sunday and continues into mid week.
Short term (through 00z sunday)...a few showers and isolated
thunderstorms are beginning to develop over northern Millard and
Juab counties this afternoon which appears to be associated with
the 700-500 Theta-East Ridge as well as the 300 mb vorticity lobe.
These dynamics should carry these into the evening but will
dissipate after sunset.
Farther north the next storm system will be moving down from
western Idaho and reach northwest Utah late tonight and reach the
Wasatch front by Friday morning. This system appears to have many
of the necessary ingredients for widespread showers and
thunderstorms as the 500 mb cold pool, jet core, 700 mb
convergence and frontogenetic forcing come together over northern
Utah and southwest Wyoming. Have beefed up the pops to likely
from Provo northward. Because the main impact will be about a 3-4
hr period and the timing is centered on midday, it looks like a
complete washout of day but this is not the case as improving
conditions will occur by mid afternoon with only isolated showers
expected beyond 3 PM in the northwest valleys.
Warm dry and breezy conditions will continue over southern Utah
but will cool down some Friday night into Saturday as the cold
front reaches that area. However, across northeasern Utah and
southwest Wyoming the upper level trough will linger into Saturday
bringing some instability showers to the region, especailly over
the mountains. Temperatures will be slightly below normal.
Long term (after 00z sunday)...big picture takeaway regarding
sensible weather for the long term period points to a marked
warming trend and largely dry conditions. Globals continue to
remain on track amplifying an upper level ridge across the western
Continental U.S. Early next week, with ridge axis eventually phasing
overhead midweek. 700 mb temp trend begins near +2 c at kslc Sunday
and climbs to +12 c by Wednesday. As such, temps by midweek are
expected to run near 10 degrees above climo areawide.
Diurnally driven convection, most likely high based and shallow per
bufr profiles, does remain a potential over the higher terrain east
of the I-15 corridor each day, but this is expected to remain
isolated at best and more than likely not much more than cu buildups
during peak heating. Have left a slight chance mention for this in
GFS/European model (ecmwf) continue to waffle some regarding the potential grazing of
a weak trough across northern portions late week, possibly as early
as Thursday (gfs). For now have trended Thursday pop grids towards climo,
with areal extent of convective potential most expansive along the
Aviation...VFR conditions are expected at the kslc terminal
throughout the taf period. Northwesterly winds are expected shift to
the southeast between 4z and 5z, but there is a 30% chance of
northwesterly winds holding on after 5z. Ceiling will gradually fall
overnight, but should remain above 7,000 feet above ground level tonight through
Friday afternoon; however ceiling could briefly fall below 7,000
feet under and in the vicinity of showers.
Fire weather...two areas of concern for showers and thunderstorms
this afternoon and evening will be across the southern mountains
associated with the old surface boundary and farther north across
west central Utah and central mountains into the uintas where a
sharpening upper level trough will act on some mid level moisture
and 700 mb convergence. These showers could produce some gusty
winds to near 40 mph due to dry lower levels with light precip
amounts in any.
A stronger trough will move south into northern Utah Friday
morning with numerous showers and scattered thunderstorms. The
brunt of this system will be from about Spanish Fork northward
where valley locations could pick up 0.05 to 0.30 of an inch and
0.15 to 0.40 of an inch in the mountains. Southern Utah will
continue to have warm and breezy conditions Friday.
The remains of the trough will linger over northeast Utah
Saturday into Sunday allowing for isolated to possibly scattered
showers and thunderstorms over mainly the higher terrain. A ridge
will move in for the beginning half of next week with a warning
and drying trend. Min relative humidity values in most valleys will lower into
the teens and temperatures climbing to 5-10 degrees above normal.
Utah...red flag warning until 8 PM MDT this evening for utz497.
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