Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
253 am MDT Monday Apr 27 2015
Synopsis...high pressure will return beginning Monday and remain
through middle week. A cold front is expected Thursday.
Short term (through 12z thursday)...
water vapor loop shows a closed low nearing the Texas pan handle
with the last piece of the trough working across Utah. A ridge is
building into the west. Amdar 400-250mb wind observations show a
100- 130kt anticyclonic jet over western Canada and the eastern
Great Basin. GOES/GPS/rap/00z slc radiosonde observation indicate the precipitable
water value ranges between 0.15"-0.20" far western valleys and
mountains...to 0.40"-0.50" across the central and eastern valleys.
Blended total precipitable water product indicates values above
normal across The Rockies and Pacific northwest...below normal
Gusty winds continue to affect canyon/downslope sections of Dixie
early this morning though speeds are just below advisory criteria.
Have cancelled the hard freeze warning for the Sanpete/Sevier
valleys as stratus hung in too long there for temperatures to cool
rapidly enough. Hard freeze conditions are still possible between
Delta and Cedar City.
Enough instability re-develops this afternoon for scattered showers
and isolated thunderstorms over the eastern mountains. An isolated
risk remains tomorrow afternoon. Otherwise a ridge of high pressure
builds in promoting a warming trend early in the work week ahead of
an approaching cold front.
Long term (after 12z thursday)...
Pacific northwest trough splits as it moves onshore Wednesday
night. Models in fairly good agreement that the northern branch
stays well north of the area as it tracks east on Thursday. It
does...however...push a frontal boundary into northern Utah during
the day Thursday that then stalls and weakens over central Utah.
700 mb cooling is modest...only a few degrees at best...but the
boundary does appear to have just a bit of moisture with it that
will help with the development of convection...primarily over the
Behind the system...a somewhat unstable zonal flow is expected to
hang around over the weekend before the southern branch of the
system finally moves onshore over Southern California/northern
Mexico on Monday. Models in better than usual agreement this far
out...keeping the system south of the area through day 7 but
bringing associated moisture and instability into the forecast area.
Have raised probability of precipitation just a bit for Monday to account for this.
Aviation...the slc terminal will see VFR conditions through the
morning with mostly clear skies. Northwest winds are expected to
become light southeasterly or light and variable between 11z and 13z
before returning to the northwest between 15z and 17z.
Fire weather...a warming and drying trend is forecast into middle
week. Northerly winds will be locally gusty across portions of
southern Utah through this evening. A few showers and isolated
thunderstorms are possible across the eastern mountains the next
couple of afternoons. Snow level near 9kft today rises to 10kft
Southerly winds will increase a bit Wednesday afternoon ahead of the
next cold front. This front is forecast to cross northern Utah
Thursday...stalling across central Utah Friday. Winds will shift to
the north with slight cooling and moistening. Isolated to scattered
showers will be a threat across the north.
Utah...hard freeze warning until 9 am MDT this morning for utz015-016.
Short term/fire weather...rogowski
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