Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
245 am MDT Thursday Oct 23 2014
Synopsis...dry and mild southwest flow will develop today and
persist through Saturday. The next Pacific cold front will arrive
Short term (through 00z sunday)...
water vapor loop shows a ridge over The Rockies...with a deep
closed low off the British Columbia coast. Amdar 400-250mb wind
observations reveal a cyclonic 100-155kt jet over the Pacific
northwest. GOES/GPS/rap/00z radiosonde observation indicate the precipitable water
value ranges between 0.25" mountains...to 0.60" most valleys.
Blended precipitable water product shows moisture tap across Pacific
northwest and northern rockies to be greater than 200% of normal for
this time of year. With the jet axis nosing into the interior
west...continue to expect an increase in middle and high clouds across
portions of western and northern Utah through tonight...before the
ridge amplifies over the region tomorrow.
700mb temperatures rebound to about +8c by the end of the short term
period Saturday. Undercut typical bias corrected guidance blend
across some northern valleys today as BUFKIT profiles indicate
mixing will still be hampered by the stable airmass in place.
By Friday...dry southwest flow aloft strengthens. At the
surface...pressure falls and increasing southeasterly pressure
gradient should support much better mixing. Gusty southwest winds
are forecast across the western valleys and in the higher terrain
(given 500mb flow increasing to 40kts). These conditions continue
through Saturday and are enhanced by increasing pressure gradient
and falling heights/pressure.
Went above bias corrected guidance for lows Friday night across the
western valleys and higher terrain given minimized decoupling
expected ahead of the next storm system.
Short range ensembles indicate that despite a dry southwest
flow...instability begins to increase Saturday. Indicated a few
buildups in the sky grids in the higher terrain. Forecast highs are
just shy of a record for Salt Lake City.
Long term (after 00z sunday)...
model to model inconsistency is the rule through much of the long
term portion of the forecast. A potent area of low pressure off
the Pacific coast Saturday morning will move into western Canada
through Sunday morning. The associated trough will then cross the
western United States...bringing much colder air to much of the
region early next week.
Models have been fairly inconsistent over the past few days
regarding the timing of the cold front on Sunday. The 00z model runs
are no different in this respect. The 00z ec also brings
another...somewhat strong disturbance down the west side of the
longwave trough Monday afternoon...which has implications for the
longevity of the precipitation across the area.
Most model guidance indicates there will be a bit of prefrontal
precipitation...though this is typically overdone. As the front
moves through northern and central Utah...a period of showers is
As the trough cross the area Sunday evening into Monday
morning...the coldest 500mb temperatures will cross the area. Expect
this to keep showers going in the mountains through at least Monday
afternoon. The ec solution would keep showers in the mountains
through early Tuesday morning. Decided to lean more toward the
slower GFS frontal timing but with the quicker end to the
Regardless of the difference of six hours or so with the frontal
timing...this system will bring a significant cold front across the
state Sunday morning through Sunday night. The precipitation band
with the front does not look impressive as it crosses the area.
Despite being somewhat weak in the precipitation department...this
cold front will bring a major change in temperatures to the County Warning Area.
After near record highs on Saturday across much of the
region...temperatures will fall to below normal levels Sunday.
Temperatures will struggle to reach the upper 50s along the Wasatch
front Sunday...and the low 50s in this same area Monday.
The differences between the 00z GFS and the 00z ec are further
magnified early next week. The previously mentioned additional
shortwave forecast in the ec prevents the development of moist
northwest flow that is apparent in the GFS solution. With the degree
of difference between the models after Monday...decided to keep the
previous forecast intact...with only low end probability of precipitation across the
Aviation...fairly typical wind forecast is expected at the slc
terminal today. Southerly winds are expected to shift to the
northwest between 19-21z.
Fire weather...temperatures rebound late week with decreasing
humidity. Another wet cold front expected next weekend. Southerly
winds are expected to become gusty ahead of the front by Friday
continuing through Saturday.
Short term/fire weather...rogowski
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