Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 232121

Area Forecast Discussion
National Weather Service Salt Lake City UT
321 PM MDT Sun Oct 23 2016

.SYNOPSIS...An unseasonably warm southwest flow will remain over
the area today. Moisture will be drawn north into southwest Utah
late today, and then spread across the remainder of the state for
early in the upcoming week. Drier conditions will return for the
middle of the week.


.SHORT TERM (Through 00z Thursday)...
Water vapor loop shows southwest flow aloft between a cold closed
low over the Gulf of Alaska and a strong ridge over Texas. A
disturbance that was over southeast Pacific Ocean near 25N 125W
yesterday morning, has been absorbed by the eastern Pacific trough
and is will approach from central California this afternoon.
MDCARS wind observations show a 85-115kt anticyclonic jet from the
Pacific Northwest across the Great Lakes. GOES/HRRR/12Z KSLC RAOB
indicate the precipitable water value ranges from 0.10"-0.20"
mountains to 0.25"-0.33" most valleys. Blended Precipitable Water
product shows a moisture plume beginning to surge north/northeast
from the Gulf of California and southern Pacific. A second plume
of moisture has advected into the Pacific Northwest, which extends
back into the central Pacific where it is substantially greater in

Models have trended a bit slower with the arrival of the moisture
plume later this evening, with activity initially further west
than previously thought.

As the aforementioned shortwave arrives this evening, it will
bring the moisture tap from the southern Pacific and Gulf of
California. Initially little if any rainfall is expected from this
high-based activity, with the impact being from locally enhanced
wind gusts due to the DCAPE evident from model soundings.

The moisture surge spreads across the remainder of the area by
late evening. Increasing diffluence aloft will combine with
increasing instability seen on the SREF to promote an increase in
coverage of showers. Went above typical blend of guidance for
overnight lows across northwest Utah given gusty southerly flow
and cloud cover.

Subtropical jet from southern Pacific interacts with the weakening
jet downstream of the trough to our northwest tomorrow, with
coupling evident between the left exit region of the subtropical
jet and right entrance region of the northern jet. This will be
favorable for showers and thunderstorms becoming more widespread,
along with storm organization considering the good chance of at
least 30kts of effective shear. Given the moist profiles, with
warm cloud layer of around 5kft, locally heavy rainfall is a
concern. As mentioned earlier, model guidance has shifted a little
to the Northwest but still near the zone mentioned yesterday, from
near Cedar City to Evanston plus about 50 miles to the northwest
and southeast of this line. As for temperatures tomorrow, cut
temperatures a bit from typical model blend in the vicinity where
the most convection is expected as outlined above, but did not get
too cute as its all based on the convective evolution.

A strong Pacific jet arrives into California late Monday, nosing
into western Utah by 12z Tuesday. The associated upper level
trough crosses Utah Monday night. Expecting this feature to shunt
the active weather to the east as the night progresses. This
results in some drying as heights rise to the west. Showers
should thin thereafter during the day Tuesday.

Snow Levels look to be around 10ft through the short term period,
potentially a bit lower during best precipitation rates.

The pattern begins to amplify Wednesday leading to warming
temperatures. Cant rule out high clouds west of the ridge axis as
the day progresses.

.LONG TERM (After 00z Thursday)...
The mean long wave pattern across the western CONUS will continue
to amplify through Thursday as the eastern pacific trough digs
south along the coast, this further intensifying mid level ridging
across the intermountain region. Dry, stable conditions with a
continuation of warming trend temps will remain the norm through
Thursday across the forecast area as such, with temps expected to
run some 10 degrees above norm for most locales during the
afternoon hours.

Regarding the eastern pacific trough thereafter, latest 12z ECMWF
trended towards the GFS and have slowed its progression and impact
down vs. previous forecasts. Said trough now looks to remain nearly
closed as gets kicked on shore (by another upstream trough) prior to
opening whilst lifting northeast through the eastern Great Basin
late Friday into the nighttime hours. The slower/further west
solution seems to have won out, with only one GEFS ensemble member
supporting the faster solution of the 00z ECMWF (and runs prior).
Lowered PoPs significantly for Friday, and focused isolated to
scattered precip largely along and west of the I-15 corridor (mainly
for the pm hours).

Though a decent moisture tap exists with this next trough, rapid NE
progression and a further western solution does look to limit
duration of precip and significance, with rapid height rises
building back in Saturday morning.


West-northwesterly winds are expected to continue at the
SLC terminal through at least 01Z, with winds likely to switch back
to the southeast around 02-04Z. Ceilings will lower through the
overnight hours, but there is only a 30 percent chance of ceilings
below 7000 feet through 09Z.




SHORT TERM...Rogowski
LONG TERM...Merrill

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