Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 231522
Area Forecast Discussion
National Weather Service Salt Lake City UT
922 AM 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.
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
12z KSLC RAOB shows a strong but shallow 8C inversion this
morning. Still expecting the inversion to erode beginning this
afternoon with south flow increasing to hopefully evacuate a good
amount of the urban haze.
As mid and upper level moisture is being advected ahead of the
eastern Pacific trough, satellite trends indicate a fairly good
area of mid and high clouds developing over Nevada and western
Utah. Have raised sky coverage to bring additional zones into the
mostly cloudy category.
Weak pressure falls, a building southerly gradient and 25-35kts of
700mb flow continue to support breezy conditions for many areas
Isolated high based showers will be possible across southwest Utah
into the higher terrain many mountain sites by late afternoon. QPF
will be meager, but these showers could bring enhanced and erratic
gusty winds judging from the DCAPE from the inverted-v soundings.
Otherwise updated the temperature/rh curve based on observations
and the latest guidance through this afternoon.
The rather warm southwest flow aloft across the Great Basin will
bring one more day of breezy and unseasonably warm conditions to
Looking at a significant change for the early portion of the
upcoming week. A weak shortwave advancing northeast towards
southern California will tap into moisture pooled off the Baja
coast. This moisture will be drawn quickly north into southwest
Utah by late this afternoon or early this evening. Could see a few
showers reaching into the southern mountains late this afternoon
or early this evening. Not anticipating much in the way of precip
as the dynamic and thermal support for lift will be quite weak
with the advancing shortwave and the lower level of the atmosphere
will initially be on the dry side.
Continued advection of moisture across Utah will leave much of the
state with PWAT values between .75 and .95 inches early in the
upcoming week. Dynamic and thermal support for lift will also
improve as a series of shortwaves ejecting northeast out of the
upper trough off the Pacific Northwest coast will cut across the
northern Great Basin/northern Rockies. Cooler air nudged into Utah
by the passing shortwaves will create a modestly more unstable air
mass to go along with the increasing dynamic support and abundant
moisture. Widespread precipitation should form across the western
half of the forecast area on Monday, with the heaviest precip
concentrated across central and northeast Utah. This precip should
continue throughout Monday night, then decrease from the west
Tuesday as heights begin to rise across the interior west. Strong
ridging across the Great Basin Wednesday will end any chance at
precip, with temps climbing once again to seasonal norms or
Persistent upper level ridging will continue across much of the
region. An upper level trough digging down the off the eastern
Pacific coast will help to shift the mean ridge eastward by
Thursday. This trough is expected to move onshore across central
California coast later Thursday. Given the ridge location, this
trough will split as it moves eastward into the Great Basin.
The 00Z GFS came in with a much harsher split, which would
dramatically lower the chances of a widespread precipitation event
across the state Friday. The 00Z EC persisted, however, with a more
favorable split for at least a 12-18 hour period of fairly
widespread precipitation across the state Friday.
Given this model to model and run to run disparity, the forecast
continues to be a blend of the much drier GFS and the wetter EC,
especially from Friday morning into Saturday. Hopefully future runs
will come into better agreement, but a combination of model issues
in the shoulder season combined with the difficulty of forecasting
the location of the split will hamper higher confidence in this
portion of the forecast.
Light and variable surface winds at the KSLC terminal
are expected to continue through 16z before becoming a prevailing
southeasterly thereafter into early afternoon. These winds are
expected to become gusty during the 18-21z timeframe, though only a
20 percent chance exists for gusts exceeding 30mph. A switch to
northwest winds is then expected during the 21-22z timeframe, though
a 20 percent chance remains that southerly winds will prevail
through the day.
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