Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 300939
Area Forecast Discussion
National Weather Service Salt Lake City UT
339 AM MDT TUE AUG 30 2016
.SYNOPSIS...A ridge of high pressure over the Great Basin will
hold in place through today, before shifting east tomorrow. An
upper level trough of low pressure will move across the region
.SHORT TERM (THROUGH 06Z FRIDAY)...
Water vapor loop shows ridging overhead with a deep trough nearing
the Pacific Northwest. MDCARS wind observations show a pair of
60-90kt southwesterly jets, one nosing into British Columbia, and
the second noising into the northern Rockies from northern
California. GOES/HRRR/00Z KSLC RAOB indicate the precipitable
water value ranges from 0.20"-0.30" northern mountains to
0.50"-0.65" southern valleys.
Convection will become more isolated, diurnal in nature and tied
to the higher terrain as anticyclonic flow develops and warming
occurs aloft. The ridge will support a continued warming and
drying trend today, plateauing tomorrow.
Moisture will begin increasing tomorrow on southerly flow ahead
of the trough easing into the West Coast. This will bring about an
increased threat of convection as well as cloudiness. Convection
should be high-based and pose a threat of strong dry microburst
Expecting convection to develop over West Central and Southwest
Utah tomorrow night given elevated instability in place with the
arrival of the southern of the pair of jets. This convection will
likely expand toward the Northeast Thursday. Have boosted PoPs
given expected coverage of showers and storms. Airmass will
continue to saturate Thursday with some areas potentially seeing
locally heavy rainfall. However, to the Northwest expect
convection to remain more high based and continue to pose the
threat of gusty microburst winds.
Synoptic winds will be increasing out of the south tomorrow and
Thursday as the trough begins to approach. Have lowered
temperatures below guidance Thursday given expected cloud cover.
.LONG TERM (AFTER 06Z FRIDAY)...
Confidence in the extended is rather low as the global models are
flip flopping their solutions in both timing and strength pass
several runs. The EC is a little broader and not as deep with the
trough moving in from the coast than either the GFS or GEM for
Friday and Saturday. Therefore southwest winds are weaker on the
EC Friday and the push of cooler is less intense on Saturday
behind the cold front. Although, currently have leaned toward the
GFS due to the GEM supporting it, the 12Z EC ensemble supports the
00Z EC operational run which indicates some run-to-run consistency
in the EC so didn`t want to ignore the EC all together.
Not too impressed with the instability associated with ejecting
short wave from the main trough as the layer of moisture is rather
shallow and the main dynamics stay north of the CWA. Therefore have
kept the best chance for showers and thunderstorms over the higher
terrain and eastern counties of our CWA where moisture will be
somewhat deeper between 06Z and 18Z Friday.
While better dynamics associated with the next lobe of the trough
swings through early Sunday, the air mass is much drier with the PWs
dropping from near 0.90 of an inch over portions of NW Utah at 06Z
Friday down to less than 0.50 of an inch by 06Z Sunday. Have removed
POPs for the Sunday period. The main trough moves through Utah
Monday into Tuesday and brings with it slightly higher PWs across
nrn portions of the CWA so have thrown in some token POPs across the
northern Wasatch and northwest corner of Utah.
Temperatures should cool 5-10 degrees below normal from Saturday
into early next week. The EC is slower to cool on Saturday across
the north as the cold front is weaker but has similar temps to the
GFS on Sunday. The GFS continues with the sharper trough and
associated cold front for Monday which I have tempered some due to
its run-to-run inconsistencies and used a blend of the EC and GFS.
Winds at the SLC terminal will likely shift from southeast to
west northwest between 20-22Z then return to southeast after 03Z
tonight. VFR conditions will prevail through the TAF period.
Yesterday`s ERC values were at or above the 97th percentile across
portions of northern Utah, while stations across southern Utah remain
below the 50th percentile, though ERC values are trending higher.
A warming and drying trend will prevail today, plateauing for
tomorrow. Convection will be quite isolated, diurnal in nature,
and tied to the mountains.
Southerly winds look to increase along the Nevada border region
late today though critical fire weather conditions expected to be
isolated at best, with sub-critical gusts most locations. Dry
microburst winds may be supported due to high-based showers during
the late afternoon and evening hours in this area as well. Though
dont believe lightning will be much of a threat.
Better chance for critical fire weather conditions due to
combination of gusty winds, dry microbursts, and low RH Wednesday
through Friday across the western valleys.
A monsoon push will increase the coverage of thunderstorms during the
second half of the work week, supporting a cooling and moistening
trend and another round of lightning.
SHORT TERM/FIRE WEATHER...Rogowski
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