Scientific Forecaster Discussion
fxus65 kslc 202229
Area forecast discussion
National Weather Service Salt Lake City Utah
429 PM MDT Wed Jun 20 2018
Synopsis...high pressure will bring a warming and drying trend
through Thursday. A series of weak storm systems will bring
somewhat cooler weather to the forecast area Friday through the
Short term (through 00z sunday)...
* hot tomorrow.
* Red flag warnings where fuels are critically dry tomorrow and
some areas Friday.
extreme drought is occurring from south of Provo south to Cedar
City and to the southeast. Severe drought is occurring surrounding
the extreme drought, in areas from Ogden southward and Duchesne
to the Arizona border. Drought conditions scale down to abnormally
dry along the Idaho and Wyoming border.
during the past 5 days, flow across the Pacific has transitioned
from zonal to slightly amplified.
Water vapor satellite shows a ridge centered over Baja California,
amplified north into Idaho. A disturbance is moving into Oregon.
Local observations and trends...
12z kslc radiosonde observation shows a 1.5c subsidence inversion near 640mb with
moderate northwest mid level flow and strong northwest flow aloft.
Precipitable water values range from 0.20"-0.40" mountains to
0.50"-0.75" northern valleys.
A 1019mb surface anticyclone is located across northwest Wyoming,
with a 1005mb surface cyclone near Kanab. This is creating a 10mb
northerly pressure gradient across the state.
24 hour trends:
* precipitable water 0.10"-0.20" lower across northern Utah and
higher across southern and eastern Utah.
* Temperatures are 5-10f warmer
* dewpoint depression 5-15f higher (drier), except 5-15f lower
(moister) eastern Utah.
with ridging surface and aloft, stable conditions through tonight.
The aforementioned system over Oregon will cross into the northern
rockies tomorrow. This will send a surface cold front into
northwest Utah around sunrise, stalling in central Utah late day.
Winds will become gusty across the region as a result, with hot
temperatures expected. With 700-500mb lapse rates steepening, sref
indicates modest instability develop across northern Utah. Coupled
with height falls and forcing from the aforementioned wave and
westerly upper level jet, a few showers and storms may develop,
mainly in the higher terrain of northern Utah. With a local near
550mb, any convective activity may locally enhance wind gusts
above 40 mph.
A trailing wave is sent downstream into northwest Utah tomorrow
night as a strong Pacific jet nears the Pacific northwest. Some
elevated instability may remain but confidence is not high enough
to carry convective wording during the overnight hours. The
aforementioned cold front should shift to the Arizona border
Thursday night into Friday morning.
With the wave crossing overhead Friday morning, believe the drier
and more stable fv3 BUFKIT forecast soundings. Took out mention of
convection Friday afternoon and evening. A second cold front
crosses the state causing slightly cooler and moister conditions.
Winds may be locally gusty in prone areas within downslope
The boundary lifts northward toward the Idaho border Saturday as
the lead wave associated with the Pacific jet crosses from
Washington into far northern Utah. Slightly warmer and drier
conditions will result. Modest instability again develops across
northern Utah, which should result in isolated convection, mainly
in the higher terrain and downstream to the northeast. Convective
initiation should be aided by lift ahead of the closed low, with
strong height falls along the Idaho border.
Long term (after 00z sunday)...
the shortwave trough digging southeast out of British Columbia on
Saturday will slowly traverse the intermountain west, exiting by
late Sunday. Cool air associated with this trough will bring a
relatively cool day Sunday, with a slight chance of thunderstorms
on Sunday afternoon in NE Utah and SW Wyoming. The highest chances
for thunder will, as usual, be over the Uinta Mountains. Wind
gusts up to 30 kts are also likely Sunday over the west desert and
A ridge will build over the County Warning Area in the wake of this trough and be
the dominant feature in the area through Wednesday. Dry and hot
weather is expected area-wide with this pattern. While there may be
some moisture sneaking under the ridge, backed off on pops
slightly Tuesday and Wednesday due to skepticism in the blended
guidance on the potential for moist convection those days.
Neither the gefs or eps ensembles are indicating noteworthy weather
in the 8-10 day period, with weak, broad troughing over the western
the slc terminal will see VFR conditions through the evening with
mostly clear skies. Light northerly winds are expected to shift
to the southeast between 03z and 05z.
erc values are running between the 80th and 96th percentile across
eastern and southern Utah, and rising above the 50th percentile
across northern and west central Utah. Values are steady or rising
except falling along the northern Utah border. 100/1000 hour fuel
moisture has risen just above historical lows across most areas.
A system will enter Oregon today and progress into the northern
rockies tomorrow. This will support a dry cold front crossing
northern and portions of central Utah tomorrow afternoon. Gusty
southwest winds will develop with a Haines of 6, much warmer
temperatures and single digit relative humidity most locations. A red flag warning
has been issued where fuels are critical.
This boundary will progress to the Arizona border Friday,
bringing a gusty northwest flow. It will be almost as warm, with
nearly as low relative humidity tomorrow. Thus, critical fire weather conditions
are forecast to persist across east central Utah zones Friday.
The boundary lifts northward into southern Utah Saturday with many
variables being similar to Friday there. A gusty westerly wind may
present a continuation of critical fire conditions across southern
The next system dives southeast from Washington Saturday morning
across eastern Utah Saturday night and Sunday. This will bring
another dry cold front through the region.
Temperatures trend warmer through tomorrow, cooler Friday, warmer
Saturday then much cooler Sunday. Tomorrow will be the driest day
with single digit relative humidity across most of the state, rising a bit
Friday across the north, little changed Saturday and a bit higher
Isolated to showers and thunderstorms are forecast primarily
across the northern mountains Thursday through the weekend.
Utah...red flag warning from noon Thursday to midnight MDT Thursday
night for utz493>498.
Red flag warning from noon Thursday to midnight MDT Friday night
Short term/fire weather...10
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