591
FXUS63 KUNR 181818
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1218 PM MDT Mon Sep 18 2017

.DISCUSSION...(Today Through Sunday)
Issued at 245 AM MDT Mon Sep 18 2017

Low amplitude upper ridging will develop over the forecast area
today as one upper trough moves off to the east and another,
stronger trough develops over the west coast. At the surface, a
tightening sfc pressure gradient between high pressure to the
east and a deepening lee side trough to the west will produce
breezy to windy conditions across much of the forecast area this
afternoon.

The weather today will be dry, warmer and breezy to windy as the
850-mb temperatures rise to the lower 20s Celsius over
northeastern Wyoming. A strong upper trough will affect the
forecast area on Tuesday. However, models still differ on the
timing of a cold front that ultimately will move through the
region by Tuesday night. Scattered showers and a few
thunderstorms should result behind the front on Tuesday afternoon
and evening, although precipitation amounts generally will be
light.

Wednesday will be another dry day as a short-wave ridge crosses
the region. Unsettled weather is then expected for the rest of
the week as a large trough becomes established across the West,
and southwesterly flow aloft prevails over the northern plains.
The best rainfall chances appear to be on Friday and Saturday.
Temperatures will also be at least 10 degrees below average for
the end of the week and into the weekend.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1217 PM MDT Mon Sep 18 2017

VFR conditions are expected through the period. A low-level jet is
expected to produce some LLWS across much of the western SD plains
tonight.

&&

.FIRE WEATHER...
Issued at 245 AM MDT Mon Sep 18 2017

The weather today will be warm, dry and breezy to windy. High
temperatures will be in the mid 70s to mid 80s with afternoon
relative humidities falling to 15-20 percent across northeastern
WY and southwestern SD. Winds are expected to reach 10 to 20 mph.
Some gusts to 25 mph are expected, most likely over parts of
Campbell county in northeastern Wyoming. A cold front will move
across the area Tuesday, followed by gusty northwest winds and a
chance of showers.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...10
AVIATION...MLS
FIRE WEATHER...10