482
FXUS63 KUNR 192003
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
203 PM MDT Sat Oct 19 2024

.KEY MESSAGES...

- Above normal temperatures and one or two chances for light
  precipitation are anticipated through next week.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 202 PM MDT Sat Oct 19 2024

One of the more notable features on water vapor imagery this
afternoon is cut-off low spinning over the Southwest. Farther north,
a jet streak is advecting deep moisture west to east from the
Pacific into the northern Rockies. A quick-moving disturbance ahead
of this jet is shifting away from our region toward the Great Lakes,
whereas a more notable shortwave trough is evident just off the
Pacific Northwest coast. Close to home, skies are mostly clear aside
from some patches of cirrus. Latest surface analysis shows mesoscale
high pressure to our south, centered over central NE, with a subtle
trough crossing the region from west to east. Relative positioning
of trough and high pressure is supporting steady southwesterly flow
over the SD plains, with more variable and terrain-driven flow near
the Black Hills into northeastern WY. After a chilly day yesterday,
temperatures have climbed back above normal this afternoon.

Through tomorrow, little change in large-scale pattern is expected.
With deep high pressure over the Southeastern quarter of the CONUS
and modest troughing over and east of the Rockies, predominantly
west/southwest flow over the region will facilitate warming low-
level temperatures. By 00z Monday, EPS, GEFS, and GEPS means all
suggest 850 mb temperature anomalies of 5-10C area-wide. During the
day on Sunday, the shortwave now approaching the Northwest coast
will kick the cut-off low east-northeastward. Over the past 24
hours, model consensus has shifted the forecast track of the cut-off
low. The bottom line is that the track of the parent low, along with
associated downstream moisture transport and precipitation
potential, has shifted southward. As such, PoPs are now confined
primarily to south central SD. Here, LREF probabilities of
measurable precipitation are approaching 50%, but probabilities
of at least 0.1" remain below 25%. The most probable scenario is a
brief period of light precipitation over this area Monday morning
through the afternoon.

As the trailing shortwave crosses the region on Tuesday, a corridor
of enhanced upper-level Q-vector convergence coincident with low-
level frontogenesis will bring another brief shot for precipitation.
Like Monday, probabilities of 0.1" of QPF or more are low (<20%),
but the swath of potential measurable precipitation is a bit
broader than the day prior. However, probabilities have also
generally decreased area-wide in the 12z ensemble suites when
compared to last evening`s 00z runs. Taken altogether, confidence
is low in the potential for precipitation on Tuesday, but even if
precipitation occurs, it will likely be brief and light.
Confidence is a bit higher in terms of cooler temperatures for at
least a day or so as an attendant low-level thermal trough skirts
the region. Thereafter, given model divergence, uncertainty is
relatively high for temperatures Thursday into Friday, but longer-
term ensemble trends and analogs continue to favor above to well
above normal temperatures returning late in the week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1051 AM MDT Sat Oct 19 2024

VFR conditions will continue through the TAF period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...10