872
FXUS63 KLBF 190935
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
435 AM CDT Thu Sep 19 2024

.KEY MESSAGES...

- Dry conditions with above normal temperatures in the 80s today
  and Friday.

- Elevated to near-critical fire weather concerns exist on
  Friday across western Nebraska due to low relative humidity
  and windy conditions.

- A much welcomed pattern shift to cool and wet conditions
  likely for the weekend with the potential for widespread,
  accumulating rain across portions of the area, especially
  southwest Nebraska (>60% chance for total rainfall of 0.25"+).

&&

.SYNOPSIS...
Issued at 425 AM CDT Thu Sep 19 2024

Recent GOES-16 WV imagery and RAP 500-mb analysis showed three
potent troughs of low pressure across the CONUS. Our weekend system
was apparent across the western US with a deep upper-level trough of
low pressure digging southward along the coast of California.
Further to the northeast of this feature, a negatively tilted trough
was exiting northeast out of the northern Plains into southern
Manitoba. The third upper-level trough of interest was noted across
the South Atlantic with an upper-level ridge just to the north,
extending northwestward into the Hudson Bay. Another area of high
pressure was centered across northern Mexico into the southern
Plains. All of these features combined has resulted in southwesterly
flow aloft across Nebraska. At the surface, an occluding low
pressure system was located over the Montana/North
Dakota/Canada border with an attendant cold front extending
southwest into central Nebraska. At 4 AM CT, temperatures ranged
from 54 degrees at Gordon and Ogallala behind the front to 69
degrees at O`Neill ahead of the front.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 425 AM CDT Thu Sep 19 2024

Today and Tonight...Quiet and dry conditions will be felt across
western and north central Nebraska as surface high pressure builds
into the region. High temperatures will remain in the above normal
range from the low to mid-80s with abundant sunshine. Due to being
on the southern periphery of the surface low, west-northwest winds
will be breezy this afternoon across northern Nebraska, gusting up
to 25 mph. Although afternoon humidity falls into the 25 to 30
percent range, these weaker winds will preclude critical
conditions across northern Nebraska. Skies will remain clear
heading into the night with low temperatures falling into the
mid-40s across the Sandhills to the mid-50s across southwest
Nebraska.

Friday and Friday Night...The upper-level ridge will build in across
the region, ahead of the strong upper-level trough pushing ashore
across southern California. This will cause temperatures to climb
into the upper-80s to low-90s which is 10 to 15 degrees above normal
for the middle of September. These anomalously warm
temperatures will support afternoon humidity values to bottom
out in the 15 to 20% range across the Sandhills. A surface
trough approaching from the west and surface high pressure
continuing across the Midwest will result in a tightened surface
pressure gradient (SPG) across the area. As a result, southerly
winds will strengthen Friday afternoon with widespread gusts up
to 25 mph, peaking up to 30 mph across the Sandhills. Although
minimum humidity values meet critical thresholds, limited
overlap of critical values with the strongest winds will likely
inhibit widespread Red Flag conditions being met. Despite this,
elevated to near-critical conditions are anticipated across
portions of the Sandhills and briefly critical conditions cannot
be ruled out midday across Fire Weather Zone 204.

 &&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 425 AM CDT Thu Sep 19 2024

Saturday through Monday...The upper-level ridge will be shunted
south as the southern California trough tracks into the Four
Corners, approaching the central Rockies on Saturday. Southerly flow
will bring an influx of moisture across the area with PWAT values
forecast to exceed 1" across the area, meeting or exceeding the 90th
percentile as highlighted by both the NAEFS and ENS ensemble
guidance. As height falls overspread the area and the previously
mentioned trough exits northeastward into the central Plains,
forcing for ascent will increase. There continues to be significant
run-to-run difference between each operational run and the NBM has
begun to trend down across the Sandhills, favoring areas to the
south and east for widespread wetting rain. When looking at
precipitation totals, NBM Probabilities for 48 hour (12Z Sat
through 12Z Mon) 0.25"+ liquid equivalent precipitation ranges
from 20 to 40% across the Sandhills to an overwhelming 60 to 80%
across southwest Nebraska. All hope is not yet lost for the
Sandhills, as rainfall amounts could increase a bit further
north should a more northern track play out. The ECMWF EFI
(Extreme Forecast Index) continues to show increased confidence
of an anomalous event with this system, such that the SoT (Shift
of Tails) is greater than 0 across the entire forecast area
with a SoT greater than 1 across southwest into central
Nebraska. Depending how the system evolves and all is said and
done, total rain amounts ranging from a few tenths of an inch to
1" or greater appears probable with the greatest probabilities
for 1"+ currently residing across southwest Nebraska. Outside
of precipitation, north-northeasterly surface flow will
strengthen with increasing pressure rises on the backside of the
surface low to our southeast resulting in gusty winds this
weekend, especially during the day on Saturday. At this time,
widespread gusts of 20 to 25 mph appears probable with the
strongest gusts up to 30 mph across northwest Nebraska where the
pressure rises will be strongest. One thing confidence
continues to increase on is temperatures falling back into the
at or below normal range this weekend, continuing into early
next week. The coolest day appears to be Sunday with highs
ranging from the upper-50s to low-70s which is 10 to 15 degrees
below seasonal values. We may even see our first night of
temperatures falling below 40 degrees Sunday night into Monday
morning. With height rises behind the departing system, skies
will begin to clear out and winds will become weak, allowing for
efficient cooling. In fact, NBM Probabilities indicates a 40 to
70% chance of Min Temperature below 40 degrees for areas
generally west of Highway 83. High temperatures moderate back
into the 60s and 70s on Monday with additional low-end
precipitation chances Monday evening as a shortwave swings
through the area.

Tuesday and beyond...Evolution of the upper-level pattern remains
uncertain during this period. Models are in general "consensus"
that northwesterly flow will continue across the region through
mid-week with the upper-level ridge building back in across the
western US. However, another large scale trough appears to move
onshore over Pacific Northwest mid-week, nudging the upper-level
ridge further east into the Plains. Although questions remain,
temperatures trending back into the above normal range and dry
conditions appears in the cards for the region. This is in line
with CPC`s 6-10 Day Temperature and Precipitation Outlooks
favoring above normal temperatures and below normal
precipitation chances returning for Nebraska.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1232 AM CDT Thu Sep 19 2024

VFR conditions are expected outside of patchy low-level fog
across central Nebraska which may encroach upon LBF for a few
hours early in the period.

Currently, southerly flow is noted ahead of a surging frontal
boundary that is fairly pronounced on radar. Current location as
of 19/0530z is an ANW to TIF to OGA line. This feature is
quickly shifting southeast and timing of this into LBF is around
19/08-09z. Ahead of this, visibilities are already dropping
modestly but the arrival of this boundary will lead to a wind
shift to the west-northwest and drier low-level air and the
expected end to any fog threat.

Additional concern with this boundary is the threat for isolated
to widespread convection across north central Nebraska. This
should remain east of Valentine which is already post-frontal
but uncertainty with southward extent and whether impacts are
felt at LBF remains medium at best. For now, will omit mention
and monitor going forward. Outside of some patchy cloud cover
early this morning, skies will remain clear with even the most
aggressive NWP guidance suggesting the same. Increased high-
level clouds will approach from the south near the end of the
period but arrival may fall just beyond the valid period.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Viken
SHORT TERM...Viken
LONG TERM...Viken
AVIATION...NMJ