100
FXUS63 KOAX 050430
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1130 PM CDT Fri Oct 4 2024

.KEY MESSAGES...

- Very high to extreme fire danger is expected across eastern
  Nebraska and western Iowa Saturday afternoon. Details can be
  found in the Fire Weather section of the AFD.

- A cold front Saturday evening will bring afternoon highs on
  Sunday into the 70s. Temperatures will gradually warm into the
  80s into next week.

- Dry, warm and sunny conditions are expected to persist through
  next weekend.

&&

.DISCUSSION...
Issued at 221 PM CDT Fri Oct 4 2024

     Today and Tomorrow...

In the wake of a cold front that moved through the area last
night, a cool post-frontal airmass remains in place across the
region, with afternoon highs expected to remain in the 70s
across eastern Nebraska and southwestern Iowa.

Overnight tonight, winds will become more southeasterly,
bringing relatively high dew points (low to mid 50s) into
portions of southeast Nebraska and southwest Iowa. As such, in
conjunction with nighttime lows forecast to be in the mid 50s,
areas of patchy fog may develop in low-lying areas south of I-80
and east of US-77. One complicating factor to fog development
will be the very fast winds at the top of the nocturnal boundary
layer. This may keep the near-surface layer of the atmosphere
mixed enough to prevent widespread fog from developing.
Nonetheless, at least isolated patches of fog appear probable,
particularly in valleys and other areas protected from the wind.
If fog develops, visibilities may occasionally drop to a mile.
Any fog that develops will quickly dissipate with sunrise,
clearing by 8 AM.

Tomorrow, a strong but dry storm system will move across the
central and northern Great Plains, setting the stage for extreme
fire danger across our area. The details of this system and
implications on fire weather can be found in the "FIRE WEATHER"
section of the AFD at the bottom. But here, it will suffice to
say that strong winds gusting to 40 mph and relative humidities
as low as 10 percent will favor rapid growth of any wildfires
that are started tomorrow.

     Tomorrow Night through Thursday...

Behind this storm system, a cool and very dry airmass will move
back into the area. High temperatures on Sunday are expected to
range from near 70 in northeast Nebraska to the mid 70s south
of Interstate 80. Temperatures will gradually warm throughout
the week next week, with high temperatures in the mid and upper
80s by Thursday. With a high-amplitude blocking ridge setting up
across the central CONUS, the jet stream will be pushed well to
our north into central Canada. As such, no rain is expected
during this forecast period.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1129 PM CDT Fri Oct 4 2024

VFR conditions are expected to prevail through the forecast
period. 04z (11 PM) observations indicate a narrow ribbon of
clouds at FL040-050 across portions of western and central IA,
which could move into the KOMA vicinity prior to daybreak. Some
patchy fog is possible late tonight into Saturday morning,
mainly along the MO River; coincident with an axis of higher
dewpoints and lighter winds. Confidence in any visibility
restriction at KOMA is too low to include in the forecast.

LLWS appears likely in the 12z-14z time frame at KOFK and KLNK
with southerly surface winds strengthening rapidly thereafter
with gusts of 25-35 kt likely by late morning into at least
early afternoon. Winds will switch to west and then northwest on
Saturday afternoon as a front moves through the area. Winds will
gradually diminish Saturday evening.

&&

.FIRE WEATHER...
Issued at 221 PM CDT Fri Oct 4 2024

There will be a bimodal risk for extreme fire danger across
eastern Nebraska and southwestern Iowa tomorrow afternoon. Ahead
of a cold front advancing northwest to southeast, extremely
deep mixing is expected to occur under strong unidirectional
flow, resulting in an afternoon boundary layer potentially 10
kft to 15 kft feet deep (potentially as deep as 600 hPa). This
will result in the efficient mixing of strong winds aloft down
to the surface, with southwesterly wind gusts up to 40 mph
possible, particularly south of I-80.

For areas across northeast Nebraska, the cold
front will likely move through before peak heating and mixing.
However, strong wind gusts of 30 to 35 mph out of the northwest
will be possible behind the front. Area-wide minimum RH values
are expected to range between 10 and 20 percent both ahead and
behind the cold front, particularly across eastern Nebraska. As
such, northeast Nebraska north of US-30, and southeast
Nebraska/southwest Iowa south of I-80 are the two areas of
greatest concern for extreme fire danger tomorrow afternoon.

Between I-80 and US-30, the scenario is more complex. Winds will
be relatively calm in this area (gusts 20 to 30 mph) owing to
the surface trough centered on the frontal zone. However, there
does appear to be a low chance for elevated dry convection (i.e.
virga) that would assist in mixing down stronger gusts
(potentially up to 40 mph) to the surface in this area.
Furthermore, wind gusts immediately behind the front (the 30
minutes or so immediately after frontal passage) will likely be
stronger than current guidance suggests, so fire weather danger
will still likely approach extreme in this area despite the
lower winds resolved in much of the short term guidance.

Portions of far east-central Nebraska (including the Omaha
metro) and southwest Iowa are in a Fire Weather Watch for
tomorrow. There are several reasons for this not being upgraded
to a Red Flag Warning yet. First is relative humidities will be
higher across southwest Iowa than the rest of the area, ranging
from 20 to 30 percent. So even though strong wind gusts up to 40
mph are expected, Red Flag Warning criteria does not look to be
met at this time. Further north in far east-central Nebraska
and west-central Iowa, relative humidities will be much lower,
somewhere between 10 and 20 percent. The limiting factor in this
region will be the strength of the winds in the afternoon, with
most wind gusts looking to remain just under 30 mph. However,
regardless of these limiting factors, conditions will still be
windy, hot and dry, bringing very high fire danger to those that
find themselves outside of the Red Flag Warning.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Fire Weather Watch from 11 AM CDT Saturday through Saturday
     evening for NEZ015-034-045-052-053.
     Red Flag Warning from 11 AM to 8 PM CDT Saturday for NEZ011-
     012-016>018-030>033-042>044-050-051-065>068-078-088>093.
IA...Fire Weather Watch from 11 AM CDT Saturday through Saturday
     evening for IAZ043-055-056-069-079-080-090-091.

&&

$$

DISCUSSION...Darrah
AVIATION...Mead
FIRE WEATHER...Darrah