450
FXUS63 KOAX 172036
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
336 PM CDT Sun Aug 17 2025

.KEY MESSAGES...

- Hot conditions remain this afternoon, with highs in the low
  90s and heat indices approaching 105 degrees.

- Thunderstorms in northeast Nebraska this afternoon are
  expected to wrap up before more chances tonight (60% chance).
  Monday night brings yet another chance.

- Heat will persist into Monday before gradually easing, with
  cooler temperatures through the rest of the week.


&&

UPDATE 3:36PM : Further fleshed out Monday`s severe weather
threat.

&&

.DISCUSSION...
Issued at 325 PM CDT Sun Aug 17 2025

.TONIGHT...

Surface analysis reveals two MCVs in the area, one near K9v9
(Chamberlain SD) and another just south of it near the SD/NE
state line close to Niobrara, NE. These two persistent features
have busted the forecast for northeast Nebraska today where a
few counties had a heat advisory cancelled due to the widespread
cloudcover and persistent showers. While indices of over 100 are
common south of I-80, some spots up north have been relegated to
the 80s all day.

The general trend has been for these showers and storms to slide
northeast into the more stable air of South Dakota and
Minnesota where the convection has produced an area of
frontogenesis. CAM guidance has been pretty awful today, but
the HRRR does suggest the convection associated with the MCV
will wrap up in this forecast area by about 6pm, trending toward
that quasi-front. Other guidance suggests some redevelopment
along the Missouri River. Should that come to fruition, a
prospective supercell would threaten with hail, damaging wind
gusts, and heavy rain. PWAT values near 2" could produce bursts
of heavy rain, but SREF probabilities of 1"/hr rainfall rates
are at generally 15% or less. I`d push that number higher in
the vicinity of supercells due to the poor model performance
today. That 15% is probably better reflective of the rainfall
associated with the possible MCS pushing through the area after
dark.

Regardless of whether supercells are able to fire this evening,
guidance has been pretty consistent on bringing the remnants of
an MCS through the area after midnight. Associated with a
shortwave working through eastern South Dakota / Minnesota, a
line of storms will work through the area from north to south.
Revved up by the LLJ, strong storms/severe weather looks
possible primarily in the form of damaging wind gusts. Current
timing has the greatest threat from about midnight to 4am with
the Omaha metro expected to see storms around 2am. These storms
should weaken as they work north to south with best chances of
LSRs north of Fremont and Omaha.

.MONDAY...

Again, overnight lows will be warm, especially over the
southern half of the CWA where mid-70s are forecast. It`ll be
difficult to cool homes with no A/C there and it is another
reason to consider a heat advisory for Monday afternoon. Have
held off on issuing one due to uncertainty with Monday`s temps.
As the forecast stands, a stripe across the mid- section of the
area will flirt with heat indices of 105 but as today`s weather
revealed, confidence is currently pretty low. Will allow
overnight / morning forecaster to make the final call with later
runs of numerical models. Regardless, it will be hot with highs
expected to peak near 90F under mostly sunny skies. Southerly
winds will become northerly by the afternoon. That wind shift
will be the easiest way to detect the cold front pushing through
the area. This front would be the most likely place for an
evening storm to develop and push east.

Have maintained 20-40% PoPs for Monday evening and overnight as
the NAM develops another MCS - from the highest peaks of the
Black Hills - directly through the mid- Missouri River Valley.
PoPs will climb if global models / CAMs catch on.

.TUESDAY AND THE REST...

Tuesday`s temperatures will fall by about five degrees as
cooler air spills into the area behind a relatively weak cold
front. Cold air advection will be most prominent in Minnesota
and eastern Iowa as the surface high misses us to the northeast.
It will still be a welcomed (minor) drop in temps and with calm
winds and partly cloudy skies, a pleasant late summer day.

The H5 pattern remains mostly unchanged from Tuesday through
Thursday with mostly dry conditions forecast (wish I could write
that part of the AFD in pencil) and temps in the lower to
mid-80s. But by Thursday, that upper ridge begins to break down
and northwest flow develops across the central CONUS by Friday.
This should bring regular opportunities for showers/thunder and
high temperatures only in the 70s for next weekend. Sign me up.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 121 PM CDT Sun Aug 17 2025

Primary concern with this TAF issuance will be where
thunderstorms will interact with aerodromes. Expect some rain
shower activity over KOFK to wrap up by about 3pm (19Z) and for
LNK and OMA to remain dry until the next best chance of
thunderstorms overnight. Have added a two hour window of
thunderstorms at KOFK and KOMA overnight, but expect tweaks as
the system shows the whites of its eyes. Perhaps a brief ob of
MVFR vis is possible with heavy rain, but have maintained VFR
conditions through the TAF due to uncertain timing and location.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Heat Advisory until 8 PM CDT this evening for NEZ045-052-053-
     067-068.
IA...Heat Advisory until 8 PM CDT this evening for IAZ055-069-079-
     080-090-091.

&&

$$

UPDATE...ANW
DISCUSSION...Nicolaisen
AVIATION...Nicolaisen