834
FXUS63 KOAX 211126
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
626 AM CDT Fri Jun 21 2024

.KEY MESSAGES...

- Very heavy rain may produce flooding in northeast Nebraska
  through Saturday morning.

- At least small storm chances nearly every day through the
  middle of next week. Severe weather will be possible at times.
  The highest chances are currently this evening and in portions
  of northeast Nebraska and west- central Iowa.

- Gradually warming temperatures through the weekend into early
  next week. Heat indices approaching 100 to 110 on Monday and
  possibly Tuesday.

&&

.DISCUSSION...
Issued at 430 AM CDT Fri Jun 21 2024

Mild temps this morning can be attributed to the southerly winds
currently flowing at 5-15 mph as the entire area is in the warm
sector of what`s been a pesky front that has passed through
the entirety of the CWA twice already with one more passage yet
to go. Today some very heavy rains have fallen just northwest
of the area with some ARIs estimated at 50-200 years.

The remnants of an MCS are producing scattered showers across
far northeast Nebraska with much heavier rains north of the
Missouri River. Widespread flood warnings are draped across
southeast South Dakota with even more heavy rain on the way.

The only flood products issued from this office was a new river
flood warning for Ponca Creek in Knox County as MBRFC forecast
had it hitting minor flood stage *prior* to the very heavy
rain just west and north of the area tonight. Timing on the
cresting and flood alleviation has been removed until we get a
new forecast from the forecast center. With Ponca Creek`s basin
extending into south-central South Dakota, expect flooding both
today and tomorrow for the gage at Verdel.

Showers and QPF will taper off over the course of this morning
before a similar set up develops tonight. Scattered storm
activity will remain mostly north of the SD/NE state line today
(north of the stalled front). 10-20% PoPs are warranted in our
northern tier of counties before later this afternoon and
evening.

Expect an increase in coverage and intensity tonight as another
plume of Alberto`s tropical moisture rides the southerly winds
into Kansas/Nebraska and interacts with the MCS/shortwave
progged to push into the area as the sun sets on the "longest"
day of the year. PoPs quickly transition from "isolated" to
"likely". An anomalous moisture profile (99th percentile of
June climatology [NAEFS]) leaves PWAT values of 2-3" in our
northern tier of counties. Expect convection to be an efficient
rain- maker with a "long and skinny" CAPE profile and the LLJ
tonight really ramping up the moisture transport. The wettest
conditions are expected in South Dakota once again. On this side
of the state line, widespread QPF is 1-2" with reports of much
more than that possible with the threat of training storms.

This rain will be falling on saturated soils where streamflow
is already running much above normal. Considering these factors,
I`ve issued a flood watch for Knox County where some flooding
at Verdel is already forecast. With greater confidence this
afternoon, we may need to expand it to include at least nearby
Antelope and Cedar counties.

Severe weather is possible too, with ample instability brought
about with the maximized sun angle quickly heating the humid air
in place in the warm sector. Low level lapse rates peak quickly
this afternoon and CIN isn`t anticipated to be an issue. Shear
will be on the weaker side, but any storm that develops will
have the ability to drop damaging hail. The best chances of
supercell development would be from 5pm to 10pm north of I-80
before the attention will turn to hydro concerns after sunset.

.SATURDAY...

This problematic front passes through the CWA one more time as
a cold front on Saturday afternoon. This will leave a wider
range of temperatures across the area. The best chance of severe
weather will occur in the late afternoon/evening hours in the
warm sector which will likely be over far southeast Nebraska and
southwest Iowa by that time frame.

.SUNDAY AND MONDAY...

The days are likely to be dry, but it`s worth noting some 10%
chances of convection on Sunday an closer to 25% chance on
Monday as deterministic models are picking up on some weak waves
working through the low-amplitude ridging forecast at H5. The
concern for Sunday and Monday will be the quickly warming temps
and resultant heat indices. By Monday, temps will peak in the
mid to upper-90s with maximum heat indices hitting a zenith
near 105. HeatRisk will manage the Red/Major category south of
I-80 on both days suggesting a need for effective cooling and
hydration for anyone spending time in the afternoon sun.

.NEXT WEEK...

A cold front will help push temps closer to normal for
Wednesday. Daily thunderstorm chances continue as do the high
dewpoints and PWAT values. Temps will climb as we approach day 8
of the forecast.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 621 AM CDT Fri Jun 21 2024

VFR conditions this morning. We`ll hold on to VFR conditions
today with winds out of the south gusting to 25 kt. Storms will
move into northeast Nebraska this evening, impacting KOFK around
01-03Z, with a greater chance leaning toward 03Z for storm
arrival. Storms will stay well north of KOMA and KLNK. Winds
should stay out of the south even after storms pass, but will be
weaker through the rest of Saturday morning. We are watching a
trend with 30% chance of MVFR cigs, 20% chance of IFR cigs
moving into KOFK after 09Z Saturday morning, but keeping this
out of the TAFs unless chances increase.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Flood Watch through Saturday morning for NEZ011.
IA...None.

&&

$$

DISCUSSION...Nicolaisen
AVIATION...McCoy