Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 190904
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
404 AM CDT Tue Jun 19 2018

.SHORT TERM...(Today through Thursday)
Issued at 345 AM CDT Tue Jun 19 2018

Forecast concerns will be heavy rain and flash flooding due to
multiple rounds of precipitation as the upper level storm system
moves little between now and Tuesday night and different parts of
the forecast area have a flash flood risk at different times over
the next few days.

Water vapor satellite imagery highlights a moisture plume that
extends from tropical depression Carlotta over Central America
northward across Texas into the Central Plains then eastward across
the Lower Great Lakes toward PA/NY.  GOES Total Precipitable Water
as a percentage of normal shows this swatch of 150-200% especially
from Nebraska toward WI to New England.

Parts of the forecast area received 1 to 3 inches of rain and that
includes 3.4 inches at Kennard in Washington County and 2.88 inches
here at the NWS in Valley.

In the very short term this morning, we have a couple of areas of
storms.  One area is moving into western Iowa while and another is
in northeast CO western Nebraska.  The first short wave continues to
push east. The RAP/HRRR are in good agreement that thunderstorms
are forecast to redevelop in parts of southeast Nebraska and
southwest Iowa this morning in thickness diffluent area where
moisture is pooled with very high h7 moisture and low level winds
have veered overnight. Localized heavy rains are possible with
these storms. The storms should generally be south of the flash
flood watch, thus have canceled the FFA that was due to expire at
18Z.

There is a slight shift of the 2.0 inch PWAT to Iowa by 12Z, however
by 00Z this extends westward into Nebraska and Iowa before shifting
eastward again by 12Z Wednesday.  PWATs remain high from around 1.5
to 2.0 inches through much of the short term forecast.

The areas that are wetter and have had above normal rainfall over
the last few weeks are areas along and north of the Platte
River...and parts of eastern Nebraska near the Missouri River into
southwest Iowa. Drier conditions include parts of the Saunders
and western Douglas Co. (although here at the NWS office we wiped
out a big deficit today) into the rest of southeast Nebraska save
for the counties near the Missouri. Flash flood guidance is in the
1 to 3 inch rain for 1 to 6hrs and the drier areas it is 2 to
nearly 4 inches. The issue is that with this airmass, 3 inches of
rain can fall in a short amount of time.

Considered a flash flood watch for areas from Platte County to
Washington County into Iowa southward. Southeast Nebraska and
southwest Iowa are at risk this afternoon and evening due to the
slow storm movement and heavy rainfall potential. Areas farther
north are at risk for flash flooding due to better antecedent
conditions and the next shortwave with substantial mid and upper
level support and abundant moisture available. Since the initial
area of concern does not have favorable antecedent wet soils, have
held off on the flash flood watch. This should give the next
shift some time to further assess where the best potential for
flash flooding is.

There is a severe weather threat again this afternoon and evening
with the storms due to heating into the 90s across the southern
parts of the forecast area, instability increases to 4000-5000J/kg and
steep low level lapse rates around 8.5 deg c/km are expected.

As the closed low pressure system moves into Nebraska additional,
more widespread rains are expected, exacerbating locations that
received rainfall over the last couple of days. Additional rains
occur Thursday, although the coverage is not as great.

.LONG TERM...(Thursday night through Monday)
Issued at 345 AM CDT Tue Jun 19 2018

During the extended, Friday, the closed low has finally pushed
far enough to the east where any precipitation is negligible and
there is a break in the rain through Friday night. A shortwave
trough will drop in on the backside with rain chances returning
Saturday afternoon for parts of the area. Spotty precipitation
lingers Sunday. The GFS/EC diverge for Monday as yet a third
closed h5 low pressure system is somewhere from from northeast
Colorado or South Dakota/Nebraska. This will be the difference
between being dry or under the precipitation shield. The current
blend used does have scattered rain chances in. As a result of
the active pattern and the track of the storm systems, below
temperatures can be expected.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1135 PM CDT Mon Jun 18 2018

SCT TSRA should be around KOMA for a few hours with then small
chances into the early morning hours. Chances are a little lower
at KLNK with activity more isolated and even less for KOFK. Some
MVFR or possibly even IFR ceilings are possible at KOFK for later
tonight into Tuesday morning. TSRA chances look fairly low until
mid afternoon, then they will increase and continue through the
evening. Outside of TSRA, expect mainly VFR conditions for KOMA
and KLNK.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Miller



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