Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 122305
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
605 PM CDT Sat Aug 12 2017

.SHORT TERM...(Tonight through Tuesday)
Issued at 322 PM CDT Sat Aug 12 2017

Fair weather today will be followed by increasing chances for
showers and storms over the next couple of days. Subjective 12Z
upper-air analysis indicates a weak upper-level ridge over ID/UT, an
upper-level trough over QB/eastern ON, and a reinforcing shortwave
trough crossing the border from Canada into MT/ND, along with a very
weak shortwave trough in western NE/western KS. A 75-95kt upper-
level jet streak extended from eastern CO to OH/southern MI. An
850mb ridge extended from central OK through the IA-NE border into
MB. with an 8C+ moisture plume poking northward through NE into
SD/ND. Surface high at 19Z was centered in north central IA/south
central MN, with an emerging surface low in north central
CO/southeast WY. As of 19Z, a few showers/storms were developing in
central and northwest NE into central SD.

Main forecast concern is potential for showers/tstorms tonight as a
more active period returns. Showers/storms in central NE will only
slowly make their way east this evening, with upper-level shortwave
along the ND-Canada border at 12Z not dropping into SD/MN until 06-
12Z. In the meantime, MUCAPE remains scant in eastern NE/northwest
IA, struggling to reach 500-750 J/kg, and should remain that way
through tonight. Will keep shower/isolated thunder wording, and have
pulled back coverage of showers/storms further to the northwest
tonight through Sunday morning.

A surface reflection of the upper Midwest shortwave should drive a
front into northeast NE/northwest IA on Sunday, and with increasing
instability across the area, would expect regeneration of
thunderstorms in that vicinity on Sunday afternoon/evening, with
activity dropping southeastward Sunday night into Monday. Chances
are higher for precipitation across more of the area with this
shortwave/frontal passage. In its wake, an upper-level ridge and
rising 500mb heights should allow warmer temperatures. The ridge
still looks "dirty," though, with plenty of moisture and enough
ridge-riding troughs to keep shower/storm chances through Monday
night and Tuesday.  Temperatures should be able to return to
readings at least closer to normal into the work week.

.LONG TERM...(Tuesday night through Saturday)
Issued at 322 PM CDT Sat Aug 12 2017

As upper-level ridge pulls away to the east on Tuesday night,
troughing takes over the Rockies, with a surface low developing
around northwest KS/eastern CO. Thus, more coherent chances for
showers/storms encroach on Tuesday evening/Tuesday night as the
suface low and upper-level trough slide toward the Plains. Slow
frontal passage should allow redevelopment of showers/storms on
Wednesday in the area, as well, before the troughing moves east,
front moves south, and activity slides out of the area, with much of
Thursday likely to be dry. Blends threw POPs into Thursday night,
but have some reservations about whether showers/storms could
develop under the mid-level ridge.  Break in rain chances could end
on Friday, with another upper trough/low moving across the northern
Plains to upper Midwest on Friday and/or Saturday. Temperatures
should remain closer to normal through the period, and highly
dependent on daily convective debris.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 605 PM CDT Sat Aug 12 2017

There is some uncertainty as to just how fast SHRA and TSRA will
move into northeast NE and affect KOFK with MVFR conditions.
Better instability is farther west, but activity should move east
with time. Clouds streaming east from the higher topped storms
will probably move over KLNK and KOMA later, but expect mainly VFR
conditions at those two sites overnight.

&&

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

$$

SHORT TERM...Mayes
LONG TERM...Mayes
AVIATION...Miller



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