Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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949
FXUS63 KOAX 192311
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
611 PM CDT Sat Aug 19 2017

.SHORT TERM...(Tonight through Tuesday)
Issued at 335 PM CDT Sat Aug 19 2017

The main forecast concerns are thunderstorm chances from tonight
into Tuesday, and sky cover for Monday.

Upper air charts from 12Z had the following main features of
interest. 300 mb winds were strongest around the mid/upper level
trough over the Great Lakes and Ohio Valley. At 500 mb, 12 hour
height falls of 30-50 meters extended from southwest Canada down
to northern California. Thermal ridge at 700 mb was over the
Rockies with the +10 C isotherm extending from southwest South
Dakota into central Kansas. Water vapor imagery early this
afternoon showed a weak shortwave trough moving through the
central Plains with stronger pieces of energy from Montana back
into the Pacific Northwest. Some monsoonal moisture was in a
couple of bands over the southwest United States, with one band of
interest curving from the Gulf of California toward southern
Colorado.

Altocumulus type clouds were moving east into parts of eastern
Nebraska as of mid afternoon, but no precipitation was occurring.
Convection allowing models (CAMs) suggest that storm chances will
increase this evening from west to east. Main area of focus for
severe potential will be mostly to our west but may spread into
parts of eastern (mainly southeast) Nebraska by midnight. The low
level instability axis will be to our west into early evening, but
may increase to over 2000 J/kg in parts of southeast Nebraska
06Z-12Z. Main hazards through sunrise Sunday would be hail and
gusty winds.

Some storms may linger into Sunday morning, with at least small
chances into the afternoon. Better focus may be along and north of
a northward lifting warm front, Sunday evening into Sunday night.
Model guidances varies with respect to where best chances will be
but proximity of front and low level jet suggest the southwest
half of Iowa.

--Eclipse Outlook--

Monday, well things are not going to be clear but probably won`t
be completely cloudy either (although the cloud trends are looking
a bit higher than the past few days). We will also have a small
chance of thunderstorms (mainly north of a line from Albion to Red
Oak) for the eclipse window (about 1130 am to 230 pm). A warm
front should stretch from west to east through the area. Generally
you would expect a trend of clearer conditions south of the
front, but no so in this case. The low clouds (if there are any)
may clear, but models continue to show mid and high level
moisture, at least immediately to the south at 18Z. For now, will
hold sky cover percentages for eclipse time mainly from 45 to 65
percent.

Models suggest that surface low pressure may track/develop quickly
into central Iowa by mid evening Monday, allowing a front to push
south toward Interstate 80. There should be heavy rain potential
for the area, especially along and north of that boundary, which
will be sinking south into Missouri and Kansas by Tuesday morning.
Some showers could linger into Tuesday morning but overall trend
should be for decreasing precipitation chances as a ridge of high
pressure at the surface build over the area Tuesday.

.LONG TERM...(Tuesday night through Saturday)
Issued at 335 PM CDT Sat Aug 19 2017

Most of this period looks drier, and have POPs 14 or less from
Tuesday night into Friday. Thunderstorm chances return by Friday
night and continue Saturday.

Lows in the 50s Tuesday night should slowly moderate to lower 60s
by Friday night. Highs are expected to be mainly upper 70s and
lower 80s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 608 PM CDT Sat Aug 19 2017

Generally, VFR conditions will persist through Sunday evening
outside of thunderstorms expected overnight. Band of storms
developing in north-central and central Nebraska are forecast to
move east and southeast toward eastern Nebraska TAF sites
overnight. Attendant MVFR/IFR cigs/vsbys in storms will likely
affect KOFK between 03Z and 06Z, then KLNK a 04Z-08Z, and KOMA
06Z-10Z.

&&

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

$$

SHORT TERM...Miller
LONG TERM...Miller
AVIATION...Dergan



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