Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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638
FXUS63 KOAX 200515
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1115 PM CST Sun Feb 19 2017

.SHORT TERM...(Tonight through Wednesday)
Issued at 307 PM CST Sun Feb 19 2017

A low-latitude short-wave trough over the southern Rockies and
northwest Mexico this afternoon will phase with a polar-branch
disturbance over the High Plains tonight with an elongated
vorticity ribbon translating through the central and northern
Plains Monday into Monday night. In the low levels, strengthening
south winds ahead of a deepening lee trough over the High Plains
have hastened the poleward flux of an increasingly moist
boundary-layer into the mid MO Valley with 20z dewpoints commonly
in the upper 40s to lower 50s.

Latest short-term convection-allowing model guidance suggests that
initial thunderstorm development will occur across the southern
Plains this afternoon into evening with activity spreading north
through central and east KS into portions of east NE and southwest
IA after 08-09z. Steepening mid-level lapse rates coupled with the
continued moistening of the environment and strengthening dynamic
forcing for ascent will be supportive of isolated thunderstorms
embedded within the broader precipitation shield. The showers and
thunderstorms are expected to shift to the east of the area by
late morning or early afternoon with no additional convective
activity anticipated along the trailing wind shift/weak cold
front which will advance across the area during the afternoon.
Skies should clear from west to east Monday afternoon, allowing
temperatures to warm to near or above record values for the day
(see the Climatology section below).

The mid-level pattern will transition to quasi-zonal in the
Tuesday-Wednesday time frame with an unseasonably warm and moist
low-level air mass residing across the mid MO Valley ahead of a
cold front which will move into the area on Wednesday. A number of
temperature records could be challenged through the first half of
the work work (again, see the Climatology section below) before a
cooler air mass filters into the region from the north by
Thursday.

.LONG TERM...(Wednesday night through Sunday)
Issued at 307 PM CST Sun Feb 19 2017

The primary feature of interest in the extended range is a
vigorous short-wave trough and associated surface low which will
track from the central High Plains through the mid and lower MO
Valleys Thursday into early Friday. We continue to see model
fluctuations in track and amplitude of this synoptic system. The
ECMWF has remained the most consistent of the available data,
indicating the surface low developing from southeast CO Thursday
morning to north-central or northeast Kansas by Thursday evening,
prior to undergoing occlusion over central or eastern IA by
12z/Friday. The deterministic GFS and GEFS mean depict similar
(albeit slightly farther south) evolutions, while the 12z
Canadian model has now become the outlier with a farther north
and slower solution.

Under a scenario similar to the ECMWF, the chance of rain will
increase from northwest to southeast across the area on Thursday.
By Thursday night into early Friday, intense dynamic forcing for
ascent coupled with rapidly deepening cold air on the backside of
the surface cyclone will yield a change over to snow within the
evolving deformation precipitation band. While exact amounts
remain uncertain, current model trends suggest the potential for
several inches of snow across parts of east-central and northeast
NE into west-central IA. In addition to the snowfall, winds will
strengthen considerably from the north Thursday night into Friday
with areas of blowing and drifting snow possible. The snow is
currently expected to taper off Friday evening with additional
chances for light snow on Saturday into Sunday.

Temperatures late this week into next weekend will be notably
colder with afternoon readings generally in the 30s north and
central with 40s southeast.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1115 PM CST Sun Feb 19 2017

Low clouds are slower to move into the area, but should still move
in overnight. Showers and isolated thunder should spread up over
southeast Nebraska and into western Iowa late tonight. The MVFR
ceilings should continue into Monday morning, then conditions will
improve to VFR. Winds will shift to the northwest as a front moves
through, but had too many groups to include all details of wind
shift for KOMA and KLNK.

&&

.CLIMATE...
Issued at 307 PM CST Sun Feb 19 2017

Given the unseasonably warm conditions expected, the following are
the record high and maximum low temperatures:

Monday/20th:    Omaha - 67/1930, 50/1930
                Lincoln - 71/1991, 51/1930
                Norfolk - 66/1930, 37/1996

Tuesday/21st:   Omaha - 72/1977, 53/1930
                Lincoln - 74/1991, 51/1930
                Norfolk - 74/1995, 40/1930

Wednesday/22nd: Omaha - 71/1982, 42/1933
                Lincoln - 74/1982, 46/1896
                Norfolk - 72/1995, 37/1998

&&

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

$$

SHORT TERM...Mead
LONG TERM...Mead
AVIATION...Miller
CLIMATE...Mead



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