Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 221132

Area Forecast Discussion
National Weather Service Omaha/Valley NE
632 AM CDT THU SEP 22 2016

.SHORT TERM...(today through Saturday)
Issued at 327 AM CDT THU SEP 22 2016

Chances for convection through the day today and tonight, then
storms returning by Saturday, are the primary forecast concerns.
Temperatures the next few days are also a focus.

Scattered showers and a few storms finally got going in parts of our
area in northeast Nebraska late Wednesday evening. Weak forcing and
capping kept storms from firing earlier in the afternoon and evening
along southward drifting cold front. Increase in low level jet after
dark promoted significant moisture transport over frontal zone, and
was enough to kick off scattered convection. Similar scenario will
continue through the early morning as jet and theta-e axis gradually
shift eastward. Expect most activity to translate east across west
central Iowa early in the day, but development into the theta-e
ridge should maintain at least a small chance for storms as far
south as southeast Nebraska and southwest Iowa.

Surface front is not expected to move much farther south, setting up
northeast to southwest just northwest of Interstate 80 this
afternoon. Low level moisture should remain in place as well with
upper 60s to low 70s dew points covering most of eastern Nebraska
and western Iowa through tonight. Forecast soundings suggest ML
and SB CAPE will top 2000 j/kg during peak heating this afternoon,
but a tendency to rising mid level heights may squash attempts at
convection much of the afternoon again. We will likely have to
again wait for low level jet to get things going near and north of
retreating frontal boundary later tonight as it moves toward the
South Dakota border by Friday morning. Will maintain at least a
chance for storms this afternoon and night near and north of
Interstate 80, but confidence in occurrence and coverage is low.

On Friday, shortwave ridging will become established across our CWA
as western low/trough progresses into the Rockies. Models are in
fairly good agreement into Saturday in taking low center from
Wyoming Friday afternoon into western North Dakota by Saturday
afternoon. This leaves eastern Nebraska and western Iowa under a
broad warm advection regime with southerly surface winds and
southwest flow aloft pumping moisture into the region ahead of
approaching cold front/dry line for Saturday afternoon. We may see
some elevated convection Friday night as one wing of warm advection
swings through the region, but better chances for more widespread
showers and storms will come Saturday as frontal boundary interacts
with deep layer moisture plume. Precipitable water values are
forecast to top 1.75 inches then, so pockets of heavy rain are
certainly possible.

Temperatures through Saturday will continue to average well above
normal. This afternoon will offer the more tricky forecast as north
to northeast winds north of cold front keep parts of northeast
Nebraska in the 70s for highs, while south of the front some 90s are
possible in southeast Nebraska and southwest Iowa. Most areas should
reach the mid and upper 80s, if not lower 90s in the south, on
Friday when we are squarely in the warm sector and should see more
sunshine. By Saturday, more cloud cover and widespread precipitation
should hold highs closer to the lower 80s many areas.

.LONG TERM...(Saturday night through Wednesday)
Issued at 327 AM CDT THU SEP 22 2016

Much cooler weather is forecast into the middle of next week, with
only small precipitation chances.

Cold front tied to deep upper low in the Northern Plains will be
swinging through eastern Nebraska and southwest Iowa Saturday night
and should be well east of the area on Sunday. Much cooler air will
follow this front into the middle of next week as upper low/trough
slowly drifts through the region. Models diverge on exact placement
and strength of the low, but are somewhat similar in showing mean
trough axis over our area at least through Tuesday. Airmass will be
characterized by 850 temperatures in the single digits (generally 2-
7C) which are almost 15C cooler than ahead of Saturday cold front.
Periodic shortwaves rotating through the region around upper low may
spark some showers from time to time, but exact timing of these
features will have to come as we head closer to next week. Otherwise
model output of highs in the 60s and lows in the 40s and 50s will be
the primary story of the longer term forecast.


Issued at 632 AM CDT THU SEP 22 2016

Mesoanalysis at 11z revealed a weak surface low northwest of KOFK
with an associated front stretching from south-central Nebraska
through the low into northwest Iowa. Low cloud/fog IR satellite
imagery suggests that this boundary is slowly edging southeast,
possibly reaching KOFK by mid morning. IFR to LIFR conditions are
currently being observed on the cool side of this boundary, so its
ultimate location is certainly critical to aviation interests.

Considerable variability exists in latest short-term model
guidance with respect to how far southeast the low clouds and fog
develop. Some solutions maintain VFR conditions at KOFK, while
others indicate MVFR to IFR conditions through the day. Based on
observational trends, we are inclined introduce temporary IFR
conditions toward mid morning with prevailing MVFR ceilings into
early afternoon. This forecast is likely to change based on
subsequent observational trends.

The front will move back through KOFK tonight with a period of
MVFR ceilings and visibilities possible. At KOMA and KLNK, Showers
and a few thunderstorms which moved through the area earlier this
morning have shifted into Iowa with lingering broken mid and
high-level cloudiness. Expect VFR conditions to prevail at these
two locations through the forecast period.


.OAX Watches/Warnings/Advisories...


LONG TERM...Dergan
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