Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 222119
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
319 PM CST Wed Nov 22 2017

.SHORT TERM...(Tonight through Saturday)
Issued at 310 PM CST Wed Nov 22 2017

Relatively mild temperatures are expected over the next few days,
with at least breezy conditions behind a cold front on Friday.

After morning lows in the teens and even some single digits,
temperatures have rebounded nicely this afternoon into the 30s and
lower 40s due in large part to plenty of sunshine and a return to
south and southwest winds on back side of surface high pressure.
Those southwest winds will continue into this evening before a
weak cold front slides through the Plains overnight. Strongest
cold advection should remain well northeast of our area behind the
front, with main weather change here being a period of light
northwest low level flow.

Surface winds turn westerly on Thanksgiving Day as pressures
lower in the lee of the Canadian through central Rockies in
response to strong shortwave rounding top of western U.S. ridge
extending from the Baja to southwestern Canada. We will feel the
affects of this system on Friday when shortwave trough sweeps
through the Plains and drives a cold front through Nebraska/Iowa
and eventually into the southeast U.S. this weekend. Ahead of the
front, downsloping southwest low level flow will increase Thursday
night into Friday morning when 850 temps surge into the mid and
upper teens across our CWA. Thus overnight lows should be halted
in the 40s. Frontal passage is expected to clear southeast
Nebraska and southwest Iowa by noon or so Friday, turning winds to
the northwest and knocking 850 temps back into the 5-10C range by
late in the day. Despite this cold advection regime, temperatures
should still rebound into the 60s by early afternoon before brunt
of cooling is felt.

Windy conditions are also likely behind front as strong cold
advection under 40-50kt 850 winds sets in. While not the most ideal
momentum transfer regime is forecast, with low level lapse rates
generally low and flow not as unidirectional with height as I`d like
to see, still expecting top-of-boundary-layer winds to mix to the
surface for several hours Friday afternoon, with gusts around 40 mph
possible.

With surface high pressure building into the region Friday night
into Saturday, expect winds to diminish quite a bit by midnight.
Meanwhile mid level heights will begin to rebound, indicating a
warmer pattern is setting up for the latter part of the weekend.
Saturday will feature plenty of sunshine, helping temps top our
mid 40s normals, with highs in the 50s and light northwest winds.

.LONG TERM...(Saturday night through Wednesday)
Issued at 310 PM CST Wed Nov 22 2017

Warm temperatures are still expected into the beginning of the work
week, with colder temps and a small chance for precipitation coming
with and behind a cold front for Tuesday and Wednesday.

Mid level flow pattern will feature building heights over the middle
of the country through Sunday before deep trough begins to approach
the region on Monday. As seems to be the case most of the time, the
GFS is a bit slower than the Canadian which is a bit slower than the
ECMWF in regards to trough progression. As such, the spread in
attendant cold frontal passage spans from Monday afternoon as per
GFS to Tuesday morning as per ECMWF. Our going forecast is a nice
blend of these timing differences, bringing cold front through the
area Monday night.

Thus for Sunday and Monday we will keep warm temperatures going as
850 temps surge into the upper teens by Monday morning on increasing
southwest low level flow. Highs Monday could reach 70 in parts of
our south given this airmass and downslope flow regime.

As cold front passes, post-frontal precipitation will be driven by
mid level dynamics associated with trough/low. And again, models
vary on degree of moisture/lift, but there is some consistency in
showing best chances will reside from northern Nebraska northward
Tuesday morning. And then again Wednesday as a secondary wave
rolls through the region. Still, amounts should remain light if
precip were to occur in our area, so no real impacts are
expected. But will have to watch the Wednesday forecast when ECMWF
wraps up surface low across eastern Nebraska and produces
potentially accumulating snows in northeast Nebraska.

Temperatures will be cooler, however, with Tuesday looking the
coldest when 850 temps drop well below 0C. Some rebound is
expected Wednesday as heights start to build into the region once
again, but if ECMWF proves correct, highs will be well below our
current 40s forecast.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1111 AM CST Wed Nov 22 2017

Expect VFR conditions through the period. Considerable high level
and some SCT mid level clouds will move across the area through
the afternoon. Winds should be somewhat gusty from the south this
afternoon, diminish this evening, then shift to the west or
northwest tonight.


&&

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

$$

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



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