Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 220538
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1138 PM CST Sat Jan 21 2017

.UPDATE...
Issued at 1130 PM CST Sat Jan 21 2017

Dense fog has again formed in our far eastern CWA, affecting a few
western Iowa counties from Harlan to Clarinda. Several short-range
hi-res models suggest a slight westward and southward expansion to
the fog, but increasing northerly winds should keep low level
atmosphere churned up enough to keep dense fog from becoming
widespread. Otherwise expect stratus expansion from southeast
South Dakota and northwest Iowa to overspread much of eastern
Nebraska and southwest Iowa through mid morning.

&&

.SHORT TERM...(Tonight through Tuesday)
Issued at 305 PM CST Sat Jan 21 2017

Potential for fog the next few nights and temperatures will be the
main forecast concerns through Monday night. Our attention turns
to precipitation chances/type/timing by Tuesday.

General large scale mid tropospheric pattern featured a ridge
over the eastern United States, a closed low over North Dakota
with a trough extending from that into Minnesota and a trough from
off the Pacific Northwest coast down into the Four Corners region.
The system over the southwest states will move eastward tonight
and Sunday, but any precipitation associated with that should
stay down across Kansas and Missouri.

Surface low near the Colorado/Oklahoma border at mid afternoon
today will track eastward into northern Arkansas overnight. In
our area, the pressure gradient will initially be very light, but
tighten a bit with north/northwest winds in the 7 to 12 knot range
by late tonight. Some fog could form again tonight, with the most
likely locations to see dense fog across southwest Iowa and
southeast Nebraska. Will not issue a headline for fog at this
point, but like yesterday, that will have to be monitored. The
stronger winds later tonight should help limit fog in our northern
zones.

North/Northwest winds will bring in some cooler air for Sunday and
Sunday night. Highs Sunday should reach the upper 30s to mid 40s
Sunday afternoon. A surface ridge axis should be over the forecast
area at 12Z Monday but then move eastward, with increasing southerly
flow. Some model output hints at possible light precipitation in
our far northwest counties as early as Monday afternoon, but using
a blend of other available output delays chances until Monday
night. This seemed to be the best solution for now. The 12Z GFS
seemed too fast with its eastward progression of the surface low
on Tuesday. A blend of the ECMWF/Canadian/NAM was used, which
would put the surface low in central Kansas by early Tuesday
evening. Did not go as aggressive as the ECMWF/Canadian/NAM models
at this time. It is interesting that the NAM showed impressive mid
level frontogenesis in a band from around Hastings to Omaha
Tuesday afternoon.

.LONG TERM...(Tuesday night through Saturday)
Issued at 305 PM CST Sat Jan 21 2017

The low pressure system will continue to lift through the region
Tuesday night with a deformation zone likely producing snow. Just
exactly where that will be is the problem. Surface winds should
also increase from the north/northwest. Precipitation potential
will be decreasing Wednesday, based on latest expected timing.
The rest of the period from Thursday through Saturday looks mainly
dry. Temperatures should be below normal through the period, but
slowly moderate. Highs will mainly be in the upper 20s to upper
30s, with lows in the teens to lower 20s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1130 PM CST Sat Jan 21 2017

Area of IFR stratus moving south from eastern South Dakota is
expected overspread all eastern Nebraska TAF sites between 09Z and
14Z. IFR cigs will linger through much of the morning, eroding
from west to east, clearing KOFK and KLNK by 18Z, then KOMA
shortly after. Generally MVFR vsbys in fog are forecast along with
the stratus. However ahead of the low clouds, some pockets of IFR
vsbys could affect KOMA and KLNK between 06Z and 12Z.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...Dense Fog Advisory until 9 AM CST Sunday for IAZ056-069-080-091.

&&

$$

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



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