Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 211752

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1152 AM CST Sat Jan 21 2017

Issued at 1142 AM CST Sat Jan 21 2017

After a short dense fog advisory extension in western Iowa, just
a few counties now reporting some lingering fog. With the
westerly/drying flow, the stratus will continue to retreat with
temperatures warming to around 45 near SD where there are
lingering clouds to the lower 50s near the KS border.


.SHORT TERM...(today through Monday)
Issued at 300 AM CST Sat Jan 21 2017

Manual 00z upper-air analysis and early-morning water vapor
imagery indicate the presence of a high-amplitude wave pattern
over the lower 48 states. An embedded short-wave trough over the
mid MO Valley will continue northeast into the upper Great Lakes
today, ahead of a potent sub-tropical-branch trough progressing
into the southern Plains. In the low levels, a moist air mass
which has contributed to areas of dense fog and drizzle/rain
showers early this morning will become displaced by a drier
boundary-layer advecting into the the mid MO Valley from the west
and northwest. Decreasing clouds coupled with the downslope, low-
level flow will yield seasonably warm temperatures by this
afternoon with highs in the mid 40s to lower 50s.

Sunday into Monday, a mid-level ridge will build east into the
Great Plains in the wake of a strong synoptic system over the
southeast U.S., and ahead of the next major trough moving onto the
West Coast. A slightly cooler air mass will filter south into the
mid MO Valley on Sunday before a deepening lee cyclone promotes a
strengthening low-level warm advection pattern over the central
Plains by Monday. High temperatures will remain above normal; in
the 40-45-degree range.

.LONG TERM...(Monday night through Friday)
Issued at 300 AM CST Sat Jan 21 2017

The primary concern in the long term is the potential for
accumulating snow Tuesday into Wednesday. Latest medium-range
guidance remains in general agreement in suggesting that a strong
synoptic cyclone will traverse the central U.S. early next week,
with the potential for a swath of heavy snow to the immediate
north of the surface low track. However, model differences do
exist in the specific track and timing of this system. The GFS is
now the most progressive solution with respect to the track of the
surface low through the central Plains, and this is a significant
departure from the previous model run. The Canadian/GEM is the
slowest with the surface low track, while the ECMWF is a
compromise between the two, exhibiting remarkable run-to-run

Given the above considerations, we are motivated to most strongly
consider the ECMWF solution which depicts a swath of potentially
heavy snow developing from northeast Nebraska into west-central
Iowa Tuesday into Tuesday night. Under this scenario, light snow
would begin late Monday night over northeast Nebraska before
becoming heavy during the day Tuesday. A mix of rain and snow or
all rain would gradually transition to all snow across the
remainder of the area Tuesday afternoon into Tuesday night with
the snow ending on Wednesday. Again, the highest probability of
significant snow accumulation appears to be over the northern part
of the forecast area, with lesser amounts farther south. Strong
north winds on the backside of the departing cyclone will be
conducive for some blowing and drifting of snow Tuesday night
into Wednesday.

The north-central U.S. will remain in northwest or north flow
aloft through the remainder of the extended range. This upper-air
pattern should yield cooler conditions at the surface with highs
in the 20s and 30s.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1142 AM CST Sat Jan 21 2017

VFR conditions are forecast for the first parts of the TAF,
however as surface winds decline tonight and reinforcing cool air
arrives tonight...look for some MVFR vsbys with patchy fog and
return of stratus MVFR/IFR cigs mainly after 06Z. The RAP/NAM are
a little more aggressive with the westward extent of the stratus
later tonight and Sunday morning. Winds should mostly be under
10kts today and light and variable after 00Z...however will
increase from the northwest to 10 to 15kts after 09-12Z.




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