Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 140947
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
347 AM CST Sun Jan 14 2018

.SYNOPSIS...
Issued at 346 AM CST Sun Jan 14 2018

At 09z...Light snow had exited the forecast area. A trough of
surface low pressure extended along the High Plains. A warm front
extended north to south just east of highway 83. Behind the warm
front, westerly winds with temperatures mainly in the upper 20s to
lower 30s existed. Skies were mostly cloudy, with patches of clear
skies over parts of the western Sandhills. The next upstream arctic
front was analyzed from central Manitoba through southern
Saskatchewan, back west into central Alberta. Temperatures were
bitterly cold from the northern Saskatchewan and Manitoba into the
Northwest Territories, ranging as low as 25 below to 40 below.

&&

.SHORT TERM...(Today and tonight)
Issued at 346 AM CST Sun Jan 14 2018

Northwest flow aloft will persist across the region through tonight.
The main forecast concern will be an arctic front dropping south
today, sweeping south through the forecast area tonight. Light snow
will also develop behind the arctic front late this afternoon and
tonight.

A warm front will push east through the forecast area today,
bringing a notable warmup. Northwest winds will increase to 10 to 20
mph late this morning and afternoon and promote mixing. Temperatures
at 850mb will rise to 0-3C across southwestern areas and from -1 to
-3C in the northeast. Existing light snow cover mainly around a half
inch along with increasing cloud cover this afternoon will limit
highs to around 45 far southwest, around 40 central areas, to around
35 far northeast. As the arctic front moves quickly into north
central Nebraska by 21z, models generate weak lift. With colder
temperatures aloft, a quick change over from a rain/snow mix to
light snow is expected. Likely pops are forecast after 21z for areas
north of a Gordon through O`Neill line. A chance for light rain very
late this afternoon, as far south as I80.

For tonight, a strong 130kt jet max will drop southeastward through
Nebraska. The 850-500mb layer will be fairly saturated, and with
weak lift, a 3 to 4 hour period of light snow is expected. Although
POPS will begin as likely early this evening, snow chances will end
for all except southwestern areas after midnight. Due to the limited
duration, snowfall amounts will be light, ranging up to an inch in
Sheridan county, and from a dusting to half inch elsewhere. Strong
subsidence and dry air work in from the north, with skies becoming
mostly clear across the northeast half late tonight. With arctic air
in place, lows will fall to 0 to 5 below across the northeast and
from 5 to 10 above southwest areas. Northerly winds will persist
from 15 to 25 mph overnight most areas. This will cause wind chill
values to fall to around 20 below across much of north central
Nebraska by 12z. A wind chill advisory has been issued beginning 10z
tonight.

.LONG TERM...(Monday through Saturday)
Issued at 346 AM CST Sun Jan 14 2018

The main forecast challenge over the long term is temperatures early
week. The combination of the closed upper low over the Great Lakes
and strong surface high over the Great Plains will cause temps 30
degrees below normal. A Wind Chill Advisory was hoisted for the
Sandhills beginning early Monday morning and continuing through
Tuesday morning. Southwest to quasi-zonal flow aloft returns
midweek, allowing for temperatures to rise to above normal levels.

Monday... Nebraska is caught between the exiting sfc low/cold front
and an approaching sfc high over the northern Plains, creating
blustery conditions. Continued using the higher winds of the Cons
solutions due to steady 1 mb/hr pressure rises, 35kt+ H85 flow, a
1.5 PV anomaly reaching 500mb, and a 110kt+ H3 jet. CAA is well
underway with H85 temps falling from -16C at 12z to -21C at 00z. As
highs only top out in the single digits across the north and
lower/mid teens southwest, wind chill criteria are met for most of
the afternoon. The winds relax overnight as the sky remains mostly
clear, which sets up the optimal radiational cooling scheme,
especially if snow pack remains (currently 2" as of 06z Sunday).
Trended Monday night lows toward the cooler MET guidance, which
results in widespread -5 to -10F southwest and -10 to -13F north.
Surface winds are slightly higher over north central Neb, which
creates wind chill indices close to warning threshold. Will let
upcoming shifts determine the need to upgrade the advisory (or
expand south).

Tuesday... Wind won`t be as big an issue as the high settles right
over Nebraska, and even return flow begins late in the afternoon.
Given plenty of sunshine and weak WAA, bumped temps up a degree or
so. Highs still remain very cold with teens north central and lower
20s panhandle/southwest. Wind chill headlines appear unlikely
Tuesday night.

Wednesday through Friday... An H5 ridge building over the Western
U.S. broadens and pushes onto the Plains while a surface high sits
over the southeast states. Persistent downslope flow and a couple
thermal axes (with the strongest coming Friday with H85 temps 10C+)
push highs into the 30s Wed and mid/upper 40s Thu/Fri. The dry
stretch continues, although of note is a weak upper low riding the
ridge on Thursday. Little to no moisture (even in the mid levels)
precludes PoP with this forecast issuance.

Saturday... The extended model suite suggests a healthy system
crossing the Plains and Midwest that will need to be watched over
the coming days. Synoptic differences exist with a negatively-tilted
trough and H5 low along the NE/KS border in the GFS, while the ECM
shows a positively-titled trough and open wave (but still decent
precip potential for Neb).

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1145 PM CST Sat Jan 13 2018

Expect MVFR ceilings across western and north central Nebraska
overnight. Ceilings will lift to vfr levels on Sunday and even
some clearing is possible Sunday. Skies will cloud over once again
Sunday afternoon from north to south as an arctic cold front
tracks south through the area. As the front passes through the
area during the late afternoon to early evening hours, the threat
for light snow will increase and ceilings will fall to mvfr
levels.


&&

.HYDROLOGY...
Issued at 346 AM CST Sun Jan 14 2018

A Flood Advisory remains in effect for the Niobrara River near
Sparks. River gages indicate a slow trend downward to near 6.2 feet.
This is slightly above the flood stage of 6.0 feet. The forecast is
for a decrease in the river stage to below flood stage later today,
then falling below action stage tonight. Will need to monitor this
and other river gages, as arctic air returning could increase ice
jamming concerns through this week.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory from 4 AM CST /3 AM MST/ Monday to noon CST
/11 AM MST/ Tuesday for NEZ004>010-023>029-036>038-094.

&&

$$

SYNOPSIS...Roberg
SHORT TERM...Roberg
LONG TERM...Snively
AVIATION...Buttler
HYDROLOGY...Roberg



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