Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 160445
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
1145 PM CDT Fri Sep 15 2017

.SYNOPSIS...
Issued at 311 PM CDT Fri Sep 15 2017

Well defined lead PV anomaly moving northeast across eastern WY on
downstream side of long wave trough located over the western US.
Ahead of this feature strong LLJ and low level warm air advection
creating a large area of mid level instability across eastern NE
into SD/MN. Within this environment SHRA and TSRA developed as a
result of forcing of a northward advancing warm front last night and
through the morning. Further west, more widespread rain and even
snow in the higher elevations across parts of MT/WY supported by
fairly substantial cold conveyor belt across southern Canada
combined with warm conveyor belt originating from the aforementioned
LLJ and warm advection pattern through the Dakotas and turning
westward and wrapping into the low. Second and more substantial
PV anomaly dropping southward on backside of upper low over
eastern WA/OR into NV/UT.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 311 PM CDT Fri Sep 15 2017

Previously mentioned PV anomaly will rotate through the upper low
across the central Rockies today. Downslope winds will drive/create
a dryline surge across northeast CO and western KS and into
southwest/central NE this afternoon. Surface low will continue to
pull northeast into western MN and weaken as it stays anchored to
broader area of weakening warm air advection. Associated subsidence
behind exiting short wave to be in place across western NE into the
afternoon. Slight precip chances near the SD border late this
afternoon but large scale subsidence should keep most of the area
dry through late afternoon.

As PV anomaly moves off the Rockies it will cause a surface low to
develop in northeastern CO and allow a cold front to drop south into
the Panhandle this evening. Upper height falls then rotate into the
western Dakotas late afternoon and evening and low level winds
respond resulting in convergence along the front across northeastern
NE and to some degree along the dryline in central NE by evening.
RAP soundings suggest inverted-V profiles in low levels west of this
line, suggesting dry air below a shallow moist layer in the mid
levels. This profile exists to some degree in eastern north central
NE in the form of an elevated mixed layer and therefore allows some
CAPE/instability to be available above low level forcing and should
set the stage for thunderstorm development if parcels can make it
above low level stable layer. Short range models differ on this
occurring, but if it does there will be decent potential for enough
instability to produce updrafts capable of supporting marginal large
hail, hence the area of marginal risk for severe storms as presented
by SPC.

Further west, weaker elevated instability moves into the NE
Panhandle this evening. Next area of height falls associated with
next PV anomaly rotating through main upper trough will allow mid
level southerly winds to increase across the west creating a new
warm conveyor belt and developing an area of strong frontogenetic
forcing in this weakly unstable environment in the Panhandle. More
widespread showers and a few thunderstorms will develop as a result
of the strong mid level forcing, moving east across north central NE
overnight. Though some instability is presented in RAP soundings in
this area it likely won`t be enough to support large hail. Good
confidence in the occurrence of SHRA/TSRA here however as this
sequence of events is supported by most models.

For saturday some lingering showers and maybe a rumble of thunder or
two will be across north central NE. But otherwise expect a lot of
cloud cover behind the front and much cooler temps. Upper low pulls
northeast into the Dakotas and although some weak forcing with
remain across north central NE this will lessen through the day.

.LONG TERM...(Saturday night through Friday)
Issued at 311 PM CDT Fri Sep 15 2017

An active weather pattern will be taking shape the next several days
as a large upper trough becomes established across the Pacific
northwest. This trough will slowly move east into the central and
northern plains by the end of next week.

Ahead of this large trough, a weak disturbance will quickly move
east across the area Sunday into Sunday night. Will include some
chance pops for precipitation with this. Appears enough instability
to include thunder.

As the upper trough slowly moves east next week, isolated to
scattered showers and thunderstorms will be possible by midweek as
southwest flow aloft becomes established on the eastern periphery
of the approaching trough. Will keep pops conservative as quite a
bit of model differences at this point.

After a cool weekend, it will begin to warm up again ahead of the
upper trough early next week. It appears highs in the upper 70s and
80s will return through much of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1145 PM CDT Fri Sep 15 2017

Low clouds will continue to push into the sandhills and
southwestern Nebraska overnight. Ceilings below 1000 FT AGL are
likely overnight and will persist through sunrise at the KVTN
terminal and through mid morning Saturday at the KLBF terminal.
Ceilings will gradually increase Saturday afternoon with VFR
conditions expected. Winds will be from the north or northeast at
10 to 15 KTS over the next 24 hours.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SYNOPSIS...Stoppkotte
SHORT TERM...Stoppkotte
LONG TERM...Taylor
AVIATION...Buttler



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