Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 192316

Area Forecast Discussion
National Weather Service North Platte NE
616 PM CDT Fri May 19 2017

.SHORT TERM...(This evening through Saturday)
Issued at 303 PM CDT Fri May 19 2017

Slow moving upper low is centered in far southeast Colorado late
this afternoon. Short-term; Hi-Res models insist this low will
track toward the northeast and be centered south of Lexington near
the NE/KS border by early Saturday morning. This places southwest
NE through the Sandhills in a favorable location for heavier
precipitation within the deformation band. The system takes on
quite a negative tilt tonight, with decent moisture advection and
isentropic lift through the night. Lift is significant, especially
within the deformation band, and dynamic cooling should allow a
mix or a brief change over to all wet snow late tonight lasting
into early Saturday morning. At this time little accumulation is
expected, but some slushy accumulation could occur on grassy
surfaces where the heaviest precipitation rates occur. Models have
been shifting this band around somewhat, and will pass along to
the oncoming shift to watch model and radar trends to see where
the band does indeed set up. This would be the area to watch for
possible accumulation.

NAM and 4KM NAM very slowly lift the upper low northward across
the forecast area Saturday. It will be weakening by this time,
but rain will still be widespread during the morning, gradually
ending during the afternoon. Very cool conditions will continue
with highs in the 40s to possibly mid 50s far southwest Nebraska.

.LONG TERM...(Saturday night through Friday)
Issued at 303 PM CDT Fri May 19 2017

The broad mid-level trough will be over the western and central
CONUS (inland from the West Coast) at the start of the period with
a closed 500 hPa low over the Middle Missouri Valley. Over the
next 24 hours the mid-level trough will be evolving and lifting
eastward encompassing much of the central and eastern CONUS by
Sunday with the upper low then over the MN Arrowhead region.
Elsewhere, a ridge will be building over the West Coast with
another ridge present over the East Coast. Thereafter, the long
wave trough will make little progress eastward with the closed low
moving over Ontario Monday.

Largely northwest flow aloft will keep conditions on the cool side
Sunday, albeit dry, as the upper low migrates northeastward.
Concerns arise regarding frost/freeze headlines wherein colder
temperatures and decent radiational cooling conditions will be
present (lighter winds and mostly clear skies). Area of concern is
primarily across northwest NEB southeast into Custer county. The
next sensible weather concern is rain chances and this falls on
Monday where a positive PV anomaly will rotate from the Northern
High Plains into western Nebraska. A surface cold is anticipated
to advance southward through the local forecast area Monday late
morning and afternoon. Increased chances for rain showers are
expected, mainly in the afternoon and evening, and there will be
the possibility of thunderstorms.

After Monday, the flow aloft becomes more meridional through
Tuesday night. Highs will be on the colder side Tuesday, back to
well below seasonal normal values (highs largely forecast 15 to 25
degrees below normal). Spread between guidance increases beginning
Tuesday with respect to phase and amplitude in the large scale
pattern. A upper level waves look to impact British Columbia
Tuesday night/Wednesday with the ridge moving over towards the
Northern Plains Wednesday. Highs are expected to trend upwards to
seasonal normal values by Thursday.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 616 PM CDT Fri May 19 2017

An upper level low pressure system in Colorado will move into
southwest Nebraska late tonight. This will bring widespread light
rain to much of western Nebraska tonight into Saturday morning.
Ceilings are currently VFR at KLBF and KVTN, while many other
location are MVFR. Ceilings are forecast to lower to IFR tonight,
then improve to MVFR by around 18z Saturday.




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