Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 121148

Area Forecast Discussion
National Weather Service North Platte NE
648 AM CDT Sat Aug 12 2017

.SHORT TERM...(Today and tonight)
Issued at 423 AM CDT Sat Aug 12 2017

Sensible weather concerns revolve around the threat for scattered
strong to severe thunderstorms afternoon to tonight  large
hail, damaging winds, and locally heavy rain are the main hazards.
Otherwise, a cool day on tap with highs expected to be about 5 to
10 degrees below seasonal normal values. Latest water vapor
imagery shows west northwest flow across the Central High Plains
and upstream a short wave trough across extreme southern Alberta-
Saskatchewan entering northern MT. Elsewhere, an upper level ridge
is present west of the short wave trough and is gradually
breaking down with an upper level trough upstream in the British
Columbia and Pacific Northwest Pacific offshore waters.

The short wave trough moving into northern MT in the small hours
this morning will continue to track southeastward into the
central Northern Plains today then enter the Middle Missouri
Valley tonight. This disturbance will provide modest large scale
forcing for ascent in tandem with amplifying low-level (850-700
hPa) warm air advection this afternoon-evening over western NEB to
help prime the environment for convection. Mid-level lapse rates
(700-500 hPa) are anticipated to steepen today to 7.25-8 C/km with
decent moisture at the surface and boundary layer. Surface dew
points are forecast in the upper 50s-lower 60s, highest in
southwest NEB to central NEB. The thermodynamic profiles should
contribute to MLCAPEs of 1000-1500 J/kg to approaching 2000 J/kg,
greatest in northwest NEB and the eastern Panhandle. Deep layer
bulk shear at 0-6 km of 35-45 kts, and largely similar effective
shear values, should be conducive for organized multicells and
supercells, the latter storm mode more so initially in the day.
While some supercells are anticipated, current thinking is this is
more likely to occur in western NEB and the eastern NEB Panhandle
late afternoon into the evening. This thinking is supported by
some of the deterministic guidance and the SPC SSEO. The latter
showing a decent signal in updraft helicity neighborhood probs and
spaghetti/paintball plots favoring the eastern NEB Panhandle and
western NEB. As the situation evolves, storm motion to the
east/east southeast is expected with storms congealing in the
evening. Activity should progress eastward with PoPs decreasing in
western NEB late evening to after midnight central. Large hail
and damaging winds are the main hazards, though a tornado cannot
be ruled out as well. Threat for locally heavy rainfall exists
also given storm coverage, precipitable water values approaching
125-150% of normal and storm motion to 20 kts. The greatest
rainfall amounts, and greatest threat for heavy rainfall, is
anticipated to be mainly east of Highway 83 and south of Highway

.LONG TERM...(Sunday through Friday)
Issued at 423 AM CDT Sat Aug 12 2017

Light patchy fog south of I-80 early Sunday morning will quickly
burn off after sunrise. Then a fairly redundant pattern sets up
across north central Nebraska with dry in the morning hours and
afternoon showers/storms. This pattern will continue through
Thursday. Storms are expected to be very isolated and generally
below severe criteria. A frontal system will move across the
northern Plains on Tuesday night resulting in a better chance for
most of the forecast area to see showers and thunderstorms. These
storms on Tuesday night have the potential to become severe.

A building upper level ridge and surface high pressure will result
in dry conditions for Friday and the beginning of next weekend.

The other main story besides afternoon storms next week will be the
increasing temperatures. While not anticipated to rise extremely
high, temperatures will slowly rise from the upper 70s to low 80s on
Sunday into the mid to upper 80s by the end of the week. Overnight
low temperatures remain fairly steady in the upper 50s to low 60s
through next week.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 620 AM CDT Sat Aug 12 2017

Local radar display shows a line of showers moving slowly east
through the central Sandhills, roughly from Anselmo to Wood Lake.
Latest surface plot and satellite imagery show largely VFR
conditions. However, sub-VFR conditions are possible with this
aforementioned activity and are also expected in the southeast
NEB Panhandle where stratus has developed over the last hour. The
latter is expected to hold MVFR to IFR ceilings with KIBM and KSNY
reporting 300 and 1600 ft AGL, respectively. Potential for
isolated showers and thunderstorms will continue through early
afternoon across much of the area. Scattered showers and
thunderstorms are then expected later this afternoon and evening
with strong to severe thunderstorms possible. Development
initially expected in northern and far western NEB with storms
moving southeastward affecting southwest, central and north
central NEB through the late afternoon and evening hours.
Potential for sub-VFR ceilings is expected then late tonight
across much of western and north central NEB.




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