Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 172055

Area Forecast Discussion
National Weather Service North Platte NE
355 PM CDT Thu Aug 17 2017

.SHORT TERM...(This evening through Friday)
Issued at 220 PM CDT Thu Aug 17 2017

Convective initiation a little earlier than anticipated with
thunderstorms developing in far southeast WY early this afternoon
and beginning to move into the far southwest Panhandle. Lightning
has been mainly inter/intra cloud with infrequent CG strikes
detected at this time. Otherwise, latest satellite imagery shows
mostly clear skies overhead with increasing cloud top cooling
noted upstream in the aforementioned area of convection.

Short wave trough apparent on water vapor imagery in central MT
will track southeastward into SD and the northern fringe of the
central High Plains by early this evening. The disturbance is
expected to provide broad large scale forcing for ascent across
western and north central NEB as it approaches and contribute to
steepening mid-level lapse rates (700-500 hPa). Meanwhile,
surface dew points will be in the mid 50s to lower 60s in extreme
north central NEB early this evening. This corridor of steepening
lapse rates will work with this moisture in support of isolated-
scattered thunderstorm potential mid afternoon into tonight. Of
further aid will be amplifying low-level warm air advection
(850-700 hPa) this afternoon into the evening at low-levels. Best
instability is expected to lie outside the Panhandle with moderate
values of MU and ML CAPE. With respect to storm mode, deep layer
vertical wind shear is about 30-40 kts and suggests organized
multicells primarily, though some supercells or supercell features
can`t be ruled out. Given the parameter space, isolated strong to
severe thunderstorms appear possible. Of which, the window for
the more this falls late this afternoon into the early evening
given current timing/trends. Shower/thunderstorm chances then
diminish through the small hours across north central NEB.
Decreasing clouds are expected from late evening into early
tomorrow morning from west to east.

Lows tonight and tomorrow`s highs will generally be near seasonal
values across much of the local forecast area. Otherwise,
tomorrow will feature mostly clear skies in tandem with scant
precipitation chances.

.LONG TERM...(Friday night through Thursday)
Issued at 220 PM CDT Thu Aug 17 2017

Large scale pattern will be fairly amplified at the start of the
period and will feature an upper level ridge across the Northern
High Plains into Saskatchewan and Manitoba with northwest flow
overhead. The ridge will shift eastward over the Central and
Northern Plains Saturday as an upper level trough digs into the
Canadian Prairies. A zonal to quasi-zonal flow is then expected
to be in place on Sunday overhead at mid-levels. Guidance then
remains in fair agreement with the large scale pattern through
Tuesday-Tuesday night. Of which, the pattern evolves with another
upper level ridge building over the southwest US/Four corners
region into the northern Intermountain West by late Monday.

Sensible weather-wise, main times of possible impacts look to
fall Saturday evening and late Sunday-Sunday night in terms of
shower and thunderstorm potential. Isolated strong to severe
storms look possible Saturday evening. With respect to the day of
the eclipse, current thinking is there is potential for some
obscuration -- more so in the form of high clouds at this time.
However, details at this time are still early and there remains a
lot of uncertainty. Of which, a lot will have to wait until the
morning of (e.g., opacity and translucent vs. transparent clouds).
Will need to further refine the forecast as we get closer.
Otherwise, 40-50% sky cover is forecast at the time of the
eclipse and no precip is in the forecast.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1236 PM CDT Thu Aug 17 2017

Latest satellite imagery shows mostly clear skies overhead.
Elsewhere, convection has started with enhanced cumulus apparent
in extreme southeast WY and modest radar returns seen on the
regional radar display. Mostly clear skies will prevail until
mid-late afternoon when high and convective clouds develop or move
into western NEB. Current thinking is isolated thunderstorms will
move off the higher terrain with some development across western
NEB with storms moving east to southeast direction this evening
into late tonight. Continued the use of VCTS at this time for
both KVTN and KLBF terminals given forecast areal coverage of
storms. Meanwhile, southerly winds this afternoon will shift and
become northwesterly over night. A gradually clearing can be
expected tonight beginning mid evening from west to east.




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