Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 182041
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
341 PM CDT Fri Aug 18 2017

.SHORT TERM...(This evening through Saturday)
Issued at 249 PM CDT Fri Aug 18 2017

Latest visible satellite imagery shows a few-sct diurnal cu
developing across the Panhandle and across southwest SD/northwest
NEB into the Sandhills. Sensible weather-wise conditions are
quiet. Water vapor imagery shows an upper level ridge roughly
across the Central Great Basin-Central Rockies into central
Saskatchewan progressing eastward as an upper level trough
advances across British Columbia to northern Alberta.

Modest 500 hPa height rises are expected to continue overhead in
tandem with northwest flow tonight as the mid-level ridge moves
over the Central High Plains. Thereafter the ridge will move to
eastern NEB-Upper Mississippi Valley by tomorrow afternoon with
zonal flow in place by tomorrow morning that will continue through
the day. Of which, a weak shortwave trough is expected to track
into the Central High Plains by tomorrow afternoon.

Clear skies combined with good radiational cooling conditions
tonight (e.g., light winds) is expected to support lows falling
to near seasonal values tomorrow morning. Tomorrow, decent
moisture delivery via return flow setting up across southwest NEB
into central and north central NEB. Meanwhile, a lee surface
trough will evolve and sharpen by the CO Front Range and Laramie
mountains. Surface dew points tomorrow afternoon forecast to range
from the mid 50s in southwest NEB to lower 60s in north central
NEB. This moisture combined with steepening lapse rates at mid-
levels (700-500 hPa from 7.5-8.5 C/km) should contribute to at
least moderate instability, MLCAPEs 1200-2000 J/kg, across
southwest NEB into north central NEB. Deep layer vertical wind
shear appears favorable for some strong to severe thunderstorms
with values of 25-40 kts promoting organized multicells and some
supercells with regard to storm mode. Severe threat is expected to
be isolated in nature with storms developing then moving east to
east southeast. Best chances in vicinity and east of trough, thus
covering the areas of southwest NEB to central and north central
NEB.

.LONG TERM...(Saturday night through Friday)
Issued at 249 PM CDT Fri Aug 18 2017

The main forecast challenges this forecast period were
precipitation chances over the weekend into Monday and the day
of the total eclipse.

A weak short wave trough will be situated across central Nebraska
Saturday evening bringing shower and thunderstorm chances Saturday
evening into the overnight hours followed by another disturbance
bringing shower/thunderstorm chances on Sunday evening into Monday
morning. Severe weather is not expected at this time, however an
isolated strong to severe storm cannot be ruled out. The main
concern will be rainfall amounts associated with the
showers/thunderstorms as several locations across north central
Nebraska saw area of 6 inches or greater rainfall this past week,
thus creating flooding concerns as the ground is still very
saturated.

As for Monday (the day of the eclipse), some models are suggesting
the possibility of a few mid to high clouds moving in mid morning
through afternoon across parts of the Sandhills. However, at this
time it does not appear to be widespread in coverage, later
forecasts will give a better handle on cloud coverage and timing.
Overall, a significant amount of uncertainty remains and this will
need to be assessed more so on the day like the character of any
high or mid clouds (e.g., opacity - opaque vs. translucent vs.
transparent). Please continue to monitor forecasts, discussions,
and social media as trends become better established and
confidence grows. At this time, another upper level trough will
move across late Monday bringing chances of showers and
thunderstorms Monday evening, the night of the eclipse.

Tuesday and beyond, another chance of showers and thunderstorms
Tuesday night associated with an upper level through, then a ridge
will build in across the west bringing drier conditions through
Thursday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1215 PM CDT Fri Aug 18 2017

Latest satellite imagery shows predominantly clear skies across
western and north central NEB. Latest surface plot shows light west
to northwest winds with most sites recording speeds between 8 and
12 kts. VFR conditions and Mostly clear skies will prevail the
next 24 hours/through the TAF period. Winds will lessen this
evening with most sites becoming light and variable by late
evening. Winds will pick up tomorrow mid-late morning, out of the
south, and up to 12 kts.


&&

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

$$

SHORT TERM...ET
LONG TERM...Gomez
AVIATION...ET



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