Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 170918
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
418 AM CDT Mon Apr 17 2017

.SHORT TERM...(Today and tonight)
Issued at 413 AM CDT Mon Apr 17 2017

The main sensible weather concerns in the short term period
revolve around potential thunderstorm activity this afternoon
and tonight. Forecast challenges include: precipitation chances,
timing, and areal coverage; general likelihood of strong or severe
thunderstorms; and high temperatures today. Initially, there was
concern for patchy fog this morning, however, whether it will
materialize is in question based on latest observation trends and
hi-res guidance. While patchy fog may occur in portions of
southwest NEB early this morning, the threat for significant
reductions in visibility appears low at this time.

Latest water vapor imagery shows a robust short wave trough moving
over the Pacific Northwest, elsewhere a low amplitude ridge is
present from the Central Rockies/Central High Plains to the
Northern High Plains. This positive PV anomaly is expected to
track quickly today into the Northern and Central High Plains,
providing large scale forcing for ascent, and will displace the
ridge downstream. As the short-wave moves eastward, it will help
prime the environment overhead with mid-level lapse rates (700-500
hPa) steepening in western NEB this afternoon, increasing them
largely to about 7.5-8.5 C/km by late afternoon. As the large
scale pattern evolves, a surface low is expected to develop today
near western WY and far southwest MT with a lee side trough
extending down the Central High Plains. This surface low is
ultimately expected to move into southeast ND/northeast SD by late
tonight. Meanwhile, adequate moisture delivery is expected to
take place with Gulf moisture being transported into western and
central NEB today. Precipitable water values will rise to about
0.75-0.9 inches by late afternoon then increasing to a bit over
1.0 inch over central NEB by mid-late evening. Thus nearing
175-200% percent of normal in portions of western and central NEB.
Forecast surface dew points are expected to increase into the
lower 50s today.

In terms of instability, moderate MLCAPE, 1000-1600 J/kg is
expected to be present over far western NEB and portions of
southwest NEB mid-late afternoon with sufficient MUCAPE available
thereafter overnight. With respect to storm mode, multicells or
clusters, and supercells would be plausible based on guidance and
forecast deep-layer shear. 0-6 km bulk shear are forecast largely
40-45 kts where development is expected. Some concern will be
areal coverage and the general evolution of convective activity
overnight. Wherein deterministic guidance and the SSEO offers a
fair envelope of solutions. While NAM12 and GFS depict more
convective activity over western and north central NEB this
evening and overnight, the SPC SSEO cycle, and its members, at 00Z
show a better signal outside the local forecast area. Wherein the
SSEO spaghetti/paintball plot shows initial development in the
Panhandle/far western NEB then shows development more so across
southwest and central SD. This seems reasonable overnight
considering general forcing and the location of the low-level
jet. As such, PoPs were limited to slight chance and chance
wording. With respect to threats, hail and strong winds would be
expected.

.LONG TERM...(Tuesday through Sunday)
Issued at 413 AM CDT Mon Apr 17 2017

Progressive, zonal mid-level flow will usher a lower amplitude
trough across the central Plains Tuesday evening and Wednesday all
the while a low level jet strengthens. Large scale ascent will
focus an area of thunderstorms over the central high plains
Tuesday evening with the convection spreading eastward across much
of the cwa overnight. Steep mid-level lapse rates when combined
with sufficient effect shear will promote elevated storms capable
of severe hail and possibly severe winds. The Storm Prediction
Center has the region outlooked as marginal, but indicates the
potential of introducing a slight risk if the overall confidence
continues to increase. The Sandhills region will sit under the
influence of the low amplitude trough well into Wednesday with
showers being the primary threat after 12z. Low amplitude ridging
will follow with dry conditions forecast into Friday.

The models have returned to a solution where an upper trough will
dig across the intermountain west and close off a low over
Colorado Friday. There remains disagreement as to where the
eventual h5 low will close, but the general trend is once again
north, now taking the low across Kansas. This is in contrast to
about a week ago when the solutions wanted to impact the Sandhills
region directly. As of the current solution, the greatest impacts
will be south of the forecast area, but some beneficial moisture
is possible for much of the forecast area. Given the southern
track, enough cold air is drawn south into the system that areas
over the western Sandhills may see a mix of rain and snow Friday
night into Saturday. The southern track also limits our convective
potential significantly. The showers will end Saturday with
transitory shortwave ridging to follow into Sunday. The next shot
at qpf arrives on Monday across our west with the next shortwave
digs south across the intermountain west.

Highs remain above normal in the 70s Tuesday. Forecast highs on
Wednesday contrast from 55 to 60 north, to near 70 south.
Temperatures cool to the mid and upper 50s by Friday and Saturday,
influenced by the upper trough and Canadian high pressure across
the region. By Sunday, upper ridge on the backside of the trough
will bring warmer highs in the 60s to western Nebraska.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1113 PM CDT Sun Apr 16 2017

Clouds will increase across southwestern Nebraska overnight and
ceilings may be around 3000 FT AGL at the KLBF terminal by 11z
Monday. Patchy fog will be possible as well with visbys as low as
4sm. Skies will clear by late morning Monday, and will persist
through the afternoon hours. Clouds will increase after 01z
Tuesday with isolated thunderstorms possible across western
Nebraska. For the KVTN terminal: Expect scattered high clouds
around 20000 FT AGL on Monday with increasing cloud cover Monday
evening. Isolated thunderstorms are possible Monday night. Given
the expected isolated coverage, will forgo mentioning them in the
06z TAF.


&&

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

$$

SHORT TERM...ET
LONG TERM...Jacobs
AVIATION...Buttler



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