Area Forecast Discussion
Issued by NWS North Platte, NE

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832
FXUS63 KLBF 231216
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
716 AM CDT Thu Mar 23 2017

.SHORT TERM...(Today and tonight)
Issued at 332 AM CDT Thu Mar 23 2017

Multiple sensible weather concerns in the short term period. The
main focus this package is directed towards strong-severe
thunderstorm chances. Severe hail and severe wind gusts are the
primary threats for any severe thunderstorms. Otherwise,
unseasonably warm temperatures will prevail today, about 16-26
degrees above normal (warmest south of I-80), under warm southerly
flow.

Amplified flow exists in the large scale pattern at the present time
with a mid-level trough currently extending from the Pacific
Northwest to California and a ridge over the Lower Southern Plains
into the Upper Mississippi Valley. The mid-level trough will advance
eastward to the Northern High Plains-Four Corners region over the
next 12 hours. A closed 500 hPa low will develop this evening and
move into far eastern CO/western KS by early Friday morning.
Deterministic guidance are in fair agreement with the evolution of
the 500 hPa pattern with the primary short wave trough forecast to
track into the High Plains mid-late afternoon. This shortwave trough
will help prime the environment with mid-level lapse rates (i.e.,
700-500 hPa) steepening across western and north central NEB in the
mid-late afternoon. Mid-level flow aloft will be increasing as a
southwesterly belt is expected to push into the area, overhead
about 50-60 kts. The the mid-level flow then becomes southerly
and the nose gets shunted into south central NEB by late evening.

Meanwhile, a lee side surface low will develop today ahead of the
upper level trough in northeast CO with a surface trough extending
from southwest NEB into the northern Sandhills by early afternoon.
The surface low will continue to sharpen and deepen as it moves into
eastern CO by early-mid evening with a surface trough then extending
from far southwest NEB into central NEB. With respect to moisture,
available moisture and delivery will not be as favorable, more so
as return flow is lacking. However, do see better moisture
transport this evening and overnight. Surface dew points within
a zone of better low-level moisture is expected to peak in the
lower 50s across central and north central NEB this afternoon.

A dryline is expected push eastward and be pronounced in western NEB
today. While agreement is generally fair with respect to surface
features/surface low, the dryline evolution varies notably. Of
which, the GFS is more aggressive in advancing it eastward through
KLBF while NAM keeps it west of KLBF. This will impact and play a
role in thunderstorm development/location. Thus will need to
watch to see the nature and degree of boundary layer mixing
today/location of dryline. In regards to instability, MLCAPE
realized between 1000-1500 J/kg is anticipated in a narrow zone in
western NEB. Given the mid-level flow, deep layer shear will be
high, 55-70 kts, with supercells possible. The primary threats are
severe hail and severe wind gusts. The coverage for strong-severe
thunderstorms is anticipated to be generally isolated at this
time. Lastly, there is small risk for a brief isolated tornado,
specifically when severe weather initially develops/early on.
Convective development appears to be favored for later in the day
 current thinking is late afternoon-early evening attributable
to cap initially present and destabilization timing. Threat for
severe weather then diminishes mid-late evening. Focus turns to
moderate-heavy rain. Wherein lower troposphere deformation zone
and boundary is expected across southwest NEB into north central
NEB overnight. Threat for flash flooding is minimal at this time
based on QPF and given current conditions.

The SLGT risk area in the SPC Convective Outlook has increased in
coverage from Day 2 (Yesterday) wherein the latest SPC Day 1 outlook
shows most of the area east of NEB Highway 61 in a SLGT risk area.
This seems reasonable given the forecast parameter space.

.LONG TERM...(Friday through Wednesday)
Issued at 332 AM CDT Thu Mar 23 2017

Low pressure will continue to move eastward across northern Kansas
on Friday. This will leave north central Nebraska north of the
system and in the rain shower portion of the system. Current
thinking is that precipitation will remain all rain throughout the
day Friday. As 850 mb temperatures drop to near freezing Friday
night, a brief changeover to snow is possible. However, with fairly
warm ground temperatures, accumulations are expected to be minimal.
Temperatures on Friday will remain cool as the cooler airmass begins
to work into the region. Expect highs only in the mid to upper 40s.

A weak upper level ridge builds into the central Plains on Saturday
and into early Sunday. A return to dry conditions and warmer
temperatures will prevail through Sunday morning. A brief chance for
some isolated rain showers returns Sunday afternoon as a developing
low off the front range of the Rockies moves eastward. However, rain
will be short lived as drier air and high pressure building south
into the region pushes the low quickly out of the area. Dry weather
then continues through Monday night. High temperatures through
Monday hold steady in the mid 50s to low 60s.

An active pattern returns to the Midwest as several disturbances
track over the forecast area. Rain chances remain in the forecast
through mid-week as a result. While none of these shortwaves are
extremely strong, locally heavier rainfall totals is possible where
showers do develop. Boundary layer temperatures remain warm enough
to keep precipitation associated with these waves as all rain. The
exception would be in the early morning hours Tuesday, Wednesday,
and Thursday mornings, where a few snowflakes could be mixed in with
the rain. Best chance for mixed precipitation will be across the
Pine Ridge region and eastern Panhandle. Daytime temperatures start
off in the upper 50s to low 60s on Tuesday, but slow decrease
throughout the remainder of the week. Highs by Thursday will only be
in the low 50s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 655 AM CDT Thu Mar 23 2017

Latest satellite imagery shows high clouds moving northeastward
across western NEB with stratus observed moving north from
northern KS. Surface plot shows mainly MVFR ceilings with the
stratus that is present across much of western and north central
NEB (though obscured by high clouds). Some patchy fog and drizzle
is expected at times early this morning across north central NEB.
Otherwise, flight category improvement is expected from west to
east mid morning to mid afternoon. Threat for showers and strong
to severe thunderstorms is expected to increase late afternoon
into the evening. Current thinking is KLBF has a greater
likelihood to be affected by thunderstorms than KVTN at this time.
Increasing chances for rain tonight across all of western and
north central NEB. IFR-LIFR ceilings expected to develop late
evening into the small hours across much of western and north
central NEB. Visibility reduction expected to be primarily low-end
VFR to MVFR, expect down to IFR in the northern Sandhills.

&&

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

$$

SHORT TERM...ET
LONG TERM...Kulik
AVIATION...ET



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