Area Forecast Discussion
Issued by NWS North Platte, NE

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354
FXUS63 KLBF 230833
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
333 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 severe thunderstorm
chances wherein severe hail and severe wind gusts are the primary
threats. 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. Meantime, mid-level flow aloft will be
increasing as a southwesterly belt, overhead 50-60 kts, is expected
to push into the area. The nose of the mid-level flow then becomes
southerly and 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
during the daytime today as return flow is lacking. However, do see
better moisture transport this evening and overnight. Surface dew
points within the 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, 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 buoyancy, 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 an 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 06Z TAFS through 06Z Thursday night)
Issued at 1146 PM CDT Wed Mar 22 2017

Expect mainly cloudy skies overnight with some clearing possible
Thursday afternoon. Through Thursday morning, low level moisture
will stream into central and eastern Nebraska which will drop
ceilings down to MVFR levels overnight. The threat for showers and
thunderstorms will increase Thursday evening after 00z Friday.
Visibilities may fall off to 4SM in any thunderstorms which impact
the KLBF terminal. For the KVTN terminal, expect showers with
visibilities down to 5 SM. MVFR ceilings are possible at the KVTN
terminal late Thursday evening and should fall below 1000 FT AGL
overnight Thursday night.

&&

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

$$

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



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