Area Forecast Discussion
Issued by NWS North Platte, NE

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934
FXUS63 KLBF 212023
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
323 PM CDT SAT MAY 21 2016

.SHORT TERM...(This evening through Sunday)
Issued at 322 PM CDT Sat May 21 2016

The main forecast challenges through Sunday afternoon deal with a
stubborn stratus deck this evening and tonight and thunderstorm
chances for Sunday.

This evening and tonight... Made little change to min temps as
persistent cloud cover is expected.  Max temps stayed cool through
the heart of the CWA today, so min temps may be a tad warm for the
central Sandhills and I-80 corridor. South/southeast low level flow
will continue to bring in moisture and result in dew points hanging
in the 50s. Continued at least schc PoP overnight as the NAM
indicates decent isentropic upglide with near saturation at 295-305K
and RAP soundings showing low level saturation and lift. GFS and ECM
also agree with continued moisture advection into the area. Expanded
the fog mention across most of southwest Nebraska overnight as sfc
dew point depressions remain generally <3F and relatively high SREF
probabilities. Surface winds will stay breezy overnight as well with
a 1000mb low over northeast CO and a 1020mb high over Iowa. Models
are consistent with near 50kt southerly flow at 850mb, although that
will likely not get mixed to the surface due to stratus.

Sunday... Lowered max temps slightly to account for morning
fog/drizzle, few showers, stratus, and the recent trend of being
cooler than guidance. Thinking stratus and fog will erode early
afternoon across the west with the help of an approaching cold
front. Lowered PoP to schc before 21z and kept chc along the Hwy 83
corridor 21-00z. NCAR WRF members initiating convection generally 20-
23z, NAM around 21z, and RAP around 21z. Although 700mb temps are
relatively warm at 10 to 12C, the front should provide enough
forcing to break the cap. NAM is the most aggressive with thunder
indices with 4500J/kg MUCAPE and LIs to -7 across the Sandhills with
the GFS and RAP being more modest with around 3000J/kg and -6 LIs.
Questions remain with the stratus and resultant daytime heating,
which lean more toward the solutions with lower instability.
Nevertheless, moisture appears sufficient with dew points near 60F
and mixing ratios surpassing 15g/kg. Forecast soundings and
hodographs show low level veering, and high resolution models hint
at 0-1km shear near 20kts, which support a small tornado threat.
Much of the CAPE falls within the hail growth zone shortly after
initiation, indicating a large hail threat. Severe indices improve
toward 00z, so left severe mention out for the afternoon grids for
now.

.LONG TERM...(Sunday night through Saturday)
Issued at 322 PM CDT Sat May 21 2016

The threat for at least isolated severe thunderstorms exists
Sunday evening. Thunderstorms initially near highway 61 should
increase in coverage and intensity as a cold pool develops across
the northwest sandhills and drives a cold front southeast during
the late evening and overnight. Have kept pops likely east of
highway 61, with 80 pops forecast from eastern Cherry county into
western Holt and Boyd county. While large hail and damaging winds
will be a threat, feel that heavy rainfall and gusty winds will
become the greater concern. With precipitable water values in
excess of one inch west of Highway 83, heavy rainfall is possible
across the eastern half of the forecast area. After midnight,
thunderstorms still likely east of Ainsworth through Broken Bow
while any lingering thunderstorms end west of Highway 61.

Monday mainly dry with the next chances monday night across
southern areas. moisture return is weak with possible showers or
storms moving in from the srn panhandle and nern Co overnight.

Shower and thunderstorm chances in the forecast Tuesday through
Saturday as a longwave trough from the west coast into the
Northern Plains persists. Better chances near 50 percent are
forecast tuesday night and again Thursday night into Friday.

Highs mainly in the upper 70s to near 80 Monday through Wednesday,
then cooler behind a cold front Thursday through Saturday in the
upper 60s to lower 70s mainly.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1222 PM CDT Sat May 21 2016

Low ceilings and strong winds will continue to affect most
terminals across western Nebraska through Sunday morning. Periods
of drizzle and mist will further reduce visibility Saturday
afternoon and evening. Scattered rain showers will move through
northern Nebraska tonight, while patchy fog will develop across
southwest Nebraska.

&&

.HYDROLOGY...
Issued at 322 PM CDT Sat May 21 2016

Minor flooding will continue on the North Platte River near Lisco
while moderate flooding to continue near Lewellen. River levels
the past 12 hours have been steady or slowly rising. Below Lake
McConaughy, the river level near North Platte was near 6.4 feet.
The river is forecast to reach moderate flood stage of 6.5 feet by
Tuesday and hold steady.

High flows are expected to continue on the South Platte River and
the Platte River due to snowmelt in Colo and the combined flow
from the North Platte River.

&&

.LBF Watches/Warnings/Advisories...
None.
&&

$$

SHORT TERM...Snively
LONG TERM...Roberg
AVIATION...Snively
HYDROLOGY...Roberg



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