Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 130435 AAC
AFDLBF

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
1135 PM CDT Thu Apr 12 2018

.UPDATE...
Issued at 855 PM CDT Thu Apr 12 2018

The SPC suggested a 5 percent chance for severe weather overnight
affecting the Ainsworth-O`Neill area in ncntl Neb. The NAM
thunderstorm probabilities were the basis for thunderstorm
chances overnight which could last until at least 12z Friday. A
new forecast is in place for thunderstorm chances throughout the
night.

&&

.SHORT TERM...(This evening through Friday)
Issued at 359 PM CDT Thu Apr 12 2018

The primary forecast challenge through Friday deals with the
expected blizzard beginning Friday morning. The 12/12z model suite
along with some higher resolution models (RAP/HREF) remain in
general agreement with a serious winter storm to cross the northern
Plains. Big change since previous forecast package was updating
headlines to Blizzard Warning for entire CWA.

This evening... Reduced PoP through 06z as any rain shower activity
will be scattered and confined primarily to northwest Neb. Mid-level
moisture profile is rather stout with the baroclinic leaf appearance
on WV/IR, but dry air remains in the low levels. Dew pt depressions
are around 25F across the region as of 20z. For any precip that
develops, can`t rule out a rumble of thunder due to steep mid-level
lapse rates and some elevated CAPE.

Tonight... Things start to come together across NW Neb with
increasing precip coverage. Subfreezing air is rather slow getting
into the area so expect mostly or all rain through 12z. Went with a
general MAV/MET blend for min temps, resulting in near 30F NW to
near 40F central/far SW.

Friday... Main deformation band develops around 12z across the
panhandle and western Sandhills. Still may be rain to start as the
band gets going, but continued CAA (H85 temps dropping to around -3C
by 18z) and increased precip rates (dynamic cooling) will lead to a
quick changeover to snow. Forecast soundings and X-sections suggest
very heavy snow within the band. Lift is nearly off the charts (>10
ubar/s), prevalent fgen that spans low and mid levels, saturation is
deep, and there are indications of theta-E folding and negative EPV.
The thermal profile stays just warm of the DGZ, which will limit big
dendrite production (aside from strong winds fracturing the flakes),
but 1 to possibly 2"/hr rates will lead to quick accumulations. The
deformation band is progged to remain nearly stationary or slowly
rotate west over the span of several hours. Broad CSI in the X-
section supports the overall deformation band structure with locally
enhanced snowfall rates. Outside the main band, light rain will
change to snow for areas east of Hwy 83 through the afternoon.
Easterly/upslope H85 flow maintains moisture advection. As far as
the wind is concerned, the upper low deepens through the day and a
PV anomaly crosses the forecast area. Kept sfc gusts around 50mph as
H85 flow approaches 55kts and the nose of a 100kt+ H3 jet brushes
the Sandhills. With the combination of heavy snowfall and strong
winds, still expecting near whiteout conditions and serious
blowing/drifting. Per previous AFD, some concerns include high sun
angle and warm antecedent ground conditions which could limit
accumulation. However, regardless of snow amounts, visibility with
falling and blowing snow warrants the update to Blizzard Warning.

.LONG TERM...(Friday night through Thursday)
Issued at 359 PM CDT Thu Apr 12 2018

Strong spring cyclone will be peaking at it`s mature stage
Saturday night. Upper level low will be centered near the NE/KS
border south of Lincoln by daybreak Saturday morning. Strong mid-
level FGEN band and trowel will be oriented northeast to southwest
across western and north central Nebraska much of Saturday night.
Snow, heavy at times will be associated with this band. In
addition, convection developing across eastern NE will rotate
westward into the area, which will likely enhance snowfall rates,
and 1 to 2 inch per hour snowfall rates cannot be ruled out in
places. This seems most likely to occur from Valentine to North
Platte eastward. This will all be accompanied by very strong North
winds, with 500 meter wind speeds supporting guidance values of
35 to 40 mph sustained. Gusts of 55 mph are also expected. GFS
indicates the potential for stronger winds, but may be overdoing
it a bit on the mixing.

The system will begin to occlude Saturday morning. FGEN will begin
to weaken during this time, but still expect at least moderate snow
to continue until around noontime along and east of Bassett to
Broken Bow. Winds remain very strong Saturday morning, on the order
of 30 to 40 mph sustained, so widespread blowing and drifting snow
will continue. By Saturday afternoon, things will begin to wind down
fairly quickly from west to east as the system fully occludes and
moves into the Mississippi Valley region. Drier air and subsidence
will quickly spread east with skies clearing by late afternoon west
of Highway 83. Winds during this time will also be trending down.

Another system will track across the northern plains mid week.
Some light rain or wet snow will be possible across mainly
northern NE with this system. Temperatures wise, no big warm ups
expected for the upcoming week, with highs averaging in the 50s to
lower 60s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1134 PM CDT Thu Apr 12 2018

VFR cigs are expected to become MVFR/IFR cigs overnight from north
to south. Rain with isolated thunderstorms is likely overnight
which will spread northeast affecting much of wrn and ncntl Neb.

IFR/LIFR is expected Friday in rain changing to snow from west to
east with winds becoming 35025G40KT. IFR/LIFR in snow, blowing
snow and low cigs is expected to continue Friday evening affecting
all of wrn and ncntl Neb. Winds increase to 35030G45KT.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Blizzard Warning from 7 AM CDT /6 AM MDT/ Friday to 1 PM CDT
/noon MDT/ Saturday for NEZ004-005-022>025-035-056>058-069-094.

Blizzard Warning from 1 PM Friday to 7 PM CDT Saturday for
NEZ006>010-026>029-036>038-059-070-071.

&&

$$

UPDATE...CDC
SHORT TERM...Snively
LONG TERM...Taylor
AVIATION...CDC



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