Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 171758

Area Forecast Discussion
National Weather Service North Platte NE
1258 PM CDT Sat Mar 17 2018

.SHORT TERM...(Today and tonight)
Issued at 349 AM CDT Sat Mar 17 2018

A broad swath of stratus extends from the upper low over Kansas City
along an inverted trough to the northeast across central Nebraska
into the Dakotas. This area of stratus is progged to move to the
east as the upper low moves east today. Areas over north central
Nebraska will be the last to clear with resultant cooler
temperatures there only in the 30s this afternoon. Some snow over
the north and will affect temperatures some. Have cut highs back
somewhat over the northwest. Left patchy fog in the forecast early
this morning with temperatures expected to fall over the west
southwest where skies are clearing out. Winds becoming southerly
this afternoon but on the light side. Highs this afternoon ranging
from the 30s north central to the 50s southwest. Clear skies tonight
with southeast winds ahead of upper trough to the west. Increasing
clouds to the northwest. Diffluence aloft over the Panhandle and
upslope flow there is the possibility for some light mixed
precipitation along the Pine Ridge. This might be starting to early
but have inherited from previous forecast and have continued to hold
continuity. Lows in the 20s and 30s.

.LONG TERM...(Sunday through Friday)
Issued at 349 AM CDT Sat Mar 17 2018

The primary forecast challenge arises from an upper low that closes
off over the central/southern Plains Sunday into Monday. The amount
of cold air with the system will play a major role in determining
precip types. Northwest flow aloft resumes midweek as a ridge builds
across the Intermountain West. The ridge then breaks down late
week, raising precip chances again.

Sunday and Monday... The closed upper low in conjunction with the
lee side sfc low emerges onto the High Plains late Sunday night.
Minor strength and path differences exist among the 00z model suite
with GFS/NAM placing the lows in SW KS while the ECM pushes it
slightly south. Nevertheless, the trough takes on a negative tilt
prior to the system. Combined with a sfc high off the FL coast, a
large fetch of southeast low level flow off the Gulf allows for
ample moisture advection. The tricky aspect is temperature due to
the lack of very cold air on the backside of the low. Despite
notable CAA, H85 temps only drop to around -3C by Monday afternoon.
Forecast sounding temp profiles indicate rain for the start of the
event (Sunday evening/night), then a gradual switch to snow from NW
to SE across the area. The probability of ice initiation in the
cloud layer is high, but much of the saturation and lift/forcing
occur below the DGZ, suggesting more of a rain/snow mix. One factor
that may tip the scale to bursts of snow is dynamic cooling. Strong
lift in the low levels and sfc wet bulb near 0C suggest enhanced
precip rates and the potential for a quicker change to snow. In the
event of (moderate?) snow, climatologically low SLR`s and sfc temps
in the lower/mid 30s would limit accumulations (and likely to grassy
surfaces). By Monday night, the bulk of the moisture will be
confined to north central Neb. A general model blend results in the
potential for 1-3" snow across the Sandhills and a slightly heavier
stripe across SW Neb. These amounts are on the lower end of the
plumes, but are reasonable given the uncertainty of ptype. Will hold
off on any winter headlines with this forecast package.

Tuesday and beyond... With the ridge returning in the West and
downslope flow taking over at H85, trends point toward warming and
drier conditions (esp. SW Neb) for Tue-Thu. The combination of the
ridge breaking down and the next set of lee side lows raises precip
chances, mainly late Thu into Fri. Temperatures should be warm
enough for all rain.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1246 PM CDT Sat Mar 17 2018

A range of cloud coverage this afternoon as stratus remains
entrenched across the central and clearing slowly in the west.
Models in fair agreement with next system moving out on the plains
where boundary layer moisture will create a challenge with ceiling
heights lowering after midnight to MVFR conditions across the
north and possibly into LIFR conditions east of a line from
Merriman to Broken Bow through 15Z. For the west and southwest
low confidence as clouds will be on the increase with how low
ceilings will go in question with VFR conditions overnight into
Sunday morning for now.




LONG TERM...Snively
AVIATION...Keck is the U.S. government's official web portal to all federal, state and local government web resources and services.