FXUS63 KLBF 201115

Area Forecast Discussion
National Weather Service North Platte NE
615 AM CDT Tue Oct 20 2020

.SHORT TERM...(Today through Wednesday)
Issued at 407 AM CDT Tue Oct 20 2020

Concerns in the forecast period revolve around the invading Arctic
airmass and threat for accumulating snow, both of which will be
covered in the Long Term discussion. Fairly quiet weather is
expected over the next 24 to 36 hours across much of western and
central Nebraska. The lone exception to this is the light rain
occurring across the Nebraska/South Dakota border early this
morning. This is occurring in an area of strong WAA coincident with
a modest low-level jet ahead of a shortwave impulse crossing the
northern Rockies early this morning. This LLJ will focus northeast
of the area prior to sunrise which will carry all precipitation with
it. Current temperatures across these areas are in the mid 30s to
low 40s and given fairly high moisture near the surface, not
expecting any wintry precip out of this activity. As the shortwave
impulse crosses South Dakota today, a weak surface low will develop
and drop a cool front through the area. Most NWP guidance suggests
this front clearing the area by the middle of the afternoon today,
with strong mid-level CAA in its wake. Given clearing skies and h85
temperatures near or slightly below normal, not expecting an overly
cool day with highs ranging from the mid 60s south of I-80 to low
50s across the northwest Sandhills. Attention turns to light
precipitation chances Tuesday evening into early Wednesday morning.
This would be supported by some weak fgen in the h85 to h7 layer.
The better forcing remains north of the area across South Dakota
with abundant dry air remaining firm across the northern half of the
CWA. Indeed, many NWP models are trending dry with only the GFS and
ECMWF advertising any QPF and even so that being limited to a
hundredth or two. Thinking the threat for any accumulating
precipitation remains north of the area and will limit any mention
to sprinkles/flurries. Surface high pressure will dive southeast
across South Dakota into eastern Nebraska for Wednesday morning.
This will put the area into southerly low-level flow which should
help in leading to a warm up for areas west of Highway 83,
particularly the eastern Panhandle, with slightly cooler
temperatures for areas east. Highs should range from the mid 60s
west to near 50 along Highway 281. Dry weather is expected for the
day with southerly winds gusting up to 25 mph during the

.LONG TERM...(Wednesday night through Monday)
Issued at 407 AM CDT Tue Oct 20 2020

Beginning 00z Thursday. Flow aloft transitions from zonal to more
southwesterly through the latter half of the day Wednesday into
early Thursday morning as a mid-level disturbance dives southeast
across the Pacific Northwest into the central Rockies by early
Thursday morning. As the polar jet dips south across the Central
Plains, lee-cyclogenesis will increase in the vicinity of a surface
warm front draped across Kansas. This frontal boundary will lift
north into Nebraska Thursday morning but its effects will be limited
locally as the elongated low pressure system quickly shifts east of
the area with the crashing cold front expected to swiftly move
through the area. A strong 1035 hPa Arctic high will move into
eastern Montana and approach the Central Plains by late Thursday.
This will lead to a large pressure gradient across the area and
pressure rises of nearly 2 hPa/hour for the late afternoon and
evening. This will translate to breezy northwest winds with gusts of
up to 35 mph likely across much of the area, lasting into the late
evening before the pressure rises relax a bit. As this front passes
through, strong vorticity advection and mid-level fgen will again
bring precipitation chances to the area. Initially, ptypes will
favor rain but as cold air floods the area we can expect a
transition to wintry precipitation during the evening into early
Friday morning. Timing of these transitions and precise ptypes to
expect are fairly low-confidence at this time. Thinking predominant
wintry precip will be snow but cannot rule out a brief period of
freezing drizzle in there as well as drier mid-level air arrives,
overspreading the low-level moisture. Will need to monitor this
potential in later forecasts. Regardless of ptype, QPF is expected
to remain fairly light therefore impacts will be rather limited with
the current forecast calling for less than an inch of snow and only
a few hundredths of ice possible from the freezing drizzle.
Temperatures Thursday will have high uncertain owing to pace of
fropa across the area but current thoughts are to see highs only in
the 30s for near the Pine Ridge to 50s and low 60s southeast of an
Oshkosh to O`Neill line with temperatures beginning to fall by the
early afternoon for many locations. As temperatures continue to fall
through the evening, expecting what will likely be the coldest
morning of the season thus far Friday. With h85 temperatures
approaching the daily minimum according to the SPC Sounding
climatology, can expect a bitter cold start to the day. Air
temperatures will fall into the teens and low 20s and combined with
winds potentially gusting around 15 to 20 mph around sunrise, will
see wind chill values approaching zero. Expecting a dry day for
Friday as high pressure continues to build in during the day with
high temperatures in the low 30s to low 40s, nearly 25 to 35 degrees
below normal for late October.

Saturday through Monday look to be fairly active as the area
encounters a 1-2 punch from a couple mid-level disturbances
traversing the northwest flow pattern. Cold air will remain in place
as surface high pressure continues to slowly track across the
Northern Plains during this time. Thinking the thermal profiles will
be cold enough to warrant entirely snow for the ptype and the raw
GFS solution advertises this along with support from the GEFS. The
ECMWF, however, is not as cold and therefore suggest a bit more of a
wintry mix. Will need to watch this potential very closely as subtle
differences in temperatures will have large implications in local
impacts. After temperatures moderate a bit for Saturday with highs
returning into the upper 30s to mid 40s, reinforcing cold air will
move in for Sunday and Monday with highs only expected to reach the
20s and 30s with morning lows in the teens and 20s Sunday morning
and teens to low single digits Monday morning with some locations
threatening record lows. This will allow wind chills to approach
zero each morning. Cold temperatures look to hold firm for the start
of the following week with below normal values expected to persist
through at least mid-week though confidence isn`t overly high as
model guidance begins to diverge beyond then.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 615 AM CDT Tue Oct 20 2020

Low level wind shear conditions continue through sunrise as lower
cigs spread through central Neb (KBBW-KONL) and a few sprinkles
pass far northern Neb this morning. A cool front crosses the
forecast area later this morning, signaling a wind shift from
south to northwest. Winds will also become gusty this afternoon
behind the front. Additional clouds work into the region later
this evening, along with light precipitation chances for northwest
Neb tonight (KGRN).





NWS LBF Office Area Forecast Discussion