Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 231803
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
103 PM CDT Sat Sep 23 2017

.SYNOPSIS...
Issued at 350 AM CDT Sat Sep 23 2017

A highly amplified h5 pattern continued across the CONUS and
Canada tonight. Closed low pressure was located over Idaho with a
trough extending south to off the coast of Baja California. High
pressure was anchored over the Ozarks with a ridge extending north
into the eastern Great Lakes. Across the central CONUS, south
southwesterly flow aloft extended from the four corners north
northeast into northern Minnesota. At the surface, a stationary
front extended from north of McCook Nebraska into far northeastern
Nebraska. Temperatures behind the front were in the 50s overnight
with some 40s noted over the eastern Nebraska Panhandle. A line
of showers and thunderstorms extended from southwestern Lincoln
county into far northeastern Cherry county.

&&

.UPDATE...
Issued at 946 AM CDT Sat Sep 23 2017

Mianly forecast change for today was to lower highs behind the
front. Some area highs just behind the front including North
Platte were lowered about 10 degrees. Also lowered or removed
pops this morning behind the departing disturbance. The next
upstream disturbance is in southeast Colorado, moving into east
central Colorado. This disturbance looks quite robust attm.

&&

.SHORT TERM...(Today and tonight)
Issued at 350 AM CDT Sat Sep 23 2017

Highs today and precipitation chances over the next 24 hours are
the main forecast challenges. For today: Looking at the latest
HRRR and NAM12 solns, the stationary front will meander across
eastern portions of the forecast area today, moving very little.
By 21z this afternoon, the front is expected to extend from
southwestern Frontier into Wheeler county. Along and east of the
front, highs will be in the middle 80s across Wheeler, far
southeastern Custer and southeastern Frontier county. Readings
will fall off quickly west of the front with highs around 50 in
the northeastern panhandle to the 70s along a line from Imperial
to O`Neill. Strong mid level warm air advection and favorable mid
level frontogenesis will spread north behind the surface front
from eastern Colorado into western and central portions of the
forecast area later this afternoon. For this morning, kept pops in
the low chance category as there will be a break in mid level
lift from near sunrise to the early afternoon hours. Beyond
midday, mid level lift will increase and persist into the
overnight hours tonight. Periods of showers and thunderstorms are
expected west of a Broken Bow to O`Neill line and have pushed pops
up to categorical overnight. As for QPF, decided to utilize a
blend of the WPC and NAM12 forecast. The 00z NAM12 came in further
west with the heaviest precipitation and initialized well with
its overnight QPF fcst. That being said, blended this and the HPC
guidance which placed the highest QPF`s along a line from North
Platte to east of Valentine. In these areas, we could easily see
upwards of 3 inches of rainfall by Sunday morning. Lows tonight
will range from the middle 60s in far eastern areas, to the lower
40s in the northeast Nebraska Panhandle.

.LONG TERM...(Sunday through Friday)
Issued at 350 AM CDT Sat Sep 23 2017

The H5 closed low near SLC 12z Sun. travels northeast toward BIS by
Tuesday A.M. Meanwhile, the Western U.S. trough transitions toward a
ridge and a cutoff low develops over the Four Corners by Wed. A new
trough digs in the Great Lakes mid to late week, placing Nebraska in
zonal then northwest flow. The surface front starts Sunday generally
from IML to ONL and works east through the day, leaving the forecast
area by 00z Monday. High pressure builds in on Tuesday, while a
stronger high drops south onto the Plains late week.

Sunday... The heaviest precip will likely be early in the day as the
first main band from Saturday night slowly pushes east. Through the
afternoon, coverage appears to take on a more scattered nature as
forecast soundings bring in bouts of dry air in the mid levels.
Maintained isoT wording east of OGA to ANW as forecast soundings
indicate some elevated CAPE (and up to 1000 j/kg in some spots).
Combined with decent deep layer shear (40+ kts), there may be just
enough to squeak out a strong or briefly severe storm. Regardless,
any rain could easily be heavy as NAEFS continues to show PWAT near
99%ile of climo. The secondary main precip band develops late Sunday
night. With the best forcing along and ahead of the front (which
will likely be east of the area), reduced PoPs for areas west of BBW
to ONL. Temperature wise, made little change to highs as strong CAA
behind the front with H85 temps dropping to near 5C support sfc
temps in the 50s. Southerly flow in SW and central Neb. through the
afternoon will support highs in the 60s there.

Monday... With the front in eastern Neb, the primary regime is CAA
and northerly flow for western Neb. Didn`t stray too far from
guidance as highs in the 50s seemed reasonable, especially given
thick cloud cover. Wrap around moisture with the sfc low and
enhanced lift from a passing H7 shortwave will support rain chances
through the day. Despite mid level dry air intrusion late Monday,
the model suite has slowed the exiting of the low level moisture.
Continued PoP through the night due to weak isentropic lift, most
evident at 300K and 305K.

Tuesday through Friday... The succession of surface high pressures
and a building ridge aloft will promote mainly fair conditions. No
true WAA scheme sets up with primarily northwest flow at H85, but
dry weather will help lead to gradually warming temperatures. Highs
recover into the upper 60s and lower 70s, still around 10 degrees
below normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 102 PM CDT Sat Sep 23 2017

IFR ceilings are forecast to persist the next 24 hours at the KLBF
and KVTN terminals. In addition, showers and thundertorms will
become widespread late this afternoon through tonight, with likely
chances into Sunday morning. Visibility reductions are currently
from drizzle and fog, with additional reductions from periods of
moderate to heavy rainfall to occur.

&&

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

$$

UPDATE...Roberg
SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Snively
AVIATION...Roberg



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