Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 220849
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
349 AM CDT Fri Sep 22 2017

.SYNOPSIS...
Issued at 347 AM CDT Fri Sep 22 2017

H5 analysis from earlier this evening had a highly amplified
pattern across the CONUS. Low pressure was noted over northern
Manitoba with a high amplitude trough of low pressure extending
southwest into central California. East of the trough, high
pressure was anchored over the lower Ohio valley with a ridge of
high pressure extending north into southern Quebec. Jose was
located off the coast of Cape Cod while Maria was located north of
the Dominican Republic. Across the central CONUS, southwesterly
flow extended from the four corners, northeast into southern
Ontario Canada. At the surface: Low pressure was located over
northeastern Colorado with a cold front extending northeast into
south central South Dakota and eastern North Dakota. South of the
low, a surface trough of low pressure extended south along the
KS/CO border. East of the front and surface trough, strong
southerly winds were present along and east of highway 83. Winds
were gusting as high as 30 MPH at North Platte and Thedford.
Temperatures were mild est of the front and were in the upper 70s,
while behind the front, temperatures were in the 50s.

&&

.SHORT TERM...(Today and tonight)
Issued at 347 AM CDT Fri Sep 22 2017

Temperatures today, followed by precipitation chances tonight are
the main forecast challenges. For Today: The before mentioned
cold front will stall across the northwestern forecast area this
afternoon. the latest HRRR and NAM12 solutions stall this feature
roughly from O`Neill to Ogallala at 21z this afternoon. South of
this feature, southerly winds and compressional warming ahead of
the front, will push highs into the middle 90s across the south
and southeastern forecast area. North of the front, highs will
reach the 70s and 80s with coolest readings across the
northeastern Nebraska panhandle. Like yesterday, with readings
reaching the 90s across southwestern Nebraska and dew points in
the 40s in the west, extreme to near critical fire weather
conditions are possible this afternoon in far southwestern
Nebraska. Minimum relative humidity will fall off to 15 to 17
percent in zone 210, however, winds will be lighter in the far
southwest as it will be co-located with the front and surface
trough. Further east, strong southerly winds are expected, however
minimum relative humidity will be much higher as dew points will
be in the 50s and lower 60s. By early evening, isolated
thunderstorms may develop east of the frontal boundary. The latest
NAM12 has h850-h700 lapse rates appg 9-10C this evening with a
weak cap noted across the southeastern forecast area. Went ahead
and kept in a mention of pops in the east this evening and shifted
these slightly farther east based on the latest HRRR and NAM12
solns. Overnight, precipitation chances will increase behind the
front across north central and northwestern portions of the
forecast area, as a mid level disturbance lifts from eastern
Wyoming into the northern Nebraska panhandle. Overnight lows will
range from the middle 40s in the northeastern Nebraska panhandle,
to the mid 60s in the eastern forecast area.

.LONG TERM...(Saturday through Thursday)
Issued at 347 AM CDT Fri Sep 22 2017

A closed low centered over the Great Basin works northeast toward
the Dakotas through the weekend as the main Western U.S. trough
progresses eastward. A secondary closed low develops over the
Desert Southwest mid to late week, keeping Nebraska primarily in
southwest flow aloft. A quasi stationary surface boundary
bisecting the state coupled with nearby sfc low and passing mid
level shortwaves will result in rounds of moderate to heavy rain
this weekend. A sfc high then takes over midweek.

The main forecast challenges during the period include temperatures
and precip intensity/placement over the weekend.

Saturday... The model suite is still in agreement with the front
stretching from near IML to OFK at 00z Sun. Very strong WAA/WVT
ahead of the front with H85 temps near 20C and dew points in the
lower 60s F. NAEFS continues to indicate this event as truly
anomalous with temps aloft near 90%ile climo and PWAT and WVT
>99%ile. Despite thick cloud cover, guidance is trending warmer
across central Neb with highs now in the mid/upper 70s from IML to
ONL and points east. On the backside of the front, still looking at
50s for highs invof the Pine Ridge. Early in the day, precip should
be more scattered as forecast soundings show remnant dry air in the
lower levels. The column quickly saturates through the afternoon
with the added forcing of a lee side sfc low and diabatic heating.
Expanded thunder mention west, where CAPE values approach 500 j/kg
in the evening. Severe threat is low as mid level lapse rates are
nearly moist adiabatic and deep layer shear will likely be too high
for the amount of instability. Definitely concerned about local
flooding issues due to training storms (storm motion lines up with
the front) and near record atmospheric moisture content. The
heaviest rain will likely occur after 03z.

Sunday... Pushed thunder mention to roughly OGA to ANW and east as
the colder air pushes across the Sandhills. Northerly H85 flow takes
over through the day, and temps struggle to reach 5C west of Neb.
Hwy 61. GFS suggests MUCAPE as high as 800 j/kg across SW and
central Neb as highs stay in the mid/upper 60s and dew points near
60F. Heaviest precip onset is similar to Saturday with possible
breaks early in the day and another round of steady rain in the
evening/night. NAEFS still shows PWAT above 97%ile of norms for this
wave.

Monday... CAA really takes over with brisk north winds and H85 temps
near 5C across the Sandhills. With off-and-on showers through the
day, most locations will remain in the 50s for highs. A third wave
of moderate to heavy rain sets up Monday evening, but the bulk of
the moisture and forcing will stay east of the forecast area. Mid
level dry intrusion works into the panhandle and SW Neb. toward the
evening, and should expect an end to precip for most of the forecast
area by 06z Tue. Frost threat returns to NW Neb. Monday night with
gradually clearing skies, lightening winds, and temps dropping into
the mid 30s.

Tuesday through Thursday... Generally quiet pattern as sfc high
moves onto the Plains. Sparse PoPs in far SW Neb. and far north
central Neb. with slowly moderating temps across the whole area.
Highs rebound to near 70F by Thu.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1105 PM CDT Thu Sep 21 2017

Clear skies continue across western and north central NEB. Latest
regional VWP plot shows the development well of a southerly low-
level jet across KS into NE. VWP 500 m AGL (~1640 ft AGL) plot
near the bottom of the hour at KLNX, KGLD, and KUEX were 47 kts,
54 kts, and 47 kts, respectively. LLWS conditions expected to
continue overnight and will affect the KLBF and KVTN terminals.
Upper height of the wind shear layer forecast about 1500 ft with
winds at the top of layer peaking 55 kts, strongest at the KLBF
terminal and east. LLWS conditions expected to end in the early
morning.

Tomorrow, another breezy day with winds out of the south. However,
lighter winds will be present across the eastern Panhandle and
northwest NEB behind a front. Slight chances for thunderstorms
tomorrow afternoon, however, higher chances/greater confidence
exists for thunderstorms in the evening hours. Mostly-partly sunny
tomorrow followed by increasing clouds late afternoon to evening.


&&

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

$$

SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Snively
AVIATION...ET


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