Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 212033

Area Forecast Discussion
National Weather Service North Platte NE
333 PM CDT Mon May 21 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 332 PM CDT Mon May 21 2018

With the upper low that brought the abnormally wet weekend now over
the Upper Midwest, our attention turns to a developing lee side sfc
low and a closed upper low over the Great Basin. Fair skies and
breezy south winds pushed temps back into the 70s across western Neb
today, right around normal. The primary concerns going forward
include thunderstorm chances tonight/tomorrow and temperatures.

This evening and tonight... Continued schc-chc TSRA across SW Neb
before 06z and north central Neb afterwards per moisture advection
from the Gulf (dew points rising into mid/upper 50s), increasing
forcing (low/mid level warm front), and modest instability (near
2000j/kg CAPE). Given these parameters, cannot completely rule out a
strong or briefly severe storm with hail. Limiting factors for
development and/or coverage include relatively dry air off the
surface, weak mid level lapse rates, and not the best shear. Despite
strongly veering winds below H7, flow is generally weak and deep
layer shear peaks at 30kts. The models suggest a modest short-lived
LLJ over the Sandhills before weakening and pushing east of the
area. Highest PoP generally east of IML-LBF-ONL where CAM solutions
(including HRRR, RAP, HREF) indicate some development. Made little
change to min temps as 50s seemed reasonable due to strong WAA (H85
temps approaching 18C by 12z) and forecast lows being toward the
middle of model consensus.

Tuesday... The thermal ridge strengthens over the High Plains with
the low just off the higher terrain. Decent southerly flow, H85
temps exceeding 20C, and mixing to near H7 support highs in the
lower/mid 80s. Brought PoP in a little earlier compared to Monday as
H5-7 fgen ramps up in the afternoon. Isentropic analysis also
suggests broad upslope and sfc dew points keep crawling up, reaching
60F over central Neb. Again, can`t rule out isolated severe given
the instability and moisture (MUCAPE near 2000j/kg), but wind
profile is nearly unidirectional and 0-6km shear is weak (generally
under 25kts).

.LONG TERM...(Tuesday night through Monday)
Issued at 332 PM CDT Mon May 21 2018

Rain chances appear to be diminishing. The models are carrying the
better focus and instability north into SD and the nrn Rockies where
an upper level low, currently across NV, will lift. Today`s forecast
limits rain chances to 40 percent or less Tuesday night through
Wednesday night with isolated rain chances thereafter until Sunday.
The likely rain chances the ongoing system will be across WY, SD and
areas north.

The temperature forecast has warmed also with highs projected to
rise into the 80s to around 90. Today`s model runs of the GFS and
ECM show no sign of a Pacific front until Friday and that will be a
very weak front. In fact, the models show no cooling with the front
and instead, show warming h850mb temperatures for the next 7 days.

The Pacific front will dry out the atmosphere for a day or two but
dew points will rise back into the upper 50s and lower 60s late next
weekend. H700mb temperatures rise through the high single digits
Celsius this week to the lower teens next weekend which supports
highs well into the 80s to near 90. Our forecast shows the warmest
highs ahead of the front Wednesday and Thursday, but later forecasts
could include a warmer forecast for the weekend, including Friday.

Another upper level low could begin to affect Nebraska Sunday and a
chance of thunderstorms are in place. There are no obvious severe
weather indicators. The local severe weather ensemble procedure
suggest modest potential through Wednesday night followed by a lull
Thursday through Saturday and an increase Sunday. This is related to
winds at 500 mb which are fairly light, less than 30kt. Thus, the
potential for long-lived severe thunderstorms appears low.

Despite the weak winds aloft, the NAM indicates dry mid level air
Tuesday evening with unidirectional midlevel winds and this could
support outflow dominate clusters of thunderstorms capable of strong
wind gusts.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1219 PM CDT Mon May 21 2018

VFR will continue through Tuesday morning for western and north
central Nebraska. The only aviation weather concerns are some
gusty south winds this afternoon and a chance of isolated
thunderstorms this evening/tonight, but coverage will be limited.
Confidence was too low to mention wx group in TAF.




SHORT TERM...Snively
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