Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 212350
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
650 PM CDT Wed Jun 21 2017

.MESOSCALE DISCUSSION...
Issued at 608 PM CDT Wed Jun 21 2017

In the interest of maintaining a flow of info...this is not the
highest confidence watch we`ve ever issued.

Updrafts are struggling to sustain themselves in an environment of
weak shear and anemic BL moisture. The altocu are moving toward
higher dwpt air...but with increased capping.

This will definitely be one of those watches in which most of the
watch is quiet. There is still potential for a couple svr tstms.
The HRRR and 18Z NAM Nest still develop potent storms near the
state line in the next 3 hrs.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 255 PM CDT Wed Jun 21 2017

Aloft: Basically zonal flow was over the Nrn half of the CONUS and
it will remain zonal thru tomorrow. However...a low was over Sask
and it will cont heading E across Srn Canada. The Westerlies will
begin amplifying and the zonal flow will gradually become more
cyclonic..espcly tomorrow as a shortwave trof rotates around the
low into MT/ND.

Surface: Occlude low pres was over Sask. A cool front extended
from ND back to NV...with a warm front from ND down into cntrl Neb
then heading E to near OMA and into the OH Vly. This front has
been reinforced with convective outflow. A 1005 mb low was near
TIF with a trof extending SSW along the CO/KS border. This low and
trof will be responsible for initiating sct tstms and tstm
clusters this afternoon/eve. Meanwhile...as the Canadian low conts
E it`s associated cool front will press further S and E...crossing
Neb during the daytime hrs tomorrow...and finally clearing the CWA
(N-cntrl KS) by midnight.

Now: We cont to monitor sat/radar for convective initiation within
the sfc trof from the Sandhills back into NW KS. SPC issued MD
1109 at 230 PM. Probability of watch issuance is currently 40%.
Reasoning from 943 AM version of this product has not changed.
Deep mixing and convergence within the trof should initiate a few
tstms that will be outflow dominant.

As usual...CAMs depict a wide variety of possibilities for
convective coverage and evolution.

Shear and instability are lowest within the trof. Any storms or
storm clusters that develop and move E will be moving into an
environment of increasing shear/instability.

Current indications are that sct tstms/tstm clusters will develop
and should be SE of the CWA by midnight.

Be sure to monitor for any statements/watches/warnings from this
office as well as support guidance from SPC.

Thu: Tstms should develop along the approaching cool front over
WY/SD tonight. This activity should cont E across SD during the
morning...but will probably send an outflow boundary S into the
CWA. It could trigger a few tstms during the AM N of I-80.

During the afternoon/eve...a few tstms could develop S of a line
from Beaver City-Columbus or even a little further S from
Phillipsburg-Geneva. Am highly skeptical of much tstm activity
over the NW 1/2 of the CWA as this area will be N of the front and
strongly capped. Bottom line is I think our fcst is too extensive
with tstm potential in the post-frontal environment.

Where sfc-based tstms to develop (SE 1/2)...certainly large hail
and damaging winds will be a threat.

High temps are very uncertain over S-cntrl Neb due to the frontal
passage.


.LONG TERM...(Thursday night through Wednesday)
Issued at 255 PM CDT Wed Jun 21 2017

This has been a hot month with 11 days of highs in the 90s at
GRI. The rest of the month is looking substantially cooler...with
a few days much cooler than normal.

Aloft: Amplification of the Westerlies was just beginning. Over
the next svrl days a broad trof will develop over the Nrn USA
downstream of a ridge along the W coast. This trof will gradually
shift into the Ern USA early next week with deamplification fcst
toward the middle of the week.

Surface: The cool front referenced above will sink SE across Neb
during the day tomorrow and will be completely S and E of the CWA
by midnight. Weak high pres will build over Neb/KS Fri. Meanwhile
another cool front will plunge into the Nrn Rockies. It will
arrive here and sink thru the CWA during the daytime hrs Sat. A
big chilly and very strong high for summertime will expand over
the Plns Sun-Mon from the Canadian Prairies to TX. It will then
head into the SE USA Tue with return flow developing here on the
Plns.

Temps will be cooler than normal Fri-Mon...with at least one day of
much cooler the normal Sat. Probably returning to near normal Tue
and then above normal Wed.

The cool fronts will shove the rich low-lvl moisture far S of the
CWA thru Mon. Once it advects back into the rgn Mon night into Tue
then the risk of tstms will return. A little/light rain generated
by fgen should accompany the front Fri night into Sat...and
possibly lingering into Sun S of I-80. Rainfall amts will be
minor.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Thursday)
Issued at 650 PM CDT Wed Jun 21 2017

Significant Wx: LLWS tonight then WSHFT early Thu PM will
necessitate changing RWYs.

Tonight: VFR multi-layered clouds before midnight mostly AOA 7K
ft. Sct SHRAs are moving in from the W and trying to become TSRAs
but they are struggling. It is unlikely they affect the terminals
...but did include VCTS/CB at EAR. Cloud debris should decrease by
midnight. S-SSW winds will average 10-15 kts and there could be
some ocnl gustiness. LLWS. Confidence: Medium

Thu: VFR with no clds AOB 10K ft until a cold frontal passage and
WSHFT occurs early afternoon. Then some stratocu could form around
4K ft. The exact timing of the WSHFT/FROPA will need some minor
refining +/- 1 to 2 hrs. Light SW winds will become vrbl then
become NE and increase to 15-20 kts with gusts up to 28 kts.
Confidence: Medium

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.
&&

$$

MESOSCALE...Kelley
SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...Kelley



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