Severe Thunderstorm Warning 46, NWS Hastings, NE

Area Forecast Discussion
National Weather Service Hastings NE
1230 PM CDT Sun May 5 2019

...Svr Wx Ops Expected this Afternoon/Evening then a Chilly Week
with Substantial Rainfall Amts Tue night into Wed...

.SHORT TERM...(This evening through Monday)
Issued at 1230 PM CDT Sun May 5 2019

Unless anything thinking changes...this will probably serve as
the final AFD for this shift as we transition into monitoring/
nowcasting and possibly warning mode.

Aloft: The longwaves over N America were characterized by a -NAO and
a -EPO. The flow was zonal but split over the CONUS with generally
low-amplitude. Thru tomorrow...W flow will remain over NEB/KS but
500 mb heights will rise about 60 m as a shrtwv ridge builds over
CO/NM associated with a cut-off low mvg onshore into Srn CA.

Surface: Weak high pres was over AR. A strong cold front extended
from the GtLks SW across NEB (roughly just N of I-80) then NW thru
WY-MT. A dryline intersect and extended S of the front thru Wrn KS.
Chilly high pres was over the Canadian Prairies. The cold front will
gradually sink S thru the CWA into Nrn KS by 12Z/Mon... probably
helped along by convective outflows. The front will cont S and
should be located from SW-NE acrs KS by 00Z/Tue. Meanwhile...the
chilly Canadian high will be building into NEB/KS behind the front.

Severe: SPC is maintaining a slgt risk for svr tstms over S-cntrl
NEB...mainly E of OLU-EAR-HJH...with a MRGL risk to the W. A few
tstms will erupt along the front and gradually move S away from the
front as outflows become established.

Temps will climb well into the 70s with dwpts in the mid 50s. With
mid-lvl LR's 7.5-8.0 C/km...this will result in MLCAPE of 1000-2000
J/kg before tstms dvlp. 0-6 km shear will be about 30 kt. Winds will
be very wk below 10K ft. This combined with deep layer flow parallel
to the front should result in multicell convective mode with tstms
quickly dvlpg into outflow dominant clusters. SigSvr parameter will
be 20-30K. So hail up to the size of golfballs will be psbl...along
with isolated downbursts.

We need to watch 3 areas this afternoon:

1) The on-going shwrs acrs the Nrn CWA. A couple slightly elevated
tstms could erupt on the Srn fringe of this activity shortly after
midday...possibly affecting Nance/Merrick/Polk counties.

2) Along the cold front acrs S-cntrl NEB after 4 PM. One concern
with this tstm potential along this front is the lack of QG forcing.
That could very well result in fewer storms with a later ignition
time.

3) Along the dryline in NW KS early this aftn. This activity could
intensify and become svr acrs N-cntrl KS as it mvs into greater
instability. The 12Z HRRRX suggests this could become a small bow
echo with damaging wind potential.

For hail...we will generally be warning on 50 dBZ at or abv 23K ft.

Tonight: Sct tstms should be E of the CWA by 05Z. Then a break
with low stratus moving in behind the front. Some mdls keep sct
tstms that dvlp over WY and the NEB panhandle going thru the night
...possibly affecting parts of the CWA after midnight. MUCAPE will
be less than 500 J/kg. So not expecting any stg/svr tstms.

Mon: Cldy/much cooler. Some sct shwrs/tstms could linger mainly in
the AM over S-cntrl NEB. Believe most of the day will be dry at
most locations. Believe mdls are overdone on QPF...except along
and N of I-80. If anything there could be some patchy drzl at
times.

.LONG TERM...(Monday night through Sunday)
Issued at 1230 PM CDT Sun May 5 2019

Aloft: The last 2 runs of global mdls cont to suggest significant
amplification of the longwaves this wk...but with the flow
remaining split. NEB/KS will be influenced by both the Nrn and Srn
streams...the Nrn stream delivering the chill...and the Srn
stream delivering the mstr and precip. The cut-off low that mvs
into the Desert SW will lift NE and cross the Cntrl Plns Wed- Wed
night. Meanwhile...the E Pac ridge will build...inducing heights
to fall in both the Nrn and Srn stream so that by Thu...troffing
will extend from Hudson Bay thru the Nrn Plns to the Desert SW.
That troffing will remain in place thru next wknd...but there are
signs that it could be E of NEB/KS by Sun with some NW flow.

Surface: The cold front that mvs thru tonight will stall acrs KS
thru Tue...but it will begin lifting N as lee cyclogenesis ensues
over CO. It still appears that the front will remain just S and E
of the CWA Wed as the CO low ejects acrs KS. Mdl and ens
clustering has the low over Nrn MO Wed night with the CWA in the
cold sector. Meanwhile...chilly Canadian high pres will be
pressing in from the N...and should eventually dive SE arriving
here Fri. That high will mv E Sat...allowing for a warm-up...while
a clipper type low dives out of Canada.

Sensible wx: Expect a very chilly week. Temps will be much cooler
than normal Tue-Thu. Temps should get back to near normal by next
wknd. Periods of rain/drzl/shwrs and a few embedded tstms Mon
night into Tue as NEB/KS will be in the RRQ of a strengthening
100+ kt jet streak over the GtLks. The steadiest rain/wettest time
periods will be Tue night into Wed as a couple jet structure
dvlps and the shrtwv trof/strongest QG forcing approaches and mvs
thru.

Windy Wed night into Thu.

QPF: mdls cont to indicate that nearly the entire CWA will see at
least 0.50" of rain...with large parts of the CWA seeing 1-2".
Can't rule out a couple spots seeing close to 3".

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Monday)
Issued at 1215 PM CDT Sun May 5 2019

Significant Wx: Sct TSRAs approx 21Z-03Z. IFR CIGs tomorrow.

This afternoon: VFR with sct CU forming. Pockets of IFR in sct
tstms that develop after 21Z. S-SE winds 10-15 kt becoming
lgt/vrbl as a cool front moves in. Erratic/gusty winds in any
tstms. Watch for TAF amendments. Confidence: Medium

Tonight: VFR to start except IFR in sct tstms...primarily before
03Z. MVFR CIGs move in after 06Z along with some light rain. NE
winds 10-20 kt. Confidence: Medium

Mon thru 18Z: MVFR CIGs lower to IFR. Some light rain psbl. NE
winds 10-20 kt. Confidence: Medium due to uncertainty on rain.

&&

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

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

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