Area Forecast Discussion
Issued by NWS Hastings, NE
FXUS63 KGID 181644
Area Forecast Discussion
National Weather Service Hastings NE
1144 AM CDT Tue Apr 18 2017
.SHORT TERM...(Today and tonight)
Issued at 337 AM CDT Tue Apr 18 2017
Aloft: The Westerlies were characterized by low-amplitude over
the CONUS with 500 mb heights near to slightly above normal. A
deep longwave trof was over the E Pac. Over the CONUS...a potent
but compact shortwave trof was over the Dakotas. This trof will
cont E into the GtLakes today leaving zonal flow over the Cntrl
Plns. Meanwhile...the leading edge of the E Pac trof will move to
the W coast and a shortwave trof will move into CA/NV this
afternoon. It will cont ENE and be over WY/CO by 12Z/Wed. A
coupled upr-level jet config will over the Cntrl/Nrn Plns tonight.
Surface: 1005 mb low pres was over SD. A warm front extended SE
thru IA into MO...a cool front extended SW into the Panhandle/
WY/UT/NV. While this low heads E into the GtLakes today...the cool
front will slowly sag further acrs Neb...gradually becoming
quasi-stationary and oriented W-E just N of I-80. Lee
cyclogenesis will begin with low pres evolving over NE CO tonight.
This low is fcst to move to near MCK by 12Z/Wed. Model signals
cont strong that one or two tstm clusters will form along and N of
the front. This will act to reinforce/strengthen the front.
Now: Small clusters of tstms have been on-going over the
Sandhills overnight. All models have struggled...attempting to
develop tstms further S from SW Neb into Wrn KS. GOES16 shows lift
is occurring and mid-lvl clouds have developed...but shwrs/tstms
have not initiated.
Weak WAA is occurring...and while at least 750 J/kg of MUCAPE is
available...there is just isn`t much (or enough) forcing. There is
still time for something to develop...but bottom line is models
Instability is diminishing as we head toward the coolest part of
the diurnal cycle. So current expectation is for ordinary tstms
with no threat of strong or svr tstms.
Today: The clusters of storms over the Sandhills will cont E
across Nrn Neb and may expand S. While some activity could occur S
of I-80...most of it should remain N of I-80. The bulk of this
tstm activity should be out of the fcst area (FA) by 10 AM. The
rest of the day will be dry for most if not all areas. A couple
models do suggest an isolated shwr/tstm could linger past 10 AM N
and E of GRI.
Once AM precip potential is done...of all the models (GFS/NAM/
NMM/ARW/RAP/RGEM)...the NAM has the least QPF today and its fcst
soundings indicate a cap. Very easily could`ve left the fcst
dry...but a couple models do try to initiate an isolated late day
shwr/tstm somewhere over the SE 1/2 of the FA. Have a 20% POP to
cover this...but with the cap and a lack of forcing it probably
will not happen.
Low stratus is trying to form this morning...so cloud cover could
be rather extensive in some areas until midday and this could
impact temps. Highs in the 70s still seem very reasonable.
Tonight: A strong low-lvl jet will form this eve...but this will
act to increase the cap further (especially in the warm sector) as
an EML advects into the FA. Tstms will probably struggle for form
most of the night...but QG forcing moving in after midnight will
supplement frontal forcing (fgen) and WAA/convergence N of the
front. Deep lift should encourage increasing tstm initiation.
MUCAPE from the 03Z/SREF could be as high as 1000 J/kg tonight in
the presence of 30-45 kts of deep layer shear. This would support
the potential for a svr hail storm or two...especially if an
elevated supercell develops.
.LONG TERM...(Wednesday through Monday)
Issued at 337 AM CDT Tue Apr 18 2017
Overview...There will be several storm systems tracking across
the region, most of them weak and not well positioned or with poor
timing for us to see much in the way of precipitation. The most
impressive storm system continues to be the Friday into Friday
night system, which is taking aim at Oklahoma and Kansas, but
could give us some moisture. There will certainly be a cool down
especially for Friday and Saturday on the cold side of the
impressive late week storm system. Even with this cool down highs
should still be in the 50s and lows above freezing.
Wednesday...Poor timing on the cold frontal passage and passage
of the associated upper wave will likely result in most areas
remaining dry and will keep only a low chance of precipitation for
our area. There could be some showers and thunderstorms north of
the warm front earlier in the day where forcing is better, but
that will largely be across northern Nebraska. Then by afternoon
when the warm sector fires thunderstorms up they will likely be
east of our forecast area or quickly exit to the east. Severe
thunderstorms will be possible in the warm sector along the cold
front, but the front would have to slow down by around 6 hrs from
what the current model consensus is for even our eastern areas to
see those thunderstorms, which is getting increasingly unlikely.
Thursday...A little cooler and dry behind the Wednesday system,
but afternoon sunshine should help to still get highs up into the
Friday into Saturday...Current model consensus takes a strong
closed upper level low to our south. The 00z GFS is the strongest
of the major forecast models while the 00Z ECMWF continues to be
weaker with this system. The canadian GEM, once the stronger of
the models with this system is now trending towards the more
southern weaker ECMWF solution. GFS Ensemble members also seem to
be trending south with the 00z run. Consequently rain chances have
gone down some with this forecast package especially for Nebraska
zones north of I-80. The system should be on the way out by
Saturday morning. Confidence is pretty good in this period being
cool on the north side of the storm system.
Sunday and Monday...We warm back up into the 60s on Sunday and
then perhaps some 70s by Monday ahead of the next storm system
which appears to be a weaker progressive system that is currently
projected to track to our north over the Dakotas.
.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Wednesday afternoon)
Issued at 1140 AM CDT Tue Apr 18 2017
A stalled frontal boundary will bring a period of variable winds
to the terminals with a general transition to an easterly
direction heading into the evening/tonight. A strengthening low
level jet over a warm frontal boundary will bring a chance for
thunderstorms mainly after midnight. Coverage of storms is
uncertain and have went with a VCTS at this time. A few storms may
linger into Wednesday, then look for a cold frontal boundary to
cross the terminals, bringing drier air and a wind shift to the