Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 191703
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1203 PM CDT Wed Apr 19 2017

.UPDATE...
Issued at 527 AM CDT Wed Apr 19 2017

Multiple channels of GOES16 imagery has shown an increasing area
of ascent and rapid cloud formation from NW KS into S-cntrl Neb
over the last 2 hrs. We`re starting to see an increase in speckled
shwr activity W of Hwy 281. We are monitoring for tstm
development. Strong storms are currently at the Nrn fringe of this
area over Valley County and we issued an SPS about 15 min ago.
MUCAPE is 500-1000 J/kg...but effective shear where these shwrs
are forming is not very good. Will cont to monitor.

638 AM UPDATE: svrl small cells have been trying but they keep
fizzling. Radar is looking increasingly quiet but we are
monitoring.

&&

.SHORT TERM...(Today and tonight)
Issued at 402 AM CDT Wed Apr 19 2017

Aloft: The Westerlies will trend toward a little more
amplification by 12Z/Thu. Currently low-amplitude WSW flow was
over the CONUS with an embedded shortwave trof over ID/WY/CO. This
trof will head into the Nrn Plns today and tonight while
amplifying due to a stronger upstream trof moving onshore in the
W.

Surface: A quasi-stationary front extended from xtrm SE Neb WSW
thru Nrn/Wrn KS to 1004 mb low pres near the CO/KS border
(although overnight tstms have muddied the temp grad over SE
Neb/NE KS). Part of this low will move NE...crossing Cntrl Neb
during the day...and into Wrn IA by 00Z. As this occurs...the
front will pivot...lifting N in advance of it and sinking S in
its wake. The front should be near a HJH-K61-RSL at 00Z and it
will more rapidly exit SE of the fcst area (FA) shortly
thereafter.

Now: strong WAA/Fgen was in progress along the Neb/KS state line
within the lower portion/cold side of the frontal zone...at the
nose of the 55 kt low-lvl jet. However...tstm development has been
limited. This is probable due at least in part to very dry air
within the EML that is being advected into the area.

There was one elevated supercell that formed within the initial
storms that fired around 10 pm last eve. It produce tremendous
hail that covered the ground and was as large as tennis balls. No
other storms were even close to svr...and after those storms
fizzled...the majority of subsequent development overnight was
over NE KS and Ern Neb.

Today: Prospects for rain are not good today...even N of the
front where ascent will occur in advance of the low. There is just
too much mid-lvl dry air...synoptic forcing too far N...a strong
cap and poor timing (meaning the front would need to be further N
and W of its expected location at 21Z.

Most locations will remain dry. We do have some 20-40% PoPs N of
I-80 (highest before noon)...but don`t bet on it.

Even where SPC has a SLGT risk of svr tstms across the SE fringe
of the FA (Mitchell and SE portions of Jewell and Thayer
Counties)...we are probably too high with PoPs. All of the model
guidance (inclusive of the 06Z NAM) blow-up the convection just E
and S of the FA. The initial updrafts and possibly the first storm
or two may form over our far SE...but they will rapidly exit and
intensify to the E and SE in the 00Z-03Z timeframe. The 00Z NMM is
the only model that fcsts more than 1 or 2 storms...and it is
probably too early with its initiation and it is W of the model
QPF clustering.

Substantial sunshine will occur along and S of I-80. A very warm
summer-like day S of the front with mid 70s to mid 80s (warmest N-
Cntrl KS).

Temps: there is uncertainty espcly in vicinity of the front.
Temps could be 2-6F warmer than we have fcst from I-80 down into
N-cntrl KS. Conversely...temps could be 3-5F cooler N of I-80.

Uncertainty also exists in how windy it will be in post-frontal
deep mixing this afternoon. The 06Z RAP and HRRR suggest we may be
5-10 kts too low.

Tonight: Any storm or 2 on-going between K61-HJH at 23Z will exit
the FA by 01Z. We can probably expect a period of windy conds
before midnight over S-cntrl Neb (NW 20-30G35 mph).

Increasing mid-lvl clouds. A minor perturbation on the tropopause
(fcst to move onshore into CA today) will be moving into WY/CO
tonight. Combined with lingering mid-lvl instability...this could
generate some sprinkles initially over Wrn KS that could expand NE
into the FA.

Cooler behind the front with temps dropping much closer to normal.

.LONG TERM...(Thursday through Tuesday)
Issued at 402 AM CDT Wed Apr 19 2017

Overview...This will mainly be a dry period with the exception of
Friday into Friday night when we stand our best chance of seeing
some rain. Southwestern zones will have the higher rain chances
Friday/Friday night based on the more southern storm track. This
time of year we also have to keep an eye out for frost and
although we are currently forecasting above freezing lows
throughout the period, it may be a close call for frost Saturday
night/Sunday morning.

Thursday...It will be cooler and dry for most areas behind
today`s system. However, afternoon sunshine and fairly light winds
will still make it feel rather pleasant as highs reach into the
60s.

Friday and Friday night...The bulk of this next storm system will
highly likely pass south of our forecast area with our
southwestern zones standing the best chance of still catching a
little light rain. Rain chances are not looking good if you live
northeast of a Hebron, Grand Island, to Loup City line and most of
the appreciable rain will likely be south of our forecast area
closer to the upper level low. There is not enough instability for
thunderstorms this far north of this system and thus am just
calling for general rain showers. The 00Z ECMWF is the driest of
the models for our area and the 06Z NAM is the wettest although
it`s not really all that wet. Friday will likely be the coolest
day of the week with highs in the 50s to around 60.

Saturday...The storm system will slide southeast of our forecast
area and we should see increasing clearing, but a cool north
northeast wind in the wake of the departing system will likely
continue to hold highs down in the lower 60s.

Sunday and Monday...We warm back up into the upper 60s to around
70 on Sunday and then perhaps well into the 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.

Tuesday...May be a few degrees cooler but still mild behind a
weak cool front associated with a passing Dakotas short wave.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Thursday afternoon)
Issued at 1159 AM CDT Wed Apr 19 2017

A cold frontal boundary is just about to reach the terminals at
the onset of the TAF period. Winds will be making the switch to a
northerly then a northwest direction behind the boundary. Cigs are
tricky with cloud heights currently varying between MVFR and VFR
however a fairly expansive area of stratus with IFR cigs are noted
behind the front. Have included a tempo group the low cloud cover
for the afternoon hours. The best chances for thunderstorm
activity later this afternoon and evening will be south of the
terminals however latest forecast models suggest the potential for
light post frontal precipitation overnight in the presence of mid
level frontogensis. For winds, northwest wind speeds will remain
steady and gusty at times into the overnight hours and deep mixing
Thursday may also produce gusts of 20kts or greater.

&&

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

&&

$$

UPDATE...Kelley
SHORT TERM...Kelley
LONG TERM...Wesely
AVIATION...Fay



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