Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 291754
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1254 PM CDT MON AUG 29 2016

.UPDATE...
Issued at 1254 PM CDT Mon Aug 29 2016

If you`ve been following our LSR`s or our social media feeds...
you`re aware of the 3-7" of rain that fell over Srn Adams/Nrn
Webster and NW Nuckolls counties last night...mainly in 4 hr
period.

Because the environment has not changed since last night...there
is no reason excessive rainfall and flash flooding can`t happen
again. Winds are very weak up to 300 mb. So steering currents are
weak as well. So we have posted a Flash Flood Watch for the SE
half of the fcst area in coordination with the Topeka/Omaha
offices.

There`s no guarantee that it happens again tonight and if it
does we are not sure where...but the potential exists for a repeat
somewhere in or near the watch. Don`t discount this situation is
your location is not in the watch. We cannot know exactly where
tstms will form.

Looking at observed soundings from DDC/LBF/OAX/LMN this morning...
the atmosphere is moist and CAPE is not excessive. While frzg lvls
are not excessively high...soundings do have a flash flood look
to them.

NAEFS indicates PW`s over the fcst area will be 1.5 to 1.75" which
is around 2 standard deviations above normal - i.e. we are very
moist. Tstms will be efficient rain producers.

&&

.SHORT TERM...(Today and tonight)
Issued at 328 AM CDT Mon Aug 29 2016

The timing and placement of thunderstorms is the main forecast
challenge in a complex weather pattern. Convection developed
earlier in the evening and has persisted into the overnight hours
across our central CWA, and significant rainfall amounts in the 3
to 5 inch range have been common across southern Adams and
northern Webster Counties where a flash flood warning is in
effect. Although convection has weakened to some degree we
continue to see new development early this morning primarily
across our western counties.

Patternwise the Central Plains is in weak flow in between a
closed low pressure system in New Mexico and ridging to the east
in the Tennessee and Ohio valleys. A plume of subtropical moisture
is streaming into our region with subtle embedded shortwave
troughs providing sufficient lift to generate convection. We will
remain in this pattern through the short term periods and cannot
rule out storms at any given time, although pinpointing the
coverage and location is challenging. Models are having a
difficult time resolving what to do with the desert southwest low
and attempt to phase it across the plains and with the progression
of this system rain chances are looking fairly promising. Weak jet
streaks around 50kts lift thru our region into tonight will
provide additional periods of lift. The mean flow actually weakens
even more so by tonight to under 10kts. Any storms which develop
will move very little and are expected to be efficient rain
produces in the presence of high lowlevel moisture with dewpoints
in the middle and upper 60s and precipitable water values
averaging an inch and a half to two inches. Once again we could
see some hefty rainfall totals in excess of two inches, and the
majority of our area is outlined in the excessive rainfall
outlook. Since overall conditions have been dry with heavy
rainfall has been isolated to this point, will hold off on hydro
related watches, but could see some rises in rivers and lowland
flooding if significant rainfall materializes especially in
locations which just saw heavy rain.

Have kept afternoon temperatures conservatively cool due to the
expected cloud cover and the potential for convection. Then
tonight readings are expected to be mild again in the 60s with
clouds and lowlevel moisture in place.


.LONG TERM...(Tuesday through Sunday)
Issued at 328 AM CDT Mon Aug 29 2016

Primary forecast concern will continue to revolve around
precipitation chances.

At the start of the long term period Tuesday morning, shortwave
troughing in the upper level is set up across the Central Plains,
sitting between areas of high pressure over the central Rockies
and Midwest region. At the surface, a weak pattern is expected to
be in place, with light/variable winds, with high pressure spread
from central Canada southeastward into the Great Lakes region.
Precip chances remain in the forecast across the entire CWA on
Tuesday with this mid/upper level trough axis around, with lift
also aided by an SW-NE orientated upper level jet streak. These
features remain a player across the area into Tuesday night and
Wednesday, with models actually in decent agreement with the
southward shift, pushing much of the better chances south of the
CWA by the end of the day Wednesday. As it does so, well amplified
ridging gradually slides into the High Plains region. The
light/variable winds starting off the period becomes more east-
northeasterly, driven by better organized high pressure sliding
across southern portions of Canada. PoPs for much of the Tues-Wed
period are in the 30-50% range, and maybe scattered in nature.
Shear/instability parameters continue to suggest severe is not
likely. Temps were cooled a bit with the higher PoPs going and
plenty of cloud cover expected, with mid 70s to lower 80s
forecast.

Compared to the past few days, models have come into better
agreement with showing the potential for some dry periods, coming
during the Thurs-Fri time frame. Do have some lingering slight
chances PoPs clipping far south-southwestern areas, sitting closer
to the better upper level forcing. Otherwise, the upper level
ridging builds further east onto the Plains through Friday, with
the main axis looking to be near the Missouri River area by 00Z
Sat. At the surface, those easterly winds through mid week will
turn more southerly, as that larger area of high pressure builds
further south into the Great Lakes/Midwest. Should see a bump up
in temps of at least a few degrees if things remain dry.

Into this next weekend, the system pushing the upper level
ridging east through the region is storm system moving onto the
West Coast, resulting in more southwesterly flow across the
Plains. Models showing that while the main trough axis looks to
remain off to the west of the area through Sunday, shortwave
disturbances ejected out ahead will once again bring periodic
thunderstorm chances to the area. Highs look to climb into the mid
80s.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Tuesday)
Issued at 1254 PM CDT Mon Aug 29 2016

Significant Wx: IFR tstms the main concern but timing is
uncertain.

This Afternoon: Multi-layered VFR clouds mainly at or above 12K
ft. But expect some CU will develop around 3K ft with isolated IFR
tstms developing especially after 3 pm. No guarantees of a direct
hit at either terminal. Winds light from the SE away from any
tstms. Confidence: Medium

Tonight: Same. The SREF guidance indicate the high probability/
chance of tstms will be 06Z-12Z. Confidence: Low

Tue thru 18Z: Consensus of guidance indicates CIGs will decay to
MVFR with IFR vsbys possible in hvy downpours. Lgt and vrbl winds.
Confidence: Low

&&

.GID Watches/Warnings/Advisories...
NE...Flash Flood Watch through Tuesday afternoon for NEZ074>077-
     083>087.

KS...Flash Flood Watch through Tuesday afternoon for KSZ005>007-
     017>019.

&&

$$

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



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