Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 261145
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
645 AM CDT Wed Jul 26 2017

...Today is a Transition Day Before a Significant and Refreshing
Multi-Day Break from the Heat and Humidity of Summer...

.SHORT TERM...(Today and tonight)
Issued at 645 AM CDT Wed Jul 26 2017

Aloft: Anticyclonic WSW flow was over the Cntrl Plns with a
subtropical high over the Srn Plns. The Westerlies were fairly
zonal along the US-Can border...but a shortwave ridge was moving
into WA/BC. This ridge will cont E to the Nrn Rockies and increase
in amplitude today and tonight. This will result in WSW flow over
the Cntrl Plns becoming NW.

Surface: A strong cool front was sagging thru the Nrn/Cntrl Plns
and extended from LkSup-MN across Neb to low pres near the CO-Neb
border. This front will cont sinking S thru the CWA today...
forcing the low into Nrn KS. The front should be fully out of the
CWA by midnight. Once the front moves thru...Nrn Plns high pres
will begin building in.

The fcst is fraught with uncertainty today...the amt of cldcover
and the amt and coverage of precip will have a significant impact
on temps. Just as one example of the uncertainty: NAM MOS offers a
high of 89F at GRI vs MAV which has 80F.

645 AM UPDATE: The back edge of last night`s sub-svr MCS is
moving E and should be out of SE counties by 9 AM.

Given the extensive cldcover...high temps were lowered a bit N of
I-80. Otherwise...still believe the we may be done for the event
(any PM tstm development will be S and E of the CWA).


Today: There are many ways this fcst could fall off the tracks.
Probably the biggest weakness is the potential for shwrs/tstms.
Much of the uncertainty is due to a lack of model agreement. Some
models fcst a cap to form at the top of the invading cool air mass
(frontal inversion). Others erode the cap and initiate shwrs/
tstms in the post-frontal regime.

Not sure which way to go. Believe the fcst is way overdone
advertising rain potential today. There is little to initiate
storms behind the front. Will daytime heating alone be enough?
This fcstr doubts it with all the lingering cloud cover. There is
some weak mid-lvl FGEN though. Again...uncertainty.

It is tough to tell where the front since this rain is messing up
the wind fields...but it appears the front will be thru most of
S-cntrl Neb by noon. The low-lvl thermal ridge E of the low will
be shunted into N-cntrl KS. So high temps were raised over
Osborne- Mitchell Counties...although this may have been a
mistake. There is a lot of cloud cover to the W.

Dwpts: one of the most interesting aspects of this fcst is that
the plume of dwpts in the mid 70s over IA/MO will circulate to the
SW behind the front. It will become extremely muggy/humid. Dwpts
were raised above fcst initialization (into the mid-upr 70s).
Dwpts of 76- 78F are fcst in the Hwy 81 corridor. What is really
concerning is the bias-corrected WRF-ARW is indicating this may
not be aggressive enough. We could see a much larger area of dwpts
77-81F!

Heat: Given the fcst high temps combined with the influx of
higher dwpts...a Heat Advisory has been issued for
Osborne/Mitchell Counties.

If clouds break up enough and sufficient heating occurs...03Z SREF
fcsts MLCAPE as high as 2000 J/kg. 0-6 km shear will be about 20
kts. An isolated svr tstm or two can`t be ruled out "if" storms
develop. If any storms develop...they will be over the SE 1/2 of
the CWA (SE of MCK-GRI-OLU).

Tonight: Any storms will gradually exit E and S of the CWA leaving
dry conditions. The 18Z/00Z NAM/GFS are fcstg a shield of low
stratus to develop across Nrn/Wrn Neb and that is probably
underway with MVFR/IFR CIGs already appearing the obs. This cloud
shield is fcst to sink S thru the CWA late this afternoon into
tonight.


.LONG TERM...(Thursday through Tuesday)
Issued at 359 AM CDT Wed Jul 26 2017

The main story through the long term is the cooler temperatures.
After the long stint of oppressive heat, highs in the 80s will be
welcome for most.

Surface high pressure will build in on Thursday as the upper flow
becomes northwesterly. Winds will be light to end the work week
and temperatures under mostly clear skies will be in the low to
mid 80s.

A weak wave will impact the area as it moves southeast into the
trough over the Eastern CONUS. This brings a chance for showers
and thunderstorms Saturday into Sunday with best chances across
western Nebraska. Overall, do not expect these thunderstorms to
amount to a whole lot and expect most areas to remain dry. Highs
for the weekend will remain in the mid 80s.

Much of the same continues into early next week as upper level
flow remains northwesterly. The main question in this period is
the chances for precipitation. There are discrepancies among the
guidance regarding how the smaller scale details will evolve and
so confidence is low on any chances for precip early in the week.
Highs will continue to be in the 80s.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Thursday)
Issued at 645 AM CDT Wed Jul 26 2017

Significant Wx: MVFR CIGs thru tonight.

Today: MVFR CIGs should develop as daytime heating commences this
AM. Some low clds 300-500 ft are around and they could temporarily
become a CIG for TEMPO IFR. E winds 8-15 kts will gradually become
N-NNE and gust up to 25 kts late this afternoon. There is a very
low chance for an afternoon TSRA mainly at GRI. Confidence: Medium

Tonight: MVFR CIGs should lower from above 2000 to below 2000 ft.
CIGs should become SCT with improvement to VFR late. This is not
depicted in the TAFs though. NNE-N winds will diminish to 10-15
kts. Confidence: Medium

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...Heat Advisory from noon today to 8 PM CDT this evening for
     KSZ018-019.

&&

$$

SHORT TERM...Kelley
LONG TERM...Billings Wright
AVIATION...Kelley


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