Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 211713
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1213 PM CDT Fri Jul 21 2017

.UPDATE...
Issued at 646 AM CDT Fri Jul 21 2017

Increased the wind speed this morning a bit as some of the low-
level jet is making its way down to the surface. Also need to
mention that dew points may mix out more in north central Kansas
and send dew points a bit lower, but we will still have elevated
heat index, but maybe not as high as some central eastern Nebraska
areas where the dew point should be higher.

&&

.SHORT TERM...(Today and tonight)
Issued at 431 AM CDT Fri Jul 21 2017

Biggest concern will be the heat index today, then the potential
development of thunderstorms late this afternoon into the evening,
with a marginal risk of a strong to severe thunderstorms occurring,
mainly north of Interstate 80.

Based on recent performance of models, I did hike up dewpoints for
this afternoon, especially central/east. We could be pushing a bit
above 110 for heat index in our northeast/east in places like York
County.

We remain under considerable influence from the upper level
subtropical high, but this is showing signs of some weakening. Also,
a shortwave trough skirting our border with Canada will skim the
Northern Plains this afternoon, possibly having an effect of modest
height falls.

At the surface, we have a surface trough just to the west/northwest
of the CWA and a warm front just northeast of the CWA, moving slowly
northeast. Farther northwest, stretching from eastern Montana into
the Great Basin, there is a cold front heading our way.

Later today, short term models generally suggest a slow migration
east for the aforementioned surface trough, and by late afternoon,
enough destabilization may occur that this surface trough could be a
focus for convection in our north. Later on, the cold front could be
a focus for more convection. Any convection along and ahead of the
front will enhanced by a 30 to 40 kt low-level jet. We could get a
strong to severe storm with MLCAPE likely topping 2000 J/Kg in our
northwest near the trough. Shear is very weak, so our only shot a
strong to severe storms will be late afternoon into the evening, and
for our north/western area near the trough. By overnight,
instability wanes, even elevated instability is rather measly, and
deep layer shear is rather weak, but the low-level jet could
possibly maintain some convection as stated earlier.

The cold front is expected to lose its punch somewhat by tonight and
perhaps stall in our southern CWA by late tonight. The greatest
chance of precipitation will lie in our north tonight, with not much
hope at all that there will be any precipitation in our south,
unless a miraculously strong cold pool develops to push convection
farther south, but for now, this does not appear likely.

.LONG TERM...(Saturday through Thursday)
Issued at 431 AM CDT Fri Jul 21 2017

Aloft: A potent shortwave trof will be moving across Srn Manitoba
Sat. The Westerlies will dip temporarily with NW flow here Sat-Sun.
Mon-Thu the subtropical high will gradually reorganize from the
Desert SW into the Srn Plns. So the Westerlies over the Nrn USA will
become zonal and then gradually transition to WNW flow as a low-
amplitude ridge builds over the Nrn Rockies by Thu.

There will be numerous low-amplitude perturbations in the flow (most
probably convectively-induced) that have little to no
predictability.

Surface: At dawn Sat a cool front will bisect Neb/KS and the CWA.
This front will cont S due to minor amplification aloft...and will
be just S of the CWA by peak heating. High pres will form over and
cross the Nrn Plns Sun and then slowly make its way E next week.
Return flow will develop here Mon as the next cool front stretches W-
E across the Nrn USA...possibly sagging as far S as the Neb/SD
border by Thu. A lot can change between now and then though.

Sensible wx details...

Rain: Typical of summer...chances are very very low...and any
limited tstm activity will be very spotty. The "best" chance for a
few storms during the extended fcst will be Sat into Sat night along
and N of the cool front.

A narrow ribbon of rich 850 mb dwpts is fcst immediately on the cool
side of the front. This will contribute MLCAPE of 1500-2000 J/kg.
Upr-lvl winds will be weak...but directional shear in the post-
frontal regime will be enough for 20-25 kts of 0-6 km shear. The
frzg lvl is fcst to fall from 14K to 12.5K ft. So some svr hail/wind
will be possible in an environment supportive of multicells.

Temps: near normal (upr 80s to low 90s by day and 60s at night).

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Saturday)
Issued at 1209 PM CDT Fri Jul 21 2017

VFR conditions are forecast for this TAF period. A surface trough
axis currently lies from far western KS northeastward through
north central NE. Winds at both terminals are forecast to remain
southwesterly this afternoon, with KGRI having more potential for
occasional gusts near 20 MPH. More light/variable winds are
expected to develop this evening/overnight, between the boundary
sinking south and potential impacts from area thunderstorms. Do
have a VCTS mention at both sites this evening, but confidence in
any timing, or if they will even affect the terminals, is pretty
low. Once the boundary sinks south early tomorrow morning, winds
through the end of the period are expected to turn more
northeasterly.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Excessive Heat Warning until 8 PM CDT this evening for NEZ064-
     076-077-085>087.

     Heat Advisory until 8 PM CDT this evening for NEZ039>041-046>049-
     060>063-072>075-082>084.

KS...Excessive Heat Warning until 8 PM CDT this evening for KSZ006-
     007-018-019.

     Heat Advisory until 8 PM CDT this evening for KSZ005-017.

&&

$$

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



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