Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 190941
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
441 AM CDT Mon Jun 19 2017

.SHORT TERM...(Today and tonight)
Issued at 324 AM CDT Mon Jun 19 2017

Light rain or sprinkles have been moving through the forecast
area for several hours. Rain has been reported at several of the
observation sites, but none have had more than a trace. Satellite
and observations have mid level clouds across the area.

Once again the time before day break will be of interest this
morning. Most of the forecast models continue to have some spotty
precipitation for at least portions of the area into the mid morning
hours. The short term models have the precipitation sinking to the
south and the trend on radar has also been moving to the south. Have
kept the low PoPs and expanded them further to the south and into
mid morning, moving them south with time. The clouds across the area
have also been moving to the south. These clouds and dew points that
have been raising during the night leave a little concern for how
low the morning lows will be. Have tweaked them up just a little for
this morning.

The clouds should continue to move out of the area this morning
and skies should be mostly sunny during the day. The only concern
is there are a few mid level clouds upstream. The sky cover today
may not be quite as clear as what is in the forecast. With a few
more clouds, there could be an impact of temperatures this
afternoon. Tonight will be dry and there will be mostly clear

.LONG TERM...(Tuesday daytime through Sunday)
Issued at 440 AM CDT Mon Jun 19 2017

General overview of this 6-day period:
Compared to recent forecast packages over the past 12-24 hours,
there haven`t really been any truly "major" changes in the general
expectations. That being said, compared to what this forecaster
was seeing 24 hours ago:
1) If for no other reason than that it`s simply getting closer in
time and confidence in the magnitudes of instability/shear are
increasing somewhat, we are starting to get a little more
concerned regarding what could be perhaps a few rounds of severe
weather this week, possibly starting as early as Tuesday
afternoon/evening mainly in southern zones, but with the overall-
highest concerns probably focused Wed-Thurs, and perhaps (lower
confidence in this) even extending into Fri-Sat as well. On their
latest outlooks, SPC has opted to extend the Day 2 Marginal Risk
(for Tues) into our far southwestern coverage area (CWA) and for
Wednesday (Day 3) they`ve already pulled the trigger on a Slight
Risk for the majority of the CWA, and from our local perspective
this seems reasonable. As days later in the work week week get
closer, wouldn`t be one bit surprised to see at least Marginal
Risks assigned to them as well.

2) Although not "wildly" different especially with regard to the
basic mid-upper pattern, unfortunately, there seems to be more
disharmony/less agreement than before mainly in the lower-level
details such as surface frontal timing/instability
levels/temperatures between the latest ECMWF/GFS solutions
especially for Thurs-Sat, and thus some uncertainty on just how
far out in time at least a low-end severe storm threat could
exist. Barring some pretty hefty changes in the model world,
however, it sure seems the chances of any thunderstorm activity
(let alone severe) should be over with for at least a few days
starting by Saturday night-Sunday.

Now addressing the basic precipitation/temperature expectations
of this latest forecast package...

Precipitation/thunderstorms:
Given that literally every single day/night forecast period from
Tuesday afternoon onward currently features at least a slight
chance of precip (PoP) for at least some portion of the CWA, this
is probably one of those forecasts that "sounds wetter than it
probably really will be". In other words, several of the
advertised shower/thunderstorm chances will likely tend to be more
isolated/scattered versus widespread in coverage, and that`s why
PoPs have been kept relatively low for now. That being said, most
areas should in theory see at least 1-2 rounds of "some" rain
during these 6 days a whole. Officially, our overall-highest PoPs
greater than 20 percent are currently focused Tuesday
afternoon/evening (in the south), Wednesday evening, Thursday
night, and finally Friday night into Saturday. However, given the
aforementioned model disparity especially beyond Wednesday, please
don`t get too caught up in specifics especially Thursday and
beyond. Have already outlined some thoughts regarding severe
storm potential this week (see above).

Temperatures:
As is often the case, confidence in temp trends are overall-higher
than precip/thunderstorm chances. Only very minor (mainly less
than 3 degrees) tweaks were made to most days/nights versus
previous forecast. So, in short: Tuesday-Thursday are clearly the
warmest/above-average days of the week, with Wednesday the
downright-hottest day with actual high temps aimed 95-100 most all
areas, and which will also likely feature 100+ degree afternoon
heat index readings in various areas (will continue this mention
in our latest Hazardous Weather Outlook (HWO)). Beyond Thursday,
confidence remains high that the final 3 days of the official
forecast (Fri-Sun) will trend cooler and even below normal, with
highs this weekend only aimed into the mid-upper 70s area-wide.
Low temps follow a similar trend, with values both Tuesday and
Wednesday nights holding up well into the 60s to near-70, but
easing back into the 50s for this weekend as the cooler airmass
arrives.

With the "big picture" expectations well-covered, will end as
usual with some attempted day-to-day details for those
interested. Again, please keep in mind that confidence in the
thunder/precip details certainly diminish especially Thurs-Sat...

Tuesday-Tuesday night:
As already discussed above, we are a little more concerned than 24
hours ago regarding the possibility of a few severe storms
erupting mainly during the afternoon/early evening especially
in/near the far southwest fringes of our CWA (mainly
Furnas/Phillips/Rooks counties area) Backing up a little, the vast
majority of the CWA should get through at least late afternoon
dry, with the main story being a return to upper 80s- mid 90s high
temps for the first time since last Friday as a somewhat loosely-
defined warm front lifts northeast. That being said, even fairly
basic fields such as wind direction are somewhat in question, as
the NAM suggests a weak front/wind shift could drop through most
Nebraska zones and promote a light north/east breeze, while most
other models show a prevailing southerly breeze. At any rate, most
all models agree on instability/mixed- layer CAPE spiking to as
much as 2000-3000 J/kg by peak heating in southwest zones, which
in the presence of fairly strong deep layer shear of 40+kt could
promote at least isolated severe storm development in that area
along a surface trough or warm front. Should storms develop, they
could quickly become supercellular/severe with a large
hail/damaging wind threat, but they could also exit the CWA fairly
quickly given the southeastward storm motion under pronounced
northwest flow aloft. Whether or not severe storms materialize in
our south/southwest during the afternoon/early evening, at least
spotty strong storms (not necessarily severe) could flare up almost
anywhere in the CWA later in the evening/overnight along/near the
nose of a low level jet axis.

Wednesday daytime-night:
As already touched on above, confidence is high that this should
be the hottest day of the week with highs 95-100 most areas and
afternoon heat index values into the 100-103 range some areas
(getting awfully close to official Advisory criteria). For most
areas, breezy south winds will prevail much of the day, but a
front approaching from the west in the afternoon should ease
speeds a bit there, but also provide the focus for potentially
robust thunderstorm development, especially a few hours either
side of 7PM. While it`s possible that warm temps aloft could
possibly inhibit storm development, the degree of instability (a
general model average of 3000-4000 J/kg) along with 35+kt of deep
layer is somewhat concerning, and hence the SPC Slight Risk
already out on the Day 3 outlook.

Thursday daytime-night:
By this time confidence in the low-level details starts to
diminish a bit, but in theory another halfway decent severe storm
risk could materialize during the late afternoon-evening as a
weak cool front sinks southward into the area and more weak
disturbances/waves work eastward into the Plains on zonal flow
aloft. Temps should be at least a little cooler than Wednesday,
but perhaps not by much if a slower frontal invasion occurs.

Friday daytime-Saturday night:
During these 48 hours, both the ECMWF/GFS generally agree in a
broad trough developing over the north central CONUS and sending a
decent cold front (by late June standards anyway) southward
through our region. HOWEVER, the latest GFS solution is
considerably faster than the ECMWF with the invasion of
cooler/more stable air. As a result, the ECMWF keeps a possible
severe storm threat going for Friday and maybe even Saturday,
while the GFS shunts any meaningful instability southward by
then. Talk about big question marks! No matter what happens
though, both primary model camps agree on a cooler airmass with
highs by Saturday only in the mid-upper 70s.

Sunday:
Obviously plenty of inherent uncertainty at the Day 7 range, but
both the ECMWF/GFS suggest a fairly pleasant, dry day with highs
again only mid-upper 70s. However, mainly in deference to the
somewhat outlier-looking Canadian model, the default model blend
used to initialize our extended forecast has resulting in some
"iffy" slight rain shower chances mainly in our KS zones.

&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Monday)
Issued at 1222 AM CDT Mon Jun 19 2017

Mid level clouds will move through the terminals through day
break. There could be a sprinkle with the mid level clouds as they
move through. Clouds should diminish during the day.

&&

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

$$

SHORT TERM...JCB
LONG TERM...Pfannkuch
AVIATION...JCB



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