Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 271147
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
547 AM CST Sun Nov 27 2016

.SHORT TERM...(Today and tonight)
Issued at 412 AM CST Sun Nov 27 2016

Overview...At least a few quick moving thunderstorms will track
across portions of the forecast area this afternoon. Can not rule
out a severe thunderstorm as well, despite the climatological rarity
for such an event in late November. Clouds and a stiff southerly
breeze will make it feel cooler today although highs should still
reach into the 50s across Nebraska to the lower 60s over northern
Kansas. Any hope for sun will come late day just ahead of an
advancing dry line.

Morning Hours...High clouds are making it difficult to impossible to
see the advancing stratus deck on satellite imagery. However,
automated surface observations at 3 am indicate that the stratus is
still south of I-70. This low stratus deck will very quickly advect
northward and cover most of the forecast area by mid morning. May
also see some patchy fog after sunrise as the low level moisture
really starts to push northward into cooler air. Drizzle or light
rain may begin to develop especially be late morning as the stratus
deck thickens.

Afternoon hours...Severe Weather Possible...
The 06z NAM takes a 1000mb low out of eastern Colorado this
morning and deepens it to a 990mb meso low in our southwestern
CWA by 3 pm, the main low will be a 985mb low over South Dakota.
Expect clearing along dry line just ahead of this meso low that
will allow for destabilization and thunderstorm development due
especially to the strong dynamics associated with the larger upper
level storm system. Dewpoints will be fairly high for this time of
year climbing to around 50F and expect we could see SBCAPE values
of 500-750 J/KG in that dry slot where the sun comes out. This
seems like a case where we could see some mini-supercells and
even that very slight chance of a rare mini-supercell weak
tornado. Here is a look at a few of the parameters of interest for
mini-supercells:

1) There is decent CAPE for November in the lowest layers with
100-200 J/KG in the 0-1km layer and overall SBCAPE of 500-750 J/KG
2) 0-1km shear value are 30-45kts
3) There is strong sfc vorticity right at the nose of the low
level CAPE max where forecast models are generating thunderstorms
4) With clearing we could see 0-3 km lapse rates jump up to around
8-9 C/km in our southwestern zones by mid afternoon.

Any severe weather this afternoon would likely be rather isolated
with just a brief window of opportunity given the marginal
instability. Based on current model runs the area to watch for
mini-supercells will be from the Beaver City and Phillipsburg area
around 3 pm moving northeast into the Grand Island to Superior
corridor by 6 pm. Any storms would be fast moving at around
55-60 mph to the northeast. Rainfall amounts will be very minor as
these would be small fast moving storms.

Tonight...The system will quickly lift northeast allowing us to
cool down and dry out. Lows will be back down into the 30s.

.LONG TERM...(Monday daytime through Saturday)
Issued at 412 AM CST Sun Nov 27 2016

With essentially all truly active weather now within the short term
periods described above, do not have quite as much to say about the
long term forecast tonight.

Here are the most important points/takeaways of this 6-day period:

1) Honestly, there don`t appear to be any "major"/impactful weather
concerns at this time. In fact, our latest Hazardous Weather Outlook
(HWOGID) carries no mentionable items for Monday-Saturday. Although
am not necessarily comfortable with our currently completely dry
official forecast (especially in the Monday-Tuesday time frame),
even the models that do show small precip chances (PoPs) during this
time are generally showing little more than sprinkles/flurries, and
often times these non-measurable precip types don`t get put into the
official forecast anyway until they get within 24 hours of
occurring. Even taking the "worst case scenario" of possible light
snowfall Monday-Tuesday, the latest ECMWF suggests only a light
dusting mainly in our far northern counties. Clearly, the focus for
much higher snow amounts (6+ inches) early this week will remain
well to our north over the Dakotas. So locally, the bottom line is
this: Although the forecast may not ultimately stay completely
precip-free through the work-week, for the most part it would amount
to only sprinkles/flurries, and nothing major.

2) Temperature-wise, we are finally going to experience a true,
multiple-day stretch of slightly-below normal, seasonably-chilly
weather for the first time this season. We are not talking "extreme"
cold by any means, but just plain typical late November/early
December cold that we have largely been lacking.
Most of the CWA has experienced a few below normal days here or
there lately (such as Thanksgiving Day), but now we are looking at a
solid 5-day stretch of slightly below normal readings centered on
Tuesday-Saturday with highs mainly only in the mid-30s to mid-40s
range and lows well down into the 20s to perhaps upper teens (for
reference, "normal"/average highs for the upcoming week average in
the mid-40s for the CWA as a whole).

3) As far as changes from the previous forecast package to this
latest one, certainly nothing major. That being said, wind speeds
for Monday-Tuesday have been raised a few MPH, and quite possibly
not enough, as both of these days (along with Wednesday) are looking
rather breezy out of the west-northwest with sustained speeds
generally 15-25 MPH and higher gusts. Temperature-wise, and going
hand in hand with "number 2" above, if anything highs were nudged
down 1-2 degrees more for a few days next week.

With the main points covered, will finish as usual with day-to-day
details for those interested, mainly focused on Monday-Tuesday...

Monday daytime-night: Although not an overly "nice" day by any
means, this looks to feature our last slightly above normal
temperatures of the week. In the mid-upper levels, a broad/large-
scale trough will be the dominant feature over most of the CONUS. On
the more regional scale, various primary models have come into
better agreement that a nearly stalled out/quasi-stationary closed
mid level low will meander over the SD/ND/MN border area through
this time, along with its associated, nearly co-located deep surface
low. Thanks to this main disturbance being just far enough away to
our north, the vast majority (if not all) "wrap-around" precip
should remain slightly north of our CWA as well. That being said,
and as harped on in "number 1" above, cannot rule out a few
sprinkles and/or flurries especially in our far northern counties
and this will bear watching. At the surface, we remain in a fairly
decent pressure gradient to the south of the deep Northern Plains
low, which will promote steady 15-25 MPH west-northwest winds with
higher gusts through the heart of the day before easing up overnight
as mixing decreases. Sky-cover wise, the official forecast reads
"partly cloudy" for most counties at this time, but this could
realistically end up trending more toward "mostly cloudy". This
could obviously play a role in high temps, and admittedly confidence
isn`t the highest as there is a fairly decent spread in model
guidance for only being Day 2. However, have hedged toward the
cooler side of things, aiming for a range from upper 40s north/low
50s central/mid 50s south. Lows Monday night are aimed a few degrees
either side of 30 all areas. Lastly, although not expected to be a
big concern (especially if areas see some rain today), our far
southwest counties could get fairly close to "near-critical" fire
weather thresholds in the afternoon if relative humidity (RH) values
trend down much farther, but at least for now they remain slightly
above the 25 percent near-critical point.

Tuesday daytime-night: In the mid-upper levels, little noticeable
change from Monday, although the aforementioned nearly vertically-
stacked mid level and surface low pressure system to our north will
edge more eastward across MN with time. Even so, several models show
that "wrap- around" light rain and/or snow could come perilously
close to especially our far northern zones, and this bears watching.
At the surface, it will be a similar day to Monday in terms of
breezy west-northwest winds, but the biggest difference will be
colder air, with high temps solidly 5-10 degrees lower. More
specifically, highs range from upper 30s far north/low 40s central
/mid-upper 40s far south.

Wednesday-Saturday: Generalizing these 4 days as a whole, in the mid-
upper levels, most of the CONUS remains in a predominantly "troughy"
pattern. That being said, on the more local level the Central Plains
region largely remains "in between" appreciable forcing for
precipitation, and hence the continued dry forecast. Initially
Wednesday-Thursday, the low pressure system to our northeast over
the MN/Great Lakes area finally starts to weaken and depart
eastward, although as it does so would still not be surprised to see
some pesky flurry activity flirt with our northern counties. By
Friday-Saturday, our flow aloft transitions to more west-
southwesterly, but both the ECMWF/GFS agree that the next primary
trough in the flow should mainly focus well to our southwest, with
both models focusing the majority of precipitation potential within
NM/TX and perhaps as close as southern KS. At the surface, the main
story locally will continue to be the aforementioned chilly temps,
with breezes continuing to prevail from the northwest nearly each
day. In fact, the high temp forecast for each of these 4 days is
quite similar/consistent, ranging from only mid-upper 30s north to
mainly low 40s south.

Peeking just beyond the official 7-day forecast, there are hints of
a modest "warm-up" around Sunday/Monday Dec. 4-5, with highs perhaps
climbing toward 50 again.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Monday morning)
Issued at 541 AM CST Sun Nov 27 2016

This continues to be a complicated TAF forecast. A low stratus
deck has developed south of I-70 and will move into KGRI and KEAR
around mid morning. This low stratus deck will likely hang around
through mid afternoon with some breaks starting to show up by mid
to late afternoon.

There could also initially be some patchy fog that rolls in
around mid morning along with the stratus, but that should sweep
north and lift by noon. Confidence in fog is low. Rain will also
be possible later this morning with even some thunderstorms around
the area this afternoon. IFR conditions are likely by mid to late
morning.

Have also become more concerned regarding low level wind shear.
Have introduced strong low level wind shear into the TAF for the
mid morning time frame.

&&

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

$$

SHORT TERM...Wesely
LONG TERM...Pfannkuch
AVIATION...Wesely



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