Area Forecast Discussion
Issued by NWS Hastings, NE

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337
FXUS63 KGID 151152
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
552 AM CST Mon Jan 15 2018

.SHORT TERM...(Today and tonight)
Issued at 459 AM CST Mon Jan 15 2018

By far and away the #1 story of these first 24 hours involves a
return to bitterly cold/dangerous temps and wind chills, as our
"balmy" 1-day warm-up yesterday (which actually exceeded
expectations a bit) quickly fades into memory. A Wind Chill
Advisory is in effect for the entire coverage area (CWA) from this
evening through Tuesday morning, with our Nebraska counties north
of I-80 already going in effect this morning.

Examining the current/recent weather scene as of 4 AM:
Overall, the evening/overnight has played out largely as expected.
The vast majority of the CWA saw only trace amounts of
rain/snow/perhaps brief sleet from our last round of wintry precip
until this weekend. However, a more concentrated swath of fairly
light, albeit wind-blown snow set up overnight mainly in our KS
zones, and continues at this time mainly within Rooks/Osborne
counties. Based on limited ground-truth reports, even the most-
affected areas of our southern CWA have largely seen less than 1"
of snow (as was officially expected), as a few of the short-term
models from last evening were proven over-done. Farther north into
Neb zones, radar shows a few random "ribbons" of passing flurries,
but these appear so fleeting/few and far between that they are not
even included in the official forecast. In the mid- upper levels,
water vapor imagery and short term models clearly depict an
expansive closed low centered over MN, with its westward extent
dropping southward through the Central Plains. The aforementioned
northwest-southeast oriented band of snow still skirting our
extreme southern zones is tied to a well-defined swath of mid-
level saturation/frontogenesis. At the surface, the obvious big
story overnight has been the southward-surging Arctic cold front,
which has already progressed to the OK border area. In the wake of
this front, the night has seen sharply falling temps and steady
north-northwest winds sustained 15-25 MPH/gusting to around 30
MPH. Actual overnight lows (through sunrise) will likely range
from around 0 north to 10-15 far south, with wind chill in the
north steadily approaching Advisory criteria already.

Now looking ahead forecast-wise through today-tonight...

Today:
Clearly our overall-coldest day in a few weeks, rivaling if not
exceeding days such as Dec. 27 and 31st, especially factoring in
winds/wind chills. In the mid-upper levels, the expansive trough
over the Upper Midwest will have our region firmly in its grip,
although all measurable snow chances will focus well to our south
and east with time. At the surface, we will remain well to the
south-southeast of strong, roughly 1050 millibar high pressure
system centered over eastern MT. As this system builds toward us
over the course of the day promoting persistent pressure rises,
this will keep north-northwest winds elevated, with sustained
speeds commonly remaining 15-25 MPH/gusting around 30 MPH. Sky
cover is a bit tricky, as while this kind of strong surface high
pressure regime often results in plentiful sunshine, there are
signs that especially our eastern zones will be prone to batches
of low clouds rotating southward around the edge of the big upper
low. As a result, the sky cover forecast basically ranges from
"mostly sunny" west to "partly cloudy" east, but overall probably
a fair amount of sun. Any lower stratus could drop random
flurries, but will not include in the forecast as this would be
very localized/brief in any given spot. Unfortunately, even
sunshine will do little to ease the sting of the cold. High temps
for the daylight hours were slashed a solid 4-5 degrees from the
previous forecast, with most of the Nebraska CWA not escaping the
single digits, and far south/southwest zones perhaps more-so
10-15. These very cold temps, in combo with the winds, will yield
widespread daytime wind chills of -10 to -20 degrees, especially
in Nebraska zones. Several of our northern counties are expected
to drop to even colder -20 to -25 values especially this morning,
and thus the Wind Chill Advisory there already goes into effect at
7AM while the remainder of the CWA (at least for now) will hold
off until 5PM.

This evening/tonight:
The cold is the big story. Although some low stratus clouds could
continue to affect mainly our eastern zones, the majority of the
CWA should see a clear/mostly clear night. The center of the
surface high pressure system will edge closer to our area through
the night, but still remain to our north over SD. As a result,
northerly breezes will remain somewhat elevated all night, with
sustained speeds generally 10-20 MPH/gusting to around 25 MPH.
Because of these winds, this is not an "ideal" radiational cooling
setup, but given the expected mostly clear skies and just brute
coldness of the airmass, have maintained actual low temps dropping
into the -4 to -10 range most areas. As the night goes on, the
entire CWA should see wind chills drop into at least the -20 to
-25 range, with a few far northern counties (such as the Ord area)
 possibly flirting with Wind Chill Warning criteria of -30. In
 coordination with LBF/OAX, have held off on upgrading any
 northern zones to a Warning, but this may need considered if
 current trends maintain/worsen.

.LONG TERM...(Tuesday daytime through Sunday)
Issued at 458 AM CST Mon Jan 15 2018

General overview of this 6-day period:
Due to more pressing issues involving the dangerous wind chills in
the short-term, will be keeping this section shorter-than-usual,
but will highlight the big stories in roughly chronological order.
Before getting into that though, a quick word of caution regarding
next weekend`s forecast: While CURRENT models show a potentially-
concerning snow storm, we want to emphasize that this is still
SEVERAL days away and subject to a considerable amount of
uncertainty. We urge anyone reading this to refrain from getting
too "hyped up" over this system, as less than a week ago we just
had a storm system that ended up looking much stronger in the
models several days out than it ended up being (at least in terms
of snow accumulation).

1) Very cold temperatures continue Tuesday into Tuesday night:
High temps on Tuesday are hardly any better than those of today,
with most of the CWA aimed into the 8-15 range, and the higher end
of this far west. Thanks to the center of the surface ridge
finally arriving over our local area, winds will be lighter than
today. Nonetheless, the Wind Chill Advisory will continue through
Noon Tuesday all areas. Tuesday night lows should not be quite as
cold as tonight, but still slightly below-zero most areas, and at
near-Advisory wind chills of -15 to -20 are likely, especially in
Nebraska areas.

2) Wednesday-Friday warm up:
Confidence remains high in a dry and warming forecast, as a broad
ridge expands over the Central Plains ahead of our next potential
weather-maker. Each day will feature a steady warm-up versus the
day before, and highs were actually nudged up 1-3 degrees each day
from the previous forecast, and potentially not enough. In other
words, we may be under-playing the magnitude of the warmer air.
Even so, we are currently calling for highs rebounding into the
20s-30s Wed, mainly 40s Thurs and upper 40s-mid 50s Fri. Obviously
this will melt any current snow cover.

2) Weekend Winter storm? (see cautionary note above!):
While Saturday daytime currently looks mainly dry, the Saturday
night-Sunday time frame has grown a bit more concerning over the
past 24 hours, as at least for now both the ECMWF/GFS are in
surprisingly good agreement showing a strong upper trough
intensifying as it lifts east-northeast across the Central Plains
toward the Upper Midwest. While we are DAYS away from having
considerable confidence in how this pans out, current models do
show a potentially potent combo of accumulating snow and strong
winds. In coordination with neighboring WFOs, have capped snow
chances (PoPs) at 50 percent for now, but this system clearly
bears close watching as it slowly nears.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Tuesday)
Issued at 552 AM CST Mon Jan 15 2018

General overview:
Confidence is high in VFR visibility and precipitation-free
conditions (save for perhaps a rogue flurry), along with VFR
ceiling the majority of the time. However, at least periodic MVFR
ceiling is possible, leaving this and also breezy north winds as
the main concerns. Read on for more details...

Ceiling trends:
Confidence has increased somewhat that the majority of the period
will feature VFR ceiling. The question is, is it a large majority
or only a slight one? Satellite imagery and short-term model
data suggest that at least brief, small-scale patches of MVFR
ceiling could occasionally develop overhead and/or drift in from
the north, with KGRI perhaps slightly more favored to see these
lower clouds than KEAR. Instead of blanketing the TAFs with
"hedgy" TEMPO groups to account for occasional MVFR, have simply
went with a prevailing "SCT025" to at least hint at the
possibility of passing low clouds. Later issuances/updates can
insert TEMPO MVFR if it appears more likely/persistent.

Surface winds:
Winds will remain pretty consistent and breezy from the north-
northwest throughout the entire period. Through the first 12 hours
or so today, sustained speeds 15-20kt and gusts to around 25kt
will be common, with slightly lower speeds with max gusts closer
to 20kt during the latter 12 hours tonight.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Wind Chill Advisory from 5 PM this afternoon to noon CST Tuesday
     for NEZ060>064-072>077-082>087.

     Wind Chill Advisory until noon CST Tuesday for NEZ039>041-
     046>049.

KS...Wind Chill Advisory from 5 PM this afternoon to noon CST Tuesday
     for KSZ005>007-017>019.

&&

$$

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



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