Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 141131
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
531 AM CST Thu Dec 14 2017

.SHORT TERM...(Today and tonight)
Issued at 420 AM CST Thu Dec 14 2017

Upper air data showing continued northwesterly flow in place across
the region this morning. It`s not as amplified as it has been, the
main upper level ridge axis being located along/just off the west
coast, while broad troughing over the eastern CONUS. While
conditions across the CWA remain dry early this morning, focus is to
the north-northwest, where satellite shows a weaker shortwave
disturbance making its way through the Northern Plains. At the
surface, the pattern is a weak one, resulting in light westerly to
calm winds. Skies are mostly cloudy across the area, helping keep
temps up a bit, 3 am obs range from the lower/mid 30s for most
locations.

Main forecast concern in the short term period comes during the
daytime hours, with precipitation chances. Models are in good
agreement showing this shortwave disturbance continuing to slide SSE
through the Central Plains today. There`s not exactly an abundance
of moisture for this system to work with, but models have been
fairly consistent showing at least scattered precipitation affecting
the CWA. Backed PoPs off a bit this morning, the better chances look
to be late morning through the afternoon hours. Continue to have the
potential for both rain and snow going, but admittedly the forecast
is on the cooler side of models/guidance for temperatures, with
highs in the upper 30s/mid 40s. Some suggest any snow would be short
lived, confined to the very start/end of the day. Either way, not
expecting much accumulation, but current forecast has a tenth or two
of snow possible across northern portions of the CWA. The light
winds in place early this morning will turn more northwesterly with
the passage of another frontal boundary, with speeds not as strong
as yesterday, but sustained speeds of 15-25 MPH are possible. The
strongest winds look to be west of HW 281. Should see plenty of
cloud cover through the day.

Outside of a lingering slight change PoP this evening, the 00-12Z
Friday period is dry. Should see diminishing sky cover, with winds
tapering off and again turning more westerly. Overnight lows tonight
are expected to fall into the upper teens to lower 20.

.LONG TERM...(Friday daytime through Wednesday)
Issued at 420 AM CST Thu Dec 14 2017

General overview of this 6-day period:
Fourth and final night on the long term desk, and compared to the
past few nights there are actually a few more relatively minor
forecast changes to discuss, mainly involving: 1) seemingly even
less chance of snow from the weekend system (not that we were
"talking it up" much to begin with) and 2) some minor upward temp
adjustments to a few days. Temperature- wise, our remarkable
stretch of mildness marches on, with 5 of these 6 days aimed 10-15
degrees above mid-December normals, and the 1 colder day (Sunday)
near-normal at worst. Typically don`t discuss matters beyond the
end of our official 7-day forecast range here, but for those
longing for more "true" December cold, current trends suggest some
legitimate below-normal readings COULD be firmly in place by next
Fri-Sat (Dec 22-23).

Likely/potential weather hazards:
With little if any apparent risk of wintry precipitation, and no
days that appear as strongly-windy as this past Mon/Wed, the only
issue currently worthy of inclusion in our latest Hazardous
Weather Outlook (HWOGID) is near-critical fire weather conditions
Friday afternoon. Considered introducing this mention 24 hours
ago, but now that it`s within the Day 2 range, confidence has
increased that especially the southwestern 1/3 of our coverage
area (CWA) will see a few hours of overlap between relative
humidity as low as 18-25 percent and southwesterly wind gusts
around 20 MPH or slightly higher. Unless wind speeds trend upward
another 5 MPH or so, this setup should be "safe" from meeting
critical thresholds that would necessitate Warning issuance.

Basic precipitation overview:
The vast majority of these 6 days currently remain dry, and with
pretty darn high confidence in remaining so. Here 24 hours ago, we
discussed how especially the ECMWF was showing potential for
perhaps as much as 1-2" of snow Saturday night into Sunday
daytime. However, even this more aggressive model has backed off
considerably, making it currently appear that even flurries may be
difficult to come by (see daily details below for more on this).
Thus the single biggest change to the official forecast from the
previous version: The entire Sat night period is now dry, and any
small chance of snow for Sunday daytime is confined to the morning
hours and mainly just in the northwest half of our CWA (and even
this appears iffy). HOWEVER, all this being said, want to caution
against completely discounting this system altogether yet, as with
it still being 3-4 days away, there is: 1) Still time for it to
"flip flop" back to showing a little snow...2) Some early hints
that perhaps a little pesky light freezing drizzle could try to
form Sunday morning. Often times, light (usually non-measurable)
drizzle doesn`t get formally introduced to forecast products until
it gets within 24-36 hours, so this will be something to keep an
eye on as the weekend arrives.

Basic temperature overview:
Above normal remains the overwhelming theme, with most areas aimed
somewhere between the upper 40s-upper 50s for highs on most days
(10-15 degrees above normal). The only colder exception continues
to be Sunday, with only upper 30s-low 40s, but this is technically
right at-to-just-above normal. Some modest increases (generally
up to 3 degrees) were made to high temps on
Friday/Monday/Wednesday based on the latest trends, with values
for the other 3 days remaining very similar. As for overnight
lows, most nights are aimed mid- upper 20s (generally 5-10 degrees
above normal), with Sunday night the main slightly- colder
exception with low 20s more common.

Will conclude with some day-to-day specifics, particularly focused
on the shifting trends for for the weekend system...

Friday/Friday night:
This will be one of the "nicer" days of the long term, featuring
mostly sunny skies (although there likely be some degree of higher
clouds), warmer temps than today, and relatively manageable
breezes averaging sustained 10-15 MPH/gusts to around 20 MPH. High
temps raised around 3 degrees all areas, aimed from around 50 east
to mid-upper 50s far west/southwest. Near-critical fire weather
thresholds are in play mainly southwestern 1/3.

Saturday daytime-Sunday night (the weekend):
As discussed above, this time frame has changed the most (at least
precip-wise) from 24 hours ago. While 24 hours ago models were
depicting a progressive, positively tilted trough advancing fairly
quickly southeastward through the Central Plains, now much more
emphasis is being put on a southern jet stream branch disturbance
ejecting northeastward out of Mexico into the eastern Midwest/OH
Valley over the course of the weekend. This in turn significantly
slows the incoming northern stream trough approaching from the
northwest, and also weakens its overall punch. In the simplest
sense, this essentially "splits" precip potential around our CWA
to both the east/southeast and west-northwest (by at least a short
distance) thus leaving us mainly dry, with remarkably good
agreement on this per the latest ECMWF/GFS runs. However, please
refer to the caveats mentioned in the "precipitation overview"
section above, as at the very least some flurries or even sneaky
light freezing drizzle could show its hand around Sunday AM.
Confidence is overall-higher in temperature trends for the
weekend. Saturday still looks mild, despite the leading edges of
a cold front working in with time. By Sunday, the modestly colder
air is firmly in place, resulting in clearly the coldest day of
the next week, with highs only upper 30s-low 40s and a steady
north breeze (not overly-windy though it appears).

Monday:
It seems lately we have had similar weather conditions repeating
themselves every few days, and this continues here, as Monday
actually looks relatively pleasant and similar to Friday, with
temps rebounding 10-ish degrees from the prior day as westerly
breezes return in the wake of the departing weekend trough.

Tuesday-Wednesday:
Although these days look to remain seasonably-mild and dry with
broad ridging aloft the dominant feature, we start to see the very
beginning stages of our eventual pattern change to colder weather
as flow aloft starts to turn from northwesterly to more west-
southwesterly as a large-scale trough develops over the western
CONUS. Although subject to plenty of uncertainty at the Day 6-7
range, Tuesday currently looks to feature some of the lightest
winds of any upcoming day, while Wednesday appears to feature
breezy-to-windy south winds (by then it will have been at least a
few weeks since we`ve had a day with somewhat strong SOUTH winds,
as everything strong lately has been out of the northwest).

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Friday)
Issued at 523 AM CST Thu Dec 14 2017

VFR conditions are currently in place at the terminal areas, but
models continue to show the potential for MVFR ceilings later this
morning. Dayshift will have to monitor the timing, current TAF may
be too quick with its arrival. An upper level disturbance swinging
southeast through the region today will bring the potential for
precipitation, and have a VCSH mention going throughout the day.
With models show precip potentially being shower-like in nature,
pinning down exact timing/location is difficult. Winds will become
more northwesterly this morning, a few gusts around 20 MPH not out
of the question during the day. Precip exits to the southeast this
evening, VFR conditions look to return.

&&

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

$$

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


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