Area Forecast Discussion
Issued by NWS Hastings, NE

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128
FXUS63 KGID 090952
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
352 AM CST Sat Dec 9 2017

.SHORT TERM...(Today and tonight)
Issued at 352 AM CST Sat Dec 9 2017

Overall, the forecast through these next 24 hours seems fairly
straightforward, featuring plenty of sun, lighter winds than
yesterday (albeit still a bit breezy) and temperature-wise a
"stepping stone" upward between yesterday`s still-coolish readings
and tomorrow`s very mild expectations (as discussed in the Long
Term section below). About the only two possible
challenges/relatively minor concerns are: 1) A handful of of our
far west-central/southwest counties are now highlighted for "near-
critical" fire weather conditions this afternoon in our latest
Hazardous Weather Outlook (HWOGID)...2) Could a deck of lower
clouds sneak into far east/northeast zones this morning and linger
part of the day?.

Taking a look at the current/recent weather scene as of 09Z/3AM:
The night overall playing out much as expected. Unlike 24 hours
ago, skies are mostly clear to clear, with only a smattering of
mid-high level clouds. In the big picture of the mid-upper levels,
water vapor satellite and short term model data reveal a similar
pattern to 24 hours ago with our region under sharp north-
northwest flow, directed between an expansive/highly amplified
ridge along the West Coast and a large-scale trough dominating the
eastern third of the CONUS. The main difference since last night
is that the upper jet core has shifted a few hundred miles east of
us instead of being directly overhead, which also signifies
modest height rises over the past 24 hours. At the surface, early
morning breezes are averaging 5-15 MPH from the northwest, within
a modest pressure gradient set up on the backside of a roughly
1006 millibar low pressure center over southern Lake Michigan.
Temp-wise, although we should still see a small drop-off toward
sunrise as breezes ease up a touch, we are still expecting lows to
end up a solid 10-ish degrees above average for the date, with
most places bottoming out upper 20s to around 30.

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

Today:
As already touched on in the opener above, most folks should find
this to me a pretty decent December day with plenty of sun,
manageable breezes and high temps at least 5-10 degrees above Dec.
9th norms (warmer than yesterday but not as mild as tomorrow). In
the mid-upper levels, northerly flow remains in place, but small
height rises continue as the western ridge edges eastward and the
eastern trough edges farther away. At the surface, generally
northwest winds will remain in place, with sustained speeds most
of the day averaging 10-15 MPH/gusting to around 20 MPH. Cloud-
wise, have high confidence in mostly sunny to sunny conditions in
most areas with only very limited high clouds. The only possible
exception could be in a few of our far east-northeast counties
mainly along the Highway 81 corridor, where a few models are more
aggressive than others in trying to bring a few hours of lower
stratus clouds into our domain mainly between sunrise and noon
(the west edge of this stratus is currently evident in
satellite/obs still well to our north over eastern SD). Have not
fully bought into this scenario, but did at least hedge some
"partly cloudy" sky cover percentages into this area in case it
occurs. Most realistically though, any possible lower stratus
should mainly remain just outside of our coverage area (CWA) into
eastern Nebraska. Temperature-wise, after aiming a touch too cool
for highs yesterday, and given a continued eastward advection of
warmer air into our area from the west, opted to bump today`s
highs up 1-2 degrees from our previous forecast. This still
results in a respectable gradient, ranging from near 40 in our far
northeast (Polk County area), to the upper 40s central (Tri
Cities) and mid-50s far west-southwest (counties such as
Furnas/Rooks). Unfortunately for fire weather concerns, roughly 5
of our far west-central/southwest counties now appear poised for a
few hours of "near-critical" fire weather conditions this
afternoon, due to the combo of wind gusts around 20 MPH and
relative humidity falling into the 20-25 percent range. Overall
though, this is a pretty marginal fire weather threat, especially
wind-wise, and certainly we appear "safe" from outright-critical
conditions that would necessitate Warning issuance.

This evening/tonight:
Not a whole lot to say here, as really it`s a pretty "quiet" and
guaranteed-dry night. Skies should average mostly clear with only
limited amounts of passing high clouds, and unlike these past two
nights, no risk of pesky low stratus clouds heading in from the
north. At the surface, a subtle trough axis will pass through
during the night, with it`s only real effect being a modest uptick
in winds, with breezes around sunset only averaging around 5 MPH
from the west, but picking up to more 10-15 MPH from the northwest
later in the night (pretty similar to the current night/morning).
These steady late-night breezes should again keep low temps above
average, and similar to perhaps a few ticks warmer than this
morning. Officially have lows aimed into the 26-29 range most
areas, but would not be surprised if several places drop no lower
than 30.

.LONG TERM...(Sunday daytime through Friday)
Issued at 352 AM CST Sat Dec 9 2017

At the start of the period, Sunday morning, models remain in good
agreement showing well amplified upper level northwesterly flow in
place across the Plains, between high pressure centered over the
OR/CA/NV border area and troughing along the East Coast. No changes
to the dry forecast. At the surface, there continues to be little
overall change, with west-northwesterly winds in place through the
day. Models still showing an area of stronger winds aloft moving
through, mainly during the first half of the day, which may be
tapped into some as mixing potential increases into the afternoon.
Sunday is still forecast to be the warmest day of the forecast
period, with 850mb temps shown to increase by 5-10C between this
afternoon and Sun afternoon. Between that and the downsloping winds,
high temperatures look to climb well into the 50s to lower 60s.
There is still some concern about fire wx, as afternoon RH values
fall into the mid teens to mid 20s. Decided to insert a mention of
near critical conditions in the HWO. Though overall wind trends
should be heading down through the afternoon, can`t rule out at
least some gusts near 20 MPH lingering around longer into the day.

Sunday night and into Monday morning, models continue to show an
upper level shortwave disturbance sliding southeast out of central
Canada, through MN toward the Midwest. While this disturbance wont`t
be bringing any precipitation to the CWA, it will be pushing a
surface cold front through. Cooler air will be advecting in from the
north through the day, and northwest wind will be on increase.
Forecast soundings show better mixing potential into stronger winds
aloft, and sustained speeds of 20-30 MPH are forecast. Gusts near 45
MPH are also not out of the question. Though cooler than Sunday,
Monday`s highs are still above normal (which is upper 30s/lower
40s), with mid 40s north to mid 50s south. Fire wx will again be a
concern, mainly across the SSW third of the CWA, and mention remains
in the HWO.

The forecast through the end of the work week remains dry.
Northwesterly flow remains in place aloft, will have to keep an eye
on a shortwave disturbance moving through during the Thursday-ish
timeframe (models vary on timing), perhaps the NNE portions of the
CWA could get clipped by some very light precip. Temperatures are
forecast to be above normal through Friday, with 40s/50s for
highs.

&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Saturday)
Issued at 1204 AM CST Sat Dec 9 2017

General overview:
Confidence is very high in VFR visibility and precip-free weather,
and is high in VFR ceiling, with only the slightest concern for
MVFR at KGRI. Really, the main aviation issue will be two rounds
of low level wind shear (LLWS), one early this morning and another
late in the period Saturday night. Read on for more element-
specific details...

Winds (including LLWS):
Surface winds will actually be relatively light throughout, with
sustained speeds prevailing at-or-below 12kt from the west-
northwest the majority of the time, and any slightly higher gusts
mainly occurring Saturday afternoon. The bigger issue will be
LLWS, and have continued/introduced two rounds: 1) Have extended
the previously-advertised mention for early this morning through
12Z, as even though it`s fairly marginal, winds increasing to
around 40kt within the lowest 1,500 ft. could create up to around
30kt of shear magnitude between the surface and this level...2)
Very late in the period another, likely stronger round will
commence with winds in roughly the lowest 1,000 ft. increasing to
around 40kt, again setting up 30+kt of shear magnitude.

Ceiling:
Although would be very surprised to see it reach as far southwest
as KGRI, it`s worth noting that some models are bringing an MVFR
ceiling within 60-80 miles northeast of there during the 12-18Z
time frame. While this obviously bears watching, confidence is
currently so low in this affecting KGRI that it will not even be
"hinted" at with a scattered low cloud mention.

&&

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

$$

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



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