Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 111119
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
519 AM CST Mon Dec 11 2017

.SHORT TERM...(Today and tonight)
Issued at 408 AM CST Mon Dec 11 2017

Quiet conditions remain in place early this morning across the CWA,
with mostly clear skies currently for most locations. Aloft,
northwesterly flow remains in place, with satellite imagery showing
a well organized vort max sliding through the eastern Dakotas. This
disturbance is also pushing a sfc cold front through the region,
with the strongest winds near/north of the NE/SD border. The
westerly winds in place overnight and some mixing have allowed for
mild temps, which at 3 am range for most from the mid 30s to lower
40s.

Models are in good agreement showing this upper level disturbance
continuing on its south-southeastward track through today, with the
brunt of the forcing remaining northeast of the CWA. A few models
show the potential for a few sprinkles this afternoon across far
northeastern portions of the CWA this afternoon, otherwise the
forecast today/tonight remains dry.

Confidence in temperatures today is certainly not the highest.
Models show cooler air advecting in from the north behind the front,
but there is some notable differences in models/guidance (as much as
10 deg for some spots) with what high temps end up being today.
Forecast highs are a blend, mid 40s north to mid 50s south, and
expect that for most the highs will be near midday/early afternoon,
with steady/falling temps through the rest of the afternoon. As far
as dewpoints go, currently they range from the upper single digits
to mid teens. Expect them to increase through the day, though how
quickly that happens varies quite a bit between some
models/guidance. Current forecast is on the slower side, with
low/mid 20s by mid afternoon. Across far southern portions, which
will be warmer/drier longer into the day, this is resulting in fire
wx concerns. See FIRE WEATHER section below for additional
information.

Of more confidence with the passage of this front is the stronger
northwesterly winds expected to develop. Winds will become
stronger/more gusty from north to south, but by mid morning or so,
all locations should have the gusts picking up. Models showing the
strongest corridor of winds aloft to accompany the initial passage
of the front this morning, diminishing some before the better mixing
picks up midday/this afternoon. Current forecast has sustained winds
peaking between 30-35 MPH, gusts around 45 MPH. Speeds are expected
to diminish this evening/tonight.

.LONG TERM...(Tuesday daytime through Sunday)
Issued at 408 AM CST Mon Dec 11 2017

General overview of this 6-day period:
In short, our incredibly dry and overall-mild start to December
continues. Very little change was made versus the previous
forecast package. Although there may eventually be a few periods
that warrant at least a sprinkle/flurry mention as they get closer
(more details below), the official forecast remains completely
void of any measurable precip chances at this time. Temperature-
wise, while nothing will be as mild as Sunday just was, every one
of these 6 days still features above normal highs in the 40s/50s
(normal/average highs for mid-December in our coverage area (CWA)
are mid 30s to low 40s). As for potential weather hazards, the
main thing will be keeping a close eye on fire weather trends,
especially on breezy-to-windy days such as Wednesday. At this
point, Wednesday is the only afternoon that solidly meets near-
critical thresholds. Please refer to the separate FIRE WEATHER
section below for additional details.

Basic upper air/surface weather pattern:
The overall large-scale pattern remains largely unchanged through
these 6 days, as ridging remains prevalent to our west and
troughing to our east, which puts the Central Plains under
persistent northwesterly flow. This pattern is normally not
conducive to significant cold-season precipitation, and this
certainly remains the case. Nonetheless, there will be essentially
3 distinct disturbances/shortwave troughs passing through over the
course of these 6 days, a few of which could potentially generate
some spotty light precipitation, so the currently completely-dry
forecast may not hold either. In the lower levels/surface, days
will feature either predominantly westerly or northerly winds,
with north winds prevailing in the immediate wake of passing upper
waves but then trending more westerly again thereafter. As a
result, we are not looking to get "blasted" by any truly cold
airmasses.

A few precipitation details:
While the going dry forecast will certainly hold firm for the
majority of this time frame, there could be a few exceptions
lurking in there, associated with the aforementioned waves
occasionally passing through. Of all the primary models, the
latest ECMWF seems most aggressive with this light/quick hitting
rain and/or snow potential. The first opportunity for possibly
needing something added to future forecasts could be as soon as
Wednesday afternoon mainly in our far eastern zones, as a compact
wave dives in from the north. However, at least for now the
NAM/GFS show this being a dry frontal passage. Disturbance #2 then
arrives for Thursday, with the latest ECMWF again suggesting some
spotty light activity. The third wave that will need watched for
future small precip chances arrives during the Sat-Sat night time
frame. Once again though, none of these are "major storms" by any
stretch.

A few temperature details:
In short, 5 of these 6 days are expected to feature rather similar
high temperatures somewhere between the upper 40s-upper 50s. The
only cooler exception at this point is Thursday, with highs "only"
aimed into the low-mid 40s at this point, although breezy winds
will admittedly make it feel colder than this. Overnight lows on
most nights are aimed a few degrees either side of 30, with
Thursday night looking like the overall-coldest night with
prevalent low 20s. Even so, we need to keep in mind that normal
lows for mid-December are in the teens!

Windiest days potential:
Although days farther down the road could eventually ramp upward
in wind potential, at this point the overall windiest days appear
to be Wed-Thurs, following a one-day respite of relatively
lighter breezes on Tuesday. At least slight upward trending is
certainly possible, but at the very least expect Wednesday to
feature sustained northwest winds around 25 MPH/gusts around 35
MPH. Thursday will probably feature similar speeds, although the
official forecast does not quite reflect this yet.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Tuesday)
Issued at 514 AM CST Mon Dec 11 2017

Main concern for this TAF period continues to lie with winds.
Strong northwesterly winds will develop today behind a passing
cold front/increased mixing into stronger winds aloft. Guidance
shows the stronger gusts starting mid morning at both terminal
sites. Peak sustained winds near 30 MPH and gusts near 45 MPH will
be possible. Speeds are expected to diminish this
evening/overnight, remaining northwesterly. Otherwise, VFR
conditions are forecast through the period, though confidence is
lower in that for this afternoon. Stratus is expected to slide in
from the north, higher end MVFR ceilings are not out of the
question. Current forecast ceilings drop to 4k ft, day crew will
need to monitor that cloud cover as it slides south and adjust
afternoon ceilings if necessary.

&&

.FIRE WEATHER...
Issued at 408 AM CST Mon Dec 11 2017

Regarding TODAY`s fire weather situation:
Ahead of the main push of cooler air behind the cold frontal
passage, fire weather concerns remain in place across far southern
portions of the CWA. Models continue to show the potential for a
relatively small window ahead of those cooler temps where near-
critical to critical conditions could be met. Reaching the wind
criteria is not an issue. There is some uncertainty due to model
timing differences with just how far RH values will drop before
those cooler temps/increasing dewpoints really start kicking in.
Decided to go with a Red Flag Warning for our 3 southern most
counties. The change from the watch was adding in Mitchell County
and removing Phillips County. Based on the current forecast, these
3 were closest to hitting both RH/wind criteria. However...this is
based on a blend for forecast temperatures, and being on the lower
side of guidance for dewpoints. Day shift will have to keep a
close eye on things, if temps increase more than forecast/closer
to the warmer models/guidance and dewpoints are slower to rise, at
least near critical conditions may be met further north than
currently forecast...and possibly critical conditions. Confidence
in especially temperatures today isn`t high.

Regarding the Tuesday-Sunday time frame:
While there may eventually be a few other days that become fire
weather concerns as they get closer and the wind/RH forecasts are
refined, at least at this point, Wednesday is the main afternoon to
watch. As it currently stands, areas mainly south of a Cambridge-
Beloit line meet near-critical thresholds thanks to the combo of
northwest winds gusting around 30+ MPH and RH values as low as 20-25
percent. As a result, will be introducing near-critical fire weather
to our Hazardous Weather Outlook (HWOGID) for Wednesday.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...Red Flag Warning from 11 AM this morning to 5 PM CST this
     afternoon for KSZ017>019.

&&

$$

SHORT TERM...ADP
LONG TERM...Pfannkuch
AVIATION...ADP
FIRE WEATHER...ADP/Pfannkuch



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