Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 261149
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
649 AM CDT Wed Apr 26 2017

.UPDATE...
Issued at 648 AM CDT Wed Apr 26 2017

With both diminished near-radar returns and also a small increase
in cloud ceilings serving as evidence, any pesky light drizzle
from the overnight hours has apparently ended, and am not
expecting it to return. As a result, the official forecast through
sunrise tomorrow is precipitation-free CWA-wide.

&&

.SHORT TERM...(Today and tonight)
Issued at 457 AM CDT Wed Apr 26 2017

With little if any potential for precipitation through the
period, the number one story involves a respectable chance for at
least patchy frost formation and/or slightly sub-freezing
temperatures across various parts of our county warning/coverage
area (CWA) late tonight into Thursday morning. While not a "slam
dunk" for frost formation everywhere due mainly to some
uncertainties regarding cloud cover, felt it was prudent to play
it safe and issue a CWA- wide Frost Advisory on this shift to
raise awareness another level. Otherwise, the other main challenge
involves a tricky cloud cover forecast, with some models
noticeably quicker than others in eroding the low stratus deck
today from west to east, which will obviously have an implication
on temperatures as well. Overall though, today offers the best
hope of the next several days for at least parts of the CWA to see
appreciable sunshine.

Taking a look at the current/recent weather scene as of 09Z/4AM:
Overall the late night largely playing out as anticipated here 24
hours ago, as the entire CWA remains socked in under a widespread
low stratus deck, and seeing chilly northwest winds sustained
generally 15-20 MPH/gusting up to around 30 MPH. With lows
ultimately expected to bottom out in the 33-37 range most areas,
we can legitimately say there is a wind chill factor this morning
with most folks heading out the door greeted by chills in the low-
mid 20s. Some models ending up being grossly overdone with rain
development Tuesday evening as there was hardly any at all, but
then overnight there has been at least one small surprise, as
both radar and occasional ground-truth observations (including
right here at the WFO) has indicated the presence of at least
patchy drizzle across various parts of the area (not really sure
why this drizzle waited until late in the night to kick in, as the
low cloud deck has been in place since yesterday?). Turning to
the big picture of the mid-upper levels, water vapor satellite
and short term analysis depicts a large-scale, slow-moving trough
axis crossing the central CONUS. For the most part though, our
local area is split in the middle between the primary mid level
waves/vort maxes, with one currently centered over the Dakotas and
helping force widespread precip especially over MN, and another
wave farther south currently swinging out of NM into the TX
Panhandle, and helping drive widespread convection across parts of
OK/MO/AR. Here in the "middle" between these main waves, we are
left void of mid level saturation but stuck with the low clouds
and (for some) light drizzle. On the surface weather map, our
gusty northwest winds are being driven by a decent pressure
gradient between a 996 millibar low near the IA/WI border area,
and high pressure building in from the northwest.

Now looking ahead forecast-wise through these next 24 hours or
so...

Today:
Getting into the daytime hours, again the biggest
challenge is determining how aggressively low clouds clear (or how
stubbornly they linger), and the resulting impact on high temps.
On the most optimistic side of things are models such as the NAM,
which steadily vacates low clouds from west-to east and actually
has all but the far northeast CWA clear by early afternoon. On the
flip- side, often more-reliable very short term models such as
the RAP/HRRR are at least a few hours slower with west-to-east
clearing potential, and suggest that as much as the east-northeast
half or so of the CWA could remain relatively "socked in" even
still by late afternoon. Admittedly just do not have a great feel
for this, so the official forecast plays somewhat of a middle
ground, but if anything leans more optimistic for all areas seeing
at least a few hours of sun (especially west), with eastern areas
perhaps not seeing much until pretty late in the day. It makes
sense that a good chunk of the area should see at least "some" sun
with the large-scale trough axis passing east of our CWA with
time. Temp-wise, obviously cloud trends could easily result in 5+
degree errors, but will aim for a modest little gradient from
near-50 far north/northeast to upper 50s far southeast. However,
if the cloudier solutions end up verifying then more of our
north/east would see upper 40s at best. Even for those areas that
see sun, northwest breezes will continue to put a chill in the
air, although the strongest speeds with gusts to around 30 MPH
will occur this morning, before a slow/gradual decrease in speeds
takes place this afternoon as the pressure gradient eases up, with
late afternoon gusts easing down closer to 20 MPH.

This evening/tonight:
The main focus remains on frost/freeze potential, but the CWA-wide
Frost Advisory valid late tonight into early Thursday morning is
not a "slam dunk" to verify all areas mainly given some cloud
cover uncertainties. In the mid-upper levels, forcing remains
fairly minimal as we see a brief break in between larger-scale
waves. Kept the forecast dry despite a few models hinting at a few
rogue sprinkles flirting with our far west late. However, this
break in forcing is small enough in time/space that the odds of
having "crystal clear" skies all night (most favorable for
widespread frost formation) is not high everywhere either. For
one thing, if the low stratus from today is stubborn to vacate our
northern/eastern counties by sunset, it`s not out of the question
that it could try to linger into the night. Meanwhile, while much
of the central/especially west should start out the night
clear/mostly clear, a gradual invasion of at least "some" mid-
high clouds from the west will likely occur as the night wears on.
On the positive side for efficient cooling/frost formation, a
surface high pressure ridge will result in northerly breezes
markedly decreasing post-sunset and especially post-midnight, with
generally light/variable breezes most areas late in the night.
All things considered, and with at least part of the night likely
to feature some decent clearing, did not stray too far from the
latest guidance and our previous forecast on low temps, with most
areas dropping into the 30-35 range, and far northern areas most
favored to perhaps see upper 20s. Some folks in these colder
forecasted areas may wonder why we`ve opted for a Frost Advisory
versus a Freeze Warning, and the short answer is that we tend to
reserve formal Freeze Warnings for widespread "hard freezes" where
places are expected to drop below 28 degrees for several hours,
and tonight is not looking like one of these setups. In summary
and in closing, despite the possible caveats for realizing full
cooling and frost potential tonight, there was enough concern to
collaborate with neighboring offices and pull the trigger on the
Frost Advisory given that at least parts of the CWA will likely
see some.

.LONG TERM...(Thursday daytime through Tuesday)
Issued at 356 AM CDT Wed Apr 26 2017

At the start of the long term period Thursday morning, models are in
pretty good agreement showing zonal to low amplitude northwesterly
flow in place in the upper levels, thanks to low pressure spinning
over northern MN and another disturbance moving out of the Rockies.
Expecting a frosty start to the day, as a surface ridge axis and
light winds look to be in place. Through the daytime hours, the
first of a couple of system to affect the area will be moving in
from the west, increasing precipitation chances. The better chances
are expected to move in during the afternoon hours, and with it
being a slower mover, chances are lingering all the way into Friday.
Models aren`t in too bad of agreement, showing the main mid level
frontogenetical band sliding from SSW to NNE, with just some minor
timing differences. Through ~12Z Friday, the better chances look to
be roughly along/south of a LXN/HJH line, moving north of that line
after 12Z Friday. Through the afternoon/evening hours on Friday,
that northward shifting precipitation looks to also be waning. Hard
to say at this point how much of a lull (and the areal coverage of
it) there may be, but the CWA will be sitting between the departing
disturbances phasing in with low pressure over Ontario and deepening
low pressure over portions of CO/NM. No notable change to the well
below normal highs expected both Thur/Fri. Normal is roughly mid
60s, forecast highs for Thur are in the lower/mid 50s, with Fri in
the upper 40s to lower 50s. Precipitation type looks to be a cold
rain, the colder temps that would support a mix of snow are expected
to remain west of the CWA, and instability/thunder chances remain
south.

Looking to the upcoming weekend (late Fri night through Sun
evening), focus remains on the above mentioned deepening upper level
low pressure system off to our WSW. At 12Z Saturday, models are in
pretty good agreement showing the upper low located over the western
CO/NM border. While larger scale lift is on the increase, at least
through 12Z Saturday, there are questions with just how far north
into the CWA any precipitation is reaching. Latest runs showing
lower chances north of the NE/KS state line. That question continues
through the daytime hours Saturday, as the main low has only shifted
closer to the OK/TX panhandle area. There is more notable
differences between models with the areal coverage, the ECMWF/GEM
are on the more liberal side with their QPF, the GFS struggles to
get to I-80. Model difference start spreading more Sat night into
Sun, a little with timing but more so with the path of the upper
low. At 12Z Sun, the ECMWF/GEM have the low centered roughly over
western portions of our CWA, the GFS is further south, along the
central KS/OK border. While both tracks bring good precip chances to
the CWA, the GFS is showing a greater impact over the eastern half
of the CWA and exiting out of the area quicker. The others affect
more of the area and are on the slower side.

Saturday morning and more so Sunday morning, colder air working in
with the system will bring the potential for at least a RA/SN mix
(if not a total switch over to SN). Saturday morning, this potential
is at this point confined to far northwestern portions of the area.
Sat night/Sun morning, at least a portion of every county in our CWA
has at least a RA/SN mix mention in the the forecast. Far western
portions may see a switch over to all snow for a period of time.
Daytime highs are forecast to reach into the 40s, but confidence in
forecast temps aren`t high with the potential for ongoing precip
during the day. Too early at this point to get too caught up in
accumulations, etc...plenty of model details yet to be worked out.
It`s something to keep an eye on, as winds may also play a
factor. Sustained speeds of 15-25 MPH will be possible.

This system is expected to depart Sunday night, exact timing yet to
be determined. While much of the area is currently forecast to be
dry, confidence isn`t high, as models showing another disturbance
quick on the heels of the last. The pattern remains unsettled for
the first half of the work week, though a more mild air mass also
looks to build back in behind the weekend low, bringing highs back
into the 50s/60s.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Thursday morning)
Issued at 648 AM CDT Wed Apr 26 2017

General overview:
MVFR ceilings will remain firmly in place for at least a
few/several more hours before lifting/dissipating to VFR levels.
Winds will remain quite breezy from the north-northwest through
today before easing up markedly this evening. Now some more
element-specific details for those interested:

Ceiling:
While confidence is pretty high that at least these first few
hours should remain dominated by MVFR, as usual there are some
question marks regarding exactly when ceilings will lift to VFR
and/or scatter out, with some guidance suggesting as early as
around 15Z at KEAR and others stubbornly holding on to MVFR at
least into early afternoon. So, as a middle ground best-guess have
continued aiming for an outright-return to VFR arriving at KEAR
by 17Z and KGRI by 19Z. Again though, could easily see this
varying an hour or two either side of this. The latter half of the
period tonight contains fairly high confidence in minimal/VFR
clouds.

Surface winds:
Breezy north-northwest winds with sustained speeds generally
15-20kt and gusts 20-25kt will hold firm through late afternoon
before markedly decreasing to around 10kt this evening and around
5kt or less late tonight.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Frost Advisory from midnight tonight to 9 AM CDT Thursday for
     NEZ039>041-046>049-060>064-072>077-082>087.

KS...Frost Advisory from midnight tonight to 9 AM CDT Thursday for
     KSZ005>007-017>019.

&&

$$

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


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