Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 251200
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
700 AM CDT Tue Apr 25 2017

.UPDATE...
Issued at 700 AM CDT Tue Apr 25 2017

Based on short-term guidance such as from the LAMP/LAV and the
in-house CONSshort, shaved another couple of degrees off highs
across most of the CWA. As a result, the majority of the CWA is
unlikely to even reach 50 today, with especially far northern
zones no better than mid-40s.

&&

.SHORT TERM...(Today and tonight)
Issued at 449 AM CDT Tue Apr 25 2017

While many folks will gladly accept the relatively small amounts
of rain that are falling/will continue to fall during the next
12-24 hours, by far the biggest story of the short-term is the
sharply cooler temperatures, as we effectively take a step back
into "March" with highs a solid 25 TO 30 DEGREES COOLER versus
yesterday for most of our county warning area (CWA) (and as
covered in the Long Term below, this is just the first in a string
of several below-average days expected to last through at least
this weekend). Highs today were lowered generally 3-5 degrees
from previous forecast in most spots, and unfortunately perhaps
not enough.

Starting with a look at the current/recent weather scene as of
09Z/4AM:
So far, the night pretty much turning out anticipated, as pretty
much our entire domain is behind a fairly well-defined cold front
stretched from west-central KS into IA. Precipitation-wise,
isolated to scattered, mainly light showers and few embedded
thunderstorms developed mainly after midnight and are in the
process of spreading north at this time. In the big-picture of the
mid-upper levels, water vapor satellite along with short-term
model data depict a series of subtle/low amplitude disturbances
passing through our local area in west-southwest flow aloft, with
the primary mid-level vort max/closed low associated with the
parent trough currently spinning over northeast WY. Broad
isentropic lift/elevated moisture advection mainly in the 850-700
millibar layer has promoted the development/northward propagation
of the generally west-east oriented band of showers/few storms
currently advecting north across mainly our Neb zones. With
elevated instability fairly meager (generally only up to a few
hundred J/kg tops), lightning production has been fairly isolated,
but nonetheless there have been a few thunderstorms out there
overnight, thus supporting our slight chance/isolated thunder
wording. At the surface, pretty much the entire CWA is seeing
north-northeast breezes at least 10-15 MPH (locally higher) in the
wake of the aforementioned cold front, which extends northeast
from a decent 992 millibar low currently centered over the
intersection of KS with the OK/TX Panhandles. Now looking ahead
forecast-wise...

Today (generally 7AM-7PM):
Hopefully nobody is expecting a real "soaker" today, as it still
appears the more widespread/somewhat heavier precipitation
chances will not arrive until late this week/weekend, but
nonetheless parts of the CWA could end up seeing generally
0.10-0.40" of rain before precipitation largely ends late tonight,
with the higher amounts favoring counties north of Interstate 80.
In the mid-upper levels, persistent modest lift will continue
through the day as the mean trough makes very little eastward
progress, with the main vort max continuing to meander over the
eastern WY/SD region. While it is almost impossible to completely
rule out a brief shower/sprinkle at almost any given point today,
it certainly won`t be an all-day "washout", and in general the
highest rain chances should largely focus north of I-80, with much
of the southern half of the CWA probably looking at a mainly dry
day, although some models such as the 06Z NAM do suggest an
increase in shower activity across more of the area by late in the
afternoon, perhaps including the south as well. As for thunder
chances, will keep a slight chance/isolated mention going this
morning, but by this afternoon, although chances are probably not
truly zero, they seem low enough to not formally mention and this
is supported by SPC SREF thunder probs. Getting back to the number
one story of the day though, break out the jackets for sure. As
earlier mentioned, high temps were decreased generally 3-5 degrees
from previous forecast, now aiming for mid-40s north, upper
40s/near 50 central and perhaps near 60 extreme southeast. If
anything though, even these updated values could still be a
little optimistic. Skies should be cloudy/mostly cloudy, as
eventually a fairly widespread low stratus deck should overtake
the area. Adding to the chill will be steady north winds, which
if anything will probably pick up a little as the day wears on
with sustained speeds generally 15-20 MPH and gusts up to around
30 MPH.

This evening/overnight:
In the big picture of the mid-upper levels, we remain subject to
some forcing, as essentially two separate disturbances that
comprise the mean/larger scale trough continue over the Central
CONUS, with the main northern wave tracking through SD while a
southern wave swings out into the southern high plains/TX
Panhandle area over the course of the night. That being said, mid
level-saturation will gradually fade/decrease from west-east over
our area, taking measurable rain chances away with it despite what
will probably be quite a bit of lingering low level clouds. As a
result, will carry some decent "chance" PoPs mainly within the
eastern half of the CWA for the evening (while leaving at least a
sprinkle possibility west), and then post-midnight will leave only
fairly small chances going generally in our southeast 1/3, but
even this could be plenty generous a the vast majority of the CWA
should have a dry late night with better precip chances focusing
well to our northeast and also south. Probably cannot rule out a
rogue sprinkle or even flurry near our far north late in the
night, but this chance seems low enough to leave out. Otherwise,
it will be a seasonably-cold and breezy/windy night, as a fairly
tight pressure gradient continues behind a fairly strong surface
low pressure system developing/tracking into the upper Midwest
(roughly 993 millibars over the IA/WI border area by sunrise
Wednesday) and a high pressure building in from the northwest. The
net result will be continued north-northwest winds averaging 20-25
MPH/gusting around 30 MPH. Low temps were changed very little from
previous, calling for mid-30s most areas but with a small gradient
from colder northwest to warmer southeast. Obviously winds will be
far too strong to support frost formation, and we are not
expecting sub-freezing values either.

.LONG TERM...(Wednesday daytime through Monday)
Issued at 449 AM CDT Tue Apr 25 2017

A cool and occasionally unsettled weather pattern is shaping up to
impact the local area through the upcoming weekend. Expect
temperatures to run 5 to 15 degrees below normal each day, with
multiple chances for precipitation impacting the plains. Seasonably
mild weather is then expected to return to start the new work week.
While much of the local area could receive some beneficial rainfall
totals over the period, there will also be a chance for widespread
frost to start the day on Thursday.

Taking a closer look...to start the extended periods...expect a cool
and breezy start to the day on Wednesday as a fairly tight pressure
gradient will be in place...with the local area situated between an
area of high pressure to our northwest and the departing low
approaching the Great Lakes. With this system well to the east of
the local area to start the day Wednesday, decided to trim the
chances for precip across the forecast area through the afternoon
hours, limiting shower chances to areas primarily east of highway
281.

With clearing skies and  an area of surface high pressure settling
in from the north Wednesday night, expect an unseasonably cold night
across the local area. These cold temperatures...combined with light
winds...will be favorable for widespread frost formation Thursday
morning. Despite a relatively high confidence of the expected frost
event, felt it was prudent to wait a shift or two before considering
the frost advisory as tomorrow mornings temps are also forecast to
reach near frost criteria...albeit the strong winds should prevent
any actual frost formation.

After a cool and frosty start to the day on Thursday, expect the
next upper level wave in northwesterly flow to be crossing the
central Rockies. This wave is expect to round the base of the trough
and begin spreading a few showers across the local area Thursday
afternoon/evening. This system will likely impact the local area for
a couple of days...not organizing and lifting northeast until Sunday
afternoon or evening. In between, expect a decent chance for showers
across the local area...but with no instability to be found, did not
include the mention of thunder at this time. Despite this, much of
the local area should see some beneficial rainfall totals between
Thursday afternoon and Sunday morning, with a very small chance for
a little snow mixed in west of Highway 281 Sunday morning...as cold
air infiltrates in behind the departing system and precipitation is
winding down. Despite expanding the area of rain/snow mix across the
local are during the pre-dawn hours Sunday, no snowfall
accumulation is expected.

Thereafter...short wave ridging will move across the local area to
start the new work week, bringing back a bit of sunshine along with
seasonable temperatures across the region. This break will be short
lived...however...as model guidance brings another relatively cool
system from the northwest Tuesday evening through Wednesday.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Wednesday morning)
Issued at 700 AM CDT Tue Apr 25 2017

General overview:
The majority of the period should feature low-end MVFR/perhaps IFR
ceiling. There is a decent chance for periods of showers today,
with perhaps a rumble of thunder yet this morning. A little
drizzle cannot be ruled out either, but seems less likely. Surface
winds will remain/become breezy from a northerly direction. Now
for some more element-specific detail:

Ceiling/visibility:
Although we are starting off VFR for at least another hour or two,
models/guidance are quite insistent that at least a low-end MVFR
ceiling will soon settle in and likely persist through the
remainder of the period. Ceiling could very well slip into IFR
range at times too, but opted to maintain low-end MVFR as the
lowest official mention for now. Maintained prevailing VFR
visibility as well, but at least brief periods of MVFR-or-lower
cannot be ruled out under passing showers and/or if any light
drizzle materializes.

Precipitation:
Have continued a generic "vicinity shower" (VCSH) mention through
00Z to cover the possibility of passing showers. A rogue rumble of
thunder cannot be ruled out for another few hours, but unlikely
beyond that. While the chance of precipitation beyond 00Z is not
zero, felt chances were low enough during the evening and
especially late tonight to omit a formal mention for now.

Surface winds:
Generally speaking, a gradual increase in speeds will occur over
the course of the period, as direction shifts slightly from
north-northeast early this morning, to more true northerly for
the majority of the period. Sustained speeds are starting out in
the 10-15kt range, but by later in the period will be closer to
20kt with gusts 25+kt lasting through the night.

&&

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

$$

UPDATE...Pfannkuch
SHORT TERM...Pfannkuch
LONG TERM...Rossi
AVIATION...Pfannkuch


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