Area Forecast Discussion
Issued by NWS Hastings, NE

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376
FXUS63 KGID 171719
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1219 PM CDT Tue Apr 17 2018

.UPDATE...
Issued at 1216 PM CDT Tue Apr 17 2018

Decided to upgrade the watch to a High Wind Warning for tonight.
The winds will be strong from the northwest at least for a while
behind the front.

&&

.SHORT TERM...(Today and tonight)
Issued at 408 AM CDT Tue Apr 17 2018

Plenty of cirrus streaming in from the southwest this morning
ahead of the next disturbance forecast to cross the Rockies late
in the day...bringing the chance for some precipitation this
evening and overnight. While there will be variable cloud cover
crossing the area through the afternoon hours...with a high
pressure ridge transitioning aloft and the thicker clouds not
anticipated until this evening...decided to increase high
temperatures a couple of degrees in most spots as any remaining
snow cover should melt and cold air advection should hold off
until well after sunset.

As we encroach on the late afternoon hours...expect modest
instability to begin to build across the local area...albeit the
focus of this instability is now east of the local area. Despite
this...the local area remains in an area of general thunder from
the storm prediction center...and for consistency sake...decided
to maintain the mention of a few thunderstorms this evening. Given
the near zero instability...severe weather is not likely...and
some very small hail at best may be realized if a few small storms
are even able to develop. Then as the main front crosses the area
late in the evening...any chance for thunderstorms will
correspondingly diminish...and we should see a few light rain or
snow showers develop in the wake of the main front. While overall
precipitation chances appeared better in yesterdays model
runs...models are continuing to generate some light qpf primarily
north of interstate 80...and a light dusting of snow could even be
seen across our far north towards early Wednesday morning with
this quick passing system.

While there is a chance for some light precip...the bigger story
will be winds and how strong they will get. Given the fact we have
had numerous high wind events with frontal passages this
winter...inherited a high wind watch for tonight...but confidence
in high wind criteria actually being met is very low...and tried
to tone down wording in the previous watch to reflect this. That
said it should be breezy overnight...but with an inversion keeping
the stronger winds aloft...think the better chance for strong
winds will actually lie during the daytime hours Wednesday. So for
the time being...kept the high wind watch going...but would not be
surprised if the day shift will need to eventually remove this
and only include some wording of strong winds in the HWO instead.

.LONG TERM...(Wednesday through Monday)
Issued at 408 AM CDT Tue Apr 17 2018

General overview of this 6-day period: Switching over to the long
term desk for the first time on this string, and despite limited
personal familiarity with these periods, it`s already clear that
there are three main stories to key on...in roughly chronological
order:

1) Wednesday is clearly the downright-windiest day of the forecast
package, with sustained speeds commonly 25-35 MPH/gusts up to around
45 MPH, before steadily diminishing by late afternoon/early evening.
Back in the day when we still issued Wind Advisories, this would be
a likely candidate, but for now we have at least introduced the
mention to the Hazardous Weather Outlook (HWOGID).
Not surprisingly given the strong winds, fire weather also looks to
be at least a "near-critical" issue in our southern
counties...please see separate Fire Weather section below for more
on this.

2) The "big" low pressure system that we`eve been eyeing for several
days now during the Friday-Saturday time frame continues a trend of
looking like less and less of a "big deal"/soaker for most areas,
mainly because its track continues trending/edging farther south. Of
course, this is both a good news/bad news trend.
Obviously on the good side, those with outdoor plans Fri-Sat may not
be dodging as much rain as previously thought (and Sunday still
looks dry). Taking a different perspective, this system had/to some
extent still has the potential to be a needed rain- maker for
especially our driest southern zones, and this southward/weaker
trend is not good in that regard. Of course, this system is still 3-
4 days out and subject to some change, but as it currently stands,
total rainfall/QPF now looks to GENERALLY only range from 0.25-0.50"
in most Nebraska zones, and 0.50-1.00" in KS zones. So, the
potential is still there for some beneficial rain especially in our
south, but perhaps not as much as it had previously looked. Also of
note, notice this paragraph has completely avoided a mention of
snow. Quite simply, that is because that other than maybe a few
rogue flakes here or there during the late night/early morning
hours, a LOT would have to change between now and Fri-Sat for this
accumulating snow to suddenly become a valid concern.

3) Temperature-wise: Although every one of these 6 days currently
features at least slightly below normal high temperatures, if
anything, highs have trended up a few degrees from the previous
forecast (especially Fri-Sun). Generally speaking, highs on most
days are aimed somewhere into the 50s-low 60s, so below normal yes,
but not nearly as cold as recently endured. Overnight lows follow a
similar trend, with most nights expected to hold up well into the
30s, and only Wednesday night looking like a widespread "minor"
freeze with upper 20s-low 30s. Given our incredibly cold start to
the month, we continue to deem it too early/soon to issue formal
Frost/Freeze headlines, but if we do in fact start putting together
a decent string of above-freezing nights as it appears we are
heading toward, then these types of headlines could become more
necessary necessarily by the last week of April and beyond.

With the big-picture message covered, will finish with some limited
day-to-day specifics...

Wednesday/Wed night: See #1 above. The biggest story Wednesday will
be rather strong northwest winds (albeit not as strong as this past
weekend), with sustained speeds commonly 25-35 MPH/gusts to around
45 MPH. These winds will be driven by an enhanced pressure
gradient/mixing on the backside of the departing Tuesday night
system. Precip-wise, the vast majority of anything that falls Tues
night should be gone by sunrise, but did linger a very small
chance/PoP for mainly flurries/very light snow in far northeast
zones in the morning.
Sky cover will likely exhibit a cloudier northeast-sunnier southwest
disparity. Temp-wise, highs actually trended down 2-3 degrees, now
ranging from upper 40s far north, low 50s central to low-mid 60s far
south/southwest. Wed night, high pressure builds in from the north
and winds steadily diminish, likely setting the stage for the
overall-coldest night of the next several, but even so barely below
freezing most areas.

Thursday/Thurs night: In many ways, especially regarding the surface
weather pattern, Thursday strongly resembles yesterday (Monday).
Under shortwave ridging aloft, departing surface high pressure will
promote east-southeast breezes generally 5-15 MPH. High temps
similar to previous forecast, mainly mid-upper 50s with some low 60s
south.
While the vast majority of these 24 hours should stay dry, some very
small PoPs enter western zones after midnight in case some spotty,
mainly rain shower activity develops.

Friday daytime-Saturday night: See #2 above for the broad
expectations/recent southern-shift/lower rain amount potential etc.
In short, while both the ECMWF/GFS show a similar, fairly potent
closed mid level low tracking east out of the southern Rockies and
into the Plains, the latest ECMWF is even farther south, tracking
the center of the system along the OK/TX border. The GFS is farther
north closer to the KS/OK border with the main track. Although it is
wetter for our CWA than the ECMWF, it still results in lower
PoPs/rain amount potential than previous forecasts, especially in
Nebraska zones.
Very generally, the overall-highest rain chances for our CWA seem to
be favoring the Friday evening-Saturday morning time frame more than
anything. Likely as a partial response to lower chances for
widespread rain, high temps have trended upward generally 2-4
degrees for these days as well.

Sunday daytime-Monday: At least for now, these two days continue
looking dry behind the aforementioned low pressure system departing
into the southeast CONUS, with slightly below to near-normal high
temps in the upper 50s-low 60s.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Wednesday)
Issued at 1216 PM CDT Tue Apr 17 2018

Main story for the period will be a front that moves through the
terminals during the night and strong north winds that pick up
behind the front. The winds will continue into the daytime on
Wednesday.

&&

.FIRE WEATHER...
Issued at 408 AM CDT Tue Apr 17 2018

Regarding "very near"-critical conditions likely in our south on
WEDNESDAY afternoon:

Of all days during the next week, Wednesday is clearly our primary
day with at least near-critical fire concerns. Winds are a "slam
dunk", with the afternoon featuring northwesterly sustained speeds
generally 25-35 MPH and gusting up to around 45 MPH. There is,
however, a small "saving grace" in that speeds should be on a slow
downward trend as the afternoon wears on. Nonetheless, marginal
relative humidity (RH) appears to be the only thing preventing this
from being an outright-critical setup, as even in our far south,
minimum RH is currently forecasted to drop no lower than 22-25
percent. So, all things considered, the overall message at this
point is that near-critical conditions will be found mainly south of
a line from Cambridge-Smith Center-Beloit. North of this line, fire
danger will obviously not be "zero" given the winds, but RH values
above 25 percent do not meet near- critical thresholds.

A review of our local fire weather criteria: "Critical" means the 3+
hour overlap of relative humidity (RH) of 20-percent-or-lower and
sustained winds/gusts of 20+MPH/25+MPH (in the presence of
sufficiently-dry vegetation/fuels). "Near- critical" means the
overlap of 25-percent-or-lower RH and sustained winds/gusts of
15+MPH/20+MPH.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...High Wind Warning from 7 PM this evening to 6 AM CDT Wednesday
     for NEZ082-083.

KS...High Wind Warning from 7 PM this evening to 6 AM CDT Wednesday
     for KSZ005-006-017-018.

&&

$$

UPDATE...JCB
SHORT TERM...Rossi
LONG TERM...Pfannkuch
AVIATION...JCB
FIRE WEATHER...Pfannkuch



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