Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 181730
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1230 PM CDT Sat Mar 18 2017

.UPDATE...
Issued at 1230 PM CDT Sat Mar 18 2017

Dwpts have plummeted into the low-mid teens along and E of Hwy
281. Amazing how localized this pocket of very dry are is. Used
the RAP model to lower fcst dwpts and get a better handle on this.


&&

.SHORT TERM...(This evening through Sunday)
Issued at 1230 PM CDT Sat Mar 18 2017

This serves as a first draft discussing map features.

Aloft: WV imagery showed a building ridge over Wrn N America with
a trof over the E Pac. Part of the trof will move onshore across
the Pac NW and into SW Canada. This will progressively nudge the
ridge E over the Plns this eve. As this ridge passes...zonal flow
will develop tomorrow.

Surface: High pres extended from cntrl Can down to KS/MO and was
departing drifting E. The weak cool front that moved thru Thu
night was stalled against the leeside of the Rockies and then
turned E into OK/AR. A cool front has moved onshore into the Pac
NW today. Cyclogenesis was occurring over AB. The Pac front will
cont pressing E/SE thru the Wrn USA while the low heads NE into
cntrl Canada. As this occurs...the front will dislodge from the
Rockies and lift E and N as a warm front. This front will pass
move into and cross the fcst area (FA) tomorrow. Meanwhile...the
Nrn portion of the Pac cool front will be racing E and will drop
into the Sandhills/Panhandle in the afternoon...poised just N and
W of the fcst area at 00Z/Mon.

Much more later this afternoon...


.LONG TERM...(Sunday daytime through Friday)
Issued at 502 AM CDT Sat Mar 18 2017

General overview of this 6-day period:
Overall, no major changes of note from the previous forecast
package. That means that in a very basic sense, the main stories
include a very warm Sunday, a few rather "pesky" chances for rain
(and perhaps a few wet snowflakes north) mainly Monday night into
Tuesday and again Tuesday night into Wednesday, followed by the
"bigger system" we have been talking about that could feature
several rounds of rain and even a few thunderstorms during the
Wednesday night through Friday time frame. Will now cover these
various things (and a few others) in a bit more detail:

1) The "big system" Wednesday night-Friday:
This remains the big "highlight" of the entire long-term forecast,
especially for those folks (probably most) who want a decent rain.
Along these lines, while it will obviously not rain these entire
48 hours or so, there are enough differences in model
timing/discrepancies that precipitation chances (PoPs) are present
throughout Wednesday night-Friday. The potential is certainly
there for some areas to pick up a half-inch or more, but given
that there are a TON of uncertainties in the details at this Day
5-7 range, we certainly cannot "guarantee" that our entire
coverage area (CWA) sees this much. Speaking of forecast uncertainty,
if anything, the latest 00z runs of primary models such as the
GFS/ECMWF/Canadian seem to be exhibiting more differences
(especially for Wednesday-Thursday) than they were 24 hours ago
regarding the position of key features such as the main mid level
low, surface low and associated fronts, but then by Friday (Day 7)
these models tend to come into overall-better agreement. Of all
things that might not necessarily "agree" the best between the
latest raw model output and our latest official forecast, it`s
that while we are currently advertising our very highest PoPs (as
high as 60-70 percent) on Thursday, it may ultimately end up being
the case that the highest PoPs need to be delayed more-so Friday
into Friday night. As for thunderstorm chances, depending on the
model, essentially the entire Wednesay night-Friday time frame
could justify at least a slight mention of storms, but for now
have confined any thunder mention to just Thursday into Thursday
night given these periods have the overall-highest confidence in
sufficient instability. As mentioned here 24 hours ago, this
system appears to have enough instability/shear to yield our
first strong to perhaps even severe storms of 2017, but it`s still
far, far too soon to talk specific threats/details. For that
matter, at this point it`s even hard to tell whether Thursday or
Friday (or perhaps even both days) would be most favored for some
stronger storms.

2) The earlier-week precip chances Monday night-Wednesday:
Obviously before we get to the bigger late-week system we first
need to try pinning down the details of the seemingly lighter
precipitation potential here. While amounts don`t look to be
substantial by any means, at least minor accumulations of rain and
perhaps a few wet snowflakes are quite possible in parts of the
area. At least for now, have kept PoPs below "likely" percentages,
however. While rain should be the dominant precipitation type,
compared to 24 hours ago, things do look a bit more favorable for
at least a dusting of wet snow especially for some places north of
Interstate 80 and especially late Monday night into Tuesday
morning, but perhaps Tuesday night into Wednesday morning as well.

3) Temperature trends:
No major changes from previous forecast here, as Sunday is still
by far the warmest day with widespread 70s/80s before a decent
cool-down to more seasonable values in the 50s/60s arrives Monday
and especially Tuesday Wednesday, which if anything could be
trending a bit cooler than before. Technically, we then show
another modest warm-up for Thursday-Friday as, but there is
plenty of uncertainty here given the timing of the incoming system
and the coverage of widespread clouds/precipitation or lack
thereof on either day. Getting back to Sunday, while still by far
expected to be the warmest day of the long term period,
confidence has diminished a bit versus 24 hours ago that our
ENTIRE area will reach 80+ degrees (especially near/east of the
Tri Cities), as there are some possible mitigating factors here.

4) Fire weather concerns:
Fortunately, barring some pretty notable increases in forecasted
wind speeds and/or decreases in relative humidity, we are
relatively confident that we will not be dealing with outright-
critical fire weather conditions on any of these days. That being
said, at least limited parts of the CWA could see "near-critical"
conditions mainly Sunday and Monday afternoons due to the
potential for localized spatial overlaps of relative humidity
(RH) 25 percent or lower and wind gusts of 20+ MPH. Fortunately on
Sunday, the main limiting factor to fire danger will be
relatively light winds and RH staying safely above 25 percent.
However, a possible exception appears to exist especially in
Dawson County, which could lie on the far eastern fringes of a
larger area of lower RH/higher mid- late afternoon westerly winds
expected to develop across western Nebraska. As a result, will
slip this "near- critical" potential for Sunday back into our
Hazardous Weather Outlook (HWOGID). Monday is then looking very
marginal even for near-critical despite modest northeast breezes,
but because the previous HWO just introduced this mention decided
to let it ride at least one more forecast package. Beyond Monday,
the rest of the week looks "safer" from fire weather issues due to
various factors including cooler temps and/or increased
dewpoints/RH.

With the main points now covered, will end with some brief day-
details, including a few minor concerns not previously mentioned:

Sunday daytime:
While confidence remains pretty high in a dry day, there is more
concern than 24 hours ago that the day could start with a pretty
decent coverage of low stratus clouds, which could be somewhat
slow to burn off/erode from west-to-east before giving way to a
mostly sunny afternoon. In addition, there are also hints that at
least patchy fog could affect mainly our far western counties
(especially Dawson/Gosper/Furnas) right away Sunday morning.
However, with overall-better fog chances looking to focus just
west of our CWA, have collaborated with the short-term forecaster
handling Saturday night`s forecast to leave this mention out for
now. Otherwise, nudged down high temps very slightly, but still
aiming for mid-upper 70s central and east to low-mid 80s west and
south. March 19th temperature records at Grand Island/Hastings
which are in the mid-80s currently appear to be "safe" by 5+
degrees.

Sunday night:
A respectable little cold front passes southward across the entire
area, resulting in breezy north winds that will likely gust to at
least 25 MPH for at least a short time. We are maintaining a dry
forecast, as despite some modest elevated instability and the
latest SPC Day 2 outlook keeping our southeast CWA in a small
"general thunder" risk, nearly all model solutions focus any
convection at least a few hundred miles east of our domain mainly
over IA/MO.

Monday-Wednesday:
See "number 2" above for more on these days, but from a basic
meteorological standpoint, we reside under generally zonal (west-
east) flow with a few small scale disturbances sparking the
various rain/light snow chances. Markedly cooler than Sunday but
still seasonable for late-March.

Thursday-Friday:
See "number 1" above for more, but again from a basic standpoint a
large-scale trough gradually invades the Central Plains and brings
halfway decent rain/thunderstorm chances (does not look cold
enough for any snow on the backside at this time). As is often the
case, the GFS is generally faster than the ECMWF solution in
bringing in the lead energy, but timing in the passage of the main
mid level low/vort max improve by Friday, and as earlier
mentioned PoPs may very well need raised for this day.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Sunday)
Issued at 1230 PM CDT Sat Mar 18 2017

Significant Wx: MVFR/IFR possible in fog/stratus 09Z-16Z Sun.

This Afternoon: VFR with SCT-BKN cirrostratus around 25K ft. SSE
winds 8-15 kts with a few gusts around 20 kts at EAR. Confidence:
High

Tonight: VFR and basically SKC to start...but MVFR or possibly IFR
stratus will invade from the SW. It is uncertain what the
coverage will look like (SCT vs BKN vs OVC) and there could be
some fog with it...with models indicating a better chance at EAR.
S-SSE winds around 10 kts. LLWS develops by 08Z. Confidence: Low

For now kept TAFs fairly optimistic given the uncertainty.

Sun thru 18Z: It all hinges on what happens overnight. See prvs
paragraph. MVFR or IFR possible. Improvement to VFR expected
around roughly 17Z. S winds around 10 kts. Confidence: Low

&&

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

$$

UPDATE...Kelley
SHORT TERM...Kelley
LONG TERM...Pfannkuch
AVIATION...Kelley



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