Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 231731
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1231 PM CDT Sun Apr 23 2017

.SHORT TERM...(Today and tonight)
Issued at 405 AM CDT Sun Apr 23 2017

Quite a variety of temperatures across the local area this morning
as sheltered areas have see temperatures dip into the middle 30s
the past couple of hours and light southerly winds elsewhere have
helped keep temperatures in the lower to middle 40s. While there
are isolated spots outside the current frost advisory are likely
to see at least some patchy frost the next few hours...the best
potential for more widespread frost remains across Phillips,
Rooks, Furnas and Harlan counties...where a frost advisory remains
in effect through 8 AM CDT.

For today...expect a breezy and seasonably warm afternoon as
surface high pressure continues to exit the region and low
pressure builds on the lee side of the Rockies. This will result
in a fairly tight pressure gradient across the local area...with
sustained southerly winds of 25 to 30 mph expected by mid-
afternoon...with locally higher gusts to 35 or possibly even 40
mph...expected later in the day. With seasonably warm
temperatures and a relatively dry airmass in place...the strong
winds and low relative humidity values will make for near critical
fire weather conditions across the entire forecast area. Despite
the greening up of fuels some the past week, conditions remain
favorable enough for rapid fire growth that these fire weather
conditions are a concern and continued their mention in the HWO.

Otherwise...above normal temperatures and strong southerly breezes
will be the rule this afternoon...with a continued tight pressure
gradient overnight expected to help mix the lowest layers of the
atmosphere...resulting in a more mild overnight period. This more
mild night will also be aided...in part...by increasing high
clouds across the region this afternoon and evening, ahead of an
upper level disturbance currently tracking across the interior
west.

.LONG TERM...(Monday daytime through Saturday)
Issued at 457 AM CDT Sun Apr 23 2017

General overview of this 6-day period:
Overall, no truly major changes from how things were trending 24
hours ago, as we are still looking at generally 2 separate,
larger-scale low pressure systems to traverse the central CONUS
during the week/weekend, with the second one being deeper/more
intense than the first. Official 7-day cumulative precipitation
forecasts from the Weather Prediction Center (WPC) are still
calling for nearly our entire county warning area (CWA) to perhaps
receive ROUGHLY 2" of rain during the next week, but as anybody
reading this knows, in all reality some places will likely receive
less and perhaps a few places a bit more. Will now run-down
5 key highlights/trends regarding this latest forecast package:

1) Model trends/timing: On a positive note, the 00z runs of the
GFS/ECMWF are in better agreement than 24 hours ago regarding the
big/synoptic scale picture, especially regarding the late-
week/weekend system, although of course there remains plenty of
variability/forecast uncertainty in surface features, instability
levels, etc. As is oh-so-typical with these larger scale systems
still several days away, the timing of the highest rain chances
have generally slowed by as much as 24 hours, meaning that our
overall highest precip chances (PoPs) are now focused mainly Fri-
Sat instead of Thu-Fri.

2) Thunderstorm/severe weather potential: It has been a challenge
the past few days trying to determine which particular periods
might warrant at least a small chance of thunderstorms versus
others that either outright don`t warrant any thunder or it`s
just too iffy/soon to "go there" yet. Undoubtedly, some of this
"thunder flip-flopping" will probably continue in the official
forecast, Hazardous Weather Outlook (HWO), etc. over the coming
days so please bear with us. As for this latest forecast package
though, a slight chance of thunderstorms (non-severe) has been
introduced/re-introduced for late Monday night, and an even more
low-confidence chance of storms has been introduced to parts of
the CWA for the very end of the official forecast Friday night-
Saturday. Officially, the latest SPC Day 4-8 Outlook now clips
our extreme southern CWA with a 15 percent severe storm
probability for Day 6 (Friday). Both the ECMWF/GFS do agree that
if there is going to be a "big day" for severe storms in the
central/southern Plains this week, then Friday and perhaps
Saturday are the primary candidates. However, from our local
area forecast perspective, we are still noting plenty of
disparity between the somewhat warmer/more unstable GFS and the
cooler/more stable ECMWF solutions for both Friday and Saturday,
so for now we are still going to shy away from trying to
confidently "highlight" either day for a formal mention of severe
storms at this time. Certainly, we do fully agree with SPC
highlighting areas south-through-southeast of our CWA (central KS
to north TX) for the greatest threat of severe storms Friday-
Saturday.

3) Temperature-wise: No major changes here either, as Monday
should by far be the warmest of these 6 days before a pretty solid
cool-down arrives thereafter. More specifically, highs Monday are
aimed mid-70s to around 80, before a notable cool-down to only the
50s for the majority of the CWA Tuesday-Saturday. Frankly, it`s
been awhile since we`ve seen a prolonged stretch of highs in the
50s so this will be a noticeable transition following the
recent/upcoming very mild stretch that lasts through Monday. Not
surprisingly, no day carries more uncertainty in temps than the
last day (Saturday), as the latest ECMWF suggests that very chilly
highs only in the 40s could occur, while the GFS suggests it could
be closer to 70. Not surprisingly, the official forecast is a
middle-ground for now. Turning to overnight lows, the mildest
night is clearly right away Monday night (mid-40s to around 50),
before a chillier regime sets in with most nights thereafter
settling between the mid-30s and low 40s. While we are currently
not calling for any sub-freezing temperatures, at least one night
(Wednesday night/Thursday AM) bears watching for possible frost
potential, but will keep this out of the official forecast for now
given confidence remains fairly low at this Day 4 range, and that
there could be mitigating factors such as increasing clouds.

4) Fire weather concerns: Although not as concerning overall as
today`s "near-critical" setup (see short term section above), we
have now introduced another near-critical fire weather mention to
the HWO for Monday afternoon. While winds will not be quite as
strong for Monday afternoon compared to today, west-northwesterly
gusts into the 20-25 MPH range do appear likely behind a passing
surface trough axis in several of our western counties, along with
an area of relative humidity (RH) dropping into the 20-25 percent
range. Overall, the greatest overlap of both the strongest breezes
and lowest RH looks to focus generally west of a Kearney-Alma
line. Fortunately, both wind speeds and RH would have to "worsen"
for this to turn into an outright-critical fire weather setup,
and besides, as mentioned here 24 hours ago, vegetation is not
quite as prone to serious fire growth/spread anymore as it was a
month ago.

5) Could some late-season snow (yes SNOW) be trying to work its
way into the forecast at some point?! Well, for now, we have no
mention of it, but believe it or not there may be two windows of
opportunity for at least a dusting or a rain-snow mix if things
start trending colder and/or wetter in later forecasts. For one
thing, at least one model (Canadian) is suggesting that a few wet
snowflakes could fall late Tuesday night/early Wednesday before
precipitation ends/moves out. However, most models move any
lingering any precip out before it would get cold enough to
support snow, so have followed this expectation for now. Farther
down the road toward the Friday night and/or Saturday night time
frame, the colder ECMWF solution is again suggesting at least some
limited, slushy snow potential mainly in our far northern/western
Nebraska counties, but at least for now the official forecast
keeps temps just warm enough to keep any snow at bay. So, in
summary, we have no official forecast mention of the "s-word" at
this time, but given the upcoming cooler temperature regime this
does bear watching just in case.

With by far the 5 most important points/topics of the long-term
forecast laid out there, will end with some pretty basic day-to-
day details for those interested:

Monday daytime:
Likely by far the warmest day of the long-term (see point 3
above). Precip-wise, maintained a small chance of sprinkles/light
rain showers for the far northern CWA in the morning as a weak,
moisture-starved wave zips through, but we probably cannot rule
out at least a few sprinkles over more of the area than currently
depicted. Have kept the afternoon dry. Winds will be quite breezy
out of the south especially in central/eastern counties through
early afternoon, with gusts 30+ MPH likely.

Monday night-Tuesday night:
These 36 hours encompass "low pressure system number 1" for the
week. Kept Monday evening dry, but precip chances ramp up
especially late Mon night into Tuesday morning, and as earlier
mentioned have a mention of thunderstorms as well, with perhaps
some very small hail not out of the question. While there are some
questions regarding how much rain will stick around into the
Tuesday afternoon-night time frame, (both the NAM/GFS are fairly
dry), confidence is high that it will be much cooler than Monday
and plenty windy with northerly gusts to around 30 MPH.

Wednesday-Wednesday night:
Despite some lingering slight PoPs in eastern zones for Wednesday
morning, the vast majority of these 24 hours should be dry for the
vast majority of the CWA as we reside "in between" systems.

Thursday-Thursday night:
"Low pressure system number 2" makes its initial entrance, but
only in the form of low-amplitude, leading energy well out in
front of the main disturbance. While rain chances exist,
especially the ECMWF suggests precip could be rather
minimal/spotty.

Friday-Saturday:
Have already discussed some of the various uncertainties for this
Day 6-7 time frame above, but very generally speaking a large-
scale and increasingly-amplified mid-upper low takes aim on the
central CONUS, bringing decent chances for at least widespread
chilly rain and perhaps thunderstorms. Given that the primary mid
level low/vort max is currently progged to be over CO by the end
of the day Saturday, precip chances will likely continue at least
slightly beyond the current official forecast period into
Saturday night and perhaps even Sunday as well. LOTS of details
yet to sort out here...

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Monday afternoon)
Issued at 1224 PM CDT Sun Apr 23 2017

VFR conditions remain in the forecast for this TAF period, with
the primary concern coming with winds and LLWS. A tightened
pressure gradient across the area has resulted in gusty southerly
winds, which will continue through the duration of the TAF period.
Sustained speeds of 15-25 MPH and gusts near 30 MPH are expected
through much of the forecast, the exception being a brief period
early this evening where speed may diminish some. Along with the
gusty winds at the surface, models continue to show the potential
for a strong LLJ developing tonight, so the threat of LLWS at both
terminal sites remains this evening/overnight.

&&

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

$$

SHORT TERM...Rossi
LONG TERM...Pfannkuch
AVIATION...ADP



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