Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 181734
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1234 PM CDT Thu May 18 2017

.UPDATE...
Issued at 1234 PM CDT Thu May 18 2017

We cont to monitor svr tstm potential. The low OVC over N-cntrl KS
is inhibiting heating and this is a major negative for svr tstms.
That said...sunshine and svr tstms will not be far away. These
storms could maintain enough of their potency to be svr as they
initially become elevated. But as they move further N the risk for
svr wx will rapidly decrease as the storms become increasingly
elevated.

&&

.SHORT TERM...(Today and tonight)
Issued at 435 AM CDT Thu May 18 2017

Quiet but breezy conditions are in place across much of the area
early this morning. Upper air and satellite data showing the area
set up under shortwave ridging, thanks to areas of low pressure
spinning over MN/WI and UT. At the surface, the main frontal
boundary has sunk well south of the CWA, currently draped across
far SW KS into east-central KS. High pressure has been building in
behind the front, keeping winds northerly through the night, and
gusty at times, esp across south central NE. Speeds have been
around 15-20 MPH and gusting to near around 25 MPH.

The main concern for today/tonight is increasing thunderstorm
chances and the potential for severe weather, mainly across the
southern half. Models are in good agreement showing the main upper
level low sliding into the Four Corners region through the day
today, then making just a bit of eastward progress along the CO/NM
border tonight. A piece of shortwave energy rotating around the
main low will drive our thunderstorm chances later today, as it
swings northeast onto the Plains. At the surface, while some
northward drifting of the warm front is shown by models today,
when it comes time for convection to get going, it looks to still
be south of the CWA (near/just south of I-70? Depends on the
model). Initial activity is expected to develop along the dry line
across central KS/OK this afternoon, with activity
moving/spreading northward as the shortwave disturbance swings
northeast. At this point, models are in pretty decent agreement
showing it being closer to 00Z before the strongest storms are
moving into southern portions of the CWA, so not much has changed
with much of the daytime hours being free of measurable precip for
most locations. Not to say it`s going to be the nicest of days
though, time heights continue to show the lower level stratus
sticking around with us being north of the warm front, with gusty
easterly winds expected. Forecast highs range from the mid 50s
north to upper 60s in the far southeast.

Some pretty hefty instability is expected to develop in the warm
sector today, which should stay south of the CWA/warm front. More
elevated instability will work further north into our CWA, with
models showing a notable range. No surprise the NAM is on the high
side of things with a small area of 2000-2500j/kg nosing in to
the far southeastern corner, others are closer to/less than
1000...the RAP is in the middle around 1000-1500j/kg. All are in
agreement with the better instability being mainly confined to
areas south of the NE/KS state line. Shear isn`t an issue. Severe
weather continues to be a concern south of I-80 (roughly where the
SPC Day 1 Marginal area starts), but especially for areas near
the NE/KS state line and into KS. No change in the thoughts that
large hail, damaging winds and heavy rain are the primary hazards.
While the best potential for tornadoes will be south of the CWA,
chances across mainly north central KS are non-zero, closer to the
warm front. Will be watching closely to see how the frontal
placement evolves through the day.

No changes were made to the Flash Flood Watch for the short term
period through 12Z Friday. Recent rains over the past few days
have left the ground pretty wet across the area. Still looking
at the potential for heavy rain accompanying the stronger storms
through tonight, and the ground won`t be able to keep up if any of
it lingers for too long.

Have pretty decent PoPs lingering all night across the CWA, though
confidence in just how much is going on after 06-09Z is uncertain.
Some models have a pretty much sharp cut off, so it`s possible
PoPs are too high later tonight.


.LONG TERM...(Friday through Wednesday)
Issued at 450 AM CDT Thu May 18 2017

Overview...The primary focus will be on the chance for showers and
thunderstorms Friday into Friday night. The major upper level storm
system is expected to track across our forecast area during this
time and exit to our northeast by Saturday morning. Rain showers
could linger into Saturday morning and then dry weather is expected
from Saturday afternoon through Sunday. We could see a return to at
least some chance for more rain by Monday and Tuesday, but these are
fairly marginal chances from generally more minor weather systems.
Friday and Saturday will be cool with highs likely only in the 50s
for most Nebraska zones to the 60s over north central Kansas. High
temperatures will generally be in the upper 60s to lower 70s from
Sunday through the middle of next week.

Friday...All major forecast models keep the sfc low and warm front
south of the Tri-Cities. One of the most northern forecast models
(00Z GFS) brings the warm front/dry line intersection point as far
north as the Beloit, KS area (Likely too far north). Although a
severe weather threat will extend well north of the front due to
elevated instability, any tornadic threat on Friday will generally
be near the front or south of the front in the warm sector.
Therefore, based on most forecast models our primary severe
weather concerns, which will likely be confined to our
southeastern zones will be large hail, damaging winds, and
possible flash flooding.

The ending time of the flash flood watch was moved up to 1 am
Saturday morning. Most of the heavy thunderstorms should have exited
east of our forecast area by then, although general showers may
linger throughout the night in some areas. There is a rather high
amount of uncertainty regarding where the frontal boundaries will
set up on Friday after the atmosphere is rather worked over Thursday
night by significant widespread thunderstorms. It is certainly
possible that the Flash Flood Watch zones could be dry slotted
Friday night with the heavier thunderstorms off to our southeast and
the deformation band rain showers to our northwest. Will allow the
Flash Flood Watch to remain in effect into Friday for now, but with
limited confidence.

Saturday and Sunday...Any instability is gone and thus although we
could see a few remaining rain showers Saturday morning,
thunderstorms are not expected. All areas should be dry by Saturday
afternoon with the dry weather lasting into Sunday. Temperatures
will be cool in the 50s to lower 60s behind the system on Saturday,
but will warm back into the upper 60s to lower 70s by Sunday.

Monday through Wednesday...We will transition into a northwest upper
level flow pattern with weak shortwaves tracking through bringing
some chances for showers and thunderstorms. However, moisture will
be more limited in this pattern and precipitation will likely not be
as wide spread or heavy as we have seen the last few days.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Friday)
Issued at 1234 PM CDT Thu May 18 2017

Significant Wx: Predominantly IFR CIGs. A period of +TSRA likely
this eve.

This Afternoon: Teetering on MVFR v IFR CIGs...but low-end MVFR
should prevail. NE winds roughly 13-23 kts. Gusty at times.
Confidence: High

Tonight: CIGs decay to IFR with a period of +TSRA. There is a low
prob for GS (small hail). VSBYs should begin to lower in light
fog after TSRAs end. ENE winds 15-25 kts except possibly
erratic near TSRAs. Confidence: High

Fri thru 18Z: IFR CIGs/VSBYs with patchy -DZ developing.
Confidence: High

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Flash Flood Watch from 6 PM CDT this evening through late Friday
     night for NEZ048-049-062>064-073>077-083>087.

KS...Flash Flood Watch from 6 PM CDT this evening through late Friday
     night for KSZ005>007-017>019.

&&

$$

UPDATE...Kelley
SHORT TERM...ADP
LONG TERM...Wesely
AVIATION...Kelley



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