FXUS63 KGID 210256
Area Forecast Discussion
National Weather Service Hastings NE
956 PM CDT Mon May 20 2019
Issued at 955 PM CDT Mon May 20 2019
Some comments regarding mainly the overnight hours, with a little
about Tuesday daytime also:
1) Overnight rain/thunder potential (through around 7 AM):
We are finally starting to see some areas of light rain showing
upon radar/obs again across parts of the coverage area (CWA),
following a multi-hour lull of almost no precipitation whatsoever
in the wake of steady rain that fell this afternoon especially
near and south of the NE-KS border. That being said, the potential
for more widespread/heavier rain is looking pretty meager for most
of the night, except perhaps those last few hours toward sunrise
when especially our southern zones (mainly KS) should see the next
larger "wave" of steadier rain start to ride up from the south.
As was largely expected here for the past 24+ hours,
today's/tonight's severe storm threat was very meager to near-
zero, and officially SPC earlier pulled the Marginal Risk from our
CWA altogether. Locally, we have pulled all formal mention of
thunderstorms for the overnight hours except for parts of KS. As
for actual NEW rain amounts through sunrise, the majority of the
CWA will probably only see around one-quarter inch or less, with
better potential for more appreciable measurable rain focusing
during the daylight hours Tuesday (see below).
2) Overnight fog potential:
Although agree with afternoon forecast discussion (below) that fog
should not be very widespread overnight (especially given the very
steady/gusty easterly winds), decided to introduce some generic
"patchy fog" and "areas of fog" to much of the CWA overnight into
Tuesday AM to cover at least limited/brief fog potential where
visibilities get reduced to only a few miles or less. Would be
quite surprised to see persistent/widespread dense fog, and a lot
would have to change from current expectations for us to need a
3) Tuesday daytime rain and thunderstorm/severe storm potential:
We fully understand that many folks (especially north of the state
line) have probably been fairly "underwhelmed" with rain totals so
far. However, some of the highest/most widespread rain potential
of all is still anticipated during the day Tuesday. This is due to
forcing becoming maximized as as the heart of the powerful upper
low pressure system currently well to our southwest over NM
gradually ejects north-northeast into the heart of our region.
Very GENERALLY speaking, we expect most of our CWA to see around 1
inch of additional rain Tuesday into Tuesday evening, with
cumulative 2-day totals mainly in the 1.25-2.00" range (generally
highest in our KS zones).
As for the possible severe storm threat Tuesday afternoon-early
evening, what is outlined below in the afternoon discussion still
very much applies. However, even at this close range there is
still some uncertainty regarding the exact position of the
effective warm front/surface low, which will have big
implications on the area most favored for possible low-topped
severe storms. That being said, compared to 24 hours ago, the most
favored portion of our CWA for possible severe has trended
southward, now mainly appearing to focus near/south of the state
.SHORT TERM...(This evening through Tuesday)
Issued at 342 PM CDT Mon May 20 2019
Widespread stratiform rain with a few embedded thunderstorms are
currently moving northeast through the southeastern half of the
forecast area. Parts of northern Kansas have seen around an inch
of rain, but overall it hasn't been as widespread as previously
expected. As this area moves off, we will just see scattered
showers and thunderstorms through the evening and into tonight.
Any severe threat has completely diminished at this point, as
widespread cloud cover has kept us pretty stable.
Tonight, a few models hint at patchy fog developing, but with
breezy east winds and cloudcover, I think that this threat is
overdone. As the upper trough approaches late overnight, we will
see another uptick in showers that will last into Tuesday morning.
The forecast for Tuesday is looking a bit more interesting from a
severe weather perspective. As the upper low moves into the area,
we will see showers taper off, and could even see some clearing
skies into our southern counties. Instability will be
marginal...likely between 500 and 1000 J/kg of CAPE...but with the
upper low moving overhead shear will be sufficient for a few low-
topped supercells. Main threats are large hail and possibly a few
brief tornadoes during the afternoon and early evening.
Total additional rainfall is expected to range from 1 to 2"
across the area. Given this forecasted rain and saturated soils, I
will maintain the flash flood watch for Mitchell County. That
said, the latest trends certainly keep the highest rainfall
farther southeast across eastern and southeastern Kansas.
Tuesday night's lows are expected to be the coldest of the week,
but we should remain frost-free with temperatures bottoming out in
the upper 30s to mid 40s.
.LONG TERM...(Tuesday night through Monday)
Issued at 342 PM CDT Mon May 20 2019
We will be between systems on Wednesday, so dry conditions are
expected prevail through the daytime. Late Wednesday night, there
is a low chance for a few thunderstorms in our south ahead of the
next upper low and in an area of convergence along the LLJ. SPC
has this area in a Marginal Risk for this timeframe. If storms can
develop in our area, its possible to have some marginally severe
elevated storms, but confidence in coverage and location is fairly
low at this point.
Stronger forcing arrives on Thursday as this next system ejects
across the central Plains. Instability on the latest GFS is
sufficient for strong storms, although not particularly high, as
temperatures will only be in the 70s. The shear is notably
strong, though, with 50kts or more of deep-layer shear. Obviously
there is plenty of uncertainty at this range, but this is
definitely another day to monitor.
The area remains in southwesterly flow aloft Friday into
Saturday, This will allow chances for rain and thunderstorms to
stay in the forecast each day...especially if the surface front
can stall in the area like the GFS indicates.
Yet another system is on-track to impact the area Sunday into
Monday, but at this point there are some significant timing
differences between the GFS and EC.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday)
Issued at 732 PM CDT Mon May 20 2019
Confidence is high in sub-VFR conditions (especially with regard
to ceiling) through the vast majority of the period, if not the
entire period. There is also a good chance of rain showers and a
few thunderstorms, especially during the latter half of the period
Tuesday daytime. That being said, compared to previous forecasts,
the likelihood of widespread measurable rain tonight is looking
less and less likely, with most precipitation consisting of little
more than occasional light drizzle. Wind-wise, the vast majority
of the period (especially first 18 hours) looks to feature a very
consistent direction/speed, with generally easterly sustained
speeds commonly 16-22KT/gusts 24-31KT. Late in the period Tuesday
afternoon, wind speeds/direction come a bit more in question as a
strong surface low pressure center approaches from the south, but
will defer to later forecasts to fine-tune this. Read on for more
details mainly regarding ceiling/visibility expectations...
Ceiling/visibility (additional details):
The vast majority of the period is expected to feature a fairly
persistent IFR ceiling. However, especially right away this
evening, KGRI could hang onto a few more hours of MVFR, while
later tonight into Tuesday some LIFR is also possible at both
sites. Visibility-wise, confidence is only medium at best for the
period as a whole. Confidence is fairly high in VFR this evening.F
or the later night/early Tuesday hours, although very breezy
easterly winds should keep considerable fog issues at bay, could
foresee occasional MVFR visibility in drizzle, and then more of a
persistent MVFR (or lower) visibility during parts of the latter
12 hours as steadier rainfall moves in.
KS...Flash Flood Watch through Tuesday evening for KSZ019.
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