376
FXUS63 KLBF 201736
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
1236 PM CDT Mon May 20 2024

.KEY MESSAGES...

* A slight risk of severe weather is possible on this evening
  (Monday evening) with large hail up to baseball size, severe winds
  up to 75 mph, and heavy rainfall up to 2 inches as the primary
  threats.

* Active weather continues through mid-week, although, severe
  potential remains low at this time.

* Cooler temperatures return on Tuesday with highs in the mid
  50s to low 60s before gradually warming through the end of the
  week (into the 70s by the weekend).

* A Flood Watch has been issued for repeating heavy
  thunderstorms across southwest/scntl Nebraska tonight.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 414 AM CDT Mon May 20 2024

The main weather story in the short term will be the potential for
severe thunderstorms this evening and into the overnight. Dewpoints
will increase across the region by late this morning and into the
afternoon as low level moisture advection intensifies. Moderate
instability will also develop across southwest and south central
Nebraska by the late afternoon. Ample instability will exist across
the region to support the development of supercells across the
Panhandle and into northeast Colorado. These storms will track
eastward into southwest and south central Nebraska by early evening.
Current model guidance suggests lapse rates above 7 C/km and shear
above 50 knots. This combined with significant CAPE (over 1500
J/kg), not to mention large CAPE in the -10 to -30 C layer, will be
enough to support very large hail (potentially up to baseball sized)
with these supercells. This environment will also create the
potential for significant wind gusts up to 75 mph.

The initial round of storms, the supercells, will have the greatest
potential to have the large hail and strong winds. As these storms
move eastward, another round of storms are expected to develop
behind them, which are not expected to be as intense as the
environment becomes worked over. However, these showers and
thunderstorms could still produce hail up to 1 inch and wind gusts
up to 60 mph for a few hours (through late evening). Eventually,
storms will weaken and congeal into a MCS for the remainder of the
overnight hours. This round will have the greatest potential to have
heavy rainfall with may result in localized flooding. At this time,
up to 2 inches of QPF are expected across southwest Nebraska and
into north central Nebraska. Have decided not to issue any flood
headlines at this time as this total rainfall will occur over 24 to
30 hour timeframe. Although, some flash flooding of low lying areas
or small streams is not entirely out of the question especially if a
heavier shower drops a half inch or more in a short period of time.
Will continue to monitor this as the event evolves tonight.

Heading into Tuesday, rain showers and embedded thunderstorms
continue throughout the day, although there are expected to be some
breaks. The severe risk is low for Tuesday as a cooler airmass
pushes in behind the departing front and the environment
remains well mixed. Still, we`ll have to be cognizant of the
flooding potential heading into Tuesday afternoon especially
across areas that have already seen heavy rainfall Monday night
and early Tuesday.

Regarding temperatures, highs will drop from the low 60s to low 70s
today into the mid 50s to low 60s on Tuesday. This will be nearly 10
degrees below normal for Tuesday (normals in the low to mid
70s).

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 414 AM CDT Mon May 20 2024

A series of disturbances will continue to impact Nebraska through
the weekend.  At this time, severe weather risk remains uncertain
with confidence remaining low on timing, track, and locations.
However, based on the latest guidance, best chance to see convection
will be in the late afternoon and early evening as diurnal heating
and instability is greatest. Will continue to monitor these systems
as the week progresses and those with outside plans in the evening
should stay weather aware and be prepared to make alternate plans.

For temperatures, cooler temperatures from Tuesday will give way to
a slow rise in temperatures into the weekend. Current model runs
indicate 850 mb temperatures to rise back into the 10 to 16 degree C
range by the weekend. While this will not equate to exceptionally
warm surface highs, especially with showers and thunderstorms each
day, highs will rise back to near normal in the mid 70s by the
weekend. Low temperatures also return from the low 40s on Tuesday
night into the low 50s by Saturday night which is just slightly
above normals for this time of year.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1235 PM CDT Mon May 20 2024

VFR conditions are expected to diminish this evening to MVFR ahead
of a thunderstorm activity tonight. As thunderstorms push through,
and showers remain, conditions are expected to drop to IFR
conditions through tomorrow afternoon. The main forecast challenge
remains the timing of thunderstorms in vicinity of the terminals,
however confidence continues to grow in timing of storms this
evening into tonight. Winds generally become easterly today, and
northerly as storms clear out, but thunderstorms will likely cause
erratic winds. Also worth mentioning that thunderstorms have the
potential to be severe with wind gusts in excess of 60 knots, which
will be difficult to lock down timing wise in the TAFs. Amendments
may be needed in later TAFs as timing of potential severe weather is
refined.

&&

.HYDROLOGY...
Issued at 1116 AM CDT Mon May 20 2024

The HRRR suggests a few repeating storms across swrn and scntl
Nebraska tonight which will likely be supercellular. This could lead
to 3 inches of rainfall. A single storm putting down 1.5 inches in
less than an hour isn`t a big problem but the second storm of the
same caliber a few hours later would probably cause flooding.

The RAP model viz Bufkit suggests deep moisture extending to
300 mb will be in place supporting heavy rainfall and it is
worth noting satellite shows an expansive plume of subtropical
moisture feeding in through the srn Rockies and Mexico. Some of
this moisture will be drawn into a developing upper low across
Nebraska tonight.

The h850-700mb moisture transport in the RAP model is perhaps modest
but the theta-e advection looks strong. Winds at h850mb are very
modest at just 10-20kts so this doesn`t appear to be a blockbuster
heavy rain event. Moisture availability and repeating storms are the
basis for a Flood Watch across swrn and scntl Nebraska tonight. The
watch outline generally follows the 100 percent probability of 1
inch of rain in 12hr shown by the HREF.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 7 PM CDT /6 PM MDT/ this evening through
Tuesday morning for NEZ038-057>059-069>071.

&&

$$

SHORT TERM...Kulik
LONG TERM...Kulik
AVIATION...Richie
HYDROLOGY...CDC