Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

000
FXUS63 KEAX 131750
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
1250 PM CDT Fri Apr 13 2018

.Discussion...
Issued at 330 AM CDT FRI APR 13 2018

Primary focus remains the potential for severe storms this evening
and tonight as a surface low slides east along the NE/KS border
and into far northern MO. Surface dryline currently extends from
Red Cloud NE to Pratt KS (and southward), and will bulge eastward
throughout the day as the surface low slowly progresses, while the
cold front swings around from the northwest and gradually catches
the dryline from north to south. Convective initiation today will
likely occur in two relatively distinct locations: near the triple
point/surface low in southeast Nebraska and northeast KS, and
possibly along the dryline in eastern KS, then storm motion will
take any storms that develop eastward into the forecast area.

Along the dryline, a very significant EML and mixing of low-level
moisture will make convective initiation slow and difficult. It is
likely many CI attempts will occur over several hours along the
eastward-moving dryline before the atmosphere moistens and cools
enough to promote isolated storm development, then the probability
of initiation will begin to increase as the cold front catches the
dryline and uses its additional lift, along with the more primed
environment, to begin more widespread development along the cold
front/dryline interface. Any initial, isolated convection that
develops will have the potential to quickly organize and rotate in
an environment characterized by 2000-2500 J/kg SBCAPE and 50-60
kts effective shear. Large hail, damaging winds, and a tornado or
two are possible with initial, more isolated convection. However,
high DCAPE and associated dry air aloft, as well as relatively
high LCLs, may limit supercell longevity and transition even
isolated supercells into mini bows as strong downdrafts quickly
begin to dominate storm morphology.

Further to the north, capping will be somewhat less significant
and lift should help overcome it more quickly, leading to earlier
and more widespread thunderstorm initiation during the late
afternoon and early evening. Stratus has begun to develop along
and north of the surface warm front draping from Hebron NE along
the MO/IA border which could limit instability, but as the warm
front lifts northward and stratus thins/mixes, CAPE should begin
to increase especially in a narrow corridor just southeast of the
triple point. Better turning of low-level winds near the surface
low and lower LCLs should provide the best environment for a few
tornadoes; however storm mode could become messy quickly with a
better potential for multiple competing and merging updrafts,
especially as storms move east into northwest MO. CAM ensembles
also support the better probability of updraft rotation, showing
the highest neighborhood probabilities of UH exceeding 75 m2/s2
mainly across southeast Nebraska, northeast KS, and into far
northwest MO before decreasing again.

By early evening, the earlier more distinct areas of convection
should grow into a more cohesive linear system along the cold
front. A distinct dryline is not expected to make it quite to the
KS/MO border before the cold front fully overruns it, pushing any
existing or developing storms more quickly to the east. Time of
day, increasing forcing, and increasingly unidirectional wind
profiles will support an upscale linear growth as the system
pushes east, but will still need to watch for QLCS circulations
embedded in the system if the downdraft does not surge ahead of
the complex. 0-3 km shear vectors ahead of the line should be
oriented SSW to SW at 35-45 kts, and while an eastward motion to
the line would limit the amount of shear orthogonal to the line,
any northeastward-moving segments could better utilize the
environmental shear and rotate. 0-1 km helicity maximizes just
ahead of the line at around 100-200 J/kg, which is certainly
sufficient for low-level mesocyclones should the cold pool/updraft
balance long enough for at least brief organization. Although
CAPE does decrease from west to east and as daylight wanes, enough
instability to support the ongoing storms will likely continue
through the length of the CWA. Effective and both the 0-3 km and
0-1 km shear remain relatively uniform -- if not even slightly
increased -- as the jet increases overnight, so will have to
monitor the potential for a few QLCS tornadoes and a widespread
damaging wind threat through the duration of the event.

Precipitation will wrap in behind the surface low late tonight
into Saturday, as will much colder temperatures. Saturation will
be primarily focused at 800 hPa and below, resulting in an initial
very light rain/snow mix or a wet, non-accumulating light snow;
however as temperatures continue to cool, dendritic growth will
become possible across northwest and northern MO, and rates may
increase enough to see a bit of snow accumulation north of I-70.
Cloud ice will gradually erode and a brief period of freezing
drizzle is possible on the very back side of the system Sunday
morning, but with marginal temperatures and some timing
differences on the exit of precipitation, the most likely precip
type will be snow or a rain/snow mix, and a gradual end to
precipitation when the cloud ice is lost. Unseasonably cold
temperatures and wind chills are also anticipated Saturday night
and Sunday morning, which could impact plants that have blossomed
in the recent warm-up.

Gradually warming temperatures and quieter conditions are expected
after Sunday.

&&

.Aviation...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1242 PM CDT FRI APR 13 2018

For this afternoon, VFR cigs and vis are expected with very
breezy southerly surface winds. Late this afternoon thunderstorms
are expected to develop near the terminals associated with an
approaching cold front. At this time STJ has the best chance of
seeing a storm compared to the other terminals. The activity
should be out of the area by 02 UTC. Winds will shift to the
northwest behind the front will MVFR CIGS developing after sunrise
tomorrow, but no issues to the visibility.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...Wind Advisory until 6 PM CDT this evening for KSZ057-060-105.

MO...Wind Advisory until 6 PM CDT this evening for MOZ043-053-054.

&&

$$

Discussion...Laflin
Aviation...Pietrycha



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.