Day 1 Severe Weather Outlook

Valid 122000Z – 131200Z

…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
KY SOUTHWESTWARD INTO AR…

…SUMMARY…
Severe storms capable of tornadoes, damaging winds and large hail,
remain possible into the nighttime hours from central Arkansas
eastward into parts of southeast Missouri, southern Illinois, far
southern Indiana, northern Tennessee, and much of Kentucky.

…20z Update — Kentucky southwestward into central Texas…

Only minor changes have been made to the core Slight and Enhanced
risk areas. The main change is to add a SIG area within a portion of
the 30% wind probability from far southeast IL/southwest IN into
portions of western and south-central KY. The 30% hail probability
has also been expanded eastward into western KY.

This area is downstream of an east/southeastward progressing bowing
segment across southern IL. As of 1920z, the KPAH VWP indicates 50
kt westerly winds as low as 1 km with a vertical wind profile
supportive of supercells. The linear segment currently over southern
IL has been showing indications of attempts to become more
supercellular as it tracks south of east along a quasi-warm frontal
boundary that has been reinforced by area of convection that has
been tracking across western into central KY much of the afternoon.
Recently, this cell has produced up to 2 inch hail in Franklin and
Williamson Counties in southern IL. Behind the ongoing
western/central KY area of convection, surface observations have
recovered, with dewpoints now climbing into the low to mid 60s. This
should result in further destabilization over the next couple of
hours across the western third to half of KY. The developing
parameter space will support all hazards, including the potential
for a strong tornado or two, damaging winds (with a swath of 65 kt
gusts possible), and large hail.

See MCDs 170 and 171 for further information about ongoing and
short-term trends/threats.

Across central/northeast TX, the Marginal risk has been adjusted
northward a bit to account for latest trends regarding the expected
location/orientation of the frontal boundary overnight.

…Lower CO Valley…

Convection is increasing across the CA deserts as the upper low
continue to pivot toward southern CA. Further thunderstorm
development is expected eastward across parts of southern AZ over
the next few hours where MLCAPE has increased to 250-500 J/kg. RAP
forecast soundings continue to indicate marginal effective shear,
but strong 0-6km shear and long, straight hodographs. Furthermore,
very steep lapse rates are in place. As a result, stronger storms
could produce near 1-inch hail through this evening.

..Leitman.. 03/12/2020

.PREV DISCUSSION… /ISSUED 1107 AM CDT Thu Mar 12 2020/

…Southern IL into Kentucky…
Water vapor loop shows a fast moving low-amplitude shortwave trough
over KS. This feature will track eastward into the mid MS valley
later today. At the surface, a low will move across MO while a warm
front becomes better established across southern IL and KY. This
boundary will likely be the focus of severe thunderstorms later
today.

A cluster of ongoing storms west of St Louis, along with new storms
forming over western KY will track eastward today along the warm
front. Despite dewpoints only in the 50s to lower 60s, sufficient
destabilization will result in MLCAPE values of 1000-1500 J/kg.
Deep layer shear will promote supercell structures capable of all
severe risks. Most 12z models show a compact low/mid level jet max
tracking across western/central KY during the afternoon. This will
lead to a corridor of impressive low-level vertical shear and
helicity – favorable for strong tornadoes if discrete convective
mode is established/maintained. Otherwise, damaging winds would be
the main threat with bowing structures. The threat may persist well
after dark into eastern KY and perhaps western WV before
diminishing.

…southeast MO into AR…
Thunderstorms are expected to develop along a trailing cold front
this afternoon from southeast MO into much of AR. These storms will
likely be supercellular with an early risk of large hail and a few
tornadoes. Storms will be active for several hours this evening
before weakening as they track into west TN.

$$

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