Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS02 KWNS 300520
SPC AC 300520
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1220 AM CDT Thu Mar 30 2017
Valid 311200Z - 011200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY AFTERNOON
ACROSS PARTS OF THE MID ATLANTIC COAST REGION...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY EVENING
ACROSS PARTS OF THE CENTRAL HIGH PLAINS...
Strong thunderstorms may impact parts of the Mid Atlantic Coast
region Friday afternoon, and portions of the central high Plains
Friday evening, accompanied by at least some risk for severe
Significant short wave perturbations continue to emerge from a
strong belt of westerlies over the mid-latitude Pacific. Another in
the series is now digging inland across the Pacific Northwest coast,
and forecast to continue southeastward today, with an embedded
lower/mid tropospheric cyclone developing/deepening as it crosses
much of the southern Great Basin by 12Z Friday. As this occurs, the
forward progression likely will slow, but models suggest that center
of circulation will gradually redevelop east southeast of the Four
Corners region Friday through Friday night, probably broadening and
weakening as it does.
As downstream short wave ridging builds across the southern Plains
through the lower/middle Mississippi Valley region, the remnants of
the closed low/short wave trough currently progressing into the
Mississippi Valley are forecast to accelerate east southeast of the
lower Ohio Valley, across and east of the Mid Atlantic Coast by 12Z
In response to these features, in lower levels, modest surface
cyclogenesis may occur, from the lee of the central Appalachians
through northern Mid Atlantic coastal areas, and to the lee of the
southern Rockies. This is expected to be generally focused along a
surface frontal zone that may advance east of much of the Mid
Atlantic coast, while stalling in more or less east-west fashion
across parts of the Southeast into the southern Plains.
It appears the front will be preceded by one or more convective
outflows across parts of the Southeast and northeastern Gulf of
Mexico, but at least seasonably modest low-level moisture is
expected to advect into the Mid Atlantic states ahead of the frontal
passage. A southerly return flow may commence across the lower Rio
Grande Valley and western Gulf coast into the southern Plains, but a
substantive/deep low-level moisture return appears unlikely through
at least 12Z Saturday.
...Mid Atlantic Coast...
Models are suggestive that forcing for ascent associated with the
approaching upper impulse may support weak early period convection
overspreading the region. In the wake of this activity, low-level
moistening, perhaps some insolation associated with breaks in
overcast, and mid-level cooling may all contribute to sufficient
destabilization for strengthening convective development near/east
of the Blue Ridge mountains. In the presence of modestly strong and
sheared lower/mid tropospheric wind fields (30-50 kt), it appears
the environment may become at least marginally conducive to
organized thunderstorm development. This may be accompanied by a
risk for marginally severe hail, potentially damaging wind gusts,
and perhaps even an isolated tornado or two before favorable
mid/upper forcing shifts northeast of the region Friday evening.
...South central high Plains...
Although models suggest considerable weakening of the approaching
closed low and associated wind fields will occur during this period,
an initial perturbation pivoting across the Rockies may still be
accompanied by a 50-70 kt southwesterly 500 mb speed maximum across
eastern New Mexico and the Texas Panhandle region by Friday evening.
Even with limited low-level moistening along the stalling frontal
zone across the Panhandle region, in the presence of lower/mid
tropospheric lapse rates that are forecast to become rather steep,
modest CAPE (at least 500 J/kg+) appears possible near and to the
cool side of the front. Initial storm development expected near the
Raton Mesa by late Friday afternoon, is expected to be maintained by
strong forcing for ascent and vertical shear, eastward along the
front across the high Plains Friday evening. As this occurs, the
environment may become at least marginally conducive to a narrow
swath of severe hail and wind.