SPC AC 210556
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1256 AM CDT Thu Mar 21 2019
Valid 211200Z - 221200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
NORTHWESTERN TO CENTRAL NEW MEXICO AND EXTREME SOUTHWESTERN
COLORADO...
...SUMMARY...
Isolated, marginally severe thunderstorms are possible over parts of
northwestern to central New Mexico and extreme southwestern Colorado
this afternoon.
...Synopsis...
A high-amplitude upper-air pattern will prevail through this period,
with a synoptic ridge moving slowly eastward from the Rockies across
the Great Plains. To its east, a strong shortwave trough now over
Lake Michigan and IL will dig southeastward and strengthen, forming
a closed 500-mb cyclone over WV and VA by 00Z. This cyclone will
phase somewhat with a weakening perturbation now located over the
Mid-South region, before pivoting offshore and devolving to an
open-wave trough late in the period. West of the synoptic ridge, a
negatively tilted synoptic-scale trough is apparent in moisture-
channel imagery, from a position offshore of northern CA
southeastward across much of CA to the northern Baja/northwestern
Sonora region. A closed cyclone should evolve in this trough during
the day, over the Sierra Nevada and western Great Basin, with the
associated 500-mb low located over southeastern NV by 00Z. By
22/12Z, the low should pivot across UT, while a basal shortwave
trough crosses AZ. Minor shortwaves will precede this feature,
within the broad area of height falls impinging on the southern
Rockies.
At the surface, a low south of ILM is expected to reach northeastern
NC by the start of the period, then deepen and move across the
Mid-Atlantic to southern New England by 22/12Z. Associated
deep-layer lift, with the approach of the eastern shortwave troughs,
will contribute to thunder potential the first 2-3 hours of the
period over eastern NC. A low-level Pacific front -- initially over
parts of AZ and Baja -- will move slowly to western NM by 00Z, then
slowly cross northern/central NM overnight.
...NM, extreme southwestern CO...
Isolated to scattered thunderstorms are expected to develop this
afternoon in a corridor from just east of the Four Corners across
northwestern to central NM. For a period of roughly 3-4 hours
during mid/late afternoon, isolated large hail and severe gusts may
occur.
Shots of large-scale DCVA/lift, related to shortwaves pivoting
around the rim of the mid/upper cyclone, will move over the
low-level frontal zone and across a narrow warm sector over the
outlook area this afternoon. In that sector, low-level theta-e
advection and diabatic surface heating, beneath a regime of midlevel
cooling, height falls and difluent cyclonic flow aloft, will
contribute to an increasingly favorable thermodynamic environment
for thunderstorms. Surface dew points should increase through the
30s and perhaps into the low 40s F, enabling MLCAPE 400-800 J/kg.
The buoyancy will develop atop well-mixed subcloud layers supporting
strong/locally severe gusts, as well as maintenance of hail to the
surface of the high desert and mountains in the outlook area.
Forecast soundings suggest effective-shear magnitudes 45-50 kt are
possible, supporting at least transient supercell potential as well
as organized multicell bands and clusters.
Into south-central/southeastern NM and far west TX, potential
becomes more isolated and uncertain, given the presence of weaker
levels of deep-layer forcing, deep shear and low-level convergence.
Strong thunderstorms may develop over higher terrain of northern
Chihuahua and far west TX after 00Z. This activity would cross over
a stabilizing boundary layer across far west TX, but also, a zone of
elevated buoyancy and low-level moisture favorable for convection
through this evening. At this time the severe potential appears too
conditional and low-end to place the already marginal outlook area
farther southeastward.
..Edwards/Gleason.. 03/21/2019
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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