SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1115 AM CST Thu Nov 26 2020

Valid 271200Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY ACROSS
PARTS OF SOUTHEASTERN TEXAS...SOUTHERN LOUISIANA AND SOUTHERN
MISSISSIPPI...

...SUMMARY...
Strong thunderstorms may impact parts of the northwestern Gulf
coastal plain Friday, and could pose at least some risk for severe
hail and strong wind gusts.

...Synopsis...
Stronger mid-latitude westerlies are forecast to remain confined to
the central/northern tier of the U.S. northward, but a strong
high-level jet emerging from the subtropical eastern Pacific appears
likely to remain influential across the Gulf Coast region and
Southeast through this period.

Within this regime, one mid-latitude wave, in phase with the
subtropical stream, is forecast to progress east of the New England
coast by 12Z Friday, followed by another perturbation digging into
and across the Great Lakes region by late Friday night.  Another
upstream perturbation, currently splitting off of the belt of
mid-latitude westerlies across the Great Basin, may evolve into a
mid-level low over Arizona, before gradually accelerating eastward
in phase with the subtropical westerlies, into/across the southern
Rockies.  

Although spread among the various model output remains largest
concerning the Southwestern perturbation, there is little suggestion
within the guidance that it will provide support for substantive
wave development along a frontal zone expected to slowly continue
advancing into the northwestern Gulf coastal plain.  This frontal
motion is forecast in response to the progression of the preceding
mid-latitude short waves, which may also contribute to a
southeastward advancement of the front off the southern Atlantic
Seaboard, while the front becomes quasi-stationary across the
eastern Gulf Coast states vicinity.

A plume of seasonably moist air will linger along and just south of
this frontal zone, though generally weak mid/upper lapse rates are
expected to temper the potential instability.

...Southeast Texas into southern Louisiana/Mississippi...
Near/just south of the surface front, it does appear that CAPE
rooted within/just above the boundary-layer may reach 500-1000 J/kg
across the coastal plain.  Deep-layer shear is also expected to
become strong, as the core of the high-level jet emerging from the
subtropics begins to overspread the region, with 30-50+ kt westerly
flow as low as the 700-500 mb layer.  However, guidance generally
indicates that low-level wind fields and forcing for ascent will
remain modest to weak through this period.

Models do suggest that a coupling of speed maxima within the
mid/upper jet may contribute to a region of strong, focused
high-level divergence overspreading southeast Texas into the lower
Mississippi Valley during the day Friday.  Perhaps aided by weak
mid-level warm advection, this is expected to contribute to 
thunderstorm development which could eventually become rooted within
the modestly unstable boundary layer.  If this occurs, stronger
cells may briefly become capable of producing marginally severe
hail. One or two small organizing clusters of storms might not be
out of the question, which could pose a risk for potentially
damaging wind gusts while propagating southeastward into Friday
evening.

..Kerr.. 11/26/2020

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