SPC 0730Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0215 AM CDT Wed Oct 07 2020

Valid 091200Z - 101200Z


At least some risk for tornadoes may accompany the landfall of
Hurricane Delta, across parts of the southeastern Louisiana,
southern Mississippi and southwestern Alabama coastal plain, mainly
Friday night.

Amplification within the westerlies across the mid-latitude Pacific
into North America may commence during this period.  This may
include a digging mid-level trough to the west of the Pacific
Northwest coast, and building large-scale ridging across the
Canadian/U.S. Rockies through the Canadian Prairies and much of the
Great Plains.  In a lingering branch split off to the south of the
stronger flow, weaker mid-level troughing is forecast to shift into
the Southwest, perhaps with an embedded closed low migrating into
southern California by late Friday night.  

Downstream, Hurricane Delta is forecast to accelerate
north-northeastward, inland of the northwestern Gulf coast by Friday
evening, with the mid-level circulation center gradually becoming
absorbed within weak troughing slowly shifting east of the southern
Great Plains.  This probably will be accompanied by the influx of
seasonably high precipitable water content within a plume across and
just east of the lower Mississippi Valley.  However, relatively dry/
potentially cool boundary-layer air as far south as the Gulf coastal
plain early Friday may be slow to substantively modify.

...Gulf Coast...
Latest model output generally suggests that surface dew points near
or just above 70F may initially be confined to immediate coastal
areas, perhaps inland some across parts of southeastern Louisiana,
to the north of Hurricane Delta at the outset of the period.  Across
the remainder of the Gulf coastal plain, surface dew points may
generally be in the mid/upper 60s F, with mid 70s+ F mostly well
offshore across the western Gulf of Mexico.  Given the warm
mid-level environment advecting inland with Delta, mid 70s F surface
dew points will probably need to be advected inland to contribute to
sufficient boundary-layer destabilization to support an appreciable
risk for tornadoes, northeast and east of the inland migrating
low-level circulation center.  At this time, most guidance suggests
that lower 70s F dew points may be advected inland in a small/narrow
plume wrapping into the circulation center, across parts of
southeastern Louisiana, southern Mississippi and adjacent
southwestern Alabama, with mid 70s F dew points lagging near/south
of immediate coastal areas.  Given the forecast strength of the
system as it approaches landfall, it is possible that this is
underdone, but the risk for tornadoes with Delta still seems largely
conditional at this time.

..Kerr.. 10/07/2020

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