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ACUS02 KWNS 221729
SPC AC 221728

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1228 PM CDT Sun Jul 22 2018

Valid 231200Z - 241200Z


A few severe thunderstorms are possible across southeastern
Louisiana Monday.  Strong thunderstorms with some risk for severe
weather may also impact the central Florida Peninsula.

Upper ridging, centered near the NM/AZ border, will remain largely
in place over the Southwest and Great Basin throughout the period.
Upper troughing, which has persisted over much of the eastern CONUS
this weekend, is expected to devolve into a weak upper low centered
over northern GA by 12Z Tuesday. Enhanced northerly flow aloft
between these two features will extend from the middle MO Valley
southward off the central Gulf Coast. Enhanced westerly flow is also
anticipated along the northern periphery Southwest ridge, from the
Pacific Northwest into the Upper Midwest. Some modest strengthening
of this westerly flow is possible across the northern High
Plains/northern Plains during the second half of the period as a
shortwave trough drops into Saskatchewan. 

Predominant surface features will be a weak cold front moving
southward/southeastward across the central Plains and upper/mid MS
Valleys and a largely stationary low over southern GA. Weak
troughing will extend from this low northwestward into the OH
Valley. Very moist southeasterly low-level flow is expected
throughout the Mid-Atlantic States.

...Southeastern Louisiana vicinity...
Thunderstorms are anticipated early in the period across the MS
Delta region as a lobe of ascent glaces the region as it rounds the
upper troughing over the eastern CONUS. Seasonally strong northerly
flow over the area will contribute to moderate vertical shear while
the typically warm and moist airmass supports moderate to strong
instability. A few of this early storms may produce damaging wind
gusts. Outflow from this early activity as well as another subtle
area of ascent (attendant to a weak perturbation within the
northerly flow aloft) will provide the impetus for additional
thunderstorm development during the afternoon and evening. Bowing
line segments capable of damaging wind gusts are possible within
this second round of storms. Storms will likely propagate into the
area of remaining instability, which will result in a
southerly/southwesterly storm motion. This storm motion would
increase storm-relative helicity (although remaining relatively
modest) and result in at least a low-end tornado threat.

...Central FL Peninsula...
Uncertainty regarding convective evolution today complicates the
forecast for Monday. There is some potential for the airmass to be
sufficiently overturned to temper additional storms Monday
afternoon. However, much of the guidance (both high-resolution and
medium-range), suggest the airmass will remain supportive of
additional storms, with the remnant outflow providing a focus for
development. Vertical shear is relatively weak but a few
water-loaded downbursts capable of damaging wind gusts are possible.

...Mid-Atlantic States...
A very moist airmass (i.e. PW values around 2 to 2.25" -- near the
daily max values based on SPC sounding climatology) will advect into
the region amidst the southeasterly low-level flow. Confluence
between the upper trough across the eastern CONUS and upper ridging
farther northeast over the northwest Atlantic Ocean will result in
moderately strong southerly mid-level flow and bulk vertical shear
on the order of 30 kt. Primary hazard over the region is heavy rain
(see WPC's Excessive Rainfall Outlook for more details) but a few
damaging wind gusts appear possible as well.

Tornado:   2%     - Marginal
Wind:     15%     - Slight
Hail:      5%     - Marginal

..Mosier.. 07/22/2018