(All days are valid from 12 UTC - 12 UTC the following day)
Note: A severe weather area depicted in the Day 4-8 period indicates 15%, 30% or higher probability for severe thunderstorms within 25 miles of any point.
PREDICTABILITY TOO LOW is used to indicate severe storms may be possible based on some model scenarios. However, the location or occurrence of severe storms are in doubt due to: 1) large differences in the deterministic model solutions, 2) large spread in the ensemble guidance, and/or 3) minimal run-to-run continuity.
POTENTIAL TOO LOW means the threat for a regional area of organized severe storms appears unlikely (i.e., less than 15%) for the forecast day.
Forecast Discussion
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 280959
SPC AC 280959
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CST Mon Dec 28 2020
Valid 311200Z - 051200Z
...DISCUSSION...
...Thursday/Day 4 and Friday/Day 5...
An upper-level low is forecast to move northeastward across the
southern Plains on Thursday as an associated cold front advances
eastward into the lower Mississippi Valley. Moisture advection
appears likely to continue ahead of the front across the central
Gulf Coast states where surface dewpoints should be in the 60s F.
Thunderstorms may develop during the day along the front with
additional convection forming further east across the moist sector.
Model forecasts suggest that a low-level jet will increase in
strength, moving north-northeastward across Alabama during the late
afternoon. Convective development may be favored on the nose of the
low-level jet during the late afternoon and early evening.
Additional storms may develop further to the west across the lower
Mississippi Valley. Low-level and deep-layer shear profiles should
be favorable for severe storms across those two areas. The main
threats would be for tornadoes and wind damage. At this point, there
is some uncertainty concerning how far the quality moisture can
advect northward. For this outlook, have drawn the 15 percent
contour across central Alabama, where there appears to be a good
chance surface dewpoints will reach the lower to mid 60s F.
On Friday, the upper-level low is forecast to move
north-northeastward into the mid Mississippi Valley as southwest
mid-level flow remains entrenched across the eastern Seaboard.
Thunderstorm development will be possible along and ahead of a cold
front as a low-level jet moves northward across the Carolinas.
Low-level and deep-layer shear profiles are forecast to be favorable
for severe storms with the main threats being tornado and wind
damage. Have placed the 15 percent contour in the area where the
chance for quality moisture and convective potential is maximized,
according the latest ECMWF solution.
...Saturday/Day 6 to Monday/Day 8...
On Saturday, an upper-level trough is forecast to move eastward
across the southern Plains and mid Mississippi Valley as southwest
flow remains over much of the Southeast. The upper-level trough is
forecast to move across the Southeast on Sunday as a cold front
advances southward across the Florida Peninsula. Severe storms can
not be ruled out during the day on Sunday in central Florida but
uncertainty concerning the model solutions is substantial at this
time. On Monday, surface high pressure across much of the eastern
third of the nation should limit thunderstorm potential.
..Broyles.. 12/28/2020
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