Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 220846
SPC AC 220845

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CDT Wed Mar 22 2017

Valid 251200Z - 301200Z

...Saturday/Day 4...
The medium-range models begin the day 4 to 8 period with an
upper-level low in the vicinity of southeast Kansas and move the low
northeastward into Missouri during the day on Saturday/Day 4. The
southern extension of the upper-level trough is forecast to move
across the lower Mississippi Valley on Saturday. To the east of the
upper-level trough, a line of storms is forecast to be ongoing
Saturday morning at 12Z near the Mississippi River. The ECMWF and
GFS solutions move this convection eastward across the central Gulf
Coast States where a wind damage and hail threat would be possible.
How the scenario unfolds with regard to instability and storm mode
remains questionable due to differences in the model solutions. The
ECMWF has been more consistent for Saturday and will favor that
solution. Due to the wider moist sector than has been previously
forecast, will expand the 15 percent contour eastward to encompass
much of Alabama.

...Sunday/Day 5...
The upper-level trough is forecast to move northeastward into the
southern Appalachians on Sunday/Day 5 and become detached from the
moist sector over the western and central Gulf Coast. Thunderstorms
associated with a marginal wind-damage and hail threat will be
possible ahead of the upper-level trough in the southern and central
Appalachian mountains.

Over the south-central U.S., the ECMWF and GFS solutions move a
shortwave trough eastward into the southern Plains on Sunday. The
GFS is more aggressive with moisture return across north Texas and
Oklahoma suggesting a corridor of instability could be in place by
00Z/Monday. This would result in a severe threat Sunday evening
across parts of central and eastern Oklahoma. The ECMWF is slower
with the shortwave trough and further west with an axis of
instability suggesting a severe threat could occur in western and
central Oklahoma. At this point, have taken a consensus of the two
solutions and introduced a small 15 percent area in central Oklahoma
extending southward along the instability corridor into north Texas.
This area would have potential for large hail, isolated wind damage
and possibly a tornado threat.

...Monday/Day 6 to Wednesday/Day 8...
The ECMWF and GFS solutions move the southern Plains upper-level
trough into the lower to mid Mississippi Valley on Monday/Day 6 and
into the western Atlantic on Tuesday/Day 7. A moist sector is
forecast to be located from southeast Texas eastward into western
Alabama on Monday. Severe thunderstorms will be possible during the
day depending upon the timing of the upper-level trough and
instability distribution. Due to uncertainties concerning these two
factors, will refrain from adding a severe threat area for Monday.
For Wednesday/Day 8, low-level moisture is forecast to return
northward into parts of the southern Plains. In addition, the ECMWF
and GFS solutions develop an upper-level low in the southwestern
U.S. The two solutions are very different concerning the details of
Wednesday`s forecast suggesting uncertainty is great at this time in
the period.

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