Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Jackson MS
314 PM CDT Thursday Apr 24 2014


Today through Saturday

Strong to severe storms will be possible this afternoon and evening
across the Delta Region and eastward along the Highway 82 corridor.
Once the boundary moves through Friday morning, expect a drying and
warming trend into the first half of the weekend. Please see long
term as confidence continues to grow on a significant severe weather
episode with multiple rounds of severe weather Sunday afternoon through

Strong to severe storms have already begun to fire this afternoon in
la and Arkansas in association with a sharp shortwave trough and along a
prefrontal pressure trough where SBCAPE values have built into the
1500-2000 j/kg range. This instability in combination with 40-50 knots
deep layer shear and near 8 c/km 700 mb-500 mb lapse rates will further
support a severe weather risk going into the arklamiss Delta
counties late this afternoon and evening. Damaging winds of 60 miles per hour and
hail to size of half dollars look to main hazards at this time. Storm Prediction Center
mesoanalysis currently depicts less then 100 m2/s2 0-1km srh within
surface based convective area. This, in conjunction with higher
local/lfcs along and east of the Delta should limit tornado potential.
However, it should be noted that hrrr continues to show 0-1km
helicity values increasing towards 150-200 m2/s2 over the Delta and
north central MS through the early evening and thus a non-zero risk
of a tornado exists. The going graphics handle the overall situation

Instability will decrease through the night after 1am as the broken
line shifts east into less supportive Thermo environment and overall
weakening trend should occur as a weak cool front moves through the
region by Friday morning. A drying trend will start Friday and go
into Saturday with a warming trend into the early weekend. After a
slightly cooler start tomorrow morning highs will rebound into the
middle to upper 70s Friday afternoon under full sun. Highs Saturday will reach
into the low to middle 80s with some areas approaching upper 80s.

A volatile episode of severe storms and heavy rain continues to look
probable late weekend into early next week. Please stay up to date
on this situation. /Allen/

Sunday through next Wednesday...

Forecast thinking is generally the same regarding the potent set-
up for severe weather and heavy rain indicated by global model
guidance for early next week...particularly from late Sunday through
Monday night...and perhaps through Tuesday into Tuesday night. All
modes of severe weather including the potential for strong tornadoes
will be possible. Significant flooding could develop if multiple
rounds of storms materialize.

Dry weather will continue through Saturday night over the arklamiss...
but dramatic changes are expected starting Sunday afternoon and going
through Sunday night as a powerful deepening cyclone traverses the
plains states and brings rapid pressure falls to the lower MS valley
region. A strengthening low level jet juxtaposed by steep middle level
lapse rates will draw rich Gulf moisture northward (sfc dewpoints
approaching 70 f) and increase low level shear and tornado potential
by Sunday evening over the Delta Region as surface- based thunderstorms
break out. The first round of storms may organize into a mesoscale
convective system tapping into very moist air with precipitable water
~ 1.75 inches. This mesoscale convective system could push across much of the arklamiss
overnight before weakening some as it outruns better upper level
support. However...expect re-newed severe thunderstorm activity
Monday as the nose of powerful Pacific jet energy rounds the base of
the deep central Continental U.S. Trough and enhances wind shear/lift and the
severe weather risk over the forecast area. Mixed layer cape > 3000
j/kg could help may for a volatile set-up with this synoptic pattern.

Cips analogs are showing very significant events for comparison to
this set-up adding more confidence that significant severe weather
and flooding will be possible...especially if a slow-moving
convective system sets up Monday night as guidance suggests. Another
concern is the possibility for the cyclonic regime to stall over the
central Continental U.S. For a longer period into Tuesday...allowing another lobe
of shortwave energy to move across the area and back flow
sufficiently for regeneration of storms. Beyond Tuesday night...
expect drier and cooler air to finally move into the region. /Ec/


Preliminary point temps/pops...
Jackson 59 81 52 87 / 17 5 0 5
Meridian 60 82 48 86 / 22 5 0 5
Vicksburg 57 81 53 86 / 23 5 0 5
Hattiesburg 63 84 56 87 / 18 5 0 5
Natchez 60 81 55 85 / 15 5 0 5
Greenville 56 79 52 85 / 71 5 0 5
Greenwood 57 78 49 85 / 62 5 0 5


Jan watches/warnings/advisories...