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Area forecast discussion 
National Weather Service Memphis Tennessee
641 am CDT sun may 24 2015

updated to add 12z aviation discussion.


Previous discussion... /issued 416 am CDT sun may 24 2015/


A large upper level low pressure system over the intermountain
west this morning will continue to lift slowly northeast today.
The upper level ridge that has persisted across the middle south for
the past few days will begin to break down as the first in a
series of shortwave impulses approaches from Texas. This shortwave
will eject northeast across the arklatex and eventually into the
middle Mississippi Valley tonight. Surface low pressure associated
with this shortwave will lift northeast from the southern into the
Central Plains overnight as well.

Deep layer shear should strengthen as a low level jet streak on
the order of 40 to 50 kts develops in advance of the shortwave and
shifts east across the western half of the forecast area this
evening. The airmass should become moderately unstable by late
afternoon as dewpoints surge to near 70 degrees along and west of
the Mississippi River and temperatures rise into the lower and
middle 80s. This should result in SBCAPE values between 1500-2500
j/kg in these areas between 21z-00z. Surface winds remain backed
as well in response to the surface wave and deep upper troughing
over the plains. This should result in 0-1 km storm relative
helicity values between 200 and 300 m2/s2. Decent low level
turning of winds through the boundary layer...low local
heights...strengthening wind fields...and moderate instability
should support a severe weather threat beginning late this
afternoon and continuing through the evening hours for areas along
and west of the Mississippi River. The severe threat should
diminish with eastward extent later this evening as the shortwave
lifts northeast and convection becomes removed from the better
shear and instability. It appears that the primary severe weather
threats will be damaging winds and a few tornadoes.

In addition to the severe weather threat...there will also be a
threat for heavy rainfall and flash flooding along and west of the
Mississippi River this evening. As convection may
tend to train across the same areas and result in several inches
of rainfall. A Flash Flood Watch will likely be needed for western
portions of the middle south later this evening and overnight. This
will be looked at closely by the day shift to determine the areal
extent of the the flood threat area.

The lead shortwave will lift northeast of the area later tonight
with residual weakening line of showers and thunderstorms draped
across areas east of the Mississippi River by sunrise Monday
morning. This area of showers and thunderstorms should continue to
move east during the morning hours and diminish in coverage. There
will likely be a lull in widespread convective activity...especially
along and west of the Mississippi River by Monday afternoon as the
middle south becomes positioned between shortwave disturbances. This
should allow the atmosphere to destabilize again with moderate
instability levels again developing. This will be highly dependent
upon mesoscale convective trends.

By Monday night...a secondary shortwave impulse should lift
northeast from the Southern Plains across the Ozark Plateau by
early Tuesday morning. Latest model guidance suggests a potential
mesoscale-low developing near the arklatex and lifting northeast
overnight. Low and deep layer wind fields should again strengthen
Monday night as they overspread the forecast area. This should set
the stage for another round of showers and thunderstorms Monday
night into Tuesday morning. There may be more potential for severe
thunderstorms during this time period...but will be highly
dependent upon the mesoscale environment and effects from earlier
convection during the day Monday. If a severe weather threat
unfolds...again the potential would exist for damaging winds and
isolated tornadoes. The bigger threat that should materialize will
be the potential for flash flooding from heavy rainfall. This
heavy rainfall should occur over areas that are expected to
receive heavy rainfall Sunday night. This should only worsen any
existing flood conditions. A Flash Flood Watch may need to be
extended through midday Tuesday to cover this potential.

Chances for showers and thunderstorms should continue into
Wednesday as a third but weaker shortwave traverses the forecast
area. Plan to continue with scattered showers and thunderstorms
in most areas.

The upper pattern temporarily becomes less amplified through the
end of next week with a humid tropical airmass remaining in place.
This will support the potential for mainly diurnal convection both
Thursday and Friday afternoon and evening. Weak wind fields but
stronger instability may support pulse strong thunderstorms during
peak heating.

Another stronger shortwave should lift out of the Southern Plains
towards the middle Mississippi Valley over the weekend with
increasing organized storm chances once again across the middle
south. Temperatures should remain seasonably warm with continued
humid conditions into next weekend.



12z taf cycle

VFR conditions expected through most of the 12z taf cycle. Southeast
winds will gradually veer S and increase to 10-16 kts with higher
gusts towards this afternoon. A shortwave trough will move across
the region later this afternoon into tonight with rain showers/thunderstorms and rain
chances increasing across the area and a potential for MVFR/IFR
conditions. Have included tempos at mem/jbr between 01z-03z...mkl
between 02z- 04z...and tup between 04z-06z.



Meg watches/warnings/advisories...


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