Area Forecast Discussion
Issued by NWS Memphis, TN

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FXUS64 KMEG 181105

Area Forecast Discussion
National Weather Service Memphis TN
605 AM CDT Sun Mar 18 2018


Updated for the 12Z Aviation Discussion


.PREV DISCUSSION... /issued 408 AM CDT Sun Mar 18 2018/

A deep trough continues to dig across the western CONUS early this
morning with downstream shortwave ridging over the Plains and
Mississippi Valley. A weak cold front moved through the area
yesterday and is expected to stall to our south this morning,
eventually lifting back north this afternoon and overnight as a
warm front. Showers and thunderstorms are occurring over southern
AR just north of this boundary and will continue to spread to the
northeast throughout the day. This convection looks to be the
response from mid-level frontogenesis along the warm front aloft
which tilts back over the cooler air mass. This frontogentic
forcing will shift northeast over the Mid-South later today and

Showers and thunderstorms are expected to become more widespread
this evening as the warm front continues to lift north and forcing
for ascent is enhanced by a strong shortwave trough moving across
the Southern Plains. This wave is progged to maintain its strength
tonight, acquiring a slight negative tilt as it moves along the
Ohio River. A few strong to severe storms are possible Sunday
night, but convection will remain elevated during this period and
the primary hazard will be marginally severe hail.

Convection is expected to be ongoing Monday morning but is
expected to be somewhat scattered. Thus, respectable clearing
should allow for sufficient destabilization of the boundary layer
to break the capping inversion by midday. This will result in a
window for potential severe weather through early afternoon,
primarily east of the Mississippi River. Hodographs east of a
Pacific cold front suggest the potential for supercells but any
storms that initiate should move quickly into middle TN and north
AL. Any supercells that develop will have the potential to
produce large hail, damaging winds, and even a few tornadoes.

The cold front will move across the Mid-South during the late
morning and afternoon, ending thunderstorms from west to east and
advecting much drier air into the region. Additional moisture will
wrap around the cyclone Monday night resulting in light rain
showers or perhaps drizzle. These showers are expected to continue
throughout the day Tuesday as a trailing shortwave trough moves
across the Mid-South. Precipitation finally comes to an end by
Tuesday evening as the trough moves east.

Cooler and dry weather is anticipated across the Mid-South
Wednesday and Thursday. Northwesterly flow aloft on the backside
of the departing trough will continue through Friday as a ridge
builds over the central CONUS downstream a trough digging over the
West Coast. Northwesterly surface winds will continue through
Wednesday morning but will weaken during the day as a 1024mb
surface high settles over the region. Strong radiational cooling
should allow temperatures to drop to near freezing by sunrise on
both Wednesday and Thursday mornings across portions of the CWA.
We`re still early enough in the season that freezes are expected
with the average last freezes of the season generally occurring
in late March. Afternoon highs during the midweek period will be
in the 50s to lower 60s.

Differences in the medium range models continue to limit
confidence in weekend rain chances. All of the GFS, ECMWF, and
Canadian indicate a deep trough over the Pacific Northwest by
Friday with a ridge extending from the Gulf of Mexico into the
Prairie Provinces of central Canada. However, the GFS breaks this
ridge down faster than the ECMWF placing forcing for ascent
farther south as a shortwave trough approaches the the Ohio Valley
on Friday night. The GFS solution gives us a modest opportunity
for precipitation whereas the the ECMWF maintains a mostly dry
forecast until Saturday. Low PoPs were continued Thursday night
through Friday night given these uncertainties but were generally
capped at 30%.

Over the weekend, the flow aloft becomes more southwesterly as the
PacNW trough moves east across the Rockies. Subtle perturbations
moving through the flow aloft will interact with a cold front in
the vicinity, increasing rain chances across the region through
the remainder of the weekend. The mesoscale details will be very
important in next weekend`s forecast but the models won`t have a
good handle on the finer details for several days.



12Z TAF cycle

Low clouds currently over northern sections of the forecast area
will gradually lift later this morning with VFR conditions
continuing over the remainder of the region through this
afternoon. Low clouds will return this evening along with showers
and thunderstorms which continue through the overnight hours.
Winds will be mainly from the northeast today at 5 to 10 knots
before shifting to the east tonight at around 5 knots.




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