Area Forecast Discussion
Issued by NWS Memphis, TN

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FXUS64 KMEG 130542
AFDMEG

Area Forecast Discussion
National Weather Service Memphis TN
1142 PM CST Tue Dec 12 2017

.UPDATE...

Updated for 06z TAF discussion

&&

.PREV DISCUSSION... /issued 944 PM CST Tue Dec 12 2017/

UPDATE...
Clear, calm and cold conditions prevailed across the Midsouth at
midevening. 9 PM CST temps had cooled into the mid 20s near the
TN River, while mid 30s prevailed over east AR.

Latest HRRR and other short term guidance shows winds may edge up
a bit over east AR prior to sunrise, which should be enough to
level off the cooldown during the overnight.

Forecast was recently updated to lower overnight lows over most of
west TN and northeast MS, inclusive of the outlying Memphis suburbs.

PWB

PREV DISCUSSION... /issued 334 PM CST Tue Dec 12 2017/

DISCUSSION...
A deep trough continues to affect the eastern CONUS with an
upstream Rex Block in place across the west. This pattern will
persist for a few more days but the ridge will gradually shift
west over the Pacific, signaling a synoptic pattern change. Until
we see this shift occur, we`ll continue to see fast-moving,
moisture-starved weather systems. Fortunately, this change looks
to occur by the end of the work week with rain chances appearing
more likely during the latter half of the weekend, potentially
lingering into early next week.

Looking back at the short-term, winds today were a bit stronger
than suggested by NWP but are finally beginning to decrease. With
relative humidity falling into the range of 30-40%, fire danger
was elevated but Red Flag criteria were never threatened. Wind
speeds will quickly decrease after sunset, setting the stage for a
cold night across the Mid-South. Dewpoints are currently in the
teens and lower 20s and skies are mostly clear. This will promote
strong radiational cooling. The caveat is that southerly winds
will begin to increase late which may prevent temperatures from
dropping too low, especially along/west of the Mississippi River.

Winds will continue to increase on Wednesday as a deepening
surface low tracks ESE near the western Great Lakes. Southwest
winds are forecast to increase to 15-25 mph, with gusts
potentially exceeding 30 mph at times, especially across the
northwest half of the CWA. Temperatures will rebound into the 50s,
pushing relative humidity down to 35% or less by peak heating.
Should dewpoints mix more readily than anticipated, relative
humidity could approach Red Flag criteria. It`s worth noting that
the Energy Release Component is in the 97th percentile across
west TN and above the 90th percentile in east AR and north MS.
This suggests a good amount of dry fuel in an area that has seen
well below normal rainfall the past 30-60 days. In summary, fire
danger will be elevated area wide and may approach critical
thresholds in some areas.

Another cold front will move across the area Wednesday evening,
ushering a cooler Continental Polar air mass back into the region
for Thursday and Friday. Highs will largely be in the 40s with
overnight lows in the upper 20s to lower 40s. A positively-tilted
shortwave trough will traverse the area Thursday night into early
Friday, resulting in increasing cloud cover. While mid-level
moisture will increase, it remains scant in both the low-levels
and aloft (specifically in the dendritic growth zone). This
indicates a low potential for rain/snow with this passing trough.
While a few sprinkles and/or flurries cannot be ruled out, the
potential really isn`t worth mentioning in the 5th/6th periods as
no impacts are anticipated.

Southerly winds are expected to resume on Saturday, concurrent
with the shifting synoptic pattern. The eastern CONUS trough is
progged to move east with a flat shortwave ridge over the Ohio
Valley (and Mid-South). The GFS and ECMWF are in fair agreement
that a southern stream shortwave trough will lift northeast
across TX Saturday night into Sunday morning. This will be the
trigger for the enhanced rain chances through the day on Sunday.
However, the models quickly diverge for early next week. The GFS
is slow in departing this trough, keeping it west of the CWA
through Monday night while the ECMWF is about 24 hours quicker.
Should the ECMWF verify, the low PoPs for Monday may need to be
removed. Regardless, with this being a Pacific trough, we`re not
anticipating much of a cool-down in its immediate wake.

Johnson

&&

.AVIATION...
06z TAFs

Surface high pressure is bringing clear skies and light winds
tonight, but a short wave trough and associated low pressure
diving out of the northern plains will lead to a tightening
pressure gradient tomorrow, in tandem with daytime surface
heating. As a result expecting gusty southwest winds to develop
at all TAF sites by late morning, with max gusts on the order of
25-30 kts at all sites but KTUP. By the evening hours winds will
weaken and veer towards the west, before an overnight cold front
swings winds back around to the north. Scattered high clouds and a
few low clouds are possible with the frontal passage, with VFR
conditions expected to prevail.

WLC

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&

$$



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