Forecast Discussion


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FXUS64 KMEG 191152 AAA
AFDMEG

Area Forecast Discussion...UPDATED
National Weather Service Memphis TN
552 AM CST Tue Feb 19 2019

.UPDATE...
Updated for 12Z Aviation Forecast Discussion below.

&&

.PREV DISCUSSION... /issued 357 AM CST Tue Feb 19 2019/

DISCUSSION...

Latest IR satellite imagery depicts high clouds covering the
region this morning. These clouds the precursor to a very active
weather pattern. Latest radar imagery depicts some light
precipitation falling across portions of north Mississippi
already this morning. Given temperatures are near or below freezing
in many locales have added a mix of rain and sleet through 9 AM,
primarily for N MS. Meanwhile, mid level analysis depicts
southwesterly flow aloft over the region, while at the surface
winds are from the north as high pressure is centered to the NW.

Showers will gradually overspread the region by this afternoon as
a warm front lifts north toward and over the region by the early
hours of Wednesday. This front will be aided by a LLJ of up to 60
knots nosing into the region this evening. This mass moisture
transport will produce near record PWAT values this evening
through Wednesday evening. Model guidance suggests Tuesday PM
values will be between 1.25 and 1.50 inches for most of the
region, with portions of N MS near 1.60 inches and up to 1.75
inches by late Wednesday. These values would all be above the 99th
percentile for February. This will result in several rounds of
heavy rainfall, and even a few embedded thunderstorms, this
afternoon through Wednesday evening.

As such, a Flash Flood Watch goes into effect for the entire area
this afternoon and continues through 6 AM on Thursday morning. By
that point in time, some 2 to 4 inches of rain will have fallen
over the area. The latest QPF has the axis of maximum rainfall
during through late Wednesday roughly along a line from Paris
southwest through Memphis and west to Forrest City. This heavy
precipitation, in addition to the recent wet conditions, will
lead to areal, river, and flash flooding for Tuesday and
Wednesday.

Rain will temporarily cease by early Thursday as high pressure
pushes in from the west. Periods of sun will be possible during
the day on Thursday as the high moves over the region. While
Tuesday afternoon highs will only be realized in the 40s, highs on
Wednesday and Thursday will be in the 50s to near 60. The lack of
precipitation will be short lived, however, as a shortwave aloft
embedded in the southwesterly flow leads to showers by late
Thursday for most of the area. A warm front moves through the
region by Friday afternoon, allowing moderate rain to fall with a
few embedded thunderstorms, as PWAT values again climb to abnormal
values for mid to late February.

By early Saturday a deep trough has dug its way into the Southern
Plains, which leaves the water hose of southwest flow aloft wide
open over the region. Not only does this set the stage for more
heavy rain Friday and Saturday, but the upper trough takes on a
bit of a negative tilt on Saturday, acting to juxtapose shear and
instability for a few strong to severe thunderstorms during the
afternoon and evening hours of Saturday. The SPC currently has
most of the region highlighted for this threat on Saturday.

As a cold front clears the region by early Sunday, dry conditions
finally return. However, the region will have received some 4 to 8
inches of rainfall from the Tuesday to early Sunday time frame.
This will likely necessitate another Flash Flood Watch for the
late week time frame. Surface high pressure remains over the
region for Monday, but models converge on yet another shortwave
and thus rainfall for the region again next Tuesday.

ZDM

&&

.AVIATION...

12Z TAFs

Midlevel moisture from subtropical jet was lifting north this
morning. Pockets of PL mixing in the RA over north MS, as the
precip fell into the initially very dry subcloud layer. NAM Bufr
soundings depicted this dry layer saturating this morning into
the afternoon, but appeared a bit to aggressive in lowering
ceilings at TUP to low MVFR at 15Z.

MVFR should prevail areawide this afternoon as SHRA expands in
coverage. RAP and NAM were in close agreement in developing a
45KT-65KT low level jet at FL020 after 21Z. The nose of 60KT FL020
winds is depicted by both NAM and RAP as edging into the
southeastern MEM TRACON in the 04Z-09Z time frame. The presence of
the low level jet exit regions suggests an elevated front near
MEM around the time of the inbound push. At that time, model
soundings depicted uncapped unstable air at FL030, just above the
low level inversion. Tall "skinny" CAPE/instability remains
through 14Z at MEM, but the frontal convergence will have lifted
out to the east by then.

PWB

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...Flash Flood Watch from noon CST today through late Wednesday
     night for Clay-Craighead-Crittenden-Cross-Greene-Lee AR-
     Mississippi-Phillips-Poinsett-St. Francis.

MO...Flash Flood Watch from noon CST today through late Wednesday
     night for Dunklin-Pemiscot.

MS...Flash Flood Watch from noon CST today through late Wednesday
     night for Alcorn-Benton MS-Calhoun-Chickasaw-Coahoma-DeSoto-
     Itawamba-Lafayette-Lee MS-Marshall-Monroe-Panola-Pontotoc-
     Prentiss-Quitman-Tallahatchie-Tate-Tippah-Tishomingo-Tunica-
     Union-Yalobusha.

TN...Flash Flood Watch from noon CST today through late Wednesday
     night for Benton TN-Carroll-Chester-Crockett-Decatur-Dyer-
     Fayette-Gibson-Hardeman-Hardin-Haywood-Henderson-Henry-Lake-
     Lauderdale-Madison-McNairy-Obion-Shelby-Tipton-Weakley.

&&

$$