Forecast Discussion

FXUS64 KMEG 221242

Area Forecast Discussion
National Weather Service Memphis TN
642 AM CST Thu Feb 22 2018

Updated to include drizzle and patchy fog this morning.



In the wake of heavier precipitation over north Mississippi...patchy
fog and drizzle have developed farther north. This light
precipitation may cause a few hundredths more of rainfall through
noon this morning...while fog may restrict visibility down to a
mile or so.



.PREV DISCUSSION... /issued 530 AM CST Thu Feb 22 2018/

.UPDATE...Aviation Discussion.

PREV DISCUSSION... /issued 352 AM CST Thu Feb 22 2018/

Currently band of moderate to heavy rainfall was to the south of
I-40 and along and north of a stalled cold front from near
Greenwood to Fulton Mississippi. Latest rainfall rates generally
ranged form a quarter to a half inch an hour. Temperatures ranged
from the upper 30s over portions of northeast Arkansas to another
balmy 70F in Aberdeen Mississippi.

For today and tonight...heavier band of rain this morning will
shift to the northern counties the next in line
shortwave embedded in the atmospheric river starts a northerly
push of the stalled front. However...a lull in the heavier
precipitation appears likely this afternoon and into the early
evening hours...before the focus shifts with the shortwave.
Temperatures today will range from the 40s north to the 70s south.
WAA late tonight will slowly bring temperatures into the 50s over
the north...with lows in the 60s across the south.

Friday and Saturday...models in better agreement this period with
regards to the timing and deepening of a surface low ejecting out
the Texas Panhandle and into the Midwest. The GFS still is more
bullish with deeper central pressure and a stronger low level
wind field. But the NAM and EURO this run have trended to
a slightly stronger system as well. Therefore pockets of heavy
rain will remain north of I-40 tomorrow and into early
Saturday along the surging/lifting warm front...and then across
the entire area later Saturday and into Saturday night as a cold
front associated with the developing low sweeps east. Collaborated
with surrounding offices and WPC of what will be a three day
moderate risk for flooding over portions of our area/flood watch.
Additional rainfall amounts of 5+ inches can`t be ruled out
leading to 5-day storm totals encroaching on 9-10 inches for some.

With regards to a severe threat...models are showing a prefrontal
trough signal forming in eastern Arkansas by 00z Sunday as the
surface wave crosses Missouri. Another feather in the cap for the
potential for surface-based convection. A 70kt LLJ from the
southwest will form just out ahead of the trough leading to an
evening period of potentially backed surface winds and few low
level mesos and/or bowing segments. Limiting factors will be
lapse rates and instability amounts after sunset. Have placed
wording in this morning`s HWO about this severe threat.

Temperatures this period will be in the 60s and 70s...with lows
falling Saturday night into the 40s and 50s behind the cold front.

Sunday through next Wednesday...most of the Midsouth looks to be
dry through Tuesday with the exception of the far southern
counties. Gulf moisture will reside just south of the CWA
however...with both the GFS and EURO showing return southerly flow
bringing rain back starting Tuesday night into Wednesday. Thus
have ramped up PoPs this period. A modified Pacific airmass will
keep temperatures above normal this period. Could it be Spring?




Relied heavily on the HRRR this update as it appears to have a
good handle on the current conditions. Rain should continue at
TUP through mid morning with only BR at MEM...MKL and JBR. Another
round of showers will approach JBR before 00z. The HRRR does keep
these showers mostly in Arkansas...but I did add showers back at
MEM at 02z. Cigs will likely remain IFR or lower through the TAF
cycle. Winds will be fairly light...although it does appear winds
are briefly gusty immediately on the back side of the rain shield.
The wind direction will shift Southerly tomorrow afternoon. Some
guidance crashes vis back to less than 1sm tomorrow night...though
the HRRR does not. Will take a middle of the road approach
tonight and carry 2sm with RA/BR at MEM, MKL and JBR. Rain is not
expected at TUP until after 12z.


AR...Flood Watch through late Saturday night for Clay-Craighead-
     Crittenden-Cross-Greene-Lawrence-Lee AR-Mississippi-
     Phillips-Poinsett-Randolph-St. Francis.

MO...Flood Watch through late Saturday night for Dunklin-Pemiscot.

MS...Flood Watch through late Saturday night for Alcorn-Benton MS-

     Flood Watch until noon CST today for Lafayette-Tallahatchie-

TN...Flood Watch through late Saturday night for Benton TN-Carroll-