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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0827Z Feb 24, 2018)
 
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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
327 AM EST Sat Feb 24 2018

VALID 12Z Sat Feb 24 2018 - 12Z Sun Feb 25 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SW OQT 20 SSE KCMB 20 SW KOPM 10 ESE 2R8 10 S LVJ 10 W DRI
20 NW POE 30 E OCH 10 NNW JSO 15 SW TYR 30 ESE LNC 10 NW CRS
15 SSE GDJ 15 ESE SEP 10 SSE MWL 15 N MWL 25 N 1F9 25 WNW 1F0
10 SW GCM 15 NW GMJ 20 SW TBN 30 ESE VIH 10 SSW DFI 10 SW CXPT
15 NNW ERI ELZ 30 S BGM 10 NW 12N 10 SE TTN 10 N APG JYO
25 N SHD 30 NW LWB 30 WSW LNP 20 SW OQT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NNE AQR 25 NNW BPK 25 NNE FAM 20 N SLO 30 WNW EYE 30 ENE FDY
20 N MFD 20 SE CGF 25 SW BFD 30 N UNV 35 SSE UNV 15 W HGR
25 W OKV 15 NE EKN 30 WNW W22 3I2 10 NNE LOZ 30 N MDQ 45 NW MEI
20 SE TVR 20 ESE MLU 20 NW BQP 35 SSW TXK 10 ENE 3T1 10 S TRL
RBD 10 NW FTW GLE 20 WNW DUA 15 NNE AQR.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NNW HTS 45 NNW JKL 20 SSW BWG MKL 25 SSE SGT 25 SSW M89
30 ENE TXK 15 ENE OSA SLR 15 W PRX 35 SW RKR FSM 15 SSE HRO
10 S FAM 20 NNW BMG 30 ESE MIE 25 SSW AOH 15 ESE MFD 20 NNE BTP
FIG AOO 10 ESE CBE 20 NNW W99 30 E PKB 20 WSW PKB 25 NNW HTS.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SE FSM 40 E UNO 20 SE MVN 25 NNE KHLB 25 SSW LCK 45 SSE LUK
20 SE LOU 30 NE DYR 15 NNW SGT 10 SSE LIT 25 SSW LIT M89
25 SSW DEQ 15 NNE LBR 35 WNW DEQ 30 NW DEQ 25 SE RKR 30 SE FSM.



***A major flash flooding event likely Saturday afternoon into
Saturday night/early Sunday morning from the lower AR river valley
into the OH valley region***

No significant changes made to the previous excessive rainfall
potential outlook from northeast TX/southeast OK northeastward
into the OH valley.  There continues to be a strong model signal
for widespread heavy and excessive rainfall over the broad area
listed above---with a very large moderate and high risk areas
maintained for the upcoming day 1 period. Organized heavy precip
expected in two distinct waves day 1.  The lead wave---currently
producing heavy rains from eastern OK---northwest
Arkansas---southern MO into south central IL will be pressing east
northeastward Saturday morning just to the north of the OH river
and into the northern mid Atlantic by early afternoon.  Rainfall
rates in this area expected to diminish by the beginning of the
day 1 period and will likely not be a flash flood threat as it
moves north of the OH river into the northern Mid Atlantic but
will further saturate the soil ahead of the more significant
precip area later day 1.  A smaller southern component of this
first wave associated with convection currently moving northeast
out of central TN will also expand northeastward into the upper OH
valley and central Appalachians Saturday morning.  This area
should be progressive but still produce locally heavy rains that
will move over lower ffg values across the central Appalachians.

This will be followed by a second and more significant wave of
heavy rains developing Saturday morning across central OK/north TX
ahead of the strong mid to upper level height falls ejecting
northeastward from the central/southern plains into the mid to
upper MS valley region.  The overall strong dynamics ahead of the
ejecting trof will support strengthening of the low level flow to
50-65 kts+ out of the south southwest across eastern portions of
the southern plains-- northeastward into the lower MS
valley---lower TN valley and through the OH valley.  Expect a well
organized convective squall line to push east northeastward across
these areas.   With pw values remaining 2-3+ standard deviations
above the mean and the very favorable dynamics ahead of the
ejecting mid to upper level trof---widespread additional heavy to
excessive rainfall amounts are likely.  While this squall line
will likely be progressive---hourly rain rates of 1.0-1.5"+ likely
along the length of the squall line into at least the 0600-0900
utc time frame early Sunday morning---with model consensus for
weakening of the squall line and rainfall rates toward the end of
the day 1 time period.  While most of the squall line will be
progressive this period---there may be a period of training along
the west to east oriented front over the lower OH valley region
from northeast AR---southeast MO---southern IL---southern
IN--northwest KY and southwest OH in the 1800 to 0600 utc time
frame. This is the axis where much of the hi res guidance is
showing a concentrated precip max this period.

Oravec