Skip Navigation Links weather.gov 
NOAA logo - Click to go to the NOAA homepage National Weather Service   NWS logo - Click to go to the NWS homepage
The Weather Prediction Center

 
 

 

Follow the Weather Prediction Center on Facebook Follow the Weather Prediction Center on Twitter
NCEP Quarterly Newsletter
WPC Home
Analyses and Forecasts
   National High & Low
   WPC Discussions
   Surface Analysis
   Days ½-2½ CONUS
   Days 3-7 CONUS
   Days 4-8 Alaska
   QPF
   PQPF
   Flood Outlook
   Winter Weather
   Storm Summaries
   Heat Index
   Tropical Products
   Daily Weather Map
   GIS Products
Current Watches/
Warnings

Satellite and Radar Imagery
  GOES-East Satellite
  GOES-West Satellite
  National Radar
Product Archive
WPC Verification
   QPF
   Medium Range
   Model Diagnostics
   Event Reviews
   Winter Weather
International Desks
Development and Training
   Development
WPC Overview
   About the WPC
   Staff
   WPC History
   Accomplishments
   Other Sites
   FAQs
Meteorological Calculators
Contact Us
   About Our Site
 
USA.gov is the U.S. Government's official web portal to all federal, state, and local government web resources and services.
 
Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0101Z Feb 25, 2018)
 
Version Selection
Versions back from latest:  0   1   2   3   4   5   6   7   8   9   10   
 
Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
801 PM EST Sat Feb 24 2018

VALID 01Z Sun Feb 25 2018 - 12Z Sun Feb 25 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 ENE ERI 20 WNW ELZ 30 NE IPT 10 WNW HPN 15 WNW BLM 10 S MIV
10 ESE ESN 20 S ADW 25 NNW FVX 20 N ROA 20 SSW 48I 25 SW CRW
15 NNW LNP 45 NW AVL 10 WNW ANB 30 ESE MEI 15 SW PIB 15 NNW PTN
10 E 7R5 10 SE EFD 25 NW DWH 35 S JSO 40 SW PBF 30 SSE M19
15 WSW CIR 10 N FOA 20 ENE GUS 20 ENE DFI CLE 15 ENE ERI.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NNE YNG 15 SSE BFD 25 WSW IPT 40 E AOO 15 WNW OKV 20 SSE W99
30 SE EKN EKN 48I 25 NNE CRW 3I2 20 NNW JKL 30 E K8A3 30 S CSV
30 E MDQ 15 E CBM 35 N MCB 35 WNW POE 30 S BAD 25 SSW ELD
15 SE PBF 20 ESE JBR PAH 10 SW RSV 10 NW MIE AOH 20 SW LPR
15 SSE CGF 15 NNE YNG.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
GEZ 20 SE AOH 4I3 35 NW HTS 10 E LEX 25 NE GLW 50 SW BNA
40 NNW TUP 35 NNW GWO 35 NNW GLH 15 NW NQA 40 SSE PAH 15 ENE CUL
20 E LWV GEZ.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 ESE LOU 20 SSW FTK 30 NW BWG 35 N HOP 10 SSE EHR 25 N HNB
10 NW BAK 15 W DAY 25 E ILN 55 SSE ILN 25 ESE LOU.



***A major flash flooding event is forecast to continue through
the evening across portions of the lower Mississippi, Tennessee
and Ohio valley regions, ending from west to east as a strong cold
front pushes through overnight.***

01z Update:

Ahead of a well-defined cold front pushing east across the region,
heavy rains associated with a strong line of convection continue
to advance steadily eastward across the lower Mississippi into the
Tennessee valley this evening.  Despite the progressive nature of
this line, these rains continue to produce widespread flash
flooding concerns as they fall onto saturated soils across much of
Arkansas into western Tennessee and northern Mississippi.  Latest
hi-res guidance shows this convection continuing to advance
steadily to the east through the evening, moving south and east of
the region overnight.  Refer to WPC MPD #0041 (valid through 04Z)
for further information regarding the near-term heavy rainfall and
flash flooding threat. 

Further to the north, convection with heavy rains continue to
develop and train along a slow-moving boundary extending across
the Ohio valley.  This is expected to continue for the next
several hours, producing heavy amounts, with flash flooding a high
concern.  Refer to WPC MPD #0040 (also valid through 04Z) for
further information regarding near-term the heavy rainfall and
flash flooding threat across this region.

Biggest change to the previous outlook was to remove the western
extent of the risk areas where precipitation has ended. 
Maintained a high risk across portions of northern Kentucky,
southern Indiana and southwest Ohio, where the latest hi-res
guidance is showing an additional 1-3 inches this evening into the
overnight.  Heaviest rains are expected to end across much of the
high risk area by around 08Z as the cold front pushes east of the
region.

Pereira 

19z Update:

The system continues to become better defined over the MS valley
with a significant flood and flash flood threat continuing into
tonight. The combination of height falls moving into the area and
the development of very impressive upper level divergence with a
dual jet structure, will provide a very favorable synoptic
environment for convection. Convection continues to stream
northeastward within the WAA regime ahead of this wave. Strong
850mb moisture transport within this band will continue to support
developing convection moving northeast across AR and along the OH
river. Meanwhile a squall line along the developing cold front has
become better defined as well over recent hours. So far there has
been enough separation of these two areas to prevent any real
robust training. As such QPF amounts from the 12Z arw/arw2 and
some older hrrr runs may have been overdone over AR, with these
solutions depicting a training scenario that has not yet unfolded.
With that said, still looking at two rounds of heavy rainfall
rates over much of AR (one with the WAA and another the squall
line), and given saturated conditions even the the 1-2" (localized
3") totals depicted by the 16z hrrr will still cause flash flood
concerns into this evening. Thus while the magnitude of flash
flooding may not be as significant as was possible...will maintain
the high risk for now until the squall line passes through.

The most concentrated area of training and repeat cells appears to
be setting up near the OH river from far northeast AR into far
southeast MO, western TN/KY, far southern IL and southern IN. The
area of strong 850 MB moisture transport ahead of the wave will
repeat across this area and run into the warm front in place. The
expectation is that the WAA convection will tend to repeat across
these areas into this evening, with the squall line from the west
eventually overtaking the lead convection. This thus sets up about
a 6 hour window OR so where locally heavy rates may be moving over
the same locations. In general expecting areal averaged amounts of
2-3" within this corridor, with the potential certainly there for
a narrow swath of 3-5". Given this will be falling over saturated
grounds, significant flash flooding will be a concern...and thus
the high risk will be maintained. Some uncertainty with the exact
axis of higher amounts remains. Thought the 12Z nam nest and nmmb
were probably too far north. Thought the 16z hrrr showed a pretty
good match to current radar and its evolution seemed reasonable,
thus the WPC QPF follows this hrrr solution the closest through
06Z tonight. The greatest flash flood threat appears to be this
afternoon through about 06Z-07z, as the convection looks to weaken
some after that and also become more progressive in nature. Given
this...opted to cut back some on the northeastward extent of the
moderate risk over portions of eastern OH and western PA. Think
rainfall magnitudes and rates will be lower here...and thus while
some areal and river flooding will be possible...significant flash
flooding appears less likely.

Chenard


...Original Discussion...

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