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 0056Z May 24, 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
856 PM EDT Wed May 23 2018

Valid 01Z Thu May 24 2018 - 12Z Thu May 24 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE LMT MHS 15 SSW O54 35 NW O54 35 SW MFR SXT 30 SE RBG
45 ESE EUG 40 E CVO 35 ESE UAO 45 NNW RDM 55 WNW 5J0 40 W 5J0
55 W BNO 40 NE LKV 65 E AAT 60 NW LOL 60 NE CIC 40 ENE RDD
45 WSW AAT 20 NNE AAT 10 W LKV 20 ESE LMT.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 WSW KGAF 25 W CWSU 10 ENE INL 30 N 8D3 15 WSW 9V9 25 WSW CDR
10 S CUT 30 WSW MBG 35 WSW KGAF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SSW UDG 25 SW UZA 15 SSW FQD HKY 10 S TTA 25 SSE EDE
15 E HSE 30 S MRH 15 ESE CPC 10 SSW UDG.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 N CVN 20 NE DHT 30 NNW LBL 25 SW HUT 20 W LTS 25 SSE LBB MDD
25 WSW 6R6 80 S E38 MRF 35 W PEQ 45 NW HOB 25 N CVN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 N MCN 25 NW JYL 15 NE LHW 15 SE MGR VPS 25 SSE HBG
25 WSW TVR 20 W LZK 25 ESE FLP M97 25 SSE GWO 40 WNW MEI
15 E MEI 60 ESE NMM 10 SSE MGM CSG 15 N MCN.


0100 UTC update

Continued to make further adjustments to the previous outlook
based on the latest radar trends, including the northeast
extension of the Marginal risk from the southern High Plains into
southwest Kansas -- where slow moving convection continues to
develop along a weak boundary extending from southwest Kansas back
into northeast New Mexico. 

Across the Southeast and lower Mississippi valley -- with the loss
of daytime heating should continue to see an overall downward
trend in rainfall rates, however some locally heavy rains may
persist through the evening hours.  This includes areas across
southern Mississippi, where some of the hires guidance shows
locally heavy amounts occurring during the evening/overnight
hours.  Therefore, the marginal risk areas across the Southeast
and lower Mississippi valley were combined to include southern
Mississippi as well. 

With the upper low lifting further out to the northeast, removed
the previous Marginal risk across the northern Rockies and High
Plains.  However, with low level warm advection and deepening
moisture expected to increase overnight, introduced a Marginal
risk east of the low from northwest Minnesota back into southwest
South Dakota.  Guidance shows a deepening moisture pool along a
warm front, supporting developing convection lifting north across
the eastern Dakotas into western Minnesota, with possible
redevelopment further to the southwest along an axis of deeper
moisture and ahead of shortwave trough lifting northeast into the
Dakotas overnight.  Overall, latest hi-res guidance does not
suggest widespread heavy accumulations across this region, however
flash flood guidance values are quite low across much of the
region. 

Pereira


1900 UTC update

Changes to the previous outlook were heavily driven by latest
radar trends. 

Over southwest MN---the marginal risk area was removed as the
previous convection has weakened and moved farther north.

Over the Southeast---the slight risk area was removed as the
convection has pushes south of where the heaviest rains had fallen
and across areas with higher ffg values.  The marginal risk area
was maintained for additional convection potential along and south
of the stationary front across this region and in the vicinity of
the nearly stationary surface to mid level system over south
central Georgia.

The marginal risk area over far eastern OK into northwest AR was
re-oriented slightly more northwest to southeast given the current
convection orientation.

Oravec

1500 UTC update


...Southwest Georgia---southeast Alabama...

A slight risk area was added to the western portion of the
previous marginal risk area over the southeast over southwest
Georgia into southeast Alabama.  Convection continues to move
slowly across portions of southwest Georgia on the southwest side
of an mcv over central Georgia.  Radar imagery continues to show
bands of convection converging from both the northwest and west
southwest into portions of southwest Georgia.  The 1200 utc HRRR
seems to have a fairly good handle on the current activity and
shows the potential for the slow movement to the southeast
continuing into early this afternoon.  Hourly rainfall rates of
1-2"+ possible in areas where the convective bands are converging.
 Please see WPC's mesoscale precipitation discussion #0188 valid
until 1730 utc for additional information across this area.

...Southwest Minnesota...

The marginal risk area over southern Minnesota into north central
Iowa was re-positioned to the northwest over southwestern
Minnesota to reflect current radar trends.  Convection has
re-focused to the north of the warm front over portions of the
Northern Plains--with activity for the time being concentrated
over southwest MN.  This activity is not being depicted in the
latest hrrr---1200 utc versions of the arw---nmmb or nam conest. 
The only indication of this activity is in the 1300 utc hrrr
experimental which shows this activity pushing to the east across
southern MN.  Confidence not high with the evolution of this
convective complex.  Low level south southwest flow is expected to
persist across this area---with model guidance showing this
helping to lift the warm front northeastward this afternoon. 
Concerns are that this convective complex could remain in place as
the outflow from this complex keeps the effective front farther to
the south---remaining a focus for additional convective
development.

Oravec

Initial discussion


...Southeast and Mid Atlantic...

Scattered convection is once again expected along and south of a
southward moving cold front. A few different forcing mechanisms
are expected to locally focus convection and produce some higher
areal averaged amounts. The first area of focus will be across
eastern North Carolina where low level convergence along the front
should be strongest. Enough shear here for some organization of
convection near the front. Storm motions should generally be off
to the south, but not all that quick, and some regeneration near
the front may lead to some brief training. The 0z HREF depicts
this scenario well, with moderate probabilities of localized 3"
amounts focused across the area. Will carry a Marginal risk here.

Another area of focus will be the lingering low/mid level low over
AL/GA. As expected, thunderstorms have concentrated near the
center of this system early this morning, producing a narrow swath
of heavy rains near the AL/GA border. With diurnal heating expect
convective activity to expand outward from the center as has
happened the past few days. Again these cells will generally be
pulse in nature and short lived. Although continued high PWATs
support brief heavy rates, and wherever cell mergers along
outflows occur, a localized flash flood risk may exist. Will see a
contraction of activity towards the center after sunset over south
GA. Although in general the model consensus seems to suggest the
focus Wednesday night will not be as concentrated/heavy as what is
occurring early this morning, there is still a threat it will be.
In fact the 06z experimental HRRR focuses a narrow training axis
across southern GA Wednesday night near the center, so something
to monitor.

May also see the terrain of the western Carolinas act as an
initiation focus for storms this afternoon. Although with drier
air moving in from the northwest the signal is not as strong as
previous days. Thus cells may generally be more isolated in nature
and short lived and thus will not carry a Marginal at this time.
Nonetheless some very localized heavy rates will be possible.


...Lower MS Valley...

The Lower MS Valley will be a focus for convection again today. A
weak shortwave trapped underneath the mid level ridge axis will
act as forcing mechanism for storms. Plenty of diurnally driven
instability forecast, and PWATs will remain well above normal.
Storms will be of the pulse variety and will generally be short
lived, however weak mean flow suggests slow cell motion. Will
probably generally see chaotic cell motion with storms forming
along outflows and quickly dissipating. The 0z HREF signal is a
little more robust than yesterday, so anticipate convection will
be a bit more widespread today, resulting in higher overall areal
averaged QPF. Not expecting any organized flash flood threat,
although where some brief cell mergers occur extending rainfall
duration, anticipate we could see a few localized flash flood
concerns this afternoon over AR and will thus carry a Marginal
risk.


...Northwest...

Widespread shower and thunderstorm activity expected across
portions of the northwest in the broad troughing. The focus for
heaviest amounts appears to be across the terrain of northern CA
into the OR Cascades, and portions of central and eastern OR.
Cells will generally be of the pulse variety and short lived,
limiting overall areal averaged rainfall. PWATs will be around
climatological maximum values though, and thus would anticipate
some localized heavy rates. The best chance for some heavier
totals is probably along/near the Cascades, where the terrain will
likely act as forcing mechanism and result in some repeat cell
activity. Given the magnitude of anomalous PWATs, weak flow and
sufficient forecast instability, will carry a Marginal risk here.

Chenard