632  
FOUS30 KWBC 160124  
QPFERD  
 
EXCESSIVE RAINFALL DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
923 PM EDT WED AUG 15 2018  
 
DAY 1  
VALID 01Z THU AUG 16 2018 - 12Z THU AUG 16 2018  
 
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF  
THE SOUTHERN HIGH PLAINS...THE NORTHERN PLAINS...AND THE OHIO AND  
MID-MISSISSIPPI VALLEYS...  
   
..LOWER/MIDDLE MISSISSIPPI AND OHIO VALLEYS
 
 
AN UPPER TROUGH WILL LIFT SLOWLY EAST-NORTHEASTWARD ACROSS THE  
MIDDLE MISSISSIPPI AND LOWER OHIO VALLEYS OVERNIGHT AND THROUGH  
EARLY THURSDAY. A CORRIDOR OF STRONGER DEEP LAYER FLOW AROUND THE  
SOUTHERN AND EASTERN PERIPHERY OF THE TROUGH WILL COINCIDE WITH A  
PLUME OF SUBTROPICAL MOISTURE AND CORRESPONDING PW VALUES THAT ARE  
ABOUT 1.5 TO 2.0 STANDARD DEVIATIONS ABOVE NORMAL. THIS WILL  
INTERACT WITH A MODERATELY UNSTABLE BOUNDARY LAYER AND FOCUSED  
SURFACE CONVERGENCE ALONG A FRONT ALONG WITH SOME EMBEDDED MID  
LEVEL VORT ENERGY FOR AN AXIS OF BROKEN AND LOCALLY ORGANIZED  
CONVECTION OVERNIGHT. SOME REMNANT DIURNAL CONVECTION THIS EVENING  
WILL CONTINUE ACROSS THE BROADER MIDWEST, BUT THE CONCERN GOING  
TOWARD 06Z AND ESPECIALLY TOWARD 12Z WILL BE AN AREA OF FOCUSED  
CONVECTION AND VERY HEAVY RAINFALL POTENTIAL EXTENDING FROM AREAS  
OF NORTH-CENTRAL AND NORTHEAST AR UP ACROSS SOUTHEAST MO, SOUTHERN  
IL AND INTO SOUTHERN IN, INCLUDING POSSIBLY AREAS ALONG THE KY  
SIDE OF THE OHIO RIVER. ACROSS THESE AREAS, THE LOW LEVEL FLOW  
WILL BECOME HIGHLY CONFLUENT AND MORE PARALLEL TO THE MEAN FLOW IN  
A WAY THAT WILL SUPPORT TRAINING CONVECTION. SEVERAL RUNS OF THE  
HRRR HAVE BEEN SUPPORTING 5+ INCH RAINFALL TOTALS THROUGH 12Z,  
ESPECIALLY OVER AREAS OF NORTHEAST AR. MEANWHILE, THE 12Z ARW2  
SUGGESTS SOUTHERN IL MAY BE MORE THE FOCUS, BUT WITH SOMEWHAT  
LESSER AMOUNTS. THE LATEST SURFACE OBSERVATIONS TEND TO FAVOR MORE  
CONVECTIVE SUPPORT AT LEAST INITIALLY OVER NORTH-CENTRAL TO  
NORTHEAST AR, AND SO WEIGHTING WILL TEND TO BE TOWARD THE HRRR  
GUIDANCE AT THIS TIME. A SLIGHT RISK AREA IS HIGHLIGHTED AT THIS  
TIME SINCE THERE IS STILL SOME UNCERTAINTY WITH THE EXACT  
PLACEMENT OF HEAVY AMOUNTS, BUT AS CONDITIONS EVOLVE, AN UPGRADE  
TO A MODERATE RISK MAY BE NECESSITATED.  
   
..SOUTH DAKOTA/NEBRASKA
 
 
A TIGHT, SLOW-MOVING MID-LEVEL LOW CENTER, AND ASSOCIATED PV  
ANOMALY OUT ACROSS THE NORTHERN PLAINS WILL CONTINUE TO FOSTER  
SOME CONCENTRATED AREAS OF SHOWERS AND THUNDERSTORMS OVERNIGHT  
ACROSS PORTIONS OF ESPECIALLY SOUTHEAST SD AND ADJACENT AREAS OF  
NORTHERN NE. FORCING ALOFT ASSOCIATED WITH THIS WILL STILL BE  
INTERACTING WITH RELATIVELY CONVERGENT LOW LEVEL FLOW AND ALSO AT  
LEAST A MODESTLY UNSTABLE BOUNDARY LAYER. A SLIGHT RISK AREA IS  
MAINTAINED ACROSS MAINLY SOUTHEAST SD, ALTHOUGH THERE MAY ACTUALLY  
TEND TO BE LOCALLY HEAVIER RAINS ACROSS NORTHERN NE INVOLVING THE  
LESS SENSITIVE SAND HILLS REGION. LOCALLY AS MUCH AS 2 TO 4 INCHES  
OF RAIN WILL BE POSSIBLE OVERNIGHT, AND THUS THE ONGOING CONCERNS  
FOR FLASH FLOODING.  
   
..NORTHEAST
 
 
AN UPPER TROUGH AND ASSOCIATED COLD FRONT WILL CONTINUE TO DROP  
DOWN ACROSS AREAS OF MAINLY NORTHERN NY AND NORTHERN NEW ENGLAND  
OVER THE NEXT SEVERAL HOURS. INSTABILITY IS WEAKENING IN THE  
BOUNDARY LAYER, BUT THERE REMAINS SUFFICIENT FORCING ALOFT AND  
WITH THE APPROACHING FRONT FOR SOME ADDITIONAL SHOWERS AND  
THUNDERSTORMS. A MARGINAL RISK AREA IS MAINTAINED LOCALLY TO  
ACCOUNT FOR AT LEAST AN ISOLATED FLASH FLOOD THREAT. CONDITIONS  
SHOULD BEGIN TO IMPROVE THOUGH AFTER 06Z.  
   
..SOUTHERN HIGH PLAINS
 
 
THERE WILL BE AN OPPORTUNITY FOR SOME LOCALLY ORGANIZED CONVECTION  
OVERNIGHT TO EVOLVE OFF THE HIGHER TERRAIN OF THE SANGRE DE CRISTO  
RANGE WHICH WILL THEN DROP SOUTHEAST ACROSS EASTERN NM AND THE TX  
PANHANDLE. THE LATEST GUIDANCE SUGGESTS AT LEAST SOME WEAK VORT  
ENERGY INTERACTING WITH A WEAK TO MODERATELY UNSTABLE BOUNDARY  
LAYER, MODEST LOW LEVEL UPSLOPE FLOW AND SUFFICIENT MOISTURE FOR  
THE POTENTIAL OF AT LEAST A BROKEN MCS. FFG VALUES MAY LOCALLY BE  
EXCEEDED GIVEN THE EXPECTATION OF SOME SPOTTY 2 TO 3 INCH AMOUNTS  
OVERNIGHT. THUS A SLIGHT RISK AREA IS MAINTAINED HERE AT THIS  
TIME, AND IS CONSISTENT WITH SIGNALS SEEN FROM THE HIRES MODEL  
CONSENSUS.  
   
..SOUTHWEST U.S.
 
 
A MARGINAL RISK AREA REMAINS IN EFFECT FOR PORTIONS OF THE  
SOUTHWEST U.S., WITH THE MAIN FOCUS ON EASTERN NV, SOUTHWEST UT,  
FAR EASTERN CA AND MOST OF AZ WHERE AT LEAST SOME WEAK TO MODERATE  
BOUNDARY LAYER INSTABILITY REMAINS IN PLACE. THE PWATS ACROSS THE  
REGION ARE RUNNING 1 TO 2+ STANDARD DEVIATIONS ABOVE NORMAL WITH A  
MORE CONCENTRATED DEGREE OF MOISTURE SEEN IN THE 500/700 MB LAYER  
AS PER THE LATEST CIRA-LPW DATA. THE LATEST GOES-16 VISIBLE  
SATELLITE IMAGERY STILL SHOWS SEVERAL AREAS OF SLOW-MOVING SHOWERS  
AND THUNDERSTORMS AND THIS ACTIVITY SHOULD TEND TO PERSIST FOR A  
FEW MORE HOURS BEFORE THEN WEAKENING. UNTIL SUCH TIME, SOME CELLS  
WILL BE CAPABLE OF PRODUCING HEAVY RAINFALL RATES THAT WILL  
LOCALLY EXCEED 1 INCH/HR. AS A RESULT, SOME ISOLATED FLASH  
FLOODING WILL BE POSSIBLE, WITH AN EMPHASIS AGAIN ON BURN SCARS,  
DRY WASHES, AND SLOT CANYONS.  
 
ORRISON  
 
DAY 2  
VALID 12Z THU AUG 16 2018 - 12Z FRI AUG 17 2018  
 
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE MIDWEST AND  
MID-SOUTH...  
   
..EASTERN MIDWEST TO THE OHIO VALLEY
 
 
TIMING OF A WEAK REMNANT LOW ACROSS THE LOWER MICHIGAN PENINSULA  
IS A BIT FASTER IN 12Z CONSENSUS OF THE GFS/ECMWF/UKMET.  
PRECIPITABLE WATER VALUES AROUND 2 INCHES AHEAD OF THE LOW ARE 2  
TO 2.5 SIGMA ABOVE CLIMATOLOGY. THIS TROPICAL SURGE WILL SPREAD  
ABUNDANT RAINFALL ALONG AND AHEAD OF THE ADVANCING COLD FRONT WITH  
THE HEAVIEST AMOUNTS FOCUSING OVER THE LOWER GREAT LAKES WHERE  
STRONGER HEIGHT FALLS SHOULD OVERSPREAD THE REGION. THE SLIGHT  
RISK WAS SPREAD SOUTH ALONG THE FRONTAL ZONE OVER IN/OH TO  
CINCINNATI AND KY.  
   
..CENTRAL TO SOUTHERN GREAT PLAINS TO THE MID-SOUTH
 
 
AN UPPER LOW OPENS OVER THE NORTHERN PLAINS THURSDAY WITH  
ASSOCIATED LOCALLY HEAVY RAINFALL SPREADING FROM SD TO IA WHERE A  
MARGINAL RISK REMAINS WARRANTED. FARTHER SOUTH, FEATURED BEST IN  
THE 12Z GFS SHIFTS EAST ACROSS OK THURSDAY. AS THE IMPULSE  
ENCOUNTERS AN INCREASINGLY MOIST AND BUOYANT ATMOSPHERE  
DOWNSTREAM, SOME CONVECTIVE COMPLEX SHOULD EMERGE BY THE EVENING  
HOURS. GIVEN WET ANTECEDENT CONDITIONS IN EASTERN OK, A SLIGHT  
RISK WAS RAISED THERE INTO AR. SHOULD THE NORTH AND SOUTH  
COMPLEXES MERGE, IT WOULD BE NEAR NORTHERN AR WHICH ALSO HAS WET  
CONDITIONS CURRENTLY. THEREFORE, THE SLIGHT RISK SPANS NORTHERN AR  
INTO WESTERN TN.  
   
..ARIZONA INTO WESTERN NEW MEXICO
 
 
HIGH PRECIPITABLE WATER AIR CONTINUES TO LIFT NORTH OUT OF THE  
GULF OF CALIFORNIA/SEA OF CORTEZ IN A MONSOONAL PATTERN. DIURNAL  
HEATING OVER THE REGION SHOULD FORCE CONVECTION OVER THE HIGHER  
TERRAIN OF ARIZONA/NEW MEXICO INITIALLY ALTHOUGH THE WEAK 700-MB  
WINDS SUGGEST THE ACTIVITY MAY STRUGGLE TO PUSH OFF THE MOUNTAINS  
INTO THE LOWER ELEVATIONS. LITTLE ADJUSTMENT WAS AGAIN NECESSARY  
TO THE MARGINAL RISK AREA.  
 
JACKSON  
 
DAY 3  
VALID 12Z FRI AUG 17 2018 - 12Z SAT AUG 18 2018  
 
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE SOUTHERN  
HIGH PLAINS...LOWER OHIO VALLEY...AND MAINE...  
   
..NEW ENGLAND INTO THE MID-ATLANTIC
 
 
A SURFACE WAVE ADVANCES FROM UPSTATE NEW YORK TOWARD UPPER NEW  
ENGLAND, PUMPING 1.75 TO 2 INCH PRECIPITABLE WATER VALUES  
NORTHWARD ALONG A TROPICAL MOISTURE PLUME. 850-MB MOISTURE FLUX  
ANOMALIES BEGIN PUSHING THE 3 TO 4 SIGMA ABOVE AVERAGE RANGE. THE  
12Z CONSENSUS OF THE PREFERRED GFS/ECMWF/UKMET FOCUS THE BEST QPF  
SIGNAL ACROSS NORTHERN MAINE. A SLIGHT RISK WAS MAINTAINED OVER  
THIS REGION WHILE A MARGINAL RISK AREA WAS MAINTAINED SOUTHWEST  
ACROSS THE MID-ATLANTIC. WHILE QPF NUMBERS ARE MARKEDLY LOWER,  
RECENT WEEKS HAVE BEEN INCREDIBLY WET SUGGESTING AT LEAST ISOLATED  
FLASH FLOOD THREATS THERE.  
   
..OZARKS EAST TO THE CENTRAL APPALACHIANS
 
 
THE SIGNAL FOR CONTINUED HEAVY RAINFALL FROM THE OZARKS TO THE  
MID-SOUTH REMAINS AS A FRONTAL ZONE STALLS ACROSS THE REGION.  
FORECAST SOUNDINGS SHOW QUASI-UNIDIRECTIONAL FLOW SETTING UP WITH  
ANOMALOUS MOISTURE POOLING ALONG IT. A MAX QPF AXIS GENERALLY SITS  
ALONG AND JUST SOUTH OF I-64 ACROSS SECTIONS OF THE LOWER OHIO  
VALLEY WHERE THE SLIGHT RISK REMAINS. GIVEN HEAVY RAINFALL  
EXPECTED DURING PRECEDING OUTLOOKS, WOULD ANTICIPATE FLASH FLOOD  
GUIDANCE VALUES TO DROP LEADING INTO THE DAY 3 PERIOD.  
 
...NEW MEXICO TO TEXAS AND OKLAHOMA PANHANDLES AND SOUTHEASTERN  
COLORADO...  
FORCING SHIFTS EASTWARD FROM AZ TO THE SOUTHERN ROCKIES FRIDAY AS  
THE HIGH RETROGRADES WEST. EXPECT DIURNALLY FORCED CONVECTION TO  
FIRST TAKE SHAPE ACROSS ELEVATED HEATING SOURCES BEFORE CONVECTIVE  
OUTFLOWS TAKE THE ACTIVITY TOWARD THE SURROUNDING LOWER  
ELEVATIONS. 700-MB WINDS REMAIN ON THE WEAKER SIDE, THOUGH EAST  
ONTO THE PLAINS THE LOW LEVEL JET GETS ORGANIZED. GIVEN  
CONSISTENCY FOR 1-3 INCHES IN THE 12Z CONSENSUS AND EXPECTED WET  
CONDITIONS TONIGHT, A SLIGHT RISK WAS RAISED FROM SOUTHEASTERN CO  
INTO THE TX PANHANDLE.  
 
JACKSON  
 
DAY 1 THREAT AREA: HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/94EPOINTS.TXT  
DAY 2 THREAT AREA: HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/98EPOINTS.TXT  
DAY 3 THREAT AREA: HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/99EPOINTS.TXT  
 

 
 
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