Flash Flood Guidance
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11
000
AWUS01 KWNH 261938
FFGMPD
PAZ000-MDZ000-WVZ000-OHZ000-KYZ000-270133-

MESOSCALE PRECIPITATION DISCUSSION 0081
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
338 PM EDT SUN MAR 26 2017

AREAS AFFECTED...WV...SOUTHWEST PA...EXT SOUTHEAST OH...EXT
WESTERN MD

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 261933Z - 270133Z

SUMMARY...MODERATE SHOWERS OVER LOW TOLERANCE GROUND CONDITIONS
WITH SOME POSSIBILITY OF TRAINING MAY POSE SMALL POCKETS OF FLASH
FLOODING CONDITIONS.

DISCUSSION...GOES-E AND GOES-16 VISIBLE IMAGERY DENOTE INCREASING
CLEARING IN ADVANCE OF STEADILY ENHANCING CONVECTION ACROSS SW WV
INTO E KY.  RECENT TEMP TRENDS AROUND 2-5F TOWARD THE UPPER
60S/LOWER 70S AND INCREASING MST SUPPORT INCREASING INSTABILITY
WITH RAP ANALYSIS SUPPORTING SBCAPES OVER 500 J/KG WITHIN THE
CLEARING.   LOW LEVEL MOISTURE FLUX/TRANSPORT PLUME IS STEADILY
INCREASING AS WELL WITH TPWS NEARING 1.0" COINCIDENT WITH
CONVERGENCE ALONG ADVANCING TROF.  THIS ALONG WITH GREATER
VERTICAL DEPTH SHOULD SUPPORT RAIN RATES IN EXCESS OF 1.0"/HR
POSSIBLY TRENDING AS HIGH AS 1.5"/HR LATER THIS EVENING.  STORM
MOTIONS ARE FAIRLY QUICK GIVEN DEPTH ENHANCED FLOW LIMITING
DURATION OF THESE RATES THOUGH AS THE CELLS LIFT NORTHEAST ACROSS
E KY INTO WV GROUND CONDITIONS ARE MUCH LESS RECEPTIVE OF THESE
TYPES OF RATES WITH FFG VALUES AOA 1.0"/3HRS EAST OF 81.5E
ROANE/CLAY/NICHOLAS COUNTIES (NORTH AND EAST).

GREATEST UNCERTAINTY IS RELATED TO THE POTENTIAL NATURE OF
TRAINING CELLS ALONG THE CONVECTIVE LINE/TRAILING TROF.  CURRENT
SATELLITE AND RADAR TRENDS SUGGEST THE ORIENTATION OF THE TROF IS
NOT IDEALLY ALIGNED HAVING MORE OF A NEUTRAL TILT FOR THE CORES TO
TRAIN.  GOES WV LOOP DENOTES MAIN MID-LEVEL TROF AXIS AND WEAK
NEGATIVE TILT IS LIFTING NORTHEASTWARD PRESSING THE NORTHERN
PORTION/FORCING FURTHER EAST WHILE CONCURRENTLY ALLOWING THE
TRAILING TROF TO LIFT NORTH SLIGHTLY.  THIS WOULD ALLOW FOR
INCREASED POSITIVE TILT TO THE CONVECTIVE LINE AND ALIGN WITH
CONFLUENT LOW TO MID-LEVEL STEERING FLOW.  THERE IS LITTLE DOUBT
THAT THIS ALIGNMENT AND TRAINING ENVIRONMENT WILL MANIFEST WITH
TIME. HOWEVER THERE IS DOUBT WHETHER THIS SETUP WILL BE PRIOR TO
THE EXHAUSTION OF THE ALREADY LIMITED INSTABILITY.

THE HI-RES CAMS SUGGESTING EARLIER TRAINING SUPPORT TOTALS OVER
AOA 1.5" OR EXCEEDING FFG VALUES THROUGH 01/02Z...SUCH AS THE HRRR
ESRL HRRR EXP AND NMMB OPPOSED BY THE CONEST/ARW WHICH ARE TOO
LATE AFTER BEST CONVECTIVE ENVIRONMENT DEGRADES.  OF NOTE...MOST
GUIDANCE IS A BIT SLOW PER USUAL IN TIMING SUGGESTIVE OF THE MORE
AGGRESSIVE SOLUTIONS.  STILL COVERAGE IS LIKELY TO NOT BE
EXTENSIVE THOUGH GROUND CONDITIONS/LOW FFG WARRANT SUFFICIENT
CONCERN FOR POSSIBLE FLASH FLOODING CONDITIONS THIS EVENING WITHIN
THE DISCUSSION AREA.

GALLINA

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...PBZ...RLX...

ATTN...RFC...OHRFC...

LAT...LON   40188060 40177990 39717945 39257962 38718042
            38058159 37868205 37938240 38308263 38758253
            39538171


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.