Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
748
FOUS30 KWBC 272228
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
627 PM EDT MON MAR 27 2017

...VALID 2227Z MON MAR 27 2017 - 12Z TUE MAR 28 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 E LOZ 25 ESE TYS 15 N AVL TNB HLX 25 NNE DAN GSO 15 ENE 47A
15 NW BHM 20 SW 1M4 MSL 35 N MDQ 20 S MQY 55 SW BNA 25 SE MKL
15 NE NQA 25 NE DYR 30 WSW FTK 35 WSW CVG MGY 35 ESE ILN
20 E LOZ.


...EASTERN U.S. CONVECTIVE ENVIRONMENT FROM OHIO TO ALABAMA TO
SOUTHWEST VIRGINIA...

STEEP LAPSE RATES...BROAD MOISTURE TRANSPORT...AND MODERATELY
STRONG HEIGHT FALLS AHEAD OF A SHARP SHORTWAVE TROUGH WILL SUPPORT
WIDESPREAD CONVECTION THROUGH THE EVENING HOURS. SEVERAL CLUSTERS
OF STORMS WERE ALREADY OCCURRING AT 22Z...AND LOCAL UPSCALE GROWTH
HAD OCCURRED IN PARTS OF AL/TN/KY. THROUGHOUT THIS REGION DEEP
LAYER SHEAR WAS STRONG...AND MATCHED FAIRLY WELL BY MODERATE
INSTABILITY...RESULTING IN MIXED CONVECTIVE MODES...INCLUDING
SUPERCELLS...AND ASSOCIATED RISK OF MANY SEVERE HAZARDS PER STORM
PREDICTION CENTER PRODUCTS. THE RISK OF FLASH FLOODING WAS MORE
CONDITIONAL...AND RELATED TO LOCAL CELL MERGERS AND OCCASIONAL
BOUTS OF TRAINING ALONG FLANKING LINES AND SOME OF THE LARGER COLD
POOLS...LASTING GENERALLY LESS THAN 2 HOURS AND OCCURRING ON THE
SCALE OF 2 OR 3 COUNTIES. MUCH...IF NOT ALL...OF THIS ACTIVITY WAS
OCCURRING IN THE SYNOPTIC WARM SECTOR WHERE INFLUENCES CAUSING
THESE OCCASIONAL BOUTS OF TRAINING WERE SOMEWHAT RANDOM AND/OR
RELATED TO SMALL SCALE TERRAIN ENHANCEMENT. AS
SUCH...PREDICTABILITY OF THE FLASH FLOOD THREAT IS LOW...BUT IT
EXISTS OVER A BROAD AREA. FLASH FLOOD GUIDANCE IN THIS REGION IS
GENERALLY 1.5 INCHES IN ONE HOUR OR 2 TO 2-PLUS INCHES IN 3 HOURS.
THE THREE-HOUR CRITERIA IS A BIT MORE LIKELY TO BE EXCEEDED ON A
LOCAL BASIS...AS MARGINAL PW VALUES AROUND 1.00 INCH AND SOME HAIL
FALL WILL LIMIT THE EFFECTIVENESS OF HOURLY RAIN RATES...EXCEPT
WHERE MERGERS OCCUR. ISOLATED TOTALS OF 2.5 INCHES CAN BE
EXPECTED.

THIS INCLUDES AREAS EAST OF THE SPINE OF THE APPALACHIANS INTO
PARTS OF THE CAROLINAS AND SOUTHWEST VIRGINIA. THERE IS ENOUGH DRY
AIR IN THE SOUNDINGS...AND THE EVENT IS NOT PURELY AN UPSLOPE
EVENT...SUCH THAT CELLS SHOULD NOT TRAIN FOR TOO LONG AT A GIVEN
POINT...BUT WITH MUCH OF THE SYNOPTIC FORCING STILL HANGING BACK
UPSTREAM...SOME OF THE EARLY DEVELOPMENT SEEN AT 22Z DOES HAVE
POTENTIAL TO POSE AN ISOLATED FLASH FLOOD THREAT.

BURKE/GALLINA
$$





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