Quantitative Precipitation Forecast
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 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
098
FOUS30 KWBC 232356
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
755 PM EDT MON OCT 23 2017

...VALID 01Z TUE OCT 24 2017 - 12Z TUE OCT 24 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
60 W BKV 40 SSE CTY 10 SSW OCF 20 ENE BKV 10 WSW LAL 30 E SRQ
20 NW PGD 30 S SRQ 50 WSW SRQ.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 E SSI 10 W LHW 15 NE AGS 30 ESE GSP 25 NNE AVL 40 SE 1A6
30 NNE 1A6 10 ENE UNI 20 NE FKL 20 SW ELZ 30 NNW IPT 30 SE UNV
15 E OMH 15 NNE PGV 20 SSE NCA 40 SSE SUT 85 SSE MYR.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 N CYZE 15 SE CYZE 25 WNW BAX 10 S RMY 20 WNW ASW 15 ENE VPZ
25 NNE VPZ 20 W BIV 25 SSW LDM 25 NNW FKS 30 WSW SJX ISQ
60 NW ERY 35 SW CWXZ 25 ESE CYXZ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 N BKW 25 ESE 48I 30 SE EKN 15 WSW SHD 10 N LYH 15 SSE HBI
35 S EQY 20 SW UZA 15 NE HKY 10 NW MKJ 10 N BKW.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
GRR 15 S MKG 25 S LDM 10 SE MBL 10 SE MGN APN 30 N MBS GRR.


...GREAT LAKES...

IMPRESSIVE CYCLOGENESIS WAS TAKING PLACE SQUARELY OVER THE GREAT
LAKES AND ESPECIALLY LOWER MICHIGAN. A 1000 MB SURFACE LOW
STRADDLING INDIANA AND MICHIGAN EARLY THIS EVENING WILL DEEPEN AT
LEAST AS FAR AS 986 MB...IF NOT LOWER...BY MORNING...WHILE IT
LIFTS NORTHWARD. ALTHOUGH RAINFALL THROUGHOUT THE REGION WAS
MAINLY STRATIFORM AND LIGHT...THIS DEEPENING WILL LIKELY GIVE SOME
BOOST TO EFFICIENCY / RAIN RATES...WITH AMOUNTS CLOSER TO 0.40
INCHES IN AN HOUR OR 0.75 INCHES IN 3 HOURS BECOMING MORE COMMON
THIS EVENING AND OVERNIGHT. THE PRIMARY AXIS WILL BE INITIALLY
ALONG THE 850-700MB FRONTAL ZONE OVER NORTHERN LOWER
MICHIGAN...THEN MAY TRANSITION TO BEING MORE ELEVATED AND LOCATED
FARTHER NORTH AND WEST...CLIPPING THE UPPER PENINSULA AS THE
CYCLONE MATURES. WHILE THESE RAIN RATES IN THEMSELVES MAY NOT
USUALLY BE SUFFICIENT TO INDUCE FLASH FLOODING...THERE ARE SOME
AREAS OF LOWERED FLASH FLOOD GUIDANCE ACROSS CENTRAL LOWER
MICHIGAN...AND THIS GUIDANCE DOES NOT TAKE INTO ACCOUNT THE
AREA-WIDE FEW TENTHS OF AN INCH THAT HAD FALLEN SINCE 18Z. AREAS
FARTHER NORTH AND WEST SAW EVEN GREATER AMOUNTS OF ANTECEDENT
RAINFALL...AT 1 TO 3 INCHES IN THE PAST 24-HOURS. STREAM MODELING
PER SOURCES SUCH AS OU/FLASH AND THE NATIONAL WATER MODEL INDICATE
POTENTIAL FOR ANOMALOUS...HIGH STREAM FLOW FANNING OUT BOTH EAST
AND WEST AS THE SWATH OF HEAVIER RAIN TOTALS OCCURS THIS EVENING
UP THE CENTER OF THE LOWER PENINSULA. GIVEN THE CULMINATION OF ALL
THESE FACTORS...WPC CHOSE TO MAINTAIN A SLIGHT RISK OF EXCESSIVE
RAINFALL...BUT POSITIONED IT FARTHER NORTH TO KEEP UP WITH TRENDS.


...MID ATLANTIC / APPALACHIANS / CAROLINAS...

PLEASE REFER TO MESOSCALE DISCUSSION NUMBER 0910 FOR SHORT TERM
DETAILS AS TO THE FLASH FLOOD THREAT THROUGH 04Z ASSOCIATED WITH
CONVECTION MOVING THROUGH THE MOUNTAIN AND PIEDMONT AREAS OF THE
VIRGINIAS TOWARD FAR WESTERN MARYLAND AND SOUTHWEST PENNSYLVANIA.
ALTHOUGH TRADITIONAL MESOANALYSES AND MODEL FORECASTS INDICATED
VERY LITTLE INSTABILITY...THE ASCENT WAS BEING MAXIMIZED VIA A 60
KNOT LOW LEVEL JET AND STRONG DEEP LAYER HEIGHT FALLS. THE RISK OF
FLASH FLOODING...INCLUDING THE WPC SLIGHT RISK AREA...WAS REALLY
TIED TO THE HIGHER ELEVATIONS WHERE THE RAIN RATES BENEFIT FROM
UPSLOPE ENHANCEMENT / CELLS FORMING AND MERGING AHEAD OF THE
PRIMARY SQUALL LINE...AS WELL AS LOWER...MORE EASILY SURPASSED
FLASH FLOOD GUIDANCE VALUES.

FARTHER SOUTH INTO THE CAROLINAS...WITH THE FORCING AND THE MATURE
SQUALL LINE MOVING DOWNHILL INTO THE PIEDMONT / COASTAL
PLAIN...RAINFALL DURATION WILL TEND TO BE MINIMIZED AT ANY GIVEN
LOCATION. FLASH FLOOD GUIDANCE ALSO INCREASES WITH EASTWARD
EXTENT...SO WPC CONTINUED TO CONFINE THE SLIGHT RISK OF EXCESSIVE
RAINFALL TO THE AREA WEST OF RALEIGH. MARGINAL RISK SURROUNDS THE
SLIGHT RISK AND INCLUDES RAINFALL THAT WILL BE CONVECTIVELY
ENHANCED...EVEN IF ONLY BRIEFLY...FROM WESTERN PENNSYLVANIA DOWN
THROUGH SOUTH CAROLINA.


...FLORIDA...

A SMALL SCALE BATCH OF HEAVY RAIN WAS FAIRLY SLOW MOVING THROUGH
THE TAMPA BAY METRO. STORMS THAT HAD DROPPED A RADAR-ESTIMATED
THREE INCHES NEAR SEMINOLE WERE DROPPING SOUTHWARD ALONG THE
COAST. THE SYNOPTIC PATTERN SUPPORTED PERSISTENT DEEP LAYER ASCENT
AROUND THE PERIPHERY OF A DEEPENING LARGE SCALE TROUGH IN THE
EASTERN UNITED STATES. THE SLOW MOVING CONVECTION WILL CONTINUE TO
BRING THE POTENTIAL FOR BRIEF HEAVY RAIN RATES EXCEEDING 2 INCHES
PER HOUR...BUT NOT LASTING MORE THAN 1 OR 2 HOURS AT A GIVEN
LOCATION. THE MID LEVEL FORCING SHOULD MAKE SOME PROGRESS EAST OF
THE TAMPA AREA BY LATE EVENING PER RAP FORECASTS...WITH THE THREAT
LIKELY DIMINISHING OVERALL AS THE BOUNDARY LAYER COOLS OVER THE
PENINSULA WITH NIGHTFALL.

BURKE
$$





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