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
   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.
 
WPC Met Watch

 
Mesoscale Precipitation Discussion: #0503 (2018)
(Issued at 855 PM EDT SAT JUL 21 2018 )

MPD Selection
 


Graphic for MPD #0503

MESOSCALE PRECIPITATION DISCUSSION 0503
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
855 PM EDT SAT JUL 21 2018

AREAS AFFECTED...NORTHERN MID-ATLANTIC STATES

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

VALID 220054Z - 220654Z

SUMMARY...VERY HEAVY RAINFALL CURRENTLY NEAR THE POTOMAC RIVER IS
EXPECTED TO LESSEN IN MAGNITUDE AS IT LIFTS NORTHWARD INTO PA. 
HOURLY RAIN TOTALS TO 2" WITH LOCAL AMOUNTS TO 4" ARE EXPECTED
THROUGH 07Z, PARTICULARLY ACROSS MD & PA.

DISCUSSION...THE 00Z SURFACE ANALYSIS REVEALS AN OCCLUDED CYCLONE
IN SOUTHERN CHESAPEAKE BAY WITH AN INCREASINGLY PRONOUNCED DRY
SLOT NEAR THE VA CAPES AND EASTERN SHORE.  VERY HEAVY RAINFALL
NEAR THE POTOMAC RIVER IS BEGINNING TO LESSEN IN MAGNITUDE AND
SHIFT SOMEWHAT EASTWARD WITHIN THE TROWAL OF THIS CYCLONE, SHOWING
UP AS A SURFACE TROUGH ACTING AS A BOUNDARY BETWEEN NORTHERLY AND
EASTERLY SURFACE WINDS.  PRECIPITABLE WATER VALUES ARE 1.6-2.5"
PER GPS VALUES AND THE WALLOPS VA SOUNDING.  INFLOW AT 850 HPA IS
EAST-SOUTHEAST AT 25-40 KTS PER VAD WIND PROFILES.  EFFECTIVE BULK
SHEAR IS 30-40 KTS IN THIS REGION, WHICH HAS ORGANIZED CONVECTION
INTO A BAND NEAR THE NATION'S CAPITAL.

THE EXPECTATION BASED ON RAP MASS FIELDS IS FOR THE TROWAL TO
MORPH INTO A PRONOUNCED COMMA HEAD IN THE NEXT SEVERAL HOURS.  THE
GUIDANCE SHOWS DECREASING INSTABILITY WITH TIME, SO BELIEVE THAT
THE ONGOING FLASH FLOOD EVENT SHOULD EVOLVE INTO A LONGER DURATION
HEAVY RAIN EVENT BY 07Z AS HOURLY RAIN TOTALS SLOWLY FADE. 
HOWEVER, EVEN BY 07Z, AVAILABLE INSTABILITY SHOULD CONTINUE TO
SUPPORT HOURLY RAIN TOTALS OVER 1", WHICH WOULD BE PROBLEMATIC IN
URBAN AREAS.  THE MESOSCALE GUIDANCE ADVERTISES LOCAL AMOUNTS UP
TO 4" IN MD/PA AND UP TO 2" IN NJ/NEW YORK CITY THROUGH 07Z. 
COMBINED WITH PREVIOUS RAINS, STORM TOTALS OF 6-7" ARE POSSIBLE
ACROSS MD BEFORE THE HEAVY RAIN SHIFTS NORTHWARD/ENDS.

ROTH

ATTN...WFO...AKQ...BGM...CTP...LWX...OKX...PHI...

ATTN...RFC...MARFC...NERFC...

LAT...LON   41427629 41317504 41007389 40747363 40357382
            39607409 38987454 38687496 38507551 38197611
            37977654 38557738 39637828 40917798


Last Updated: 855 PM EDT SAT JUL 21 2018
 

NOAA/ National Weather Service
National Centers for Environmental Prediction
Weather Prediction Center
5830 University Research Court
College Park, Maryland 20740
Weather Prediction Center Web Team
Disclaimer
Credits
Glossary
Privacy Policy
About Us
Career Opportunities
Page last modified: Wednesday, 13-May-2015 19:29:02 GMT