Severe Thunderstorm Warning 170, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
928 PM EDT Sun Jul 23 2017

.SYNOPSIS...
High pressure remains off the southeast coast. A weak boundary
will remain near the area through Monday before stalling south
and east of the area Tuesday. An upper level trough of low
pressure will move over the northeastern US early in the week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Have had a couple of waves of showers/thunderstorms so far this
afternoon/early evening...the most prolific of which dropped
between 3-5 inches (radar estimated) across northeast Maryland.
The forecast area presently in a lull radar-wise, but that
likely won't be the end of the precip potential tonight.

Mesoscale analysis suggests 1000-1500 J/kg MLCAPE still present
across much of Maryland and adjacent Virginia. The 00Z LWX RAOB
confirms this. Effective shear, fortunately, a bit less than
this afternoon, but still around 20-25 kt. A cap evident around
500 mb on the sounding.

As a weak surface boundary drops toward the forecast area
tonight, subtle height falls likely will erode the inhibition,
making it possible for another round of convection...unrelated
to the activity currently in the upper Ohio Valley. RAP/HRRR
composite suggests that showers/thunderstorms will develop
somewhere near the Blue Ridge/Catoctins just after dark and
track toward Baltimore and Washington toward midnight. After
that, details diverge. But given recent rains (and ongoing
flooding) and precipitable waters at or above 2 inches in the
metros...will be keeping the Flash Flood Watch in place through
the early overnight.

Would still not rule out localized severe weather. However, if
will take a more vigorous updraft to collapse and produce
downburst winds. Some CAMs suggesting thats possible...even
after midnight. Otherwise, there will a decreasing trend between
midnight and sunrise. Will be utilizing the latest obs and
composite meso models to fine tune temperature forecasts.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
Frontal boundary will finally try to push through the area
Monday. Most guidance continues to be stubborn with convective
coverage...though believe at least isolated showers and storms
are possible as the front encounters a warm and unstable
airmass. The strongest storms would be capable of gusty winds
and locally heavy rainfall.

Some improvement from the heat Tuesday...as front stalls to the
S/E of the area. High temperatures will generally top out in
the mid to upper 80s. Dewpoints will fall back into the
60s...which should feel more pleasant after the extended stretch
of hot and humid weather.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Wednesday should be the pick day of the week with high pressure
centered over New England, and extending down over our region. That
should keep temperatures slightly below normal, and humidity in
reasonable check with dewpoints in the 60s. By the time we get to
Thu, the high has slipped off to the east and southwest flow returns
with a rebound in temps and humidity. Late in the week, probably
Friday, our next cold front is slated to push through from the
northwest. Current indications are that it will stall just offshore
with an area of low pressure forming along it off the Delmarva Sat
and Sun.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
VFR conditions will prevail through Monday...outside of
thunderstorm activity. Another wave of showers and thunderstorms
will be possible late this evening into the overnight hours.
Flight restrictions will be brief, vsby more than ceiling,
related to the rainfall. There may be some gusty winds, but
confidence in details low.

An isolated storm is also possible Monday...though most sites
should remain dry. VFR returns Tuesday.

VFR conditions expected Wed and Thu. Lowered vsbys and cigs are
possible on Friday from the expected cold front with its showers and
thunderstorms.

&&

.MARINE...
Mesoscale models have consistently been suggesting that 20 kt
wind gusts possible up the Bay in southerly channeling tonight.
Based on this consistency and presence of outflows from nearby
showers/storms, have opted to raise a Small Craft Advisory for
the mid Bay and mid-lower tidal Potomac through 4am. (Threat of
the Potomac likely south of the Route 301 Bridge.) In addition,
thunderstorms capable of producing gusty winds above Special
Marine Warning criteria will be possible tonight.

A couple of thunderstorms will be possible on Monday as well.
Otherwise, winds will be below SCA thresholds. No marine
hazards Monday night or Tuesday.

Other than thunderstorms (most likely on Friday), no widespread
marine threats are anticipated Wed through Friday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flash Flood Watch until 3 AM EDT Monday for DCZ001.
MD...Flash Flood Watch until 3 AM EDT Monday for MDZ004>006-011-013-
     014-503>508.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 4 AM EDT Monday for ANZ533-534-536-
     537-543.

&&

SYNOPSIS...MSE
NEAR TERM...HTS
SHORT TERM...MSE
LONG TERM...MSE/CAS
AVIATION...HTS/MSE/CAS
MARINE...HTS/MSE/CAS

Hazardous Weather Outlook
National Weather Service Baltimore MD/Washington DC
510 PM EDT Sun Jul 23 2017

ANZ530>543-DCZ001-MDZ011-013-014-016>018-508-VAZ052>057-241045-
Chesapeake Bay north of Pooles Island MD-
Chesapeake Bay from Pooles Island to Sandy Point MD-
Chesapeake Bay from Sandy Point to North Beach MD-
Chesapeake Bay from North Beach to Drum Point MD-
Chesapeake Bay from Drum Point MD to Smith Point VA-
Tidal Potomac from Key Bridge to Indian Head MD-
Tidal Potomac from Indian Head to Cobb Island MD-
Tidal Potomac from Cobb Island MD to Smith Point VA-
Patapsco River including Baltimore Harbor-
Chester River to Queenstown MD-Eastern Bay-
Choptank River to Cambridge MD and the Little Choptank River-
Patuxent River to Broomes Island MD-
Tangier Sound and the inland waters surrounding Bloodsworth
Island-District of Columbia-Southern Baltimore-Prince Georges-
Anne Arundel-Charles-St. Marys-Calvert-Southeast Harford-
Prince William/Manassas/Manassas Park-Fairfax-
Arlington/Falls Church/Alexandria-Stafford-Spotsylvania-
King George-
510 PM EDT Sun Jul 23 2017

This Hazardous Weather Outlook is for the Maryland portion of the
Chesapeake Bay, Tidal Potomac River, and adjacent counties in
central Maryland and northern Virginia as well as the District of
Columbia.

.DAY ONE...Tonight

Thunderstorms over central and northern Maryland, as well as the
District, will be capable of producing flash flooding late this
afternoon into tonight. A flash flood watch has been issued for
that potential. Consult that product for more details.

Isolated damaging wind gusts are also possible across the region
and over the waters.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Please forward any thunderstorm damage or heavy rain reports to
the National Weather Service.

MDZ003>006-501>507-VAZ025>031-036>040-050-051-501>508-WVZ050>053-
055-501>506-241045-
Washington-Frederick MD-Carroll-Northern Baltimore-
Extreme Western Allegany-Central and Eastern Allegany-
Northwest Montgomery-Central and Southeast Montgomery-
Northwest Howard-Central and Southeast Howard-Northwest Harford-
Augusta-Rockingham-Shenandoah-Frederick VA-Page-Warren-Clarke-
Nelson-Albemarle-Greene-Madison-Rappahannock-Orange-Culpeper-
Northern Fauquier-Southern Fauquier-Western Highland-
Eastern Highland-Western Loudoun-Eastern Loudoun-
Northern Virginia Blue Ridge-Central Virginia Blue Ridge-
Hampshire-Morgan-Berkeley-Jefferson-Hardy-Western Grant-
Eastern Grant-Western Mineral-Eastern Mineral-Western Pendleton-
Eastern Pendleton-
510 PM EDT Sun Jul 23 2017

This Hazardous Weather Outlook is for eastern West Virginia,
northern and central Virginia, and central and western Maryland
with the exception of Garrett County.

.DAY ONE...Tonight

Thunderstorms over central and northern Maryland will be capable
of producing flash flooding late this afternoon into tonight. A
flash flood watch has been issued for that potential. Consult that
product for more details.

Isolated damaging wind gusts are also possible across central and
northern Maryland.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Please forward any thunderstorm damage or heavy rain reports to
the National Weather Service.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
804 PM EDT SUN JUL 23 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0745 PM     FLASH FLOOD      1 NNW HAVRE DE GRACE    39.56N  76.11W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            800 BLOCK OF TYDINGS ROAD CLOSED DUE TO HIGH WATER.

&&

EVENT NUMBER LWX1702504

DH

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
832 PM EDT SUN JUL 23 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0233 PM     MARINE TSTM WIND 2 NNE NORTH BEACH       38.73N  76.53W
07/23/2017  M40 MPH          ANZ532             MD   BUOY

0257 PM     MARINE TSTM WIND 10 ENE PLUM POINT       38.68N  76.33W
07/23/2017  M47 MPH          ANZ541             MD   BUOY

0344 PM     TSTM WND DMG     2 SSW DARLINGTON        39.61N  76.21W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            TREE DOWN IN THE 3600 BLOCK OF HARMONY CHURCH ROAD.

0557 PM     FLASH FLOOD      ABERDEEN                39.51N  76.17W
07/23/2017                   HARFORD            MD   EMERGENCY MNGR

            SEVERAL ROADS CLOSED DUE TO HIGH WATER IN THE ABERDEEN
            AREA.

0602 PM     FLASH FLOOD      1 N ABERDEEN            39.52N  76.17W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            VEHICLE TRAPPED IN HIGH WATER NEAR INTERSECTION OF
            ABERDEEN THROUGHWAY AND PARADISE ROAD.

0622 PM     FLASH FLOOD      1 NNE ABERDEEN          39.53N  76.17W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            VEHICLE STRANDED IN HIGH WATER NEAR THE INTERSECTION OF
            WINDEMERE DRIVE AND PLEASANTWIND DRIVE.

0629 PM     FLASH FLOOD      ABERDEEN                39.51N  76.17W
07/23/2017                   HARFORD            MD   FIRE DEPT/RESCUE

            SEVERAL SWIFT WATER RESCUES UNDERWAY IN LOW DRAINAGE
            AREAS.

0643 PM     FLASH FLOOD      1 ENE ABERDEEN          39.52N  76.16W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            VEHICLE STRANDED IN HIGH WATER IN THE 500 BLOCK OF
            NORTH PHILADELPHIA BOULEVARD.

0745 PM     FLASH FLOOD      HAVRE DE GRACE          39.54N  76.10W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            REVOLUTION STREET CLOSED DUE TO HIGH WATER BETWEEN
            LEWIS LANE AND SOUTH JUNIATA STREET.

0745 PM     FLASH FLOOD      2 ENE ABERDEEN          39.53N  76.14W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            PULASKI HIGHWAY CLOSED DUE TO HIGH WATER BETWEEN
            ABERDEEN THROUGHWAY AND OLD POST ROAD.

0745 PM     FLASH FLOOD      1 NNE ABERDEEN          39.52N  76.17W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            ABERDEEN THROUGHWAY CLOSED DUE TO HIGH WATER BETWEEN
            PARADISE ROAD AND HILLCREST DRIVE.

0745 PM     FLASH FLOOD      HAVRE DE GRACE          39.55N  76.10W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            NORTH JUNIATA STREET CLOSED AT OTSEGO STREET DUE TO
            HIGH WATER.

0745 PM     FLASH FLOOD      1 N HAVRE DE GRACE      39.56N  76.10W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            SUPERIOR STREET CLOSED AT NORTH JUNIATA STREET DUE TO
            HIGH WATER.

0745 PM     FLASH FLOOD      1 NNW HAVRE DE GRACE    39.56N  76.11W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            800 BLOCK OF TYDINGS ROAD CLOSED DUE TO HIGH WATER.

&&

EVENT NUMBER LWX1702489 LWX1702490 LWX1702491 LWX1702494 LWX1702496
LWX1702497 LWX1702495 LWX1702498 LWX1702499 LWX1702500 LWX1702501
LWX1702502 LWX1702503 LWX1702504

DH

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
859 PM EDT SUN JUL 23 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0858 PM     FLOOD            2 SW HAVRE DE GRACE     39.53N  76.13W
07/23/2017                   HARFORD            MD   911 CALL CENTER

            PULASKI HIGHWAY STILL CLOSED DUE TO RESIDUAL FLOODING
            BETWEEN ABERDEEN THROUGHWAY AND OLD POST ROAD.

&&

EVENT NUMBER LWX1702505

DH

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