Areal Flood Warning 21, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1012 AM EDT Thu Apr 30 2020

.SYNOPSIS...
A strong cold front will cross the area early this evening.
Weak high pressure will build to our south heading into the
weekend, with another cold front approaching from the west
Sunday night.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
In terms of the rainfall, forecast mainly on track with no
substantive changes required. The leading edge of rainfall
approaching the Bay, with the back edge crossing the
Appalachians. The axis of heaviest rainfall approaching the I-95
corridor. Timing/amounts remain about the same. Widespread 1-2
inches expected with deep moisture (12Z LWX RAOB precipitable
water 1.36") and confluence feeding this system. High end total
around 3 inches likely, but with warm rain processes, its
always possible that a few locations may exceed the upper end
of the envelope.

The other hazardous element to address are the winds. Guidance
suggesting that a 50-60 kt low level jet will be developing over
the Delmarva today. The LWX 12Z RAOB indicates such winds
already present. The challenge will be, given saturation, how
efficient will the mixing be. Best estimation suggests not very.
However, model soundings for sites along the western shore do
have full mixing of around 45 kt less than 1000 ft off the
surface. That's hard to bet against, especially with a signal of
a fine line embedded within the rain shield. Have issued a Wind
Advisory to address this threat through 1800 UTC (2pm).
Extrapolation would take this feature onto the Eastern Shore by
then. Believe that the wind threat would largely be east of the
forecast area (ie: over the Eastern Shore) this afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
Rain will end by 00Z tonight with cloudy skies remaining. Fcst
for Fri has trended drier with closed low expected to track
farther south across srn VA. Most of the showers should remain
over central VA closer to the h5 low track, however, widespread
clouds and cool temperatures are expected. Dry conditions
expected Fri night through Sat night as upper level
convergence and sfc high pressure build over the region.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
High pressure situated over our region will slowly move off of the
eastern sea board on Sunday. A warm front is forecast to move to our
north on Sunday leading to the formation of  a weak southerly flow.
Dew point temps are forecast to hover in the mid 40s Sunday morning
but slowly rise throughout the day. There will be a chance for some
showers with the warm front during the Sunday afternoon period but I
expected showers to be isolated in nature. Some guidance has a
chance of precip Sunday morning but I believe the threat will be
limited by low dewpoints and a westerly flow aloft. A progressive
surface low will move along the front and through our region. The
flow aloft is zonal in nature which suggest the low should move
quickly through our region Sunday evening. Both Ensembles and
deterministic models have a range of rain totals between a 0.25 and
0.75 inches of precipitation. The models all vary on where the main
axis will set up over our region Sunday evening. Since we are
expecting significant rain today, the already saturated ground could
lead to an isolated threat for flooding Sunday evening and into
Monday.

There is decent agreement that the surface low should move out of
our region by Monday morning. High pressure will build back over our
region through the middle parts of next from the northwest. Another
system moving eastward from central plains is forecast to drop just
south of our region. If this low shifts further northward, our
region could observe another round of rain on Tuesday and possible
Wednesday from multiple lows passing near our area. There remains a
lot of uncertainty on where these lows will move and how many lows
will form at this time. Any additional rainfall on already
saturated ground could lead to isolated instances of flooding.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
IFR cigs expected today in mdt to hvy rain. Gusty srly winds
this morning diminishing in the afternoon from west to east.
MVFR cigs could linger through the night into Fri. Improving
conditions Fri night through Sat.

VFR conditions are expected for most of the day Sunday but a
progressive low will bring rain Sunday evening along with a chance
for subVFR conditions. VFR conditions should return Monday and into
Tuesday before another system potentially brings more precipitation
and subVFR conditions.

&&

.MARINE...
Gale Warning has been issued for today. Winds diminish below SCA
by midnight tonight. Possible SCA again Saturday.

Small Craft Advisories aren't likely at this time Sunday and
Monday.

&&

.TIDES/COASTAL FLOODING...
water level forecasts have been on track so far this morning.
Based on this performance (and observations) have added
Charles/King George to the Advisory for today and Harford (Havre
de Grace) to the Warning this PM. So, for the current tide cycle
moderate flooding adjacent to the northern Bay (due to water
piling in south flow) and minor flooding adjacent to the mid
Bay, lower tidal Potomac and DC/Alexandria.

The next challenge will be how quickly the water recedes. Still
have a couple of Watches in effect at sensitive locations
tonight/tomorrow due to this uncertainty. Hopefully will have a
better feel for that by early this afternoon. Do have an
Advisory for Calvert through Friday morning because of higher
confidence.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flood Watch through this evening for DCZ001.
     Coastal Flood Watch from late tonight through Friday afternoon
     for DCZ001.
     Coastal Flood Advisory until 2 AM EDT Friday for DCZ001.
MD...Flood Watch until 2 PM EDT this afternoon for MDZ003-502.
     Flood Watch through this evening for MDZ004>006-011-013-014-
     016>018-503>508.
     Coastal Flood Advisory until 1 AM EDT Friday for MDZ016.
     Coastal Flood Watch from 6 PM EDT this evening through Friday
     morning for MDZ017.
     Wind Advisory until 2 PM EDT this afternoon for MDZ011-014-017-
     018-508.
     Coastal Flood Advisory until 6 PM EDT this evening for MDZ017.
     Coastal Flood Advisory until noon EDT Friday for MDZ018.
     Coastal Flood Warning until 11 PM EDT this evening for MDZ508.
     Coastal Flood Warning until 6 PM EDT this evening for MDZ011-
     014.
     Coastal Flood Watch from 6 PM EDT this evening through late
     tonight for MDZ014.
VA...Flood Watch until 2 PM EDT this afternoon for VAZ025>031-
     036>040-503-504-507-508.
     Flood Watch through this evening for VAZ050>057-501-502-505-
     506.
     Coastal Flood Advisory until 1 AM EDT Friday for VAZ057.
     Coastal Flood Advisory until 2 AM EDT Friday for VAZ054.
WV...Flood Watch until 2 PM EDT this afternoon for WVZ050>053-055-
     502-504>506.
MARINE...Small Craft Advisory from 6 PM this evening to midnight EDT
     tonight for ANZ530>534-537>543.
     Gale Warning until 6 PM EDT this evening for ANZ530>534-
     537>543.
     Small Craft Advisory until 6 PM EDT this evening for ANZ535-
     536.

&&

SYNOPSIS...LFR
NEAR TERM...HTS
SHORT TERM...LFR
LONG TERM...JMG
AVIATION...LFR/JMG
MARINE...LFR/JMG
TIDES/COASTAL FLOODING...HTS

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1141 AM EDT THU APR 30 2020

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

1138 AM     FLOOD            BROADWAY                38.61N  78.80W
04/30/2020                   ROCKINGHAM         VA   DEPT OF HIGHWAYS

            MULTIPLE ROADS FLOODED AND CLOSED IN THE BROADWAY,
            GENOA, AND COOTES STORE AREAS.

&&

EVENT NUMBER LWX2001093

JE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1206 PM EDT THU APR 30 2020

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

1146 AM     NON-TSTM WND DMG 1 SSW SOTTERLEY         38.36N  76.54W
04/30/2020                   ST. MARYS          MD   DEPT OF HIGHWAYS

            MARYLAND ROUTE 245 CLOSED DUE TO DOWNED TREE AND WIRES.

&&

EVENT NUMBER LWX2001094

KJP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1207 PM EDT THU APR 30 2020

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

1154 AM     FLOOD            8 W STRASBURG           38.99N  78.51W
04/30/2020                   SHENANDOAH         VA   DEPT OF HIGHWAYS

            SEVERAL ROADS CLOSED DUE TO FLOODING IN THE ZEPP AREA.

&&

EVENT NUMBER LWX2001095

JE

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1219 PM EDT THU APR 30 2020

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

1144 AM     NON-TSTM WND DMG 1 NNW WOLFSVILLE        39.58N  77.56W
04/30/2020                   FREDERICK          MD   DEPT OF HIGHWAYS

            MARYLAND ROUTE 17 CLOSED NEAR MARTIN ROAD DUE TO TREE
            AND WIRES DOWN.

&&

EVENT NUMBER LWX2001096

KJP

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