Forecast Discussion for Willowsford Farm and vicinity from the NWS in Sterling, Virginia

FXUS61 KLWX 170038

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
838 PM EDT Thu Aug 16 2018

High pressure will start slowly moving east out of the area
today. A cold front will approach the area on Friday, passing
slowly off to the southeast on Saturday. The front will remained
stalled to our south Sunday and Monday before lifting northward
as a warm front on Tuesday.


Widely scattered (gusty) showers and thunderstorms are rolling
through the I-81 corridor as of mid evening. These will
gradually weaken through midnight as they move east. Additional
scattered showers and perhaps a thunderstorm are expected
overnight as a shortwave trough approaches from the west.
Therefore, have maintained a chance of showers overnight over
the Potomac Highlands and the Alleghenies given the proximity of
the trough to our west. Some patchy fog could be realized
toward morning at the favored locations. Lows tonight will hold
in the upper 60s to lower 70s, continuing the muggy stretch.


A cold front still progged to approach from the west on Friday,
with much of the shower and thunderstorms holding off east of
the Blue Ridge until the afternoon and evening hours. Our
western zones will see a chance of showers/storms during the
morning hours. Ahead of the front and upper trough, winds will
turn more southerly, pumping in moisture across the area. Given
temperatures in the low to middle 90s, CAPE will be plentiful
ahead of the above features. Some strong to severe storms could
be realized Friday afternoon and evening, with damaging wind
gusts being the primary threat. Localized flooding will also be
a threat with any strong thunderstorms with precipitable water
values nearing two inches.

As stated, temperatures will be a touch warmer on Friday, and
given the rise in dewpoints (lower 70s), heat indices will near
the century mark for some locations. Showers and storms will
wane late Friday evening and into the overnight hours. Lows
Friday night in the upper 60s to low 70s.

The front will likely hold off just to our west come Saturday
morning, passing through the region throughout the day. As such,
additional showers and thunderstorms are expected Saturday
afternoon and evening, with again a threat for isolated
flooding in any strong showers and storms. Temperatures will be
cooler on Saturday and with ample cloud cover over the area, not
seeing a big threat for severe storms, but there could be some
isolated strong storms. WPC highlights much of the region in a
Marginal Risk for excessive rainfall on Saturday.

The front will push off to our south and east come overnight
Saturday, with showers and storms decreasing as well. Highs and
lows Saturday and Saturday night will be closer to normal for
middle of August.


On Sunday, model guidance suggests that a surface front will be
stalled out over central or southern Virginia. Aloft we`ll have
zonal flow overhead at mid-levels and a low-amplitude shortwave
trough located just off to our west at jet level. It appears as
thought the best chance for afternoon showers and thunderstorms will
be across southern portions of our area (closer to the surface
front), but a shower or storm can`t be ruled out anywhere.

On Monday, shortwave ridging will build in aloft ahead of a higher
amplitude trough that will be approaching from the midwest. This
shortwave ridge should suppress the development of storms, leading
to mostly dry conditions on Monday.

The aforementioned trough will move over the Great Lakes on Tuesday.
Meanwhile, it`s associated area of low pressure at the surface will
track northeast from the Ohio Valley to Ontario. Low-level southerly
flow out ahead of the trough will transport a moisture rich airmass
into the region (precipitable water values over two inches). Higher
moisture levels when combined with ascent downstream of the trough
should lead to development of showers and thunderstorms Tuesday
afternoon. The upper trough and surface cold front associated with
the system is still expected to be to our northwest on Wednesday.
Showers and storms will again be possible Wednesday as the surface
front works its way across our area.


Predominate VFR conditions are forecast through tonight as high
pressure remains over the region. A few showers may impact MRB
this evening and overnight, but confidence in occurrence and
impact is low at this time. Patchy early morning fog may impact
CHO/MRB Friday morning with MVFR VIS in and around daybreak.

An upper trough and associated cold front will near the
terminals Friday afternoon and evening. Some strong to severe
storms may bring periods of IFR/LIFR conditions as they traverse
the terminals. Convection wanes Friday night with low clouds and
fog a possibility. Afternoon/evening showers and storms will
once again be possible through the weekend as the frontal
boundary lingers nearby, with Saturday carrying the higher
chances. This will increase the likelihood for episodes of sub
VFR conditions.

Intermittent sub-VFR conditions could be possible in association
with any thunderstorms that pass through Sunday, Tuesday or


Sub SCA conditions dominating over the waters through tonight.
Small Craft Advisory conditions are expected Friday afternoon
and Friday night ahead of the trough and associated cold front.
Wind gusts of 20 to 25 knots will be conceivable during this
timeframe, with higher gusts possible in thunderstorms.

Showers and scattered thunderstorms will likely trigger Friday
afternoon and may impact the waters during the evening hours.
Some storms could be strong to severe and require Special
Marine Warnings. If navigating the waters Friday, be sure to
have a way to receive any warnings when/if they are issued.

The front will cross the waters during the day on Saturday, with
additional showers and thunderstorms expected. Outside of
convection, winds will be lighter on Saturday, but the threat
for gusty winds in and around any showers and storms will
continue. Sub SCA conditions return Sunday and Monday as the
boundary resides to our south and the gradient remains weak. The
front will lift northward on Tuesday as a warm front,
increasing southerly winds over the waters and the likelihood
for SCA wind gusts to return.


Excess fresh water input from the Susquehanna River is pushing
tidal anomalies into the 1.5 to 2 feet range at Havre de Grace
this evening. The next high tide is the higher of the two, and
considering anomalies are holding steady and the last tide cycle
came within a few tenths, it seems likely the next cycle will
result in minor flooding. Therefore, have issued a Coastal Flood
Advisory for the overnight high tide cycle.


MD...Coastal Flood Advisory from midnight tonight to 8 AM EDT
     Friday for MDZ508.
MARINE...Small Craft Advisory from 4 PM Friday to 6 AM EDT Saturday for



NWS LWX Office Area Forecast Discussion