TM () > TW — Sunday, December 16, 2018

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Last 72 Hours: Observations

Currently: 44°F Radar@PatPend@TerpWeatherWeather

USNO Clear Sky Chart

Flood Warning
Coastal Flood Watch
Hazardous Weather Outlook

Today: Occasional rain or drizzle, mainly before 5pm. Patchy fog. Temperature falling to around 36 by 4pm. North wind around 11 mph. Chance of precipitation is 90%. New precipitation amounts between a quarter and half of an inch possible.

Tonight: A chance of rain or drizzle before 8pm. Patchy fog before 8pm. Otherwise, cloudy, then gradually becoming partly cloudy, with a low around 35°. Northwest wind 7 to 11 mph. Chance of precipitation is 30%.

Monday: Mostly sunny, with a high near 51°. West wind 7 to 15 mph, with gusts as high as 23 mph.

Monday Night: Partly cloudy, with a low around 31°. Northwest wind 10 to 14 mph, with gusts as high as 22 mph.

Tuesday: Sunny, with a high near 44°. Northwest wind 8 to 11 mph.

Tuesday Night: Mostly clear, with a low around 28°.

Wednesday: Sunny, with a high near 47°.

Wednesday Night: Partly cloudy, with a low around 34°.

Thursday: A chance of showers after 8am. Mostly cloudy, with a high near 52°. Chance of precipitation is 50%.

Thursday Night: Showers, mainly after 8pm. Low around 45°. Chance of precipitation is 80%.

Friday: Showers. High near 56°. Chance of precipitation is 80%.

Friday Night: Showers likely. Mostly cloudy, with a low around 40°. Chance of precipitation is 60%.

Saturday: A chance of showers. Mostly sunny, with a high near 49°. Chance of precipitation is 30%.

Baltimore/Washington Forecast Office

Forecast Archive | Observations Archive

FXUS61 KLWX 160206

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
906 PM EST Sat Dec 15 2018

Low pressure will pass to the south and out to sea through
Sunday. A cold front approaching from the Great Lakes will cross
the Mid-Atlantic Monday. High pressure will follow through
Wednesday, before another large area of low pressure approaches
from the Tennessee Valley Thursday into Friday.


Upper low/attendant surface reflection nearing the central
Appalachians is bringing steeper mid-level lapse
rates and frontogenesis, resulting in an increase in steadier
rain this evening. Enhancement seen in IR/water vapor satellite
loops with the band lifting north from central VA/Shenandoah
Valley, indicating good lift and rain rates. This band is
expected to lift north through the remainder of the CWA over the
next few hours, possibly becoming hung up across northern
Maryland due to the pivoting motion of the forcing around the
low. An additional 1-2 inches of rain is likely through
tonight mainly near and north of US-50. Therefore, will
continue with the Flood Watch given saturated ground and streams
and creeks already running high. Isolated rainfall rates of one
inch per hour are possible, but should be brief (not last for
an entire hour) in any embedded convective elements.
Mesoanalysis indicates around 100 J/kg of MUCAPE along the band
of heavier rain, but so far no lightning has been observed.

Given the current progression, it`s possible some heavier rain
rates linger across the north until 3-4 AM. Rain should become
lighter after that, as the best forcing from the upper low
begins to lift to the north and east, but continued moist
easterly flow is expected to result in at least patchy light
rain and drizzle through the remainder of the overnight.

Hi-res guidance has temperatures falling to near freezing by
daybreak near and above 3000 feet, with a chance of freezing
rain over over these locations after 4am. Given a persistence of
this trend, will keep the Winter Weather Advisory to account
for this, which continues through much of Sunday. Overall, it
seems temperatures/dew points (area-wide) are falling more
slowly than previously forecast, so this higher elevation icing
threat may be pushed back into Sunday.


Low pressure continues departing to the east Sunday, with
residual onshore flow/moist low-level resulting in a
continuation of occasional rain or drizzle, before northwest
flow begins to dry us out by later tomorrow.

Temperatures should remain largely above freezing in the lower
elevations, but if clouds clear out enough prior to dawn and
winds remain light, could see a few readings around freezing,
causing some isolated icy patches first thing Monday morning.

Monday looks to be a breezy day as a dry cold front (forced by
northern stream shortwave energy) dives southeast from the Great
Lakes and crosses the area during the day. Winds could gust up
to 30 MPH, and temperatures should respond by falling below
freezing area-wide Monday night. By this time, however, any wet
surfaces should have dried since rain will have ended 24+ hours
prior and wind should help dry things out as well.


During the middle of the week, a ridge of high pressure will extend
from the surface through 250 mb. Therefore, anticipating mostly
sunny to sunny skies Wednesday. With 850 mb temperatures near 4 or
5C, temperatures should be a pinch cooler than normal (mid-upper 40).

Mid-high clouds will start spreading across the skies Wednesday
night as a jet max approaches ahead of the next trough axis. This
will result in mostly cloudy conditions by dawn Thursday.

For the end of the week, a trough axis will be steepening near the
Mississippi Valley, and sweeping across the eastern seaboard Friday-
Saturday-- a similar setup to what we`re experiencing currently.
This consequently develops a cut off low in the midwest/upper Ohio
Valley...and could spawn cyclogenesis somewhere in the southeastern
United States. While the details still need to be sorted out, it
would lead to another wet Thursday-Saturday. At the present time,
Thursday night into Friday may be the wettest period...subject to
change, of course.

Thermally speaking, most of this precipitation would fall as rain.
However, will need to watch the evolution to see how quickly cold
air wraps around the back side of the low vs precipitation exits. If
cold air comes in quick enough, then there could be some mixed
precipitation at the end of the forecast period.


IFR/LIFR expected into Sunday morning, though there could be
some interludes of low end MVFR. Some guidance indicates IFR may
begin lifting as early as 15-18Z, though there`s a moderate
chance it will linger until early evening when winds turn more
northwesterly. Moderate rainfall will taper to lighter rain and
drizzle late tonight into midday Sunday.

Conditions will gradually improve Sunday night before VFR
returns solidly by Monday. N flow 10 kts or less, but a few
gusts 15-20 kts possible this evening. LLWS possible tonight
with increasing E flow to 35-40 kts around 2-3kft.

NW winds could gust 25-30 kts Monday, with gustiness possible
again Tuesday (likely lighter for a time Monday night with less
mixing). Otherwise VFR expected.

VFR conditions anticipated for Wednesday, but cigs may drop Thursday
as precip approaches. Flight restrictions possible.


SCA for most waters tonight. BUFKIT soundings show marginal
mixing up to about 1000 feet above the surface where winds are
25+ kts. A lull in the winds is possible early Sunday as the
gradient relaxes when low pressure makes its closest approach.
Latest guidance indicates winds remain elevated on the northern
part of the Bay as the low passes to the south, so have extended
the SCA through Sunday. Increasing NW winds behind the low
appear to start as early as the afternoon hours Sunday, and
continue into Sunday night, though SCA may be questionable on
the narrower inland waterways. Winds will be reinvigorated
behind a dry cold front late Monday, lingering into Tuesday.
Can`t rule out a few gusts to near gale force during this time.

Winds anticipated to be light Wed. In the return flow Thu, the
gradient does increase, but suspect mixing will be poor.


About 1-2" of rainfall was observed overnight last night into
this morning, with another 1-2" likely this evening and
overnight, especially near and north of US-50. Minor flooding
being observed in metro DC as well as portions of eastern
WV, western MD, and the Shenandoah Valley. Elsewhere, streams
and creeks remain elevated, so any additional rain will likely
result in renewed flooding concerns through tonight. Latest
hydrologic forecasts indicate the likelihood of river flooding
at numerous points over the next couple days.


Water levels running around a 1 1/4 ft above normal this evening.
However, a low astronomical tide has precluded any flooding
issues thus far. While continued northeast flow favorable for
piling water into the mouth of the Chesapeake Bay, they are not
favorable for driving water into the Maryland portion of the
Bay. Therefore, will be continuing with forecasts suggesting
nothing higher than action stage through the weekend, primarily
at Straits Point, although will be including Annapolis for the
Sunday night and Monday tide cycles.

We will also be monitoring the combination of rainfall and snowmelt
across the area this weekend. The resultant rises on area rivers
likely to pass through Georgetown and Southwest Waterfront somewhere
in the Monday timeframe...possibly causing inundation from
freshwater influx.


Rainfall totals continue to creep upward, with Baltimore MD and
Washington DC setting the annual record already. Here are the
current rankings for wettest year on record (through 4 PM December

Washington DC area (DCA)
1. 62.32 inches (2018)
2. 61.33 inches (1889)

Weather records for the Washington DC area have been kept at
what is now Ronald Reagan Washington National Airport (DCA)
since 1945. Precipitation records observed downtown extend the
period of record back to 1871.

Baltimore MD area (BWI)
1. 66.91 inches (2018)
2. 62.66 inches (2003)

Weather records for the Baltimore MD area have been kept at
what is now Baltimore-Washington International Thurgood Marshall
Airport (BWI) since 1950. Precipitation records observed
downtown extend the period of record back to 1871.

Dulles VA area (IAD)
1. 65.67 inches (2003)
2. 63.09 inches (2018)
3. 59.05 inches (1972)

Weather records have been kept at what is now Washington Dulles
International Airport (IAD) since 1960.

NOTE: All climate data are considered preliminary until
reviewed by the National Centers for Environmental Information


DC...Flood Watch until 6 AM EST Sunday for DCZ001.
Winter Weather Advisory from 4 AM to 7 PM EST Sunday for
Winter Weather Advisory from 4 AM to 7 PM EST Sunday for
Small Craft Advisory from noon to 6 PM EST Sunday for
Small Craft Advisory until midnight EST tonight for ANZ534-537-



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