January 18, 2021
Washington DC Climate Report
Solar Noon: 12:18;
Last 72 Hours: Observations
...THE WASHINGTON NATIONAL DC CLIMATE SUMMARY FOR JANUARY 17 2021...
WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST
VALUE (LST) VALUE VALUE FROM YEAR
MAXIMUM 49 2:32 PM 74 1943 43 6 40
MINIMUM 33 2:37 AM -5 1982 28 5 29
AVERAGE 41 36 5 35
YESTERDAY 0.00 1.09 1994 0.09 -0.09 T
MONTH TO DATE 1.29 1.53 -0.24 1.30
SINCE DEC 1 6.25 4.58 1.67 4.58
SINCE JAN 1 1.29 1.53 -0.24 1.30
Forecast updates at 6 AM ET
Today: Cloudy, then gradually becoming mostly sunny, with a high near 49°. Southwest wind 7 to 11 mph.
Tonight: Mostly cloudy, with a low around 34°. Southwest wind 3 to 6 mph.
M.L.King Day: Partly sunny, with a high near 46°. Southwest wind 6 to 13 mph, with gusts as high as 20 mph.
Monday Night: Mostly clear, with a low around 30°. West wind 6 to 10 mph.
Tuesday: Mostly sunny, with a high near 48°. West wind 6 to 9 mph.
Tuesday Night: Partly cloudy, with a low around 32°.
Wednesday: Sunny, with a high near 41°.
Wednesday Night: Mostly clear, with a low around 26°.
Thursday: Partly sunny, with a high near 45°.
Thursday Night: Mostly cloudy, with a low around 35°.
Friday: Partly sunny, with a high near 47°.
Friday Night: Partly cloudy, with a low around 29°.
Saturday: Sunny, with a high near 41°.
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Time and Date
Discussion updates at 4 AM ET
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
904 PM EST Sat Jan 16 2021
Low pressure earlier over the Delmarva will further strengthen
across New England this afternoon. High pressure will then
build south of the region through the first half of next week
before another potential storm system approaches the latter half
of next week.
.NEAR TERM /THROUGH SUNDAY/...
The upper level trough is slowly pulling away from our region
this evening. Winds out of the west to northwest are leading to
drier air being advected east of the Allegheny front. Sky cover
has cleared out of most areas east of the Allegheny front which
should allow temps to drop down into the 20s but they will be
prevented from dropping further due to winds staying elevated.
Within the post-frontal air mass, the column has undergone
notable drying per 12-hour precipitable water trends with a
decrease from 0.67 to 0.22 inches. The 12Z upper air from KIAD
shows the enhancement in 850-700 mb lapse rates, indicative of
the approach of lower heights upstream. The GOES-16 water vapor
channels show the center of the circulation of this system over
eastern Ohio with multiple embedded vortices pivoting around
this low. Each of these vorticity maxima will act as an impetus
toward enhanced shower activity. With low freezing levels area-
wide, snow showers should be the more likely precipitation type.
However, the marginal surface temperatures will preclude
accumulations where current readings are in the low to mid 40s.
15 to 20 degree dewpoint depressions are noted in surface
observations, but wet-bulbing effects would still keep
temperatures above freezing.
Along and west of the Allegheny Front, a Winter Weather Advisory
has been issued from 4 PM this afternoon until 7 AM Sunday. This
covers Garrett, western Grant, and western Pendleton Counties
where 2 to 4 inches of snow are likely. The current radar
mosaic shows snow showers increasing in coverage over areas of
western to central West Virginia. Given the steep lapse rates
aloft and ample forcing with the upper trough, there is the
potential for snow squalls late this afternoon into the evening
hours. The 12Z ECMWF instantaneous lightning flash density
product shows the slight potential for thundersnow, but its a
downward trend from the 00Z solution.
Overnight temperatures will generally remain at, or below the
freezing mark across the region. The usual milder spots would be
within the DC and Baltimore city centers, as well as near the
tidal Potomac and Chesapeake Bay. Mountain locations can
anticipate lows in upper teens to 20s, coolest where
accumulating snow has occurred.
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
By Sunday morning, the early weekend upper low will be
positioned over Maine with a brief period of shortwave ridging
over the Mid-Atlantic. Quickly on its heels will be a secondary
trough set to dig through the Tennessee River Valley later in
the afternoon. Mostly sunny skies are expected for the first
half of Sunday across the region. The exception would be along
and west of the Allegheny Front where conditions remain overcast
with accompanying passing snow showers. As warm advection
increases Sunday afternoon ahead of the approaching shortwave,
expect an uptick in mid to high clouds through the evening and
into the overnight. This will bring another round of upslope
showers to the Allegheny Front Sunday night into Monday.
Another 2 to 4 inches of snow accumulations are possible with
this second batch of shower activity. Across the remainder of
the area, do not anticipate any of this precipitation to work
its way into the I-95 corridor. Mostly cloudy skies are expected
the first half of Monday, with increasing sunshine later in the
day in the wake of the shortwave passage. Brisk westerly winds
gusting 15 to 25 mph will occur with wind chill temperatures in
the 30s. High and low temperatures will remain seasonable into
early next week.
.LONG TERM /TUESDAY THROUGH SATURDAY/...
General zonal flow set-up aloft looks to remain in place throughout
most of next week. This will result in generally dry
conditions across the area, with temperatures near seasonal
averages. However given the pattern, weak pieces of shortwave energy
may develop within the flow which could spark weak areas of surface
low pressure during this time. As such, will see some continued
chances for upslope snow showers along/west of the Allegheny Front.
With that being said, two separate cold front will cross the region
next week; with the first being late Wednesday into Thursday.
Guidance has continued the trend of this FROPA lacking any
significant moisture and thus appears to result in overcast skies
for most of the CWA with upslope snow showers over the mountains.
The second FROPA is slightly more pronounced but also does not pack
a significant amount of moisture which seems logical given an
already cold airmass in place. However, at this time,
this appears to be the next best shot at any measurable precip
across the region. As a result, snow showers are likely to continue
over the mountains with rain/snow showers possible throughout the
remainder of the CWA depending on the exact timing of the
front. Simultaneously, a strong low may develop over the South-
Central US which has been indicated by guidance over the last few
days. With this low being more confined in the southern stream, at
this time appears to track mainly to our south Friday into Saturday.
Overall, while no largely impactful weather is expected during the
long term, will have to continue to monitor the forecast trends as
the pattern does appear to be slightly more variable in nature.
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