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Area Forecast Discussion (AFD)

Issued by Baltimore/Washington (LWX)

                            
000
FXUS61 KLWX 191933
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
Issued by National Weather Service Mount Holly NJ
233 PM EST Mon Nov 19 2018

.SYNOPSIS...
A weak area of low pressure over the Ohio Valley will ride 
along a stationary boundary situated near the Mason Dixon Line 
tonight, with a cold front crossing the area during the day on 
Tuesday. Low pressure will move across the northern Great Lakes 
on Wednesday, pushing a strong cold front through the region  
Wednesday night. High pressure of Canadian origin will build to 
our north for the remainder of the work week before another
system threatens the area over the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Weak low propagating along the front will lift northeast tonight
further away from the region. The front will finally begin to
make progress through the region as a cold front through the
early morning hours.

Along and just behind the front, we could see light
precipitation, primarily west of the Blue Ridge. With the
exception of higher elevations in WV, MD, and VA Highlands, 
most of the region should remain well above freezing. Thus, if 
any precipitation occurs, it will be mostly rain. In the higher 
elevations of the Appalachians however, a rain snow mix 
changing to all snow is possible. There is limited moisture with
this system though, so if any snow accumulation occurs it 
should be less than one inch, or less than 2 inches along the 
Allegheny Front.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...

Precipitation will come to an end as the northwesterly flow
behind the cold front will lead to dry air advection. The one
exception is along the Allegheny Front, where orographic lift
could result in lingering light showers.

With the cold air advection behind the front, temperatures will
be considerably lower than on Monday. Highs will be about 10 to
15 degrees lower than highs on Monday, or about 5 to 10 degrees
below normal.

On the back side of the low, expect a tight pressure gradient,
resulting in northwesterly winds gusting up to 25 mph at times
and up to 30 mph along ridge lines.

By Tuesday night, winds will start to diminish and skies will
clear out. This will set the stage for efficient radiational
cooling conditions. Consequently, widespread freezing conditions
are expected across the region, with the exception of the urban
centers where the temperatures may stay just above freezing.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
High pressure builds in for Wednesday, continuing a trend of
below normal temperatures.

A dry, arctic cold front is expected on Thanksgiving. The air 
behind this front is the coldest of the season so far, with 
temps likely not getting far from the freezing mark on 
Thanksgiving Day, and possibly reaching the teens in many areas 
Thanksgiving night. See the climate section below for a few 
notes on how rare this cold spell might be, though the midnight 
temperatures will affect this.


Did not make many changes to the grids beyond Thanksgiving as
there is still considerable uncertainty with the weekend
systems. Many models trended slower with the onset of
precipitation, now depicting precipitation not arriving until
early Saturday morning. While a later onset would be good news
for most of the region, with the chance for precipitation type
to be all rain increasing, there remains significant chance of 
some wintry weather at the onset especially west of the Blue
Ridge with the potential for cold air damming. Just how 
persistent this wintry weather will be is yet to be determined, 
but anyone with travel plans Friday night into Saturday should 
keep an eye on evolving forecasts.

The low will likely pass us by Sunday and with a more Pacific- 
type air mass following it, the storm looks likely to do what 
the system last week did... nudge the coldest air back north of 
the region and leave some more moderate temperatures over our 
region for Sunday. Uncertainty regarding the timing of a system 
quickly following on the first one's heals makes the forecast 
for Sunday uncertain, but some rain is possible per the GFS, for
example. Other models, notably the ECMWF, allow for more of a 
gap between the systems, which would make Sunday a fairly decent
travel day. Stay tuned...

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
VFR with dry conditions is expected at all the terminals through
00Z. A weak area of low pressure will passing along and to the 
north of the terminals tonight, with MRB serving to see the best
chance of MVFR VIS/CIGs due to -SHRA, all other terminals 
likely to remain VFR and mainly dry. 

A cold front will cross the terminals early Tuesday with winds 
shifting out of the northwest. Gusts up to 25 KT will also be
possible after 15Z. A stronger but dry cold front will move 
through the terminals late Wednesday into Wednesday night, 
maintaining gusty northwest winds with VFR VIS/CIGs prevailing.

VFR conditions expected Thursday and Friday as high pressure
builds in behind another cold front. Gusty NW winds may be an
issue, with gusts likely in the 20-30 knot range.

&&

.MARINE...
Winds are expected to remain below Small Craft Advisory
conditions through tonight as winds should stay mostly light. A
cold front will move through the waters on Tuesday with 
increasing northwesterly winds expected, thus an SCA goes into 
effect Tuesday morning and persists for portions of the waters 
into Tuesday night. A brief lull may be realized Wednesday 
morning over the waters as the gradient weakens, however another
strong cold front is expected to sweep through the waters late 
Wednesday into Wednesday night bringing solid SCA gusts over the
marine district.

Small Craft Advisories are likely Thursday and may continue into
Friday as another cold front slides across the region.

&&

.CLIMATE...
Unseasonably cold weather is looking increasingly likely to
briefly take hold of the region on Thanksgiving. Daytime 
temperatures are likely to stay in the 30s, and it could be the 
coldest Thanksgiving in over 20 years, depending on the readings
at midnight. Here are the benchmark readings to compare this 
Thanksgiving to:

Washington DC area
Year High Elapsed
2017  47   1 year
2013  40   5 years
2000  38  18 years
1996  35  22 years
1930  30  88 years
The high has not been lower than 30 on Thanksgiving since
official temperature record keeping began in 1872.

Baltimore MD area
Year High Elapsed
2017  44   1 year
2013  38   5 years
2000  37  18 years
1996  33  22 years
1930  31  88 years
The high has not been lower than 31 on Thanksgiving since
official temperature record keeping began in 1872. 


Rainfall totals continue to creep upward, with Baltimore setting
the annual record already. Here are the current rankings for 
wettest year on record (through November 18th):

Washington DC area (DCA)
1. 61.33 inches (1889)
2. 60.83 inches (2003)
3. 60.09 inches (1878)
4. 58.58 inches (2018)
5. 58.17 inches (1886)
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. 63.18 inches (2018)
2. 62.66 inches (2003)
3. 62.35 inches (1889)
4. 58.98 inches (1979)
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. 59.17 inches (2018)
3. 59.05 inches (1972)
4. 58.09 inches (1996)
5. 55.43 inches (1979)
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 
(NCEI).

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 9 AM Tuesday to 5 AM EST Wednesday 
     for ANZ530>534-537>543.
     Small Craft Advisory from 9 AM to 6 PM EST Tuesday for ANZ535-
     536.

&&

$$
SYNOPSIS...BKF/99
NEAR TERM...BKF/99
SHORT TERM...BKF/99
LONG TERM...RCM/99
AVIATION...BKF/RCM/99
MARINE...BKF/RCM/99
CLIMATE...