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Area Forecast Discussion (AFD)

Issued by Baltimore/Washington (LWX)

FXUS61 KLWX 220158 AAA

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
858 PM EST Mon Jan 21 2019

Arctic high pressure will build over the region through Tuesday, 
before sliding off the Mid Atlantic coast Tuesday night. A cold 
front will move into the Ohio Valley on Wednesday and across our 
area Wednesday night and into Thursday. Another cold front will 
cross the area on Friday as high pressure builds back over the 
region the first half of the weekend.



Arctic high pressure will build over the region tonight. Despite
this, 24-hr model trends in temperatures show no change or in
some cases temperatures a little warmer east of the mtns. Over
the higher elevs, expect temperatures to rise overnight due to
warm air advection aloft. 850 mb temps over the Appalachains are
expect to rise from -15C to -4C by daybreak. Already have seen a
+9C increase at 850 mb at IAD since 12Z today. Will be adjusting
temps upward a bit east and several degs higher over the mtns.
Still very cold nonetheless. 


High pressure over head will continue to shift east on Tuesday, and 
off of the Mid-Atlantic coast into Tuesday night. This will bring 
lighter winds as return flow settles in. High temperatures on 
Tuesday will be in the upper 20s and mid 30s, under mostly sunny 
skies. Clouds will be on the increase on Tuesday night as an 
approaching low pressure/cold front approaches the Mid-Atlantic coast. 
Light wintry precipitation is possible ahead of this boundary over 
areas west of the Blue Ridge late Tuesday night. 

As the boundary approaches on Wednesday and southerly flow advects 
warm air into our region, rain is expected to overspread over our 
CWA. High temperatures are expected to be in the 40s and low 50s. 
The boundary will be slowly moving across as waves of low pressure 
track along it. Periods of moderate to heavy rain are possible.

Overnight low temperatures will be in the 30s and 40s, with upper 
20s at higher elevations. West to northwesterly flow settles in 
behind the front late Wednesday, with possible upslope precipitation 
west of the Allegheny Front.


A wave of low pressure will be crossing our region early Thursday 
with rain. A period of heavy rain is possible, with potential for 
a bit of wintry weather towards the back side. Guidance has not 
quite settled on the exact track of the low, so this will influence 
future temperature and p-type forecasts, but odds favor rain for the 
metro, with a better chance of wintry weather well north and west. 
Dry weather should return behind the system Thursday night along 
with cooling temps. 

Another front, this one more arctic in origin, will cross the region 
Friday. Guidance had previously hinted some snow squalls could 
accompany this front, but latest runs have backed off on this 
somewhat. That said, a stray snow shower east of the mountains 
still can't be ruled out. Behind this second front, arctic high 
pressure will then settle over or just south of the region for 
Saturday, resulting in a pretty cold start to the weekend. Sunday, a 
deepening trough dives southeast across the Plains into the 
southeast, potentially generating some sort of coastal system. GFS 
keeps this system south and east, but 12Z GGEM brings it much 
closer. 12z ECMWF stalls the system off the southeast coast.
Ensemble spread is large, but upper height pattern suggests
coastal storm potential Sunday into early next week.


A high pressure system will build over the terminals tonight 
and winds will be on the decrease. VFR conditions and lighter 
winds are expected Tuesday and into Tuesday night. 

A cold front will approach and moves across our area Wednesday into 
Wednesday night. This will bring rain and sub-VFR conditions at 
times, along with an increase in winds.

IFR likely Thursday as wave of low pressure spreads rain across the 
region. VFR should return Thursday night and Friday.


Small Craft Advisory (SCA) through tonight with decreasing 
winds as high pressure builds overhead. Winds will remain below
criteria into Tuesday into Tuesday night as high pressure 
slides east off of the Mid-Atlantic coast. Winds may increase 
above SCA criteria on Wednesday into Wednesday night with cold 
front moving over the waters.

Potential for Small Craft Advisories exists Thursday as a front 
stalls in the area and a wave of low pressure rides northeast 
up the front. Another weak boundary could induce small craft gusts 
on Friday, though odds of this are lower.


Persistent and strong northwest flow will yield blowout conditions
through tonight.


MD...Wind Chill Advisory until 10 PM EST this evening for MDZ501.
VA...Wind Chill Advisory until 10 PM EST this evening for VAZ503-
WV...Wind Chill Advisory until 10 PM EST this evening for WVZ501-
MARINE...Small Craft Advisory until 6 AM EST Tuesday for ANZ530>543.