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FXUS61 KLWX 180148

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
848 PM EST Sat Feb 17 2018

Low pressure will track northeastward along a stalled frontal
boundary well to our south through tonight. High pressure will 
build in from the west on Sunday, migrating offshore by Monday. 
Low pressure will move northeastward toward the Great Lakes 
Monday, lifting a warm front northward through our region. A 
cold front is poised to approach the region during the middle
portion of the work week.


Low pressure is beginning to develop off the Delmarva coast.
However, regional radars suggest that the main area of
precipitation moving onto the Eastern Shore. Rain had spread
north to DC metro prior to its ending. So, believe that the 
accumulating snow has already fallen. With that in mind, have
cancelled the Winter Weather Advisory for the Shenandoah Valley
and the DC metro area. 

Am still watching precip tracking across Pennsylvania, which 
could affect northern Maryland. Also, only recently has the 
snow pulled away from metro Baltimore. Anticipate the rest of
the Advisory will be able to be dropped before midnight.

That turns the focus to the upslope potential. The best
shortwave energy will be crossing in the 06-09 UTC window. That
makes for a limited opportunity for additional accumulation...
perhaps another inch or two. Considering reports to this point,
warning criteria may not be reached. However, do not have the
confidence to downgrade at this time.

Temperatures will be hovering in the lower 30s for much of the 
night. Given snow and ice on the ground, slippery conditions may
be an issue, and will strongly consider a Special Weather
Statement to cover it. Am also concerned that the snow/ice on the
ground will result in fog development since there will be 
little ventilating wind until dawn.


High pressure quickly moves in behind the exiting low pressure 
area to the northeast, resulting in a dry and clear conditions. 
After a cold and perhaps icy start to the morning, temperatures 
will rebound nicely, topping out in the mid 40s to lower 50s 
region wide. High pressure shifts offshore Sunday night, keeping
a light return flow over the region and temperatures above
normal. Low pressure will move northeastward toward the Great
Lakes region on Monday, which will help lift a warm front
through our area. With warm air advection ongoing, could see
some shower activity on Monday, not a complete washout, but 
definitely an increase in cloudiness. Highs Sunday/Monday will 
be above average, ranging in the low to mid 50s. Lows Sunday 
night will likely remain above freezing, and Monday night will 
remain in the upper 40s to near 50 degrees.


High pressure will be offshore on Tuesday with return flow well
settled over our region and an upper level ridge centered over 
the SE CONUS. Dry and above normal temperatures are expected 
Tuesday, with highs reaching the 70s for most of our CWA. 

A similar scenario is expected on Wednesday before a slow moving 
cold front approaches from the west. Guidance disagrees on the 
timing of the front, but there seems to be a consensus between some 
deterministic and ensembles that it will most likely move through 
later Wednesday or early Thursday. The front will stall nearby 
Thursday and into Friday which could keep the unsettled weather 
through the end of the week, with cooler -but still above normal- 
temperatures over our area. The front will lift as a warm front on 
Saturday, continuing the chances of rain over our area.


All precipitation has moved east of the terminals. However, low
clouds linger. Am becoming concerned that without any
ventilating wind, the clouds will remain and may be joined by
developing fog. Pretty much have status quo (IFR) in the TAFs 
for a couple of hours past midnight. Will need to reassess what 
to do thereafter. 

VFR conditions will prevail Sunday and Sunday night. Light 
winds at 10 knots or less are expected.

A warm front will lift north of the area on Monday, bringing a
threat for shower activity and the potential for episodes of 
sub VFR conditions.

VFR conditions expected Tuesday and part of the day 
Wednesday before sub-VFR periods possible late on Wednesday and into 
Thursday when unsettled weather could affect our area.


With low pressure crossing the region through tonight, expect a
weak gradient which will keep winds below criteria threshold. Winds
will remain below advisory criteria through Monday as high 
pressure traverses our region and moves offshore, delivering
light southerly winds over the waters.

Winds are expected to remain below SCA criteria on Tuesday, 
even though they will be breezy. Similar conditions expected on 
Wednesday, therefore no small craft advisory expected these 
days. Winds will decrease on Thursday and remain below criteria.


A period of exceptional warm weather is expected Tuesday and 
Wednesday. Temperatures will be approaching if not exceeding record 
values. Below is a listing of record warm highs and record warm lows 
for this period.

Record warm daily maximum temperatures
SITE   TUE 2/20   WED 2/21
DCA    76 (1930)  75 (1953)
BWI    76 (1930)  74 (1930)
IAD    70 (1971)  70 (1997)

Record warm daily minimum temperatures
SITE   TUE 2/20   WED 2/21
DCA    59 (1939)  51 (1954)
BWI    57 (1939)  49 (1981)
IAD    46 (1981)  45 (1981)


MD...Winter Weather Advisory until midnight EST tonight for 
VA...Winter Weather Advisory until midnight EST tonight for VAZ028-
WV...Winter Weather Advisory until midnight EST tonight for 
     Winter Storm Warning until 2 AM EST Sunday for WVZ501-503.



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