National Weather Service Raw Text Product

167 
FXUS61 KLWX 120058
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
758 PM EST Sat Mar 11 2017

.SYNOPSIS...
High pressure will gradually build over the region through 
early Monday. Low pressure will impact the Mid-Atlantic Monday 
night into Tuesday with upper level low pressure then over the
are through Wednesday. High pressure will return toward the 
area Thursday through Friday with a cold front Saturday.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
Winter storm watch issued for most likely areas to receive
heavy snow. See short term section below.

High pressure over the area will produce clear skies and a cold
mid March night. Lows primarily around 20...a little warmer in
the cities.

And no problems Sunday through Monday. High pressure will move
offshore Monday. High temperatures both days around 40. Sunday
night another cold one with lows in the lower 20s.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
Winter storm watch I-95 and west to portions of the Potomac
Highlands (western five counties have a one inch higher 
snow criteria), then south to north-central VA including all of
our Blue Ridge. One issue is this snow will occur in longer than
12 hours. Criteria is 5 inches in 12 hours and 7 inches in 24
hours. Therefore, central Shenandoah Valley and central VA was 
not included at this time.

Southern stream low pressure will lift north along the NC coast
with an inverted trough bringing snow onset on a southeasterly
flow in the evening. Warm air advection precip like this often
starts earlier than models indicate. This could put onset during
daylight, so the first of the snow will be used for
cooling/saturation. That southeast wind will also bring the
rain/snow line into southern MD and possibly near/over I-95.
This line will be key (as usual) for snow totals in the metro 
area. The heaviest snow often occurs just on the cold side of
the rain/snow line. Hence the watch includes zones with I-95.

Elevation typically plays a role with March snow and areas of
central MD above 500ft stand to see the greatest snow (also
because of the track). One foot is possible along the Blue
Ridge/Catoctin mountain and higher elevations of MD like Carroll
county. Later shifts will continue to assess the rain/snow line
and storm track. Please see our snow forecast and probability maps
on our winter page at weather.gov/lwx/winter.

Edited previous:
All eyes continue to be on Monday night/Tuesday. GFS has never 
had this system particularly well "put together" - it's had a 
coastal low developing around midnight Monday night while the 
upper low has lingered over the Ohio Valley, with everything not
coming together until these lows phase near New England. As I 
wrote yesterday this would not be what we want to see to get big
snowfall totals in the Mid-Atlantic.

And now the Euro..although it is still forecasting the better
track for snow...is coming in a little faster and farther 
offshore.

It is hard to get large snowfalls at this time of year because
of sun angle. However, the best chances for heavy snowfall are 
overnight Monday.

Heavy snow looks to be over by Tuesday afternoon as the low
pulls farther northwest.

By Tuesday afternoon expecting snow showers across the area 
ahead of the approaching upper low. It will still be cool with 
highs only in the upper 30s on breezy northwest winds.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
The cut-off H5 low will be centered over Pennsylvania at the start 
of the period on Tuesday night. The low will push northeast 
towards the Canadian Maritimes Wednesday, and the mid-Atlantic 
will be under H5 height rises through Friday. With surface high 
pressure building at the start of the long term, conditions 
should remain dry except in upslope snow regions where 
accumulating snow can be expected Wednesday and Thursday.

On Friday, surface low pressure over the mid-Mississippi Valley will 
deepen and develop a coastal low near the Chesapeake Bay for 
Saturday. This will lead to unsettled conditions on Saturday, with a 
good chance of precipitation and continuing below normal 
temperatures.

Surface temperature during long term period will be significantly 
below climatology, with daytime highs approximately 20 degrees 
normal through Thursday.  Warm air advection initiating late 
Thursday will start moderating the temperatures Friday and Saturday, 
but still forecast 20 degrees below normal, along with likelihood of 
precipitation on Saturday.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
VFR tonight through Monday. Expect clouds to lower Monday night
with snow developing. IFR conditions expected in snow, heavy at
times across the DC metros Monday night into Tuesday.

In the extended from Wednesday through Saturday, strong winds are 
forecast during the daylight hours on Wednesday, which may lead to 
air traffic restrictions.

&&

.MARINE...
SCA in effect until early Sunday morning, then no problems
Sunday. SCA again Monday night and Tuesday.

Northwest gales are likely during the daylight hours for at
least portions of the area on Wednesday, then likely 
diminishing to small craft wind conditions on Thursday.

&&

.CLIMATE...
A shot of very cold late season Arctic air has arrived. Here 
are the daily cold temperature records for March 12th.

March 12th
Site   Record daily low   Record daily cold high
DCA    11 degrees (1900)  30 degrees (1900/1888)
BWI    12 degrees (1900)  29 degrees (1984)
IAD    18 degrees (1998)* 36 degrees (1998/1984)
*Also set in 1984/1969

The presence of a fresh snow pack may allow particularly cold
air on Thursday night when a high pressure ridge builds 
overhead.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Winter Storm Watch from Monday evening through Tuesday 
     afternoon for DCZ001.
MD...Winter Storm Watch from Monday evening through Tuesday 
     afternoon for MDZ003>006-011-013-014-503>508.
VA...Winter Storm Watch from Monday evening through Tuesday 
     afternoon for VAZ027>031-039-040-051>055-501-502-505>508.
WV...Winter Storm Watch from Monday evening through Tuesday 
     afternoon for WVZ050>053-055.
MARINE...Small Craft Advisory until 5 AM EDT Sunday for ANZ530>534-537-
     539>541-543.
     Small Craft Advisory until 9 PM EST this evening for ANZ535-
     536-538-542.

&&

$$
Update...Jackson
Previous...Woody!/JEL