Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS62 KRAH 182008

Area Forecast Discussion
National Weather Service Raleigh NC
408 PM EDT Sun Mar 18 2018

Weak high pressure will extend across the southern middle Atlantic
states through tonight. A warm front will retreat north across the
southeastern U.S. Monday, ahead of a series of low pressure systems
that will track along the front, and across and offshore the
Carolinas, Monday night through early Wednesday.


As of 350 PM Sunday...

WV satellite imagery indicates the ridging aloft that was over the
MS Valley in 12Z RAOB data has expanded ewd to the Deep South and
upr Midwest; and this ridge will continue to expand ewd across the
sern U.S. tonight. While doing so, however, a srn stream
perturbation, now evident in WV imagery invof the ArkLaTex, will
deamplify while tracking across the TN Valley and srn Appalachians
and consequently cause the preceding ridge to flatten with time.
Associated mid to high level moistening will spread newd across cntl
NC late tonight, along with weak forcing for ascent focused in the
mid levels after 09Z.

Additionally, a low to mid level warm air advection regime, and
contribution to forcing for ascent, will develop on the wrn
periphery of a weak ridge/antic-cyclone drifting to the srn middle
Atlantic coast. Initially clear skies will consequently become
cloudy or mostly so from west to east, from a developing multi-
layered cloud deck overnight. A little light rain will also be
possible over the far srn and wrn Piedmont toward daybreak, with
otherwise dry conditions.

Temperatures will likely reach lows earlier than is typical, then
rise with the development and ewd expansion of the clouds - in the
wrn Piedmont around or shortly before midnight, ranging to an hour
or two before sunrise in the Coastal Plain. As such, low
temperatures are expected to range from lwr-mid 30s in the nrn and
cntl Coastal Plain to mid 40s over the srn and wrn Piedmont.


As of 400 PM Sunday...

A progressive trough aloft now over the cntl Rockies, one that will
have become a compact closed mid-upr low as it migrates across the
cntl Plains tonight, will deamplify as it tracks enewd across the
lwr OH Valley and cntl Appalachians Mon-Mon night. This trough/low
will support Miller "Type B" surface cyclogenesis, with a parent
cyclone tracking from a position now over the Front Range of the
cntl Rockies to the lwr OH/TN Valley by Mon eve, with subsequent
energy transfer to a secondary wave forecast to track across cntl NC
Mon night.

The result will be a cloudy Monday, but not particularly wet owing
to a lull between the weak srn stream forcing for ascent late
tonight, and the later arrival of the forcing accompanying the
deamplifying closed low Mon night. Rain will become widespread with
the passage of the upper and lower waves Mon night, particularly
along and north of the track of the surface wave - over the nrn
Piedmont, where rainfall amounts as high as three quarters of an
inch to one inch appear probable. Srn counties will meanwhile
experience an increasingly convective character of the
precipitation, not as uniform, and with a slight chance of thunder,
where milder and slightly unstable conditions, particularly with
respect to elevated parcels, are likely to materialize.

Temperatures, hindered by the multi-layered overcast, will be cooler
Mon, ranging from lwr 50s over the nw Piedmont to upr 50s-near 60s in
the srn Coastal Plain, with lows Mon night ranging from mid 40s in
the cool/stable wedge north of the low track, to low-mid 50s south.


As of 210 PM Sunday...

Longer range forecast remains on track for a cold and unsettled
Tuesday through Thursday with a warming trend toward the weekend.

A brief lull in the precip is generally expected on Tuesday as the
first in a series of disturbances shifts to the east of the area.
However, skies will continue to remain mostly cloudy to overcast
will low level moisture lingering. Highs on Tuesday are expected to
range from the mid 40s north to the lower to mid 60s south.

Additional mid/upper level energy is expected to dive southeastward
and into our area for Tuesday night into Wednesday. Models
continuing to advertise the potential for some wintry precip late
Tuesday night into Wednesday morning across the area, with the best
chance of seeing some light accumulations of snowfall across the
climatological favored northern Piedmont. The system will be similar
to the last one, where the boundary layer will need to cooled by
melting snow in order bring temps down to near freezing. Have kept
temps ranging from the lower/mid 30s to lower 40s for the entire
wintry event.

Dry weather will return for late week with the mid upper level
trough axis expected to shift to the east of the area. The next
system is expected to approach the area next weekend, with
increasing chances for showers. Temperatures will make a run toward
seasonal normals by the weekend.


As of 215 PM Sunday...

Under the influence of a ridge of high pressure over the srn middle
Atlantic states, VFR conditions will persist through tonight.
However, veering low/mid-level winds to a sly component, on the wrn
periphery of the ridge, will favor the development and newd
expansion of VFR (5-15 thousand ft) ceilings overnight-early Mon,
with a subsequent lowering of ceilings to MVFR range and an
increasing probability of rain, after 12Z.

Outlook: The passage across the Carolinas of a series of low
pressure systems will result in sub-VFR conditions and periods of
rain, probably mixed with or briefly changing to snow at nrn TAF
sites late Tue night or Wed, through Wednesday. Drying and a return
to VFR conditions from west to east will occur as the trailing low
lifts away from the middle Atlantic coast Wednesday night.





LONG TERM...BSD/Franklin
AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.