Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus62 krah 011733 
afdrah

Area forecast discussion
National Weather Service Raleigh NC
1235 PM EST Wed Mar 1 2017

Synopsis...
warm southwest flow will continue across the region today ahead
of a strong cold front approaching from the west. The cold front
will cross the area tonight, followed by cool high pressure for
the later half of the week.

&&

Near term /through tonight/...
as of 1050 am Wednesday...

Potential for severe storms with damaging wind gusts appears
slightly higher, primarily west and north of Raleigh late this
afternoon into the evening hours.

Early morning analysis depicts a conditionally stable air mass as
12z gso sounding depicts a strong cap between 850-750mb. In
addition, very strong winds noted just off the surface with 40kts
observed at 1000 ft. As temperatures rise to around 70, breaking the
sfc based inversion, should see an increase in the sfc winds with
gusts 30-40 mph. Plan to handle gusts with a Special Weather Statement but may need to
issue a short fuse Wind Advisory by mid day.

While a few showers may skirt the northwest Piedmont early this
afternoon, the better forcing for scattered-numerous showers and
storms appears to arrive in our region after 21z. Sfc dewpoints this
morning are in the upper 50s-lower 60s west and low-mid 60s east.
These values are a few degrees higher than projected. In addition,
low stratus absent across much of the northwest Piedmont, allowing
this region to warm faster than earlier thinking. The expected
string heating late this morning-early afternoon along with the
approach of a slightly cooler air mass aloft may be enough to
erode/break the 850-750mb cap, leading to a better potential for
strong/severe storms. This threat appears most likely across the
western Piedmont into the far northern Piedmont along the Virginia
border counties.

Still some uncertainty as to the probability of severe storms in the
rdu Metro area and points east-se as system projected to go through
mid-late evening hours when the near sfc air mass will begin
nocturnal stabilization. If storms arrive in the Raleigh area closer
to 7 or 8 PM, the threat for locally damaging winds will increase.

Afternoon temperatures near 80 northwest to the low-mid 80s southeast still appear
on track.

&&

Short term /Thursday through Thursday night/...
as of 400 am Wednesday...

After lingering mid level ceilings and perhaps a few sprinkles over
the far sern counties early Thu, cirrostratus within the axis of a
150 kt wswly gradually edge swd and out of central NC throughout the
day. Downslope nwly flow will help offset waning cold air advection. Highs in the
upper 50s to Lower-Middle 60s, with gusts up to 25 mph until midday-
early afternoon, before cold air advection diminishes by afternoon.

Surface high pressure will ridge overhead from the SW in advance of
a clipper frontal system approaching from the NW, so temperatures
will have the potential cool into the upper 20s to Lower-Middle 30s.
Thu night.

&&

Long term /Friday through Tuesday/...
as of 355 am Wednesday...

A progressive pattern aloft will result in a transition from a
departing trough in the eastern U.S. Fri-Sat, to ridging
through early next week. The trough will reach maximum amplitude
as a shortwave trough in northwest flow aloft amplifies across the
Middle Atlantic States during the day Fri. This trough will be
followed by a less amplified/shear vorticity maximum that will
migrate through the northwest flow, with a brief period mid level warm air advection
cloudiness, on Sat.

At the surface, a clipper surface wave accompanying the
aforementioned shortwave trough in northwest flow aloft will track
across the nrn Middle Atlantic States, while the trailing nrn
stream surface cold front will sweep across central NC during
the day Fri. Given both 1) a tendency for the models to advect
cold air across the Appalachians too quickly, and 2) the
prevalence of a downslope/compressional warming flow component
throughout the day, temperatures are expected to recover into
the middle 50s to lower 60s. Cold and dry advection within a
deeply mixed (800-750 mb) boundary layer will support afternoon
wind gusts up to 25-30 mph, which will make it feel cooler.

Incoming cp surface high pressure behind the front on Fri will
result in a hard freeze Fri night-Sat morning, when
temperatures are expected to fall into the Lower-Middle 20s over
the Piedmont, to upper 20s to around 30 degrees over the
sandhills, srn coastal plain, and urban areas. Temperatures
will gradually moderate thereafter, as the surface ridge moves east
and modifies, with 50s on Sat replaced by 60s-70s by early next
week.

After a dry weekend as the ridge moves overhead and offshore,
the approach of the next frontal system will result in a chance
of showers late Mon-Tue.

&&

Aviation /18z Wednesday through Monday/...
as of 1235 PM Wednesday...

Windy conditions will persist through early evening as SW sfc winds
will frequently gust between 30 and 40 mph with a sporadic gust
around 45 mph. These strong winds are ahead of a cold front that
will sweep across our region later tonight.

Ahead of the front, expect a band or two of showers and
thunderstorms. Expect MVFR/IFR ceilings and visibilities in vicinity
of the heavier showers and storms. The stronger storms will be
capable of producing wind gusts 50-60kts. These bands of convection
will likely affect The Triad region between 22z-01z, the krdu
vicinity between 02z-05z, and krwi and kfay between 04z-07z. The
threat for damaging wind gusts will be highest in vicinity of The
Triad, with the threat dwindling farther east.

The cold front will cross The Triad just prior to midnight, the krdu
vicinity between midnight and 2 am, and krwi and kfay between 2 am
and 5 am. The passage of the front will be noted by sfc winds
veering to the NW, with gusts 18-23kts probable.

Other than gusty sfc winds Thu and again Fri, VFR parameters
expected across central NC Thursday through Sunday. The chance for
sub-VFR ceilings or visibility restrictions due to fog will begin to
increase on Monday.

&&

Fire weather...
as of 550 am Wednesday...

Critical, or nearly so, fire weather conditions still probable Thu
and especially Fri.

Much drier air will overspread central NC following a cold frontal
passage, and accompanying line of showers and storms, tonight. The
drier air, combined with afternoon temperatures in the upper 50s to
middle 60s on Thu, will result in minimum relative humidity values
between 20 and 25 percent Thu afternoon. However, nwly winds, which
will gust between 20-25 mph through 1 PM, will subside during the
afternoon (when critical relative humidity values are met). Nonetheless, there may
be a several hour period centered around noon Thu when marginally
critical relative humidity values between 25-35 percent overlap with
the aforementioned stronger winds; and increased fire danger may
result.

These conditions will also set the stage for Fri, when daytime
heating and a secondary cold frontal passage during the afternoon
will result in critical relative humidity values for several hours during the
afternoon. In addition, breezy wly to nwly surface winds are
forecast to be sustained between 15-20 mph, with 25-30 mph gusts.
These conditions for increased fire danger to red flag will likely
be coordinated with the ncfs later today and/or on Thu.

&&

Climate...
record highs for March 1st:
rdu: 82 (set in 1997)
gso: 77 (set in 2012)
fay: 87 (set in 1918)

&&

Rah watches/warnings/advisories...
none.

&&

$$
Synopsis...Smith
near term...wss
short term...mws

National Weather Service Glossary of Abbreviations