Area Forecast Discussion
Issued by NWS Blacksburg, VA
FXUS61 KRNK 271749
Area Forecast Discussion
National Weather Service Blacksburg VA
1249 PM EST Sun Nov 27 2016
High pressure will drift across the region today. Meanwhile, a
broad upper low will develop across the central U.S. during the
early part of the week sending a cold front into the eastern U.S.
Tuesday providing beneficial rainfall to the region. Another wave
of low pressure will develop across the southeast states by
midweek bringing another surge of rainfall to the area.
.NEAR TERM /THROUGH TONIGHT/...
As of 1230 PM EST Sunday...
Dew points across Northwestern North Carolina have been lowering
all day due to better mixing. We have lowered afternoon relative
humidities and warmed temperatures in this area for the
afternoon update. No other major changed were needed elsewhere.
As of 345 AM EST Sunday...
Another dry day expected across the region today as a large
Canadian high pressure area settles over the region. The high will
shift eastward to the coast by Monday morning as a broad,
deepening low pressure area begins to take shape in the central
U.S. as the result of strong pacific energy shifting into the
Low clouds lingering in upslope areas near the Alleghany front
gradually eroding from the south and east. Both KBLF and KLWB lost
their low ceilings within the past couple of hours. Expect a more
substantial erosion of these clouds after daybreak as the upslope
winds end and the cold pool aloft begins to lift northeast out of
the area. Thus, skies should be mostly clear through much of the
day after mid-morning until high clouds from the upstream system
begin to spread into the region after sunset, but more
substantially so after midnight.
A pesky pocket of cold air aloft will linger through the morning
hours across eastern WV, but lift out by afternoon. The 0C 850mb
isotherm will lift from the northern part of the CWA this morning
to northern WV/northern VA by evening. This combined with a
gradual turn of the winds to the southwest will allow max temps
today to be around 10 degrees warmer than what was observed
Saturday afternoon, especially western areas where it was cloudy
much of the day. Minimum temperatures Monday morning will be
highly disparate as a result of near calm winds in the deeper
valleys, but increasing winds at ridge tops as a stronger low-
level jet moves eastward toward the region. These factors along
with an increase in high clouds will overall result in milder min
temps than what we are seeing this morning, but some of the deeper
valleys will still drop down in the mid and upper 20s before
daybreak, while some ridgetops may stay closer to 40F.
.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
As of 200 AM EST Sunday...
During this portion of the forecast, the upper ridge that has
been positioned over the east coast will shift east into the
western Atlantic. A broad upper trough and associated upper low
are expected to take up residency across the central portion of
the country. This transition will help open the Gulf of Mexico and
allow moisture rich trajectories to enter into our region.
A cold front associated with the main upper low is expected to move
into and through the area on Tuesday. In advance of this feature,
low level 850 mb winds are progged to increase to as much as 50 to
60 kts late Monday afternoon and overnight. Concern turns to surface
wind gusts with the potential for at least wind advisory speeds and
gusts across the higher elevations of the southwestern portion of
the forecast area. Will highlight this concern in the updated
Hazardous Weather Outlook.
Rainfall is expected to come in two waves. The first will be
immediately in advance of and concurrent with the passage of the
Tuesday cold front. Guidance varies on how much of a break in the
activity will occur Tuesday night. However, there is agreement for a
second wave to lift out of the Gulf of Mexico on Tuesday night and
head northeast across our region by Wednesday morning or afternoon.
By late Wednesday night this feature is either east of the region,
or along the eastern half of the region.
Precipitation totals are expected to be substantial. Totals from the
first wave are currently forecast to be on the order of one-half to
two-thirds of an inch over most of the area. The region immediately
near the crest of the Blue Ridge can expect higher amounts, near the
one to one and one-half inch range. The second wave of precipitation
potentially could produce more precipitation than the first round.
Amounts are currently forecast to average one and one-half to two
inches of rain for most of the region. East of a Danville to
Buckingham line totals will be less with a little over one inch
expected. Immediately near the crest of the Blue Ridge, totals will
be higher, closer to two and one-half inches.
While the chances are on the low side, guidance is suggesting some
very weak surface based instability across the far southeastern
portion of the forecast are both Tuesday and Wednesday afternoons.
Our previous forecast was already offering a slight chance of
thunder in a small part of this area Wednesday. The forecast this
morning will expand this area a little farther westward. The
inclusion of a slight chance of thunder on Tuesday is a new edition
to the forecast.
Temperatures will be on the mild side given the strong warm air
advection that will be dominating our weather regime. Expect
readings to trend milder for lows and high temperatures through
Wednesday. Wednesday night will be cooler than Tuesday night as
colder air associated with the upper trough axis draws closer to the
area. Average temperatures on Wednesday are forecast to be around 20
degrees above normal.
.LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 122 pm EST Saturday...
Thursday will see winds shift to the northwest behind the front.
Will have chance pops Thursday, except likely in the far nw as
think shortwave shifts across the mountains aiding upslope
showers. Notable pressure rises are evident as surface low
pressure deepens over NJ, but 850mb jet appears weak mainly under
30 kts, so overall breezy with sustained winds of 10 to 15 mph
with gusts 20-25 mph, mainly mountains. Highs will be cooler
Thursday from the mid to upper 40s mountains to the mid to upper
For Thu night-Sat, models diverge with the GFS showing continued NW
flow in the low levels with fast westerly flow aloft while the ECMWF
similar aloft but less moisture. GFS showing continued threat of
some precip in the western slopes of SE WV into Saturday. Setup
favors slight chance at least, so will lean that way, but overall
should be clearing and somewhat breezy into Friday night, with
colder air sliding in, allowing some snow to fall in the mountains
of WV, though not expecting much.
Highs Fridays somewhat similar to Thursday, a few degrees cooler
perhaps. Zonal flow aloft keeps it seasonal into Saturday with lows
in the upper 20s to lower 30s, and highs from the lower to mid 40s
west to lower to mid 50s east.
.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
As of 1230 PM EST Sunday...
High confident forecast for VFR conditions through the TAF valid
High pressure will remain centered over the region through tonight,
then slowly moves off the NC/VA coast on Monday. While this high
lingers over the region, winds will continue to be light and
variable through the TAF period. Some high clouds will invade the
region from the southwest late tonight into Monday morning.
Extended aviation discussion...
A broad and deepening area of low pressure across the central U.S.
will drift slowly east through the week bringing at least two rounds
of rainfall to the area, one Tuesday, and another Wednesday into
Thursday as a wave of low pressure moves northeast from the central
Gulf coastal region. Expect periods of sub-VFR ceilings and
visibilities through much of the period as a result. Strong
southeast winds also possible around KBLF Monday night as well as
some of the higher ridges along the western slopes. Cold front
crosses the area Thursday bringing a return to VFR east of the
mountains while upslope sub-VFR cigs likely linger across the
Alleghanys, with some upslope rain or snow showers possible.
As of 430 AM EST Sunday...
High pressure will drift across the region today with a very dry
air mass remaining in place. Fortunately, winds are expected to be
light, so despite minimum relative humidity values in the 20-25%
range, locally lower, and very dry fuels, light winds will
preclude the issuance of any Fire Danger Statement or Red Flag
Warning at this time.
Monday will still be dry ahead of the much anticipated rain system
for Tue-Thu. Southerly winds will be on the increase as a strong
LLJ approaches the region from the west. Relative humidity values
will be on the increase, but perhaps not quickly enough,
especially at higher elevations, to preclude some brief fire
Rainfall still looks promising for midweek in two waves. The first
round will come with a frontal system Tuesday, bringing 1/2 to 1
inch, mostly west. The next round, potentially more significant,
arrives Wed-Thu as a wave of low pressure moves northeast from the
central Gulf Coast states. Rainfall potential with this system
could be in the 1 to 2 inch range. All good news for the severely
drought stricken area that has seen little to no rainfall during
the past two months.