Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 271153
Area Forecast Discussion
National Weather Service Blacksburg VA
753 AM EDT Sat Aug 27 2016
A weak cold front will drop south across the area today and weaken.
High pressure will be the dominant weather feature into Sunday, with
just a chance for an afternoon shower or thunderstorm mainly along
the Blue Ridge. Another weak cold front may slowly slide southward
into the area by the middle of next week and continue the chance for
a shower or thunderstorm from the Blue Ridge westward.
.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM EDT Saturday...
Upper ridge will remain over our region today and tonight. A weak
cold front across northern Virginia this morning will drop south
today and weaken. Low level moisture and light winds will produce
areas of low clouds and fog this morning especially along and west
of the Blue Ridge. This fog will lift by mid morning.
It will be another hot and humid afternoon with the chance for
isolated cooling diurnal showers and thunderstorms mainly for the
southern Blue Ridge heading into the northwest mountains of North
Carolina. The day one convective outlook placed the threat for more
organized thunderstorms with a marginal risk to the northwest across
the Midwest. High temperatures this afternoon will range from the
lower 80s in the mountains to the lower 90s in the Piedmont. Heat
index values may be around 100 degrees in the Piedmont this
afternoon. Any convection will fade quickly this evening, leaving
partly cloudy conditions. Light winds and low level moisture will
create pockets of fog and stratus tonight into Sunday morning. Low
temperatures will vary from the lower 60s in the mountains to the
lower 70s in the Piedmont.
.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
As of 430 AM EDT Saturday...
High pressure aloft will continue to linger over the region, but
weaken slowly through the period. This will allow a west-east
oriented cold front to drift into the region from the north by
late Monday, then drift very slowly toward the NC/VA border by
Wednesday. The front combined with abundant low-level moisture and
strong heating will result in widely scattered afternoon/evening
showers/thunderstorms. Activity will tend to be most numerous near
the front and across the mountains.
Weak surface high across the northeast states will briefly attempt
to push a drier air mass into the region Sunday. With the
aforementioned front still well to the northwest, diurnal
showers/thunderstorms should be confined mainly to the western
areas, mainly along/west of I-77. The surface high will weaken for
Monday and the front will drift into northern areas, which will
result in increased coverage of diurnal convection across the I-64
corridor. By Tuesday, as the front continues it very slow
southward push, expect a slightly better chance of
afternoon/evening showers/thunderstorms into the southern and
eastern parts of the CWA. It should be noted that all three of
these days, given the very weak dynamics aloft, pops were kept
at or below 30 percent.
850mb temperatures will hover near +20C throughout the period,
which is only a degree or two cooler than what was observed across
the CWA yesterday/Friday. This will continue to result in
widespread mid 80s or higher western areas to lower 90s Piedmont.
With high moisture content, minimum temperatures will be well
above normal in the 65 west to 70 east range. Max and min
temperatures will thus continue to average near 10 degrees above
.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 445 AM EDT Saturday...
The upper ridge continues to weaken and shift to the southwest of
the region through the period as troughing begins to take shape
across the Great Lakes and northeast U.S. The weak frontal
boundary will continue to gradually sink southward through the
period and by Friday should be located across northern GA into
SC, with drier northwest flow evident across the Mid-
Atlantic/Central Appalachian region. Isolated to widely scattered
diurnal showers/thunderstorms should continue near the front, thus
mainly impacting areas east/south of the Blue Ridge Wednesday,
then south of the NC/VA border during the remainder of the period.
Regarding the potential for tropical systems to impact the area
this period, this is beginning to appear increasingly unlikely as
the upper trough digs into the region from the north resulting in
northwest flow aloft and lowering heights. Most models, barring
the Canadian, now depict a weak tropical wave or disturbance
moving across Florida, then turning northeast and tracking just
off the SC/NC coast toward the later part of the week. This would
have little to no impact on the RNK CWA.
The development of the trough and associated lowering heights
aloft will lead to lower temperatures as 850mb temperatures fall
back to +15C or lower. The ECMWF is not as sharp with the trough
across the northeast U.S., so feel that cooling advertised by the
GFS may be a tad overdone. At any rate, we should start to see
temperatures drop back closer to seasonal normals through the
period, namely max temperatures in the 70s west to 80s east and
lows in the 50s west to 60s east.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 745 AM EDT Saturday...
The upper ridge will remain across our region today into tonight.
A shallow backdoor front will drop southward into our region
and weaken with time. Patchy low clouds and patchy dense fog this
morning will give way to bkn low end VFR cigs as easterly maritime
upslope flow develops behind weak backdoor front. Convection
should be confined to the western periphery of the wedge boundary
this afternoon, generally west of most TAF sites. Not enough
confidence or coverage to warrant including in the TAFs at this
time. Any convection that does develop will dissipate quickly
after 00Z. Stratocumulus deck will likely diminish after dark and
easterly flow subsides. However, the combination of the clouds and
easterly flow puts in question the amount of fog/low clouds that
will develop early Sunday morning. For now, have not advertised
anything worse than MVFR visibilities for Sun morning. Winds will
be northeast to east 5-8 kts through much of the TAF valid period.
Medium confidence in cigs and vsbys through the TAF valid period.
Medium to high confidence in wind speed/direction through the TAF
Extended aviation discussion...
A weak west-east oriented front will drift south through the
forecast area Sun-Mon. Isolated diurnally driven convection will
be possible along the front, mainly north of I-64 Sun, toward the
I-64 corridor Mon, then toward the NC/SC border by Tue. Coverage
will be limited in duration and area on all days and have minimal
impact on the TAF sites. Late night/early morning fog/low clouds
are possible, but not a certainty. At this time, it does not
appear that any tropical systems will impact the CWA.
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