Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 270856
Area Forecast Discussion
National Weather Service Blacksburg VA
456 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 /09Z SATURDAY THROUGH WEDNESDAY/...
As of 146 AM EDT Friday...
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. For this morning, expect low clouds/fog
overnight given moist dewpoints and light winds. It appears the
greatest likelihood for MVFR/IFR conditions at KBCB with LIFR at
KLWB. The weak northeast flow may trapped moisture and produce
additional cloud cover along/east of the Blue Ridge. MVFR
conditions may be possible at KDAN and KLYH this morning.
Lingering fog/stratus will burn off by mid morning returning VFR
conditions into early this under a scattered- broken 4-6 kft
cumulus field. Isolated diurnal convection is possible this
afternoon with the best chance across southwest portions of the
forecast area. Coverage of storm will be too isolated for mention
at taf sites. Winds will remain light and generally under 10
Should see a repeat tonight with any lingering evening convection
fading after sunset followed by late night mainly valley sub-VFR
in fog/stratus with light winds.
Medium to high confidence in ceilings,visibilities and winds
during the taf period.
Extended aviation discussion...
A weak front will remain over parts of the area Sunday. Isolated
to scattered diurnal showers and thunderstorms still possible into
Sunday evening. Coverage will be limited in area and duration.
Monday high pressure bubbles in but still a very humid airmass to
keep isolated mountain storms around in the afternoon, but mainly
VFR. Another front situated north of us Tuesday could enhance the
convective threat, mainly over the mountains and north of ROA/LYH.
Front should cross the region later Wednesday with possible sub-
VFR at times in pre-frontal convection Wednesday afternoon.