Scientific Forecaster Discussion
fxus61 krnk 222001
Area forecast discussion
National Weather Service Blacksburg Virginia
401 PM EDT Mon may 22 2017
a cold front from Pennsylvania to northern Georgia will move
southeast and stall across North Carolina by Tuesday as high
pressure wedges down the Appalachians. Yet another area of low
pressure will arrive midweek with added rainfall likely for
Wednesday and Thursday. Friday will be the drier day this week.
Near term /through Tuesday/...
as of 300pm EDT Monday...
Water vapor loop showed a well defined short wave over Arkansas
early this afternoon. Models track this feature into southern
Surface and 850mb front cross the area this afternoon, but with
little change in air mass behind it. 850mb winds back to the
southeast by midnight brining the deep moisture north along the Blue
Ridge and foothills. Best convergence will be from 12-18z/8am-2pm
Tuesday. GFS may have some convective feedback and may be moving the
wave too fast and too far northeast compared to other guidance. Some
decent isentropic lift on the 3km NAM Tuesday morning. Leaned toward
NAM and wpc for quantitative precipitation forecast .Will have to monitor amounts since some
locations have had lots of rain in the past 72 hours and have
saturated soils as a result.
Surface front reaches central North Carolina as high pressure moves
from West Virginia into Pennsylvania. By Tuesday morning the in-situ
wedge will be in place down the Appalachians aided by precipitation
on the cool side of the front. Clouds and precipitation will keep
temperatures down on Tuesday. Trending toward cooler guidance for
Short term /Tuesday night through Thursday night/...
as of 330 PM EDT Monday...
Large upper trof will be traversing the eastern US, keeping US in a wet
pattern through the period.
Multiple waves along the front to our east will be pulling away from
the region Tuesday night. However, a low over the Ohio Valley will be
captured by the upper trof as it closes off and the stacked system will
wrap up a cold front a push it into our area from the west Wednesday
morning. There will be a bit of an in-situ wedge ahead of the front to
limit instability and convective development, but good isentropic lift
and dynamic support will make for widespread rainfall and some possibly
some embedded thunder from lift over the stable layer. Also, there may
be a very narrow window just ahead of the front where The Wedge has
weakened that may allow for deeper instability to support elevated
convection in a highly sheared environment. While the overall
probability of severe weather is low, the situation bears watching
until fropa occurs early Wednesday night. Expect some lessening of
showers overnight Wednesday night in Muddy dry slot of stacked low
spinning over the Ohio Valley.
Diurnal heating will pop showers and thunderstorms with steepening
mid/upper lapse rates under the cold pool aloft as the upper trof
swings through. Small hail/graupel in low topped convection look
possible mainly west of the Blue Ridge. Showers/storms taper quickly
with loss of heating in the evening, leaving some lingering upslope
precipitation west of the ridge into Friday morning.
Long term /Friday through Monday/...
as of 330 PM EDT Monday...
Our unsettled pattern will continue through the weekend as a
progressive upper ridge moves across the eastern US, followed by the
development of another closed low moving through the upper Midwest.
This will allow a frontal boundary to sink into the region from the
north and stall on Saturday, with a series of waves shearing off to our
north dragging along weak, occluded fronts. While not likely a complete
washout, we look to keep a good chance of showers and thunderstorms in
the forecast through the weekend and into the first part of next week.
Aviation /20z Monday through Saturday/...
as of 145 PM EDT Monday...
Last of the stable air and IFR stratus was moving out of
southwest Virginia as seen on satellite pictures and as
depicted on the lifted index analysis. Winds had come around to
the west for the rest of the area. A cold front extended from
southwest Pennsylvania to northern Georgia with scattered
thunderstorms beginning to develop along and ahead of the front
in northern North Carolina. Have a tempo group in the kdan taf
for thunderstorms late this afternoon.
There will be a break in the precipitation this evening then once
this front advances farther into North Carolina deeper moisture
will return into southern Virginia with a wedge of high pressure
developing along with widespread light to moderate rain. Models
showed the best lift from 12z/8am through 18z/2pm Tuesday.
Expect MVFR to IFR clouds to develop after midnight as surface
and low level winds back to the southeast Tuesday morning. High
confidence on the occurrence of MVFR ceilings and visibilities
with medium confidence on the timing.
Extended aviation discussion...
The chance of precipitation continues Wednesday and Thursday
with sub-VFR conditions associated with any of the
precipitation. Friday will be drier with a better chance of VFR
ceilings and visibilities. Another front reaches the area for
Saturday with more precipitation and sub-VFR conditions.
as of 345 PM EDT Monday...
An inch to inch and a half of rain is expected tonight and
Tuesday. Amounts will have to be monitored as some locations
along the Virginia/North Carolina border, especially carrol,
Patrick and Henry counties in Virginia and Stokes, Rockingham,
and Caswell counties in North Carolina. Ffg along parts of the
southern Blue Ridge was in the 1.5 to 2.5 inch range.
More rainfall is expected Wednesday and Thursday, which could
lead to small stream and river flooding. Models continue to
favor areas along/east of the Blue Ridge, possibly resulting in
another 1 to 3 inches of rain.