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000 
FXUS61 KRNK 221917
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
317 PM EDT Tue Aug 22 2017

.SYNOPSIS...
A Bermuda high off the coast will keep a warm and moist airmass
in place across the Appalachians and central mid Atlantic 
region into tonight. A cold front will slowly move through the 
area tomorrow, bringing a better chance for showers and storms 
to the region. Cool dry high pressure will settle over the
region Friday and into the weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 300 PM EDT Tuesday...

Surface high pressure continues to track east into the 
Atlantic. Replacing this surface ridge is a lee trough draped 
over the piedmont. Over the Great Lakes is a cold front that 
will track over the Ohio Valley tonight. The combination of the 
lee trough and the front to the west will keep warm moist 
southwesterly flow into the region. HiRes and 12Z NAM models 
were showing diurnal orographical convection along the Blue 
Ridge this afternoon. However, GFS/ECM kept areas along and east
of the Blue Ridge dry as heights increase from the Bermuda high
building westward across the southeastern states. In verify the
models, both were right and wrong this afternoon. Showers did 
develop along the Blue Ridge but the areal coverage was small 
and the showers were short-lived. A few showers may pop up along
the Blue Ridge and over the foothill counties through the rest 
of the afternoon, but all should be gone by sunset.

Our better chance for widespread rain will come tonight into 
the day Wednesday as the cold front moves from the Ohio Valley 
southeast into the Carolinas. Some HiRes models are bringing 
prefrontal showers into the Greenbrier Valley as early as 8PM 
this evening. Most models are slower with an arrival time around
midnight. SPC has SE WV and SW VA in a marginal risk for severe
storms into this evening. 

Frontal showers will begin to move across the mountains after 
midnight but areal coverage may be less as winds aloft become 
westerly quickly. Models are also keeping the stronger chance 
for convection north of the area (best jet dynamics) and 
southwest across the Tennessee Valley (stronger short wave/best 
instabilities). This will leave some of the area in a rainfall 
minimum (Blue Ridge/foothills). During the day Wednesday, the 
front will merge with the lee trough somewhere over the VA/NC 
piedmont. At this time, models have strong to severe storms 
forming south towards Greensboro and Raleigh NC Wednesday 
afternoon or later. This stronger line of convection could 
develop further north over Southside VA as temperatures warm 
into the upper 80s and low level winds back temporarily to the 
southwest. It will all come down to the location of the front 
during peak heating.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 230 PM EDT Tuesday...

Best convergence moves past Danville and to the southeast early
Wednesday evening. Will stay close to a blend of the GFS and 
NAM for timing on the clearing. Sharp drop in precipitable water
values to less than one inch in the mountains on Wednesday 
night. Expect precipitation to be gone well before the clouds 
finally clear. 

Another short wave Thursday night and Friday morning. This will
re- enforce the subsidence, drying and cooler air mass. By 
Friday morning the upper trof axis will be approaching the East 
Coast. 

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 1230 PM EDT Tuesday...

Friday night and Saturday surface high pressure will be 
centered over the Great Lakes. Saturday night through Sunday the
high will progress down the east side of the Appalachians. 

Short wave crossing the northern tier states Friday and 
Saturday will turn south into the Mississippi Valley on Sunday. 
Nothing close to consensus in the models after Sunday reguarding
any interaction between this troughing and the tropical system 
moving north through the Lower Mississippi Valley. Not expecting
any impact in the Mid Atlantic region from neither of these 
systems before Monday at the earliest. 

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
As of 120 PM EDT Tuesday...

Surface high pressure continues to track east into the 
Atlantic. Replacing this surface ridge is a lee trough draped 
over the piedmont. Over the Great Lakes is a cold front that 
will track over the Ohio Valley this afternoon and overnight. 
The combination of the lee trough and the front to the west will
keep warm moist southwesterly flow into the region. HiRes and 
12Z NAM models are showing diurnal orographical convection along
the Blue Ridge this afternoon. However, GFS/ECM keeps areas 
along and east of the Blue Ridge dry as heights increase from 
the Bermuda high building westward across the southeastern 
states. If diurnal convection does form, HiRes models have them 
fading during the evening. With questionable coverage this 
afternoon, we will keep the forecast dry and amend if storms 
approach a TAF site. 

Our better chance for widespread rain will come tonight into 
the day Wednesday as the cold front moves from the Ohio Valley 
southeast into the Carolinas. Some HiRes models are bringing 
prefrontal showers into the Greenbrier Valley as early as 8PM 
this evening. Most models are slower with an arrival time around
midnight. Sub-VFR conditions likely to start towards sunrise 
across the mountains and during the afternoon for areas east. 

Extended Aviation Discussion...

Flying conditions should slowly improve Wednesday night and 
continue into the weekend as high pressure builds over the 
region.

&&

.EQUIPMENT...
As of 310 PM EDT Tuesday...

KFCX doppler radar is expected to be back in operations as early
as Wednesday evening (Aug 23rd). Technicians replaced the bull 
gear Sunday and reassembled the radar today. Calibration work 
will continue through the day Wednesday.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...RCS

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