Area forecast discussion
National Weather Service Blacksburg Virginia
726 PM EDT Wednesday may 22 2013
Synopsis...
a large low pressure system will track from the Central Plains into
the Great Lakes by Thursday. This system will push a cold front
through the area Thursday into Thursday evening...followed by
high pressure on Friday.
&&
Near term /until 6 am Thursday morning/...
as of 300 PM EDT Wednesday...
Scattered strong to severe thunderstorms developing this afternoon
mainly across the mountains in the warm and unstable air. The
main threats for this afternoon into tonight are heavy
rain...winds (dcapes Ard 1000 in region) and hail (with wbz Ard
10kft). Convective available potential energy of 1 to 3 j/kg as seen on the Storm Prediction Center mesoscale anal were
forecasted by modified soundings this morning. Leaned probability of precipitation tonight
towards rnk wrfarw which placed this afternoons convection quite
well. NAM...GFS and ecwmf continue showers and thunderstorms into
tonight especially in the west. Expect areas of fog overnight
where rain falls this afternoon into tonight. Played low
temperatures tonight from middle 50s in the northwest to the middle 60s
in the southeast.
&&
Short term /6 am Thursday morning through Saturday/...
as of 300 PM EDT Wednesday...
European model (ecmwf)/GFS blend followed this period...as timing looks good for the
front arriving in the area Thursday morning and exiting by Thursday
evening in the east. Main forcing will be weakening but enough low
level convergence and decent flow aloft to maintain a broken line of
showers and storms into the mountains Thursday morning shifting east to
the Piedmont by midday. Dry slot works into the southwest around
late evening with strong shortwave following into WV/Virginia by Friday
morning. This will enhance the shower activity in the WV mountains
although airmass overall will be drying out.
Severe threat Thursday will be east where some sun may occur early
enough to destabilize the airmass. Not outlooked though but cannot
rule out an isolated wind gust over 50 miles per hour or hail.
The change in airmass will be noticeable Friday as dewpoints drop
into the 30s and 800 mb temperatures drop to near zero. Not seeing much cloud
cover after late morning so sunshine may work to balance out the
cold air advection. Still leaning toward the European model (ecmwf) MOS with lower to middle 60s
mountains to lower to middle 70s east. Downslope may enhance the
heating as well...and could be several degrees warmer but breezy
conditions at times hinders warm ups.
Not of the question to see some small hail producing showers across
the Alleghany Highlands Friday as the upper trough axis moves
across...but again appears GFS/European model (ecmwf) dry it out too much.
Friday night stays breezy as temperatures drop into the 30s/40s. Not seeing
frost/freeze issues at this point given winds but a few higher
elevations like Hot Springs could slip toward 32f Sat morning.
Saturday will be fall like with mostly sunny skies and northwest breeze.
Highs will range from the middle 60s mountains to lower 70s east.
&&
Long term /Saturday night through Wednesday/...
as of 1245 PM EDT Wednesday
Expect cool trough to linger into Sunday before lifting east.
Meanwhile a strong trough digs into the Pacific northwest by Monday
with increasing heights arriving over our area next week. The
weather pattern will be mainly dry Sat night-Monday...but as we can
see with a westerly flow aloft the chance that convection that fires
along a warm front over the Ohio/middle Mississippi Valley could shift
east and affect our mountains.
Will lean toward an European model (ecmwf)/wpc blend solution. This will keep the
chance probability of precipitation in the area by Monday afternoon through Tuesday. The
warm front lifts north toward the Great Lakes by midweek with
heights continuing to build. At the surface...high pressure will be
situated across the middle Atlantic coast then shift off the coast
midweek. Dewpoints will be increasing again by next week with temperatures
warming back to normal or just above.
&&
Aviation /23z Wednesday through Monday/...
as of 605 PM EDT Wednesday...
Two bands of convection ongoing at this time with outflow driven stronger
storms nearing klyh/kdan and the next weaker axis of mostly rain showers
along the western slopes. In between mostly VFR with a few lighter
rain showers remaining in the rain cooled air along/west of the Blue
Ridge. Expect will see a period of rain showers/isolated thunderstorms and rain affect the
eastern sites with brief MVFR in heavy rain during the next hour
or two. Thinking that rain showers will weaken more over the west given
lack of residual instability so including more thunderstorms in the vicinity/vcsh across
kblf/klwb through midnight. Once rain showers coverage starts to
wane...will see quite a bit of fog and stratus fill in bringing
more widespread MVFR/IFR overnight with still a few rain showers likely
lingering in spots.
Lots of uncertainty late tonight and into the day on Thursday with
models bringing a decent swath of showers/thunder into the west
after daybreak and slide this area east by midday. This right
ahead of the actual surface front and since supported by several
models will include more MVFR in rain showers from west to east during
Thursday. Degree of deeper convection remains iffy pending amount
of afternoon heating before another piece of upper level energy
starts to arrive across the far west late in the day. This may
bring another band of rain showers/thunderstorms and rain to the western sites. MVFR looks
to linger across the southeast wva sites into Thursday evening given
increasing upslope flow...with improving flying conditions elsewhere
overnight.
Strong high pressure will bring much drier air by Friday with VFR
likely to prevail through the weekend into early next week.
&&
Rnk watches/warnings/advisories...
Virginia...none.
NC...none.
WV...none.
&&
$$
Synopsis...jh/kk
near term...kk
short term...wp
long term...wp
aviation...jh/kk/rab
