Area forecast discussion
National Weather Service Blacksburg Virginia
209 am EDT Thursday may 23 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 this morning/...
as of 925 PM EDT Wednesday...
Convergence zone associated with the band of earlier convection
over the mountains remains stuck along the foothills this evening
under broad SW flow aloft per evening soundings. However expecting
a gradual propagation of rain showers/thunderstorms and rain to the east via outflow
although an axis of heavier rain showers may continue to remain locked in
across the south for a while longer. Latest guidance also tending
to keep probability of precipitation going across the central/east before another band
arrives from the west ahead of the front late. Thus have upped
probability of precipitation to likelys for a few more hours in all except the far north
and east with a continued heavy rain threat per moist precipitable waters and
some training of cells. Severe threat looks quite isolated at best
given more shallow nature to storms as instability continues to
wane so will adjust the severe weather potential statement to highlight more of a heavy rain
threat. Otherwise appears that persistent cloudiness combo with lingering
rain showers will limit fog coverage with patchy coverage espcly west
late. Adjusted low temperatures down given cooling from rainfall/outflow
but still muggy with lows mainly upper 50s to lower 60s.
&&
Short term /6 am this 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 /06z Thursday through Monday/...
as of 200 am EDT Thursday...
Frontal system responsible for convection last two days will
finally move through the forecast area late in the taf valid
period...generally from 20z west to 04z east. Pre-frontal
convection this morning should limit convective with actual
frontal passage. Main concern in the short term is residual
rain showers/isolated thunderstorms and rain traversing the region from SW-NE...mainly across
the Piedmont. See no reason for this activity to not continue
through the night. New and stronger convection...developing now in
western WV...west of crw...should reach lwb-blf late
tonight/early Thursday morning...reaching roa/bcb around
daybreak...then lyh/Dan during the middle to late morning into the
early afternoon. Expect mostly MVFR ceilings overnight...although VFR
at times with just middle-high clouds until stronger activity arrives
around daybreak. Scattered -shra should persist behind the stronger
convection until the front actually arrives during the afternoon.
At this point...pattern shifts to more of a winter pattern with
typical upslope clouds/-shra lwb-blf with MVFR ceilings. East...toward
roa/lyh/Dan...ceilings should improve to VFR with precipitation ending by late
afternoon/evening. Visibilities mostly VFR...except MVFR in areas of
br/-shra and/or thunderstorms and rain. Winds south-southwest-SW 5-8kts until frontal
passage this afternoon...then west-southwest-west 7-10kts...with low end gusts
blf and roa especially.
Medium confidence in ceilings and visibilities through taf valid period.
Medium confidence in thunderstorms and rain timing and coverage.
High confidence in wind speed/direction through taf valid period.
Extended aviation conditions...strong high pressure will bring
much drier air by Friday with VFR likely to prevail through the
weekend into early next week. Some upslope clouds linger into Friday
across southeast WV. Increasing potential for northwest flow driven thunderstorm
activity early next week...most conditions overall VFR for the
most part.
&&
Equipment...
the National oceanic and atmospheric administration weather radio at Roanoke Virginia is off the air this
evening due to a problem at the transmitter site. Restoration time
is unknown at this point.
&&
Rnk watches/warnings/advisories...
Virginia...none.
NC...none.
WV...none.
&&
$$
Synopsis...jh/kk
near term...jh/kk
short term...wp
long term...wp
aviation...rab
equipment...jh
