Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
727 am EDT Sat Mar 28 2015
high pressure over the Great Lakes today will move southeast and
will centered over the middle Atlantic region Sunday. A cold front over
the central United States on Sunday will move east and cross through
the region on Monday.
Near term /through tonight/...
as of 410 am EDT Saturday...
Area radars were detecting two areas of light precipitation this
morning. One mainly east of Lynchburg and Danville and the second in
the western upslope areas...spilling into the foothills of Virginia
and North Carolina.
Water vapor satellite loop showed a short wave crossing into eastern
Virginia. The feature was within the high amplitude long wave upper
trough and both will move east of the forecast area this morning.
Short range models have precipitation ending in the eastern County
Warning Area by 14z/10am. The passage of the short wave had enhanced
upslope winds in the west. 850 mb winds will peak around 30 to 45
this morning...then gradually diminish this afternoon. Even through
the lift is adequate...the moisture will diminish by noon...ending
the snow showers and flurries in the west.
After sunset...expect any remaining cloud cover to dissipate.
Surface high pressure will be centered over the forecast area by
morning. Winds will decouple overnight and with surface dewpoints in
the teens and single digits...the dry air mass will result in large
spread between maximum temperatures today and lows tonight.
Record lows are possible Sunday morning in
Lynchburg...Blacksburg...Danville ... and Bluefield.
Short term /Sunday through Tuesday night/...
as of 415 am EDT Saturday...
Will start Sunday morning off with high pressure overhead...
resulting in a chilly beginning to the day. The high will shift
southeast...allowing southerly windflow to take over by early
afternoon ahead of another approaching cold front. Despite abundant
sunshine through much of the day...upper level troughing along the
Atlantic coast will limit heating...with afternoon high temperatures
ranging from the upper 40s west to the low 50s east.
Cloud cover will increase Sunday evening...with rain showers...and
possibly snow showers across the higher ridges...entering southeast
West Virginia after sunset. Shower activity will then pass from the
mountains east across the Piedmont...most likely in a broken line of
brief shower activity. Behind this line...winds will shift westerly
and downslope...causing rainfall to diminish east of the Continental
Divide...leaving only residual upslope showers along the western
ridges. With very little time for moisture to build ahead of the
approaching cold front...believe we will see mainly less than a
tenth of an inch of rainfall...with locally higher amounts. No snow
accumulation is likely where snow does occur.
High pressure building behind the cold front is Pacific in
origin...meaning not as chilly as the Canadian airmasses that have
brought significantly below normal temperatures. As such...the
warming affect of downslope wind flow combined with abundant
sunshine as clouds clear by afternoon will cause Monday afternoon
temperatures to range from the low 50s west to the middle 60s east. A
tight pressure gradient as high pressure builds in will ensure gusty
conditions...and would not be surprised to see 40 miles per hour gusts across
the higher ridges during the afternoon.
High pressure will be in control Monday night...with temperatures
falling generally into the middle to upper 30s. The high will slide to
our south on Tuesday...allowing winds to shift more southwesterly
ahead of another clipper system moving across the lower Great Lakes.
This will cause afternoon temperatures to warm into the low 60s
west/upper 60s east. The clipper cold front will begin to push
across our area Tuesday night.
Long term /Wednesday through Friday/...
as of 1215 PM EDT Friday...
Models continue to focus on both lead southern stream energy heading
east across the middle Mississippi Valley later in the week in advance of
more pronounced digging northern stream 500 mb troffiness by Thursday.
Although phasing looks rather unlikely...appears deepening moisture
transport from the Gulf will be in place allowing an initial shot of
showers to get lifted north out of the dampening southern wave. This
along a surface warm front ahead of the northern trough/cold front that
should enhance lift espcly western half later Wednesday night into
Thursday evening. Thus running with mainly low probability of precipitation mountains Wednesday night
and high chance to likelys Thursday given the overrunning nature to the
warm advection precipitation. Weak cold front arrives by Friday but
uncertainty in how far through the region the boundary makes it if at
all given differing guidance solutions of more energy spilling into the
upper trough to the west. For now will run with chance probability of precipitation on Friday
which supports the previous slower ec solution.
Temperatures to rebound to above normal levels by middle or late week given
flatter flow aloft and low level warm advection by Wednesday into
Friday when should see widespread 60s/70s for highs.
Aviation /12z Saturday through Wednesday/...
as of 725 PM EDT Saturday...
Deep upper trough will sweep eastward through the area this
morning and a short wave within the trough will move off the
Virginia coast. Winds will gust from the northwest up to 30
knots...especially at higher elevations this morning behind this
short wave. High confidence of occasional MVFR ceilings and
visibilities with heavier snow showers on the western slopes of
the Appalachians...including at kblf through 15z/11am.
Moisture erodes by this afternoon so region will be VFR late
today and through tonight. Winds will diminish this afternoon and
will become light and variable at area taf sites overnight.
Extended aviation forecast...
VFR conditions are expected through Sunday under high pressure.
There is a potential for strong gusty winds behind a cold front
Monday and Tuesday. Some MVFR ceilings will be possible across the
mountains with an Alberta clipper Monday night and Tuesday.
as of 455 am EDT Friday...
Record lows for March 29:
Roanoke......19 in 1982
Blacksburg...17 in 2001
Lynchburg....23 in 1923 and 1982
Danville.....23 in 1966
Bluefield....19 in 1966 and 1982
Lewisburg....18 in 1983
near term...air mass