Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Columbia SC
325 am EDT sun may 28 2017
ridging over the region will weaken on Sunday as a frontal
boundary slowly slides into the area. The front will stall over
the area early this week providing chances of showers and
thunderstorms each day through Saturday.
Near term /through tonight/...
upper ridge to our south, with upper trough over the central
Continental U.S.. a series of upper impulses will move east, tracking mainly
just to our north. Surface wave over NC with surface
front/trough stretching back to the west, appears will generally
remain in place due to nearly parallel flow aloft. Combination
of better moisture, upper energy and surface boundary providing
focus for clusters of thunderstorms along this area. Activity
is dissipating as it approaches our forecast area due to a drier and more
capped atmosphere. In the near term, most high resolution model
output generally suggests that cluster of thunderstorms to our
west-northwest will gradually weaken as the activity shifts to the ESE,
remaining outside our forecast area. Some varying solutions in latest high
resolution models regarding convection later today. Old outflow
boundaries from previous convection could prove important today
as far as a focusing mechanism for convection, with some
uncertainty on placement and timing. Cloud cover from previous
convection could also affect convective potential. Atmospheric
moisture is expected to increase some over our forecast area with some
weakening of the mid level cap expected. Strong instability and
considerable deep layer shear forecast today. Mid level cap
still evident in soundings but not as strong as yesterday.
Temperatures expected in the lower 90s to support isolated to
scattered convection with a severe threat. Damaging winds appear
to be the primary threat given freezing level around 15kft and
fairly unidirectional hodographs. Storm Prediction Center has forecast area in a marginal risk for
severe. Used a model blend on pops, which provides generally
slight chance south to chance central and north forecast area.
Short term /Monday through Monday night/...
upper level ridge will remain to our south, with upper trough to
our north. Westerly flow aloft with embedded impulses. Surface
low pressure well to our north/NE will shift farther NE and bring
down a weak surface boundary slightly farther south into the
northern/central fa, along with some continued increase in
moisture. Model blend yields chance pops. Strong instabilities
Monday will provide a severe threat. Storm Prediction Center has region in slight risk
for severe Monday.
Long term /Tuesday through Saturday/...
no changes made to the ongoing forecast for this time period.
Previous discussion follows: models are in good agreement
through the long term with some differences in location on
Friday and Saturday. Frontal boundary will remain stalled over
the region through the period with potential for convection each
day. Tuesday currently presents some concern as instability
will be moderate...pwat values around 1.6 inches and Storm Prediction Center slight
risk for the area. Chances of convection will continue Wednesday
through Saturday...however with the front becoming more diffuse
across the region potential for severe convection is currently
lower. Temperatures will be near to slight above normal with
afternoon highs in the mid 80s to low 90s and overnight lows in
the mid 60s to around 70.
Aviation /07z Sunday through Thursday/...
VFR conditions generally expected through the 24 hr forecast
Another 25 knot low level jet is forecast which along with
convective debris clouds should limit fog development. A light
southwest wind should prevail through the predawn hours and then
pick up to around 10 to 12 knots with gusts to 20 knots
possible after 16z.
A frontal boundary will approach the forecast area on Sunday
bringing a chance of showers and thunderstorms, although the
best chance will be north of the taf sites, so have not included
mention for now.
Extended aviation outlook...a cold front will stall in the
region through early next week. The front will help support
scattered thunderstorms and associated restrictions.