Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
730 am EDT Thursday Oct 23 2014
Synopsis...a strong upper level low over the middle Atlantic coast
slowly track northeast and offshore today. High pressure will build
into the region from the west through Saturday.
Near term /through tonight/...
as of 300 am Thursday...
The upper low spinning off the middle-Atlantic coast will lift
northeastward and away from the region today. Northwest flow will
continue over NC...though weakening as the pressure gradient
relaxes...with very dry air east of the mountains. A few wind gusts
are still possible...especially this morning and across the coastal
plain. The 850mb thermal trough will shift east of the area and
thicknesses will start about 5m higher than yesterday...supporting
highs a degree or two warmer in the 66-70 range.
Tonight...a deamplifying shortwave crossing the middle-Mississippi
River valley will likely spread some cirrus across the area after
midnight. Currently...it doesnt appear the cirrus will be very
thick...but if it is then forecast lows of 40-43 may be too cold.
Short term /Friday and Friday night/...
as of 300 am Thursday..
High pressure will extend into the area form the deep south Friday
..with a disturbance poised to dive from the upper Midwest across
the Carolinas Friday night. With very little deep moisture to
interact with...the shortwave will cross the area relatively
unnoticed. Thicknesses rise another 10m by Friday
morning...yielding highs in the lower 70s. Lows Saturday night in
the middle 40s.
Long term /Saturday through Tuesday/...
as of 235 am Thursday...
For Sat-sun night: as the middle level shortwave trough axis moves east
of the forecast area early Sat morning... a benign west-to-east-
moving warm front will shift through the area Sat with light surface
flow backing from northwest to west-southwest. Given the dry and stable air on
forecast soundings and surface high pressure ridge nosing
northeastward into NC... expect little more than scattered flat cumulus
Sat. A fast-moving and weak cold front is then expected to drop into
NC from the northwest late Sat night... a result of strong vorticity
sweeping across the northern Great Lakes on the south side of a middle level
low that will move from southern Ontario across southeast Quebec through Sun
morning. We may see a period of broken clouds with the cold front
passage... but it will remain dry as the effects of the cold front
will be muted by the lack of moisture as well as the suppression of
the (elevated) lift to our north. And the latest GFS/European model (ecmwf) show
little to no drop in thicknesses... with the front just brushing
across northern NC. The GFS in particular holds all cooler air north of
the border and keeps central NC thicknesses 20-30 M above normal.
Even the more subdued European model (ecmwf) has trended milder. So... expect
saturday's slightly above normal highs in the low-middle 70s to hold
firm for Sunday as well... and could even be a couple degrees warmer
across southern NC. Lows in the upper 40s to near 50 Sat night. Expect
temperatures to be a tad cooler Sun night... low-middle 40s... as high
pressure builds into and over NC from the northwest... allowing for good
radiational cooling with a lack of clouds and a dropoff of winds
For Monday-Wed: dry and warming. The middle level low over the St Lawrence
Valley and northeast states will move over and off the Canadian
Maritimes... as middle level ridging builds from the Southern Plains
eastward to over and just off the southeast coast through Wednesday. As
the surface... the high overhead Sun night will ease slowly off the
coast with increasing thicknesses through middle week. The GFS/European model (ecmwf)
take a longwave trough through the plains and into the Great Lakes
Tuesday/Wednesday with a corresponding surface cold front... however there is
much uncertainty regarding the speed of approach of this trough and
front toward NC. Will maintain temperatures a bit above-normal and a trend
toward increasing clouds as low level flow introduces gradually
improving moisture... but with no appreciable rain in sight. -Gih
Aviation /12z Thursday through Monday/...
as of 730 am Thursday...
Northwesterly flow on the southern fringe of an upper low off the
middle-Atlantic coast will maintain VFR conditions through the taf
period. Will likely see some wind gusts into the 15-20kt
range...especially through midday and at points east of
krdu/krwi/kfay...with a gradual weakening of winds through the late
afternoon and evening hours as the pressure gradient weakens. Light
northwesterly winds are expected tonight.
Outlook...a prolonged period of VFR conditions will persist into the
weekend/early next week as the weather remains dominated by dry
northwesterly flow aloft and surface high pressure.