Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
637 PM EST Wednesday Nov 25 2015
high pressure extending from the Atlantic Ocean to the eastern
United States will keep dry weather and above normal temperatures
over the Ohio Valley through Thursday. A slow moving cold front
will bring the threat for rain Friday through Sunday. Temperatures
will stay above normal on Friday before cooler air filters in for
Saturday and Sunday.
Near term /until 6 am Thursday morning/...
low to middle level flow will remain south to southwest overnight as
high pressure slowly pushes off the New England coast. Some warm air advection in
the form of clouds will increase over the area. With clouds and
the wind staying up over the northwest...lows will drop into the
middle 40s. Lesser clouds and lighter winds will allow lows to drop
into the middle 30s far east/southeast.
Short term /6 am Thursday morning through Friday night/...
models have trended a bit slower with a cold front that is
forecast to drop through our region late Friday into Friday night.
Have used a blend of the NAM/GFS/ECMWF through Thursday
night...then the GFS/European model (ecmwf) Friday into Friday night. The main
affect obviously will be to slow down the onset of rain associated
with the frontal system.
With skies ranging from partly to mostly cloudy...and a warm
southerly flow...Thanksgiving is expected to be dry. Highs will
range from the upper 50s to the lower 60s...or about 10-15 degrees
above normal for late November.
For Thursday night into Friday...clouds will continue to thicken
from the northwest as aforementioned cold front slowly sags
southeast into the Great Lakes. Low level jet/convergence and
upper support will gradually push rain slowly east/southeast into
Friday. It now looks like the far southeast may be able to squeeze
out another dry day. It will remain warm Thursday night into
Friday with temperatures above normal.
For Friday night...models begin to slowly show some differences on
how fast the front will sag south...and how far south it will get
before it either stalls or becomes quasi-stationary. In either
case...rain will move southward affecting the entire region
overnight with probability of precipitation decreasing across our northwest late.
Long term /Saturday through Wednesday/...
on Saturday morning...a plume of moisture with a long Diagonal
trajectory will extend from the Pacific Ocean near Mexico to the
Canadian maritime provinces...and beyond. A deep and slow-moving
area of upper low pressure will persist over the western
states..with a Flat Ridge in the southeast that will only flatten
further over the weekend and into early next week.
At the surface...a cold front will be moving south through the
forecast area on Saturday morning. However...this will not spell an
end to the precipitation. A strong inversion will remain in place
across the region...with plenty of moisture and middle/upper level
forcing keeping rain likely through the weekend...especially in the
southern half of the forecast area. Probability of precipitation have been adjusted upward
given the increased confidence on Saturday and into Sunday...with
some challenges in the pattern evolution becoming more pronounced
going into early in the week.
As the southeastern ridge flattens...the moisture plume will
eventually shift to the south...with some disagreement on how much
of the forecast area ends up dry on Sunday. The 12z European model (ecmwf) kept a
more northerly solution...which seems to be in opposition to its 00z
run and the 12z Gem/GFS forecast scenarios. A consensus supports
some degree of whittling away the probability of precipitation from the northern sections of
the forecast area on Sunday night and into Monday. A slightly slower
solution is also preferred with the eventual progression of the
upper low in the west...though rain chances will again increase by
Monday night into Tuesday as this system moves through the Great
Lakes and Ohio Valley. Based on gfse spreads and the overall suite
of model guidance...confidence in the timing/placement/magnitude of
the weather features beyond the weekend is not particularly high.
Temperatures will drop significantly from Friday to
Saturday...thanks to the cold front moving south through the area.
However...with the warm starting point at the end of this
week...conditions will still end up very close to normal (perhaps
slightly below). A more significant drop in temperatures is likely
near the end of the extended forecast period (middle of next
week)...once the upper low ejects eastward and another cold front
Aviation /00z Thursday through Monday/...
VFR conditions with some cirrus are expected through the period.
Models are continuing to indicate low level moisture streaming in
around 5-6kft tonight which was removed from a broken deck to a few-
scattered during the overnight. South winds will relax and turn east of
south but kday should see a continued 10kt overnight. Winds will
pick up tomorrow during the day and western taf sites should see
some higher gusts to 20-22kt...lessening with the setting sun.
Outlook...MVFR/IFR ceilings and visibilities possible Friday afternoon into