Scientific Forecaster Discussion
fxus61 kpbz 111816
Area forecast discussion
National Weather Service Pittsburgh PA
116 PM EST Mon Nov 11 2019
rain will increase later today, then change to snow this evening
with passage an upper-level trough. Record-breaking low temperatures
may occur tomorrow night.
Near term /through tonight/...
GOES water vapor imagery shows a significant upper-level low digging
across the north-central Continental U.S. This morning. At the surface, a
frontal boundary currently extends from the Pittsburgh area
southwestward through the Ohio Valley towards the Mississippi Valley.
At this time, little in the way of precipitation is currently
situated near or along the front. Cloud cover on the north side has
kept the temperature below 50 degrees as of noon today, but southward
towards the Mason-Dixon, the temperature has already risen to around
60 degrees in a strong warm advection regime.
Mesoanalysis shows that a frontal wave has developed and is
currently positioned in the Ohio Valley, somewhere in the vicinity of
Cincinnati. As the aforementioned upper trough digs into the Great
Lakes, cyclogenesis of this wave is anticipated under the right-
entrance region of the upper jet as it shifts northeastward up the
As this happens, a strengthening temperature gradient and
frontogenetical forcing in conjunction with the upper-level
divergence will promote a growing precipitation field along and on
the west/upstream of the frontal boundary and the developing surface
low. Precipitation should overspread eastern Ohio and far northwest PA by
late afternoon, eventually reaching Pittsburgh in the evening, and
ridges shortly thereafter.
Precipitation type will initially be rain at the onset and first few
hours of precipitation, but will transition to snow as very cold air
filters in behind the departing and strengthening low as it ejects
to the northeast. Forecast soundings suggest that the surface will
see snow when the surface/low-levels can support snow... so expect a
transition when the surface temp gets within a few degrees of the
freezing mark. This will likely be in the late evening for Franklin
southwest towards Zanesville, midnight or early am for the Pittsburgh
Metro, and by 3am or so for everywhere else.
Snowfall will come from two mechanisms. The first of which is the
aforementioned frontal-precip. The second is that of lake-effect snow
through the day Tuesday. Snowfall accumulation associated with the
frontal-precip will likely end dawn Tuesday as the system departs.
Accumulations of somewhere between 0.5 and 1 inch is expected for
lower elevations and south of I-80, while areas north of I-80 and the
ridges may see upwards of 2 inches by this point. Snowfall
accumulation at onset may be delayed by warm ground temperature, but
should quickly begin to accumulate as the very cold, Arctic air
filters in. The lake-enhanced snowfall will be talked about in the
undermentioned short-term section of this afd.
Short term /Tuesday through Wednesday/...
while the bulk of frontal precipitation will exit shortly after the
thermal profile becomes cold enough for snow, strong northerlies in
conjunction with an upper trough axis moving over the warm Great
Lakes will promote fairly widespread coverage of snow streamers
across the County Warning Area from Tuesday and into Tuesday night.
Between the frontal/synoptic-scale precipitation and subsequent
lake-enhanced snowfall, accumulations of around an inch are to be
expected area-wide. The outer snowbelt counties near/north of
Interstate-80 may receive between 2 and 6 inches, while the higher
elevations from The Laurels south through West Virginia may receive
upwards of 3 inches. Therefore, a Winter Weather Advisory has been
issued for these counties tonight into tomorrow.
Shower coverage will decrease Tuesday night as the upper trough axis
passes and high pressure builds into the lower levels. The resultant
backing of wind from northwest to west will quickly end snow shower coverage
for the County Warning Area.
Highs on Tuesday will struggle to reach 30 before dropping into the
teens by Wednesday morning. A few cities may break or tie their
record daily low temperature.
Cold weather will continue on Wednesday as the low-level ridging
becomes centered across the County Warning Area. Expect another day where the
temperature remains below the freezing mark W/ increasing upper
clouds moving in from the west.
Long term /Wednesday night through Sunday/...
another quick-moving shortwave will move north of the region
Thursday. With the path of the wave and a dry atmosphere in place,
appears any light snow showers will remain north of the region.
Looking ahead, temperatures will gradually moderate as the synoptic-
scale wave pattern becomes less amplified. The next chance of
widespread precip will likely be at the end of the weekend or early
Aviation /18z Monday through Saturday/...
VFR conditions is expected to prevail into the early evening hours,
with the exception of fkl, as a low pressure system pivots across the
Ohio River valley and pushes in drier air from the south.
With the help of a digging upper-level trough in the mid-west, the
frontal boundary will finally pass through our entire region late
this evening. Expect rain showers and widespread IFR conditions just
before midnight. Rain should transition to snow by late eve/overnight
in cold advection after frontal passage. Gusty northwest wind is expected this
eve/overnight with a tightening pressure gradient and mixing behind
Lake-enhanced snow showers tomorrow may bring periods of reduced
visibility; however, confidence is too low at the moment to pinpoint
which sites and time-frame specifically.
with building high pressure Tuesday night into Wednesday, VFR
conditions shall return. Fkl may experience restriction until
Wednesday night if lake-enhanced snow showers prevail.
Maryland...Winter Weather Advisory from 1 am to 7 PM EST Tuesday for mdz001.
PA...Winter Weather Advisory from 7 PM this evening to 7 PM EST Tuesday
Winter Weather Advisory from 1 am to 7 PM EST Tuesday for paz074-
WV...Winter Weather Advisory from 1 am to 7 PM EST Tuesday for