NWS Wilmington, OH wrote its last area forecast discussion before the first event at Jan 31, 10:13 PM EST, 1 hour 47 minutes earlier.
Area forecast discussion, Jan 31, 10:13 PM EST, 1 hour 47 minutes before
AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
1013 PM EST Thu Jan 31 2019
.SYNOPSIS...
A potent disturbance will bring accumulating snow and ice
tonight through Friday morning. Mainly dry weather and warmer
temperatures are expected for Saturday and Sunday in the
circulation around high pressure centered to the southeast. Rain
showers will be likely on Monday along a weak cold front.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
The smattering of IFR-type visibilities (2SM and below)
spreading into the ILN forecast area is an indication that
accumulating snow has started. With surface high pressure moving
eastward into Pennsylvania, an elevated warm front is now moving
into the area from the south, with 925mb/850mb temperatures
forecast to warm significantly through the overnight hours --
creating a deep isothermal layer. This warm advection will also
result in some forcing, currently manifested in the light echoes
being observed over southern Illinois. Meanwhile, the majority
of the snow currently being observed is a result of a mid-level
and upper-level forcing, with a 100-120 knot 300mb jet streak
rounding into the area at the base of the large-scale eastern
CONUS troughing.
Precipitation amounts are likely to be heaviest where these two
sources of forcing end up combining to some extent, and the 00Z
NAM and recent HRRR/RAP runs have suggested this may occur just
slightly further south from the previous forecast. As mentioned
earlier, there will be a deep isothermal layer in place, though
the degree to which this layer will be fully saturated is still
one big source of uncertainty in this forecast. It is
interesting to note that this isothermal layer is expected, for
most of the ILN forecast area, to be just barely too warm to
fully tap into the dendritic growth zone (DGZ). Further north,
the isothermal layer may align with the DGZ quite well, but
with much lower confidence in saturation. Because the thermal
profile, saturation, and forcing are not quite in perfect
alignment, that may keep this from being a higher end (warning
criteria) event. Nonetheless, there is enough forcing for
several inches of snow, especially with decent snow ratios
expected -- even if not quite in the heart of the DGZ. This
forecast update has slightly increased the numbers, with a
southward shift of about half a row of counties, putting the
maxima in the west-central portion of the forecast area (a
solid 4" expected for Preble County, for example). If anywhere
may be close to warning criteria, it could be Franklin IN /
Butler OH / Warren OH, where the 4" criteria may be close.
Outside of the snowfall numbers, no changes were made to the
headlines or other elements of the forecast. The point to
emphasize here is that the cold ground conditions are going to
make this snow stick very quickly, and perhaps limit the
effectiveness of treatment. Thus, the advisory through the
Friday morning commute appears very well warranted.
Previous discussion >
A rather potent mid level disturbance traveling from the
northwest will impact the ILN area with wintry precipitation
beginning in western counties this evening. Snow already
evident over Illinois will move across Indiana to our area, with
snow probably starting in the far west shortly after 7 pm.
Effects will vary from north to south. Northern locations under
an area of about 0.25 inch water equivalent with SLRs greater
than 10 to 1 will receive the most snow, with 2 to 4 inches
expected roughly along I-70 from Dayton to Columbus. Models are
less generous with snow accumulations farther south, with around
2.5 inches likely at Wilmington, down to around an inch or less
along and south of the Ohio River including Cincinnati and
Portsmouth.
This scenario will lead to hazardous travel, requiring a winter
weather advisory for the entire area, starting at 7 pm north,
midnight at Wilmington, and 4 am south.
Temperatures are forecast to exhibit a gradual non-diurnal
warming trend overnight, with single digit to teen readings this
evening rising the low teens to low 20s by 6 am.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Snow will be ending Friday morning as the disturbance tracks
quickly east. Freezing drizzle is forecast to occur near the
end of the event when ice nucleation should cease as mid level
moisture decreases, adding a few hundredths of glaze.
Once precip ends Friday afternoon, the Arctic airmass will be
kicked northeast by a southerly low level flow containing warmer
temperatures. Though wintry accumulations will keep readings
from rising too fast, we should still see highs from the upper
20s north to the mid and upper 30s south, followed by a modest
drop Friday night.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Early on Saturday, temperatures will be in transition back
above freezing across the CWA as the edge of a warm front lifts
north. Weak winds will veer toward the southwest to continue the
next surge of enhanced WAA that will bring high temps near or
above 40 degrees. The NAM and GFS are more bullish on producing
weak and widely scattered showers to the west, but decided to
keep dry pops through Saturday. Model soundings currently show
evidence of a saturated BL with a shallow layer of mid level
saturation, but without much forcing and a narrow dry air
intrusion, not expecting measurable precip a this time. However,
far northern areas could see a sprinkle or two overnight.
Conditions will be warm on Sunday as temps rise into the low to
mid 50s paired with mainly dry conditions from weak high
pressure over the Carolinas. Models are in poor agreement with
whether or not there will be a mechanism to squeeze out a bit of
low level moisture during the late evening timeframe as a weak
shortwave generates some marginal mid level energy. Expect that
the NAM is just too moist at this time.
The next system will work in on Monday as low pressure tracks
toward the northern Great Lakes. Showers will develop along and
ahead of a cold front during the day and into the evening hours.
The first wave of showers looks to be tied to a potential pre-
frontal surface trough. The synoptic upper level trough
structure seems to vary with depth and tilt. Current progs show
the GFS digging deeper and becoming more negatively tilted than
the ECMWF with deep layer saturation. Depending on which
scenario plays out, could see an increase in anticipated
precipitation efficiency. Will be keeping an eye on instability
over the next few days, but being this far out warranted
excluding any mention of thunder. Expect temperatures to shift
sharply back down toward climatological norms once the front
exits overnight on Monday.
We may see a lull in pcpn coverage on Tuesday as the cold front
continues to lay out across the region. It will be a little
cooler but still are expecting above normal temperatures with
highs ranging from the mid 40s northwest to the upper 50s
southeast.
Models are then in fairly decent agreement in bringing a large
scale mid level trough into the northern and central Plains
Wednesday into Thursday. As this occurs, a wave of low pressure
will move northeast through the Ohio Valley and Great Lakes,
followed by a cold front. Showers will be likely on Wednesday
with mild temperatures in the 50s to the lower 60s. Much colder
air will filter into the region Wednesday night into Thursday,
which may bring a threat of some wintry pcpn in the wake of a
cold front by Thursday. Highs on Thursday will range from the
upper 20s west to the lower 40s east.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected to start the TAF period, but snow
will move into the area over the next few hours, leading to
diminished conditions. The snow should be light at first,
leading to MVFR visibilities, but a period of IFR/LIFR
visibilities and MVFR ceilings will be likely with the heaviest
snow -- particularly for the KDAY/KCMH/KLCK/KILN airports where
several inches of accumulation are possible. After the snow
comes to an end, there is also a chance for some freezing
drizzle, particularly at KILN/KCVG/KLUK. However, visibilities
should be improving by afternoon, though ceilings may remain
MVFR/IFR until near the end of the TAF period. Winds should
remain at or below 10 knots through the forecast period.
OUTLOOK...MVFR ceilings may continue into Saturday. MVFR
conditions are expected again at times from Sunday night
through Tuesday morning.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...Winter Weather Advisory until 10 AM EST Friday for OHZ026-034-
035-042>046-051>056-060>062-064-065.
Winter Weather Advisory from 4 AM to 10 AM EST Friday for
OHZ077>082-088.
Winter Weather Advisory until 10 AM EST Friday for OHZ063-
070>074.
KY...Winter Weather Advisory from 4 AM to 10 AM EST Friday for
KYZ089>100.
IN...Winter Weather Advisory until 10 AM EST Friday for INZ050-058-
059.
Winter Weather Advisory from 4 AM to 10 AM EST Friday for
INZ073>075-080.
Winter Weather Advisory until 10 AM EST Friday for INZ066.
&&
SYNOPSIS...Coniglio
NEAR TERM...Coniglio/Hatzos
SHORT TERM...Coniglio
LONG TERM...Hickman/KK
AVIATION...Hatzos