1029 AM EST Sat Feb 25 2017
A much cooler airmass will continue to settle into the region
today as a weak upper level disturbance brings a few rain and
snow showers. High pressure will build into the Ohio Valley
tonight into Sunday, leading to mainly clear skies. Seasonable
temperatures will remain in place across the area for Sunday.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Cold air will continue to rush into the region today. Decent PV
anomaly moving across the area for the first part of the day and
with current returns on radar increased precipitation chances. Winds
will be gusty with wind gusts up around 35 mph at times. Snow
squall parameter is highlighting the area especially across
northern portions of the forecast area today. Expect scattered
snow showers and with the gusty winds, visibilities will be
reduced at times. Snow shower activity will decrease later today
and taper off this evening.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
The trough axis will push off to the east tonight with surface
high pressure building into the region later tonight. This will
lead to decreasing clouds southwest to northeast and overnight
lows in the low to mid 20s. Mostly sunny skies are expected on
Sunday with highs in the low to mid 40s.
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Sunday night surface high pressure will be centered near the
coast of NC with southwest flow across the region. At the same
time an upper level disturbance over AZ will eject east and push
towards the forecast area. Both the GFS and ECMWF have come
into fairly good agreement here with this system ejecting east
and spilling vorticity across the area Monday morning. As this
happens high cloud bases will thicken and slowly lower with
precipitation moving in from the west. Initially Monday morning
a rain/snow mix will be supported with the entire sounding below
freezing except right at the surface. Behind the remnant
shortwave Monday afternoon dry mid and upper level air will work
into the area helping to cut off the precip a bit.
Monday night into Tuesday morning there will be a brief break as the
next upper level disturbance over the Mountain West gets its act
together. Later Tuesday morning into afternoon the upper level
disturbance will push northeast into Minnesota pulling a warm front
north across the area. Widespread overrunning will commence with
PWATs approaching 0.85". Widespread weak lift will also accompany
the WAA which is supported by GFS omega fields. Tuesday afternoon a
surface low will track northeast towards WI allowing temperatures to
rise into the 60s. Shear values Tuesday afternoon will also become
impressive as ILN gets warm sectored with SFC- 3 KM shear 40 + kts
at times. GFS soundings currently show a CAP across the area though
which would limit convection across the region.
Tuesday night into Wednesday morning another upper level disturbance
will swing around the base of the upper level trough axis centered
over the Western United States and push towards the forecast area.
As this happens another surface low will form in the plains and push
northeast along a baroclinic zone. At the same the upper level jet
will begin to strengthen and briefly place ILN in a RRQ. Also a weak
split will occur in the jet. The GFS/ ECMWF/ and CMC all show this
happening. The difference between the three is placement of the
baroclinic zone (e.g., front), and track of eventual surface low as
it heads northeast. The NAEFS shows PWAT anomalies of 2 SD. The GFS
also has a PWAT of 1.35" just south of the region. As mentioned
above though these small differences in track between models has a
big difference on rainfall distribution. The ECMWF is furthest north
with the second surface low and has heavier rainfall totals across
our northwestern zones while the GFS is furthest south with the
track and has the heaviest totals across central KY. The CMC is a
compromise between the two and have trended the forecast this
direction. Given the RRQ, splitting upper level jet, abundant
moisture and lift have raised PoPs for Wednesday.
Wednesday evening into Thursday morning a stronger upper level
disturbance will push east over the area finally pushing the surface
cold front through the area. Thursday afternoon into Friday another
upper level disturbance will head southeast out of southwestern
Canada and bring a chance of snow and rain to the area Friday
morning. GFS soundings completely saturate Friday morning with almost
the entire forecast sounding below freezing. As of now mostly snow
Friday morning would be expected given the thermal profile of the
GFS. Eventual track and strength of this disturbance remains in
question though as the ECMWF is weaker with the disturbance so have
kept PoPs at chance for now. Friday night into Saturday surface high
pressure will dip south into the area from Canada and bring below
normal temperatures to the area. Saturday afternoon the surface high
pressure will already be east of the forecast area as the upper
level trough axis heads east.
.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
A narrow dry slot is working east across the area early this
morning but it will be short lived as the leading edge of the
lower startocu is progressing into western Ohio attm. This is
associated with a mid and upper level trough axis that will
swing east across the area through this afternoon. This will
help the stratocu field pivot eastward across the TAF sites
through the rest of the morning. These clouds will likely start
off as a lower VFR deck and then transition into a period of
MVFR cigs from late morning into the early afternoon hours.
Forecast soundings are showing a little bit of low level
instability today and this may be enough to produce scattered
shower activity later this morning and into the afternoon. The
best chance for this appears to be at the northern TAF sites so
will carry a VCSH to account for this. Any precipitation may
start out as rain but should transition to snow for at least
the western TAF sites as colder air filters into the region.
High pressure will begin to build in from the southwest
tonight. This will lead to decreasing clouds through the
remainder of the TAF period.
OUTLOOK...MVFR ceilings and visibilities possible Monday,
Tuesday night, and Wednesday.