Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
607 am EST Friday Jan 30 2015
high pressure will build over the Ohio Valley tonight in the wake
of a departing cold front. This high will weaken on Saturday and a
warm front will develop along or just north of the I-70 corridor
on Sunday. Low pressure will cross east through the southern Ohio
Valley Sunday night...with a shot of Arctic air blasting the
region on Monday and Monday night.
Near term /until 6 PM this evening/...
a brief line of snow showers will cross southeast through the County Warning Area
this early morning...with scattered generally light snow showers
found behind it through about daybreak. This should result in a
dusting to a quarter inch of snow for much of the region...but
moreso northeast of Cincinnati and south of the I-70 corridor
between Dayton and Columbus. Northwest winds today will keep a
cool airmass over the region with highs ranging from around 20
north of Columbus to around 30 southwest of Cincinnati.
Short term /6 PM this evening through Monday/...
a more interesting and/or problematic forecast is in store for
this period. High pressure will build into the region tonight and
exit on Saturday. Overnight Saturday will see a warm front develop
along the I-70 corridor. Moisture will stream into the region and
precipitate as it gets lifted when it approaches the convergent
boundary of the warm front.
Very little to note at 500 mb but the 800 mb low is prognosticated to track
eastward right along the warm front following the I-70 corridor. The
surface low will remain a good bit further south than
this...likely skirting east through northern Kentucky. The precipitation
along the I-70 corridor will be all snow. South of the Ohio River
rain will prevail through the day Sunday and change to snow Sunday
night as the cold air gets pulled in in the wake of the surface
low. In southern Ohio and far southeast Indiana...placement of the
rain/snow mix remains in high question but there will be a good
bit of both.
Would have issued a watch for a wedge of counties surrounding
Dayton for Sunday and Sunday night. The 24 hour criteria of 8" and
6" for a tier of counties north of Cincinnati appear to be a
realistic estimation of what to expect. Being that far out in time
and with the models still waffling between a warmer northern storm
/NAM/ and a colder yet drier southern low track /Canadian/...the
middle of the Road approach combining the GFS and European appears
to be a reasonable consensus.
Headlines will most likely be issued within the next 24 hours. A
prolonged snowfall event will see accumulations over 6" north of
the Ohio River...topping 9" in spots around metropolitan Dayton. This is
expected to begin a little before midnight for Indiana counties
and spread east...remaining north of the Ohio River through
daybreak Sunday. The southern extent will begin to fill in and
will likely be rain for a good bit during the day for many
Kentucky counties. As the system cools and sweeps through...there
should be enough lingering moisture to eke out a solid 2-4" for
Kentucky counties through daybreak Monday.
At this moment in time...a swath of 8" is expected for much of
the County Warning Area...but will accrue over a 24-30 hour time frame which may
preclude watch and warning headlines. There remains enough
uncertainty in the temperature profile along and just north of the
Ohio River that a snow/rain mix for a longer period would
significantly cut expected snow totals that are around 6". There
is still too much leeway for the surface system to move around to
accurately say that these snow totals are solid numbers but they
should alert the region that adverse weather is expected on
Sunday...especially Sunday night when any rain will definitely
change to snow.
Long term /Monday night through Thursday/...
for Monday into Monday night...Arctic high pressure will traverse
the region. Temperatures will not warm that much from Monday
morning lows...ranging from the lower teens north to near 20
south. Temperatures will drop Monday night as skies become mostly
clear early...followed by some increasing clouds from the west
overnight. Some locations will go below zero with single digits
along and south of the Ohio River. Winds will increase and some
wind chill values will likely drop into the 10 below to 20 below
zero range in the coldest air.
For the remainder of the extended...the GFS and European model (ecmwf) are fairly
similar with synoptic systems except for Tuesday where the GFS
tries to spread isentropically driven precipitation into the region. Have
gone with the dry European model (ecmwf) solution. Another Arctic front is expected
to arrive by middle week. Some warming will occur ahead of the front
with temperatures returning to cold values behind it. There will
be a chance of rain/snow Tuesday night into Wednesday with a
return to dry weather and Arctic high pressure by Thursday.
Aviation /12z Friday through Tuesday/...
a broken band of snow squalls associated with a secondary cold
front is moving south southeastward over the southern portion of
the forecast area and is expected to bring MVFR ceilings and visibilities
with its passage. The squalls should be south of kcvg/kluk by
13z. Behind the front high pressure will build across the area today
and persist through the night. Clouds are expected to
significantly decrease for a few hours this morning in the early
portion of the forecast period. However due to the high
uncertainly on exactly when these breaks will occur have not
detailed this information in the tafs. In these breaks we should see
some sun which will allow for the formation of a MVFR SC deck during
the middle morning. These MVFR ceilings are expected to persist will into
the evening and nighttime hours before they start to dissipate
from southwest to northeast with the clearing line reaching the
kcmh/kluk area around 08 to 09z. After that skies should be
Surface winds will be northwest 10 to 15 knots with gusts to 20
knots into the early afternoon hours. Winds will decrease through
the afternoon and becoming light and variable this evening. By
Saturday morning winds will become south at 3 to 5 knots.
Outlook...significant snow accumulations...IFR ceilings and
visibilities likely Sunday into Sunday night with MVFR conditions
possibly continuing into Monday.