Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Wilmington Ohio
100 am EST Tuesday Mar 3 2015

Synopsis...
moisture being lifted up and over retreating cold air will bring
areas of freezing rain...possibly mixed with sleet...across most
of the area Tuesday morning before changing to rain by Tuesday
afternoon as temperatures warm. Later Tuesday afternoon...moderate
rain will develop and spread across much of the area...but
especially northern Kentucky and southern Ohio where locally heavy
rain will be possible. The combination of rain and melting snow
may cause flooding. As colder air moves into the area Wednesday
afternoon...rain will change to snow and a period of heavy snow is
possible for northern Kentucky and southern Ohio. The entire
system shifts east of the area by Thursday afternoon with drying
conditions for the end of the week and into the weekend.

&&

Near term /until 6 am this morning/...
only some tweaks to the forecast for tonight. The biggest change is
that temperatures over portions of the northern counties have
fallen rapidly under the mostly clear skies. So adjusted their
lows down...but the temperatures should begin to rise across the
entire forecast area after midnight.

The second and more minor change has to do with probability of precipitation. Latest NAM
is slower in bringing in precipitation Tuesday morning. The rap and the
hrrr lift a light band across portions of the forecast area between 12z-15z
then pretty much leave the rest of the forecast area dry through 15z. Backed off
on the beginning of the probability of precipitation by an hour or two...but didnt go as
drastic as the rap/hrrr with this update.

&&

Short term /6 am this morning through Wednesday night/...
not too many times do we issue back to back to back advisory/watch
products but the pattern necessitates it to raise awareness for
multiple threats beginning Tuesday a.M. And continuing into early Thursday.

First off...the Tuesday morning freezing rain/sleet potential.
This is not as clear cut as originally thought. Very clear per
02.12z guidance that very strong moisture flux/transport will get
going after midnight tonight to our southwest...with sref 850mb
transport magnitudes of 5+ sigma above climatology as low level jet
ramps up downstream of approaching northern stream trough slipping through
the upper MS valley. However...ambient airmass /esp below 500 mb/
is extremely dry per 02.12z Kiln sounding and forecast soundings
through Monday night. Model qpfs have been trending lighter/drier in
the Tuesday morning time frame which is worrisome...but have also
seen time and time again where strong warm air advection/moisture
transport/isentropic lift signals use moisture efficiently to
wring out light quantitative precipitation forecast over retreating Arctic domes. Thus...am
running with higher precipitation chances than models on Tuesday morning in
this scenario given the very strong transport signal and
retreating Arctic Dome. Not only is there that aspect...but
boundary layer warming will be racing north on developing south-southeasterly
flow. Current forecast is best current estimation of overlap
between advancing areas of light rain...increasing boundary layer
warming...and timing of the two...which spells a two to five hour
period /least in the south and more in the north/ of light
freezing rain potential. Given virtually no impact or chance to
mix with sleet across southeastern ind/southwestern Ohio/cntl Ohio...have opted for
Freezing Rain Advisory here for light ice amounts that may cause
travel issues. Further north...depth of cold air and perhaps a
little longer duration may allow for more freezing rain/sleet combo so
Winter Weather Advisory there. Too much risk to let this situation go
without an advisory as magnitude of warming/moistening aloft may
allow for a more rapid development and better coverage than models
are showing. The difference between 02.12z NAM/European model (ecmwf) /meager on
quantitative precipitation forecast and coverage/ to 02.12z sref /high probabilities of not only
measurable freezing rain but some hints of up to 0.10"/ spurred the
decision to move to advisory on this issuance.

Next up...moderate to heavy rain and potential flooding. This
signal has been very long advertised per analogs and
anomalies...and now it/S time to switch higher res deterministic
guidance for details. The pattern supports a continued long feed
of moisture transport along and ahead of a slowly moving frontal
zone Tuesday afternoon into Wednesday morning. Big push of very
anomalous/deep moisture...with precipitable water running 300% normal and 3
sigma above climatology on Tuesday night. 70+kt low level jet around
backside of southeastern Continental U.S. Ridging should focus/funnel moisture into
the Ohio Valley and it seems potential for excessive rain is
shifting a tad South West/time over the last 24 hours. Currently
expect the heaviest rainfall footprint /via long duration train of
moderate/sometimes heavy rain/ to be along and south/east of I-71
which is where Flood Watch has been placed. Plenty of snow/frozen
soils to contend with so straightforward to get Flood Watch out
today. Amts from 1-2" - and while convection isn/T going to play a
huge role - convective elements via modest destabilization above
the stable boundary layer will certainly cause
concern...especially south/southeast County Warning Area in northern Kentucky/scntl Ohio.
Could see Brush Creek basin...lower Scioto...and Kentucky/Licking
rivers in Kentucky really respond to this...as 0.5" to 1.00" snow water
equivalent tied up in the snow pack is released rather quickly
with temperatures approaching 50f in the south. Am a little more than
concerned for northern Kentucky/far scntl Ohio so hoping for a slow release
from the snow pack and rain amounts on the lighter end of the spectrum.

Finally...potential winter storm. Low confidence here but a signal
I could not ignore. 02.12z models continue to stabilize somewhat
on cold air oozing into the frontogenetically forced precipitation region
that will be ongoing across northern Kentucky/southern Ohio. 02.12z GFS and its
prior runs seemed way too cold in the boundary layer and thrown
out. Much more consistency from NAM/European model (ecmwf) and that is where
forecast is based. A long duration right entrance region of the
jet/fgen forced band of precipitation will continue Wednesday afternoon/night
into Thursday morning as the cold air overtakes it. There/S a
scenario /one of several/ where 12-18 hours of moderate snow
occurs from northern Kentucky into southern Ohio...and some solutions are extreme
in snowfall amounts. Anecdotally...have to acknowledge that the
pattern and forcing supports a potential higher-end snow
accumulation. But using climatology and what will likely be a slower
transition to snow...and March insolation /even through clouds/ that
will keep anything but heavy snow rates from accumulating too
much. It/S Wednesday night that has my attention as a possibility
of really accumulating snow under cloak of darkness with continued
banding/fgen forcing in the right entrance region of the jet that
moves only very slowly southeast from Wednesday afternoon into Thursday morning.
Will have to watch areas back from cvg to iln to south of cmh for
possible expansion of watch if some of the more dire /quicker
changeover/ situations get more support in the ensembles. Have
taken a very conservative approach to snowfall forecast in our
southern areas and currently indicating 4-7" which necessitates a
watch centered on Wednesday night...again...with need to watch that this
may get expanded in time.

&&

Long term /Thursday through Monday/...
another round of cold Arctic air is on tap for Thursday as Arctic
high pressure builds east into the region. Temperatures will
struggle to warm into the middle teens north to the middle 20s south.
These temperatures are some 25 to 30 degrees below normal for early
March. Needless to say...some record low maximum temperatures may be in
jeopardy. They are 24...22...and 20 at cvg...day...and cmh
respectively. We are currently forecasting 21...17...and 19 at
cvg...day...and cmh respectively. Who has fresh snow cover...and the
amount of clouds...will ultimately play a role on how warm it gets
despite an increasing sun angle for early March.

For Thursday night...the Arctic high will move east across the Ohio
Valley. At this time...the best chance for winds to become light or
calm will be along and south of the Ohio River. With clear skies
expected...temperatures will likely drop below zero in most spots.
Again...knowing how cold it will get at this time is difficult which will
depend on snow cover and how deep that snow cover is for maximum
radiational cooling effects. Have gone conservative at this time...but
getting lower than what is forecast is certainly possible. Will
forecast lows generally in the zero to 5 below range. Record lows of
2...0 and 2 at cvg...day and cmh will also be in jeopardy.

For the period Friday into Friday night...high pressure moves east
while a weak cold front drops southeast into the Great Lakes. Mostly
sunny skies are expected on Friday with an increasing southerly
return flow. Again...difficult to know how warm it will get on
Friday as shallow Arctic air will likely get mixed out but lingering
snow cover and a strong March sun angle will be in play. Will range
highs from the middle 20s north to the lower 30s south. Lows Friday
night will generally be in the teens.

For Saturday into Saturday night...have leaned toward the European model (ecmwf) for
the movement of synoptic scale systems. A weak front drops through
our area on Saturday/Saturday night. Front appears moisture starved
so have kept the forecast dry with only some increase in clouds.
Temperatures will warm into the 30s and 40s on Saturday...but will
still average below normal for early March.

High pressure briefly builds into the area for Sunday...followed by
another weak front on Monday. Front on Monday may bring a low chance
for rain and/or snow. Temperatures will be similar to Saturday/S
readings...30s and 40s...but for the most part averaging a little
bit below normal for early March.

&&

Aviation /06z Tuesday through Saturday/...
VFR conditions are expected for the early part of the taf period.
However a band light precipitation will spread across the
terminals after 09z. Expect this to be freezing rain with light
ice accumulations. At this point expect the band to move through
any one spot within three hours. Appears that there will be a lull
in precipitation with temperatures warming above freezing before
any thing else develops. However ceilings will be dropping to MVFR
as the initial precipitation pulls out. Winds will be veering to
the south and slowly strengthening. Showers will develop
around/after 18z. Conditions should remain MVFR but there could be
some brief drops to IFR particularly in any heavier showers.
Evolution of precipitation becomes more uncertain further out in
time. Precipitation may become more widespread as a cold front
sags into the area...especially for the Cincinnati sites as well
as Kiln. Where this occurs IFR conditions will become more
prevalent.

Outlook...MVFR/IFR ceilings and visibilities will continue through
Wednesday night with accumulating snow. MVFR ceilings will
potentially linger through Thursday.

&&

Iln watches/warnings/advisories...
Ohio...Freezing Rain Advisory from 7 am this morning to 1 PM EST this
afternoon for ohz053>055-060>065-070>072-074-077.
Winter Weather Advisory from 7 am this morning to 1 PM EST
this afternoon for ohz026-034-035-042>046-051-052-056.
Flood Watch from this evening through Wednesday afternoon for
ohz063>065-071>074-077>082-088.
Winter Storm Watch from Wednesday afternoon through Thursday
morning for ohz081-088.
Kentucky...Flood Watch from this evening through Wednesday afternoon for
kyz089>100.
Winter Storm Watch from Wednesday afternoon through Thursday
morning for kyz089-090-094>100.
In...Freezing Rain Advisory from 7 am this morning to 1 PM EST this
afternoon for inz058-059-066-073-074.
Winter Weather Advisory from 7 am this morning to 1 PM EST
this afternoon for inz050.
Flood Watch from this evening through Wednesday afternoon for
inz075-080.

&&

$$
Synopsis...binau
near term...sites
short term...binau
long term...Hickman
aviation...

National Weather Service Glossary of Abbreviations