NWS Louisville, KY wrote its last area forecast discussion before the first event at Mar 4, 9:01 PM EST, 1 hour 29 minutes earlier.
Area forecast discussion, Mar 4, 9:01 PM EST, 1 hour 29 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
901 PM EST SUN MAR 04 2012
.Update...
Issued at 900 PM EST Mar 4 2012
Precip event is well on its way into the area. HNB's visibility has
dropped along with temperatures, so snow is ongoing there. 88D
returns are getting heavier over southeast Illinois, just ahead of
the shortwave now over west central Illinois, so the heavier snow
band for the night may be trying to get its act together. Have
updated the snow forecast for these trends. The new totals are
still around an inch in the warmer Metro, where onset of a rain snow
mix should begin in the next hour or two before transitioning to
just snow around or soon after midnight. Totals west and east of the
metro should be higher, with 1-2 inches to the west and 1-3 inches
in the east. Given the new snow forecast, have decided to expand the
winter weather advisory slightly south, into Hancock, Grayson, and
Hart counties. Still think south central Kentucky will get spared
from too much accumulating snow thanks to their much warmer start to
the evening.
Update issued at 638 PM EST Mar 4 2012
Temperatures did end up warming up pretty quick this afternoon in
the clearer skies on the back side of the departing upper trough.
Still, the next system, a clipper, is on track for coming down into
the region overnight. With the warmer temperatures to start, it will
take a little while longer for the rain to transition over to snow,
but should see a mix at Louisville starting around 10 PM and BWG
after midnight. LEX is cool enough now that as soon as the precip
starts there it should be a mix before changing over to just snow by
just before midnight. For KSDF think the precip will be all snow
with accumulations starting around 06Z.
With this updated timing, have updated the forecast snowfall as
well. Still have an inch or more in the current advisory area, with
the highest totals over the Bluegrass, 2-3 inches. Have dropped the
forecast for Louisville down to around an inch, with higher values
in the counties to the north and east. Will have to monitor radar
trends for the southwest to see if any expansion of the advisory
area will be needed, but BWG currently is 50, so even if heavier
snow falls there it will take some time to start accumulating.
.Short Term (Tonight through Monday)...
Updated at 315 PM EST Mar 4 2012
...Accumulating Snows Coming To Southern Indiana and Portions of
Central Kentucky Tonight...
A rather deep upper level trough axis is currently located over the
region today. The combination of the this trough and the cold air
aloft associated with it has led to the development of scattered
snow showers/flurries in the east...with generally sprinkles in the
west. This trough will shift off to the east this evening, and with
the loss of heating, the snow flurries are likely to diminish in
intensity and coverage later this afternoon. However...more weather
is to come this evening.
As the upper trough heads east, an upstream Alberta Clipper is
forecast to move southeast from the upper Midwest and into the Ohio
Valley tonight. Despite having relatively little moisture, a strong
mid-level jet streak with accompany this clipper as it moves
through. As the jet cyclonically curves over the region tonight,
the models are still projecting a decent amount of lift with this
system. Indeed, upstream observations over Iowa do indicate some
moderate to occasionally heavy snow. Precipitation should push into
the region from the northwest...probably after 05/01Z or so.
Overall thermal profiles are cooler and this actually agrees quite
well with what we've seen from the AMDAR data out of KSDF this
afternoon. Thus, feel that the initial mix of rain/snow is going to
end up being more of just plain snow in the north...with the mix
being confined our southwest and far south locations. Precipitation
is expected to increase in intensity overnight as the mid-level jet
axis approaches. It does appear that a band of moderate-heavy snow
will develop...but the exact area is still a bit difficult to pin
down.
Based on the the model consensus, it appears that the heavier
snow band may develop along a line from Jasper to Louisville to just
south of Lexington. While the soundings have trended colder aloft,
surface temperatures have been running a bit warmer than guidance
today. Based on the 04/09Z SREF...surface temperatures are probably
going to drop to near freezing by morning. So with surface
temperatures expected to be above freezing during the event, some of
the snow will likely not stick to roads...but will in the grass and
elevated surfaces. However, inside the heaver band, the snow fall
will likely be heavy enough to counter act the warm temps and
accumulate on some road surfaces. At this time, the Winter Weather
Advisory will continue across the region. Based on upstream obs and
trajectories, we will expand the advisory slightly to west and about
one row of counties to the south. In general, we feel that one to
two inches of accumulation is likely in the advisory area. Some
isolated amounts or an isolated swath of 3 inches will be possible
in a few areas that get under the heavy band.
For areas south of the advisory...mainly across far southern KY, the
combination of a warmer lower atmosphere and less moisture will
result in much lighter accumulations. A dusting or a minor
accumulation will be possible late tonight.
The snow should star to wane from west to east late tonight. We
believe that the snow will likely end in the I-65 corridor by 4-5 AM
with the snow exiting the I-75 corridor by 700 AM or so. So the
advisory timing remains unchanged. Clearing skies and high pressure
will build into the region on Monday with highs ranging from the
upper 30s in the northeast to the mid-upper 40s in the southwest.
.Long Term (Monday night through Sunday)...
Updated at 310 PM EST Mar 4 2012
Surface high pressure will quickly slide east Monday night and set
up across the East Coast through the middle of the work week. Aloft,
ridging will slide east as well, with southwesterly flow anticipated
by Tuesday. Temperatures Monday night and Tuesday will be tricky
given the expected snowfall. Clear conditions combined with the
newly fallen snow across portions of the CWA will create generally
mid-upper 20s for overnight lows.
A warming trend will begin Tuesday as south to southwesterly surface
flow develops. Highs Tuesday will range from the mid 50s across the
Bluegrass to upper 50s and low 60s across the west and southwest,
where there will be less ground moisture from the recently fallen
snow. By Wednesday, high temperatures should reach the low to mid
60s on breezy to windy southerly flow. Temperatures Wednesday night
will remain rather mild, with mid 40s to low 50s expected as a cold
frontal boundary approaches from the northwest.
The frontal boundary will slowly move to the southeast as it nearly
parallels flow aloft Thursday through Friday. There is quite a bit
of spread in the ensemble solutions by Friday, but the latest NAEFS
data suggests a closer alignment with the ECMWF. This supports a
general timing of the boundary pushing into the region Thursday,
lingering across the area Friday, then sliding to the southeast by
Saturday. Given this current timing, showers will overspread the
area Thursday and Friday, with a few thunderstorms possible as it
pushes through. However, the exact timing remains dependent on the
location of a southern stream cut off low, which is expected to be
located somewhere across the central CONUS.
Highs Thursday will remain warm ahead of the frontal boundary, with
low to mid 60s expected. Given the frontal passage, cloud cover, and
precipitation, temperatures generally in the mid and upper 50s are
anticipated Friday. Surface high pressure will quickly move by to
the north Saturday, providing dry conditions and high temperatures
in the upper 40s to low 50s. However, these conditions will be short
lived, as we quickly warm up Sunday on southerly flow with the cut
off low across the central CONUS edging closer to our region. Highs
in the low and mid 60s are expected with perhaps a slight chance of
showers across mainly our western CWA.
&&
.Aviation (00Z TAF Issuance)...
Updated at 620 PM EST Mar 4 2012
Upper level shortwave is moving quickly toward the region at this
hour from Iowa. Airmass now is pretty dry, but upstream obs indicate
that precip that is falling is moistening it up quickly. With
somewhat warm temperatures at the start expect precipitation to
start off at rain at all sites before transition over to just snow
at KSDF and KLEX, with IFR conditions likely in the heaviest snow.
The timing for the snow will be quick, with conditions improving
before sunrise at all locations, though MVFR cigs may hang on into
mid morning. Winds will come around to northwesterly on the back
side of the precip and remain through the day Monday.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...WINTER WEATHER ADVISORY UNTIL 7 AM EST /6 AM CST/ MONDAY FOR
INZ076>079-083-084-089>092.
KY...WINTER WEATHER ADVISORY UNTIL 7 AM EST /6 AM CST/ MONDAY FOR
KYZ023>025-027>043-045>049-053>057-063>067-077-078.
Updates..........RJS
Short Term.......MJ
Long Term........MJP
Aviation.........RJS