Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 031122
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
622 AM EST Tue Mar 3 2015

...Updated Aviation Discussion...

.SHORT TERM (Now through Wednesday Night)...
Issued at 342 AM EST Tue Mar 3 2015

...Heavy Rain with Potential Flooding Followed By a Significant
Winter Storm...

The first concern for the short term period will whether or not any
freezing rain will impact the far northern portion of the forecast
area this morning. Have kept slight chance pops in for the early
morning hours. However, it looks like most of the precipitation will
be north of the forecast area. Therefore, will not issue an SPS at
this time for freezing rain and icing, but will continue to monitor
the trends and issue any headlines as needed. Temperatures should
rise above freezing across the entire area by 14Z.

Heavy Rain...

A warm front will lift north across the region this morning with
temperatures warming quickly. Southerly winds will also usher in
much more moisture with precipitable water values rising well above
an inch. Showers will increase through the day, particularly across the
northern half of the forecast area. Further to the south they look
to be more scattered in nature, particularly this morning but
increase through the afternoon. Some thunderstorms will continue to
be a possibility as well. Temperatures today will rise into the 50s
across most of the region by afternoon and around 60 near the KY/TN
border.

A low pressure system across Canada will drag a cold front through
the area tonight. Showers will continue in the wake of the front with
a band of moderate to heavy rain developing across the forecast
area. The highest rainfall amounts through 12Z Wednesday continue to
be along and south of the Ohio River with two to two inches
possible. North of the River amounts will be up to one and a half
inches. Will continue the Flood Watch south of the Ohio River as
this is the area that is expected to see the most impacts both from
the rainfall and additional melting snow.

Winter Storm...

The focus then shifts to the transition to winter precipitation and
the possibility for a significant winter storm. Temperatures will be
falling Wednesday in the wake of the cold front. The lower Ohio
Valley will be situated in the right entrance region of a 180 knot
upper level jet with a PV anomaly swinging through Wednesday
night. Precipitable water values will continue to be anomalously
high in the 0.8-1 inch range. Precipitation will start to diminish
somewhat on Wednesday morning, particularly across southern IN and
north central KY. However, a secondary wave of precip is the
expected to build in during the afternoon and evening with the PV
anomaly.

There is fairly good agreement within the model guidance this
morning regarding thermal profiles and changeover from rain to sleet
to snow. The wild card remains the NAM which continues to be much
warmer aloft and at the surface, which would result in significant
differences in snow/sleet totals. Have leaned away from this
solution for now, but it bears watching.

Precipitation should begin to transition Wednesday morning from the
northwest from rain to snow. Soundings show at least some warm layer
aloft, so think a short period of sleet will be possible. Far
southeastern portions of the forecast area will be the last to
transition to snow and this may not be until midnight or later
Wednesday night. Thus, think that snow totals around the Lake
Cumberland area will be lower, but sleet totals may be higher. For
the 0-6Z period Thursday, a good band of snow still looks like it
will set up south of the Ohio River and north of the Cumberland
Parkway. In this band 1-2" per hour snowfall rates will be possible
for a number of hours. After 06Z snow will start to slowly move out
from west to east, though some snow shower will likely continue into
Thursday morning.

Given some lingering uncertainty in the warmer solutions, will
continue with the Winter Storm Watch for now. Thinking in totals
remains similar to the previous forecast with conservatively 4 to 8
inches of snow and sleet accumulation across the area. However, some
areas across central KY do have the potential to see 10+ inches
before all is said and done.

.LONG TERM (Thursday through Monday)...
Issued at 330 AM EST Tue Mar 4 2015

Certainly looks like a more quiet forecast period than the short
term above. Biggest concern will be how cold it gets Friday morning
as high pressure moves overhead. With the snow in our forecast
before-hand and clearing skies, temperatures could bottom out close
to records, if not all time March records. Here are those records
for our area:

       Mar 5         Mar 5        Mar 6        Mar 6
     Cold Highs  Forecast High  Cold Lows  Forecast Lows
BWG    27, 1960      25           1, 1960      5
SDF    26, 1960*     25          -1, 1960      4
FFT    22, 1960      23          -3, 1960      -1
LEX    22, 1960      22          -2, 1960      2

* indicates the most recent time this record occurred

All of the Cold Low records above also are the all time record lows
for March. The record Cold Highs are roughly 6-10 degrees colder
(and they all occurred in 1980. Have gone under guidance for those
lows above, and still feel like I have not gone quite low enough.
These numbers are supported by some of the better performing models
during previous cold spells.

After that morning, we should see a slow moderating trend. Another
weaker cold front will approach slowly perhaps getting into the area
Sunday. Model QPF indicates some light values are possible Saturday
night and Sunday, nothing as significant as the midweek system
though. Another similar front looks to cross the region Monday, with
similar light QPF. Opted to put in some light precip Sunday night
and Monday in the east given flow aloft adding an upslope component
with the terrain there.

&&

.HYDROLOGY...

Issued at 310 AM EST Tue Mar 3 2015

Rivers have returned to normal winter flow, but soils remain
saturated from recent snowmelt. The rest of the snowpack will be
added to the mix with Tuesday`s warm temps, and rises from heavy
rainfall will be quick due to saturated soils.

Still expecting 1.5 to over 3 inches of rain across central Kentucky
before the changeover to snow on Wednesday. This will likely produce
widespread minor flooding in the Salt, Green, Licking, and Kentucky
basins. Residents in flood prone areas should closely monitor water
levels over the coming days and be prepared for possible flooding by
mid to late week.

&&

.AVIATION (12Z TAF Update)...
Issued at 620 AM EST Tue Mar 3 2015

Ceilings are starting to come down as expected this morning, and
conditions should remain poor for flying the next 30 hours. The first
system causing these issues is a warm front lifting across the region
over the next few hours and then behind it a cold front will glide
slowly through by the end of the period. The chance for showers this
morning picks up quickly with IFR conditions likely. We may see some
breaks with better conditions, but the prevailing type should be IFR
through the day. Conditions should worsen by evening, with some cigs
near airfield mins. Winds will pick up from the south and southwest
ahead of the front, which is progged to pass through SDF around 06Z Wed
and a little later at the other sites. Guidance calls for cigs to
remain LIFR behind this front, but time-height sections call for a
little lifting and will be optimistic for now. In the 15-18Z time
period Wed, we could see a transition from all rain to some sleet or
snow mixed in. Confidence not high enough to put in TAFs at this point.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...WINTER STORM WATCH from Wednesday morning through Thursday
     afternoon FOR KYZ023>043-045>049-053>057-061>065-070>072.

     FLOOD WATCH from this evening through Wednesday afternoon FOR
     KYZ023>043-045>049-053>057-061>067-070>078-081-082.

     WINTER STORM WATCH from Wednesday afternoon through Thursday
     afternoon FOR KYZ066-067-073>078-081-082.

IN...WINTER STORM WATCH from Wednesday morning through Thursday
     afternoon FOR INZ076>079-083-084-089>092.

&&

$$

Short Term........EER
Long Term.........RJS
Hydrology.........CMC/EER
Aviation..........RJS




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