Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 041716

1216 PM EST Wed Mar 4 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 855 AM EST Wed Mar 4 2015

No changes to the headlines at this time.  Did delay the transition
to wintry precipitation just a bit, with Louisville mixing by 20-22Z
and snow 23-01Z, Lexington mix 22-00Z and snow 00-02Z, Bowling Green
mix 23-01Z and snow 04-06Z, and Lake Cumberland mix 02-04Z and snow
08-10Z.  This resulted in a slight tweak downward for snow amounts
in southern Indiana, but this will still be an impactful storm.

In the meantime, steady light to moderate rain will continue into
this afternoon. We can expect another half to three quarters of an
inch of rain this afternoon in Kentucky.  Minor flooding issues will
continue as a result.

Issued at 620 AM EST Wed Mar 4 2015

Have tweaked timing of transitions based on the 06Z model
runs...pushing the times back an hour or two. Totals came down a
little as well, but still roughly within the ranges posted on our
web briefing slides. Updated products will be out shortly.

.SHORT TERM (Now through Thursday)...
Issued at 325 AM EST Wed Mar 4 2015

...Flooding Threat Ongoing and Winter Threat Imminent...

Well-advertised plume of deep moisture is bringing moderate rains to
a large portion of the region early this morning. Given saturated
grounds and some residual snows have had some reports of higher
water in typically flood prone areas. Thus issued an earlier areal
flood warning across our northern stripe of counties. Still
monitoring area rivers and have several warnings out for those
already for forecast rain amounts. This forecast package will have
an additional 1-3 inches of liquid QPF, with the peak axis running
from Morgantown to Bardstown to Lexington. The northern stripe of
counties in IN should get another inch to inch and a half, with the
most liquid falling to daybreak then transitioning over to a wintry
mix. Given higher liquid QPFs through the daytime period, decided to
expand the flood watch through 00Z Thursday. Day shift can cancel
the back side of it as snow becomes the dominant p-type.

Speaking of that mix, an AMDAR sounding out of IND at 06Z indicated
a warm nose around 800 mb which translated to a -RAPL report. The
GFS had the best handle on the strength and depth of this nose, with
the NAM similar but not as strong. Thus for this package leaned the
MaxTAloft forecast more towards the GFS, but did blend some with the
NAM. Based on that thinking, have shifted transition times a little.
In most cases have from north to south a period of an hour or two
with a RAPL mix then just PL then a transition to SN. That
transition should start in our far northern counties in the 10-12Z
time frame, in Louisville in the 14-16Z time frame, LEX 16-18Z, and
BWG 21-23Z. The precip type should go to all snow over our north in
the 15-17Z time frame, then 19-21Z for Louisville, 23-01Z for LEX,
and 01-03Z for BWG. Given the earlier start time in the north,
decided to add a segment to our winter storm warning to get it
started around daybreak north of the Ohio River and including
Trimble county. Also pushed the now "middle" segment of the warning
to start at 17Z. Could have gotten cute and added a fourth segment
to allow a later start time for the southern part of that middle
segment, but three already seems like too many. Will give a good
description of transition times in briefing slides online, so check
those out.

The period for heaviest snowfall would appear to be from 00-06Z, as
a jet strengthens over Michigan, with our area in the right rear
quadrant of the jet, allowing for maximum lift here. Profiles also
show heavier bands of snow possible with rates of 2"/hour possible
where those bands set up. Snow totals are from the forecast QPF and
steadily increasing snow ratios through the period. Still have a max
along the corridor from Hartford to Shepherdsville to Georgetown
with 10-12" areal averages. Have values of 6-8" across my far north
and 4-7" along my TN border. Those southern counties may see a brief
period of freezing rain this evening as temperatures crash down
there with sunset. Have ice accumulations a little under a tenth of
an inch down there to account for that possibility.

As for temperatures, our warmest values should be this morning, with
readings holding steady or declining through the rest of the day.
Lows tonight mostly will be in the teens and highs Thursday in the
20s. Those readings on Thursday would break record cold high
temperatures for the day.

.LONG TERM (Thursday night through Tuesday)...
Issued at 200 PM EST Mon Mar 3 2015

Thursday Night - Friday Night...

...Temperature Records in Jeopardy...

The center of the Arctic high pressure will slide over the area by
Friday morning, with any lingering stratocu diminishing after the
first half of the evening. Winds may not go completely calm, so with
the potential of lingering clouds and some light winds don`t think
we`ll have perfect radiational cooling. Given that, am reluctant to
go as low as some of the raw guidance would suggest. Although, it is
still possible given the expected fresh snowpack. Overall will keep
forecast lows generally in the 0 to -3 range over the heaviest
snowpack just south of the river. Will go 0 to 6 above north of the
river and across south central KY where less snowpack is expected.

For Friday, agree with previous forecast that areas under the fresh
snowpack will likely not make it out of the mid 20s, with southern
Kentucky most likely to see highs in the 30s.

Based on the Thursday Night and Friday temps, below are some records
that may come into jeopardy.

Here are those records for our area:

       Mar 5                   Mar 6
       Record Cold Highs       Record Cold Lows

BWG    27  1960                        1  1960
SDF    26, 1960                       -1, 1960*
FFT    22, 1960                       -3, 1960*
LEX    22, 1960                       -2, 1960*

* indicates the all-time March record low

Will be cold again on Friday night, although not as cold as a steady
southerly flow combines with some mid and upper level sky cover.
Will go 10 to 15 above over the snowpack with upper teens possible
in our extreme north and south.

Saturday - Tuesday...

...Dry with Temperatures Moderating Back Toward and Above Normal...

Shallow NW flow aloft should dominate the upper air pattern, with
weak surface ridging also in place. This will lead to dry conditions
with temperatures gradually trying to moderate. There will be a few
disturbances that pass through the NW flow aloft, but they all
appear to be moisture starved and doubt we`ll see much more than an
increase in sky cover with each passage.

Did try to keep the snowpack in mind through the weekend, keeping
temps down over where the best snow cover is anticipated. Will
likely have to be more dramatic with these values at least through
the weekend should the snow be fully realized. By Saturday, temps
should warm to the upper 30s (snowpack) and low 40s elsewhere.
Saturday night lows will still find their way into the low 20s.

It is worth noting that we should be able to work on melting any
existing snow pretty heavily through the end of the weekend, and
that may lead to more flooding concerns as we add to the already
swollen river/streams and saturated ground.

Temps begin to make progress toward the normal mark on Sunday and
Monday with highs in the mid 40s Sunday and in the 45 to 50 range on
Monday. We could be above normal by Tuesday with highs in the mid
50s as the upper flow flattens out.


.AVIATION (18Z TAF Update)...
Issued at 1210 PM EST Wed Mar 4 2015

Complex winter system moving through the Ohio Valley today into
tonight which will continue to bring IFR to LIFR conditions.

Already getting reports of sleet mixing in around the Louisville
metro, so will initialize KSDF with -RAPL.  Will transition to -SNPL
at 19Z, going to all snow by 22Z.  Think vsbys within the snow will
likely be 1/2SM or less given the expected high intensity.  Cigs may
bounce over the next few hours between IFR and MVFR, but think IFR
cigs will be the most prevalent.

Will bring -RAPL into KLEX by 20Z, transitioning to all snow by
23Z.  The snow will be heavy once it transitions, so vsbys 1/2 to
1/4 of a mile are likely for a long duration tonight.  Cigs will
be IFR, perhaps high-end LIFR at times.

Will continue with -RA through 23Z, before bringing in -RAPL.  Sleet
will likely last a few hours longer at KBWG, transitioning to all
snow by 02Z.  The best forcing looks to pass just north of KBWG, so
will not hit the vsbys quite as hard with this package, but LIFR
vsbys are still likely.

All sites will slowly improve through Thursday morning as the snow
ends and cigs begin to rise.  Winds will be out of the north through
the period around 10 knots.



     FLOOD WATCH until 7 PM EST /6 PM CST/ this evening FOR

     WINTER STORM WARNING from 7 PM EST /6 PM CST/ this evening to 1
     PM EST /Noon CST/ Thursday FOR KYZ066-067-073>078-081-082.


     FLOOD WATCH until 7 PM EST /6 PM CST/ this evening FOR INZ084-



Short Term.....RJS
Long Term......BJS
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