Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 270524
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
124 AM EDT Fri Mar 27 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 928 PM EDT Thu Mar 26 2015

Forecast is in good shape, no significant changes necessary.  Light
rain should be moving out of the east in the next hour or two.
Clouds will decrease overnight.  Despite some clearing skies and a
damp ground, dry air coming in on north breezes at and near the
surface should prevent fog from forming overnight.

.SHORT TERM (Now through Friday Night)...
Issued at 200 PM EDT Thu Mar 26 2015

Main forecast concerns are precipitation trends through this evening
then the unseasonably cold conditions heading into this weekend.

Mid afternoon surface analysis shows low pressure across West
Virginia with a pronounced cold front stretching back from through
eastern Kentucky into central Tennessee. Northwest winds and post
frontal stratus encompass much of the area as readings have
steadily fallen since morning. Much of the area is in the 40s.

The upper levels are characterized by a digging trough with its axis
from St Louis to Dallas. A PV anomaly is noted in water vapor
imagery near Arkansas and this is helping to fuel additional
showers across southwest Kentucky. A 130 kt jet lies north of the
area, putting the Ohio Valley favorably within the right entrance
region. Until the upper level forcing passes, scattered showers
will pass through central Kentucky and southern Indiana. Areas along
and west of I-65 should see an end around 6 pm, then between 6 and 9
pm for areas east. Rainfall amounts look to be 1/4 inch or less.

RH fields in the low levels show clouds will be on the decrease
overnight as drier northwest air arrives. We`ll have a steady north
gradient but plan on lows to fall into the 30s region wide. For
Friday, still looking like a brisk, unseasonably cold day with highs
again stuck in the 40s. The low level lapse rates and cold air aloft
will likely result in partly/mostly cloudy cumulus clouds by late
morning through the afternoon. 26.12z and hi-res models still
suggesting light showers could develop with precipitation mainly
falling as rain but could not rule out a snow or sleet pellet at
times.

Canadian high pressure builds in tomorrow night though its axis
remains to our west for much of the night. Northerly winds will keep
the boundary layer stirred, holding lows up though mid 20s region
wide still looks good. Would not be surprised if some outlying,
sheltered locations drop into the upper teens briefly.

.LONG TERM (Saturday through Thursday)...
Issued at 250 PM EDT Thu Mar 26 2015

Canadian surface high and upper trof over the eastern CONUS will
keep the first half of the weekend unseasonably cool. While it is
difficult to discount the nearly-April sun angle, 850mb temps only
recover to -8C by 00Z Sunday. This yields a max temp forecast in the
upper 30s/lower 40s, just skirting the cooler end of MOS guidance.
Saturday night will be a matter of just how efficiently we radiate
before developing return flow starts to mix the boundary layer. If
radiational cooling is maximized we could be as cold as Friday
night, if not a bit colder. This forecast in the lower/mid 20s is
close to guidance, and is the warmest likely scenario
notwithstanding the possibility that temps start rising before
daybreak Sunday if the SE return flow is strong enough.

Sunday will be a transitional day between the cold/dry weekend and a
milder, progressive pattern heading into next week. Return flow will
allow temps to recover well into the 50s, which is still below
normal this time of year. Clouds will increase late in the day as a
weak front approaches, but will keep the POPs out of the forecast
until Sunday night.

Progressive pattern next week will begin as mainly NW flow but will
flatten out around mid-week. Have pretty much followed the latest
ECMWF, which is slower with the Sunday night cold front and drier
with the disturbance that passes to our north and east late
Tuesday/Tuesday night. Timing differences aside, model precip
appears overdone especially with the first front, as depth of
moisture is lacking. Will limit POPs to chance on Sunday night into
Monday. Expect the second front to also go through dry.

A more robust system will develop by Wednesday night and Thursday,
but model solutions still differ. GFS appears dominated by the
southern stream while ECMWF favors the northern stream, but by then
the upper pattern is flat enough that we do tap enough Gulf moisture
and warm advection to support precip chances. Still not about to go
likely 6-7 days out but will go high-end chance on Wednesday night.
Wednesday`s 20-30 POP is even a bit generous, but wanted to wait for
more continuity and/or agreement in the models before removing the
mention. Temps above normal Mon-Thu.

&&

.AVIATION (06Z TAF Update)...
Issued at 120 AM EDT Fri Mar 27 2015

Have a general north to northwest wind out there now, continuing to
bring in some drier air. Till that air gets in here though, we have
a few VFR-based clouds out there, and even some light restrictions
in vsby at LEX. An upper level disturbance still looks to move into
the region this afternoon, bringing additional cumulus clouds as
well as some isolated showers. The chance still is too low to put
into the TAFs just yet.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

$$

Update.........13
Short Term.....ZBT
Long Term......RAS
Aviation.......RJS





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