Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 271232
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
732 AM EST Fri Feb 27 2015

...Forecast Update...
Issued at 730 AM EST Fri Feb 27 2015

Quick update to keep flurries in the forecast a little longer down
south. Have returns on radar over our southwest forecast area. BWG
ASOS is not reporting snow at this point, but would not be surprised
to see some flurries down there.

.SHORT TERM (Now through Saturday)...
Issued at 315 AM EST Fri Feb 27 2015

In the near term, surface front has passed well south of the
region.  Some partial clearing has worked into the region, but we`re
still dealing with one persistent area of low clouds and
flurries...mainly between Louisville and Owensboro.  Within the last
hour, this band has started showing trends of moving southward and
we expect this trend to continue through the morning.  The snow is
very light and a dusting at most will be possible as it moves
through.  Elsewhere, clear to partly cloudy skies were noted with
temperatures generally in the lower teens in the north with upper
teens to around 20 in the south.  We expect temperatures to continue
to drop a few more degrees before bottoming out around sunrise.
Coldest temps look to be in our far NE Bluegrass sections where
single digits are likely this morning.

For today, high pressure will continue to build in from the
northwest.  In general, partly to mostly sunny skies are expected.
A southwesterly flow aloft will likely spread some mid-high level
cloudiness in during the afternoon.  Highs today will generally top
out in the upper teens to the very low 20s across the far north.  In
areas along the river down to the WK/BG Parkways, lower 20s are
likely.  The warmest readings will be down across southern KY where
mid-upper 20s will be possible.

For tonight, high pressure will generally be centered over Ohio.
This would usually result in good radiational cooling.  However,
model cross-sections suggest we`ll have mid-high level cloudiness
continuing to move from the west/southwest.  Thus, this is likely to
retard radiational cooling across much of the region...expect the
far NE Bluegrass region.  Current thinking is that we`ll see
readings generally in the lower-mid teens over the south/southwest
with single digits up over our far NE counties.

For Saturday, we`ll see continued mid-high level cloudiness stream
across the region.  Clouds will likely lower during the afternoon
hours as deeper moisture starts to advect in from the west.  Highs
are expected to moderate somewhat with highs in topping out in the
upper 20s in the north with lower-mid 30s across the south.

.LONG TERM (Saturday Night through Thursday)...
Issued at 300 AM EST Fri Feb 27 2015

...Active Long Term with multiple systems affecting the OH Valley...

System #1 Sat night-Monday Morning

Well...aloft we have broad upper level trough from Glacier NP MT to
Yosemite NP Ca will deepen through the extended will keep Ohio
Valley in SW flow for the bulk of the extended.  By Monday morning
the trough will deepen from Great Basin NP NV to Joshua Tree NP Ca
to Channel Islands NP CA.  Well...Arctic high pressure moves east
over the Shenandoah NP MD allowing sely to sly flow over CWA ahead
of the next.

Deep-layered isentropic lift will begin Sat night, with models
continuing to focus the greatest lift and moisture over nwrn CWA.
Sounding profiles show RASN with perhaps a little IP mixed in. Made
tweaks to fcst and took out the FZRA. Ensembles and individual model
ensemble members focus the highest pops and QPF amounts north of the
BG Parkway. This is closer to a weakening warm frontal boundary.
The PWATs increase from 0.5 Sat evening to 1 inch Sunday night.
These PWATS are 1-2 standard deviation high and with wsw 850 llvl
jet of 40 knots, there should be consistent pcpn efficiency.

By Sunday night, a cold front will move through the region. However
this will keep pcpn across the area with likely POPS.  Late Sunday
night, thermal profiles change with nly sfc winds and wly winds
right off surface and sets the stages for 3-4 hour winds of fzra
across nrn 1/3 of the CWA.  Changed the grids to fzra from 9-12z for
now.  The pcpn will end from nw to se monday morning. This front
will not make typical frontal changes as the airmass does not change
much.

Wx Break... High Pressure Monday aftn and Mon Evening...
Behind the front the GFS advertising (GEM is much different) with a
1035 mb high quickly moving through, bringing some thinning in the
cloud cover and maybe some sun Monday afternoon across CWA before
the next stronger system moves in.  Have increased temps a few
degrees to near 50 on Monday.

Storm 2 Monday night through early Wed...

After the transitory high pushes through, CWA will return to a
southwest flow aloft and another warming trend. Monday night and
Tuesday we will return to a WAA pattern with that moisture already
in place. MEX gives 66 on Tue...and its leaning in the right
direction with strong swly llvl flow (even despite rain and cloud
cover). Increased temps 3-4 degrees to low 60s.

Forcing commences between 06-12z and have likely pops increasing to
categorical pops.

Flooding Comments...

With all this rain in the forecast, have some concerns for flooding.
First is the present snow pack, which has roughly half an inch to
two inches already on the ground waiting to melt. Second, the ground
has a thin layer of frost just underneath the surface and even if
this goes away by next week the ground is still pretty saturated.
There is a cornucopia of moisture and theta e advection.  PWATS are
2-3 SD above normal, and this sure looks like a Maddox heavy rain
event and could lead to some flooding issues. There is plenty of
forcing with this system with 300 mb jet of 140kts.  Sfc low will
track from the Land of Enchantment Monday night to the Sunflower
State Tuesday and to the Empire State Wed.  High probability of 2-4
inches of rain Tuesday-Wednesday. Stay tuned for updates as we fine
tune this forecast over the coming days.

The models support some tsra, albeit mostly elevated based off the
soundings.  The wind fields and the BUFKIT soundings look similar to
Feb 5-6 2008, but not as strong or not as saturated sounding.
There could be strong to severe storms Tuesday night near the CWA.
thunder as well and cannot rule out severe weather as well.

Wed afternoon-Thu...

GFS once again advertises a secondary wave and a snow and ice
event.  Will follow the progressive flow of the Euro and move this
system from NW to SE on Thu and not "touch this, as we have to get
through with the first 2 systems.  Will go for a blend of model and
guidance temperatures as well that period.

&&

.AVIATION (12Z TAF Update)...
Issued at 605 AM EST Fri Feb 27 2015

Batch of snow flurries continues to work its way down the I-65
corridor this morning.  The overall intensity continues to wane as
drier air pushes into the region from the north.  We expect some
scattered low clouds to continue at the terminals this morning, but
we expect ceilings to stay at/above VFR thresholds.  Surface winds
will remain out of the north to northeast this morning.  We still
believe that a scattered cu field will develop this afternoon and
then fade by sunset. Surface winds will remain out of the north this
afternoon.

&&

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

$$

Update.........RJS
Short Term.....MJ
Long Term......JDG
Aviation.......MJ





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