Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 221950

Area Forecast Discussion
National Weather Service Louisville KY
250 PM EST Wed Feb 22 2017

.Short Term (Now through Thursday Night)...
Issued at 150 PM EST Wed Feb 22 2017

Latest water vapor imagery and 500 mb heights showed an upper low
just west of Tampa with weak ridging over the lower Ohio Valley. At
the surface, high pressure was centered over the mid-Atlantic with
low pressure over the Upper Midwest. Winds were light and out of the
south, and mid afternoon readings were in the upper 60s to low 70s
with a mix of sun and clouds.

For tonight, the main concern is fog/stratus potential. A weak front
northwest of the area will slip southeast toward the area but wash
out as it approaches. Forecast soundings show some saturation taking
place in the low levels after midnight which may bring a round of
patchy fog to parts of the area. Right now, the best potential for
fog looks to be across southern Indiana and north central Kentucky.

On Thursday, the aforementioned washed out boundary will lift north
as a warm front thanks to a developing low over the central Plains.
Showers and maybe a thunderstorm could develop on this boundary as
it lifts through during the late morning and afternoon hours.
Otherwise, plan on highs in the low/mid 70s with breezy southerly
flow by afternoon. The boundary remains well mixed Thursday night
thanks to the deepening low to our west and steady south winds.
Readings will stay up in the upper 50s to low 60s. Record warm
minimums are forecast.

.Long Term (Friday through Wednesday)...
Issued at 235 PM EST Wed Feb 22 2017

...Record Warmth and Strong to Severe Storms Possible Friday Night...

A strong cold front will approach the region late on Friday. Ahead
of it, the lower Ohio Valley will be deep within the warm sector,
and highs should easily eclipse records for the date, but could also
approach all-time February high temperature records, especially at
Louisville which is 78 degrees. Plan on highs in the mid/upper 70s
with a few location hitting 80 degrees. It will also be quite breezy
with steady south winds 15 to 25 mph and gusts 30-35 mph at times.

The 22.12z guidance remained consistent from previous cycles showing
a frontal passage in the evening hours. The environment along/ahead
of the front is expected to be characterized by surface dewpoints in
the mid/upper 50s generating SBCAPE of 1000 J/kg within a strong
wind field. 0-6 km bulk shear remains on the order of 40-50 kts. The
GFS soundings still show a rather stout cap at about 800 mb that
doesn`t break until very late in the afternoon or early evening.

At this piont, the best focus for strong to severe storms looks to
be across east-central IL, central IN and west-central OH. It`s
possible stronger storms could fire up along a pre-frontal trough
across southwest and southern Indiana by mid/late afternoon if the
cap is weaker than the GFS solution. After sunset, a strongly
forced line of storms will likely approach the area but coming
with increasing nocturnal stability limits overall severe threat.
However, strong forcing along the frontal interface, combined with
the strong wind fields will likely keep the storms strong to
possibly severe as they come into our western forecast area late
Friday evening. We believe the highest risk of severe weather
Friday late afternoon and evening will be in areas along and west
of I-65. Damaging winds will likely be the main severe weather

Strong cold advection on Saturday will keep temperatures down over
what we see on Friday.  Highs Saturday will likely top out in the
lower 40s across southern Indiana and northern KY with mid-upper 40s
elsewhere.  Winds will remain gusty out of the northwest, so
Saturday looks to be a rather raw day across the region.

Another fast moving southern stream system is forecast Monday across
the lower Ohio Valley as deep southwesterly flow continues across
the central and southeast CONUS with antoher system possible Tuesday
and/or Wednesday. Overall the theme is for periods of moderate to
heavy rainfall from Monday through Wednesday with mainly above
normal temperatures. Highs during the period will likely top out in
the 60s with overnight lows in the upper 40s to the lower 50s.

Total rainfall amounts through the next 7 days will likely average
in the 2-3 inch range across the state...with some isolated spots
possibly seeing up to 4 inches of rainfall.


.Aviation (18Z TAF Update)...
Issued at 1215 PM EST Wed Feb 22 2017

Weak and sloppy gradient in place between the cutoff low over the
Gulf of Mexico and weak northern stream system moving into the Great
Lakes, with light SW winds. Plenty of stratus this morning has
lifted, and is now just barely VFR. Expect to maintain status quo
until after midnight tonight.

Look for stratus to build down into MVFR, with ceilings likely going
fuel-alternate well before daybreak. Could see IFR at times,
especially if hi-res guidance like the GFS LAMP is to be believed,
but with only moderate confidence in fuel-alternate, will not take
it down that far. Both MVFR ceilings and visibilities will persist
most of the morning as another weak front starts to impinge on the
Ohio Valley from the north. Any precip chances associated with that
front are beyond the scope of the LEX TAF, and probabilities are too
low for inclusion in the planning period at SDF.




Short Term........ZT
Long Term.........ZT
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