Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 252304

Area Forecast Discussion
National Weather Service Louisville KY
704 PM EDT Sat Mar 25 2017

...Updated Forecast and Aviation Discussions...

.Forecast Update...
Issued at 700 PM EDT Sat Mar 25 2017

Minor updates to the precipitation chances this evening. Initial
line of showers with isolated thunderstorms now lies more or less
along the I-65 corridor, and will slowly lift north/northeast. It`s
running into a less favorable environment, so thunder chances remain
slight. In its wake, there`s a break back toward southwest KY and
western TN, but hi-res models continue to advertise more development
this evening as the PV anomaly over western MS lifts northeast
toward the area. Should see the highest coverage of showers and
perhaps a t-storm from very late this evening, but mostly after
midnight through mid-morning Sunday.

Otherwise, forecast remains on track. Adjusted temperatures and wind
fields to latest observations and blended guidance.


.Short Term (Now through Sunday Night)...
Issued at 300 PM EDT Sat Mar 25 2017

Now - Sunday Night...

Vertically stacked low is currently centered over S Missouri, and
will very slowly meander to the mid Mississippi River Valley by dawn
tomorrow. Ahead of this feature, a plume of Gulf moisture is poised
to ride over our region later tonight under deep southerly flow. In
the meantime, we`ll enjoy a mild and mostly dry afternoon with temps
likely topping out in the upper 70s. Stronger gusts in the 30 to 40
mph range earlier this afternoon should subside by 5 or 10 mph late
this afternoon and this evening as increasing sky cover limits
deeper mixing a bit.

Still like the idea of a slow arrival, and will not carry
categorical pops until sunset and after. However, do have scattered
coverage in our west late this afternoon and evening. Still not
overly impressed with severe potential, however expect to at least
have some instability so can`t rule out a brief strong storm or two
across our west in the early evening. As mentioned in the previous
discussion, showers and storms arrive across the rest of our CWA
more toward diurnal minimum and should limit the severe threat.
Don`t plan on any changes to the HWO wording at this time.

Overnight categorical pops suggest that virtually everyone should
get in on the rain chances. Some rumbles of thunder can also be
expected up to and around the midnight hour. Temps will be mild and
should only drop to the mid and upper 50s.

The upper low will wobble to the lower Great Lakes by Sunday evening
with numerous showers and a few storms in the morning tapering to
isolated to scattered coverage from west to east in the evening.
Most spots expected to see around a half an inch of rainfall total.
A few instances of brief heavy rainfall are possible late tonight
and early Sunday so can`t rule some locally higher amounts. Overall,
temps won`t be as warm as today, but we should still peak in the
upper 60s to near 70 on steady southerly flow.

A few showers may hold on in our east Sunday evening, but expect to
be dry Sunday night as shortwave ridging builds in. Lighter winds
and partial clearing should allow temps to drop into the low to mid

.Long Term (Monday through Saturday)...
Issued at 300 PM EDT Sat Mar 25 2017

Monday - Tuesday...

Shortwave ridge axis will quickly move over our area on Monday,
between a pair of upstream and downstream shortwave troughs. We
should be mostly dry on Monday under the brief subsidence, however
forecast soundings continue to show plenty of destabilization ahead
of the upstream trough. Will keep low chances of a shower or storm
in through the day, with increasing chances that evening and night
as the better forcing/steeper lapse rates arrive. Given the look of
thermodynamic profiles Monday evening, a few stronger storms are
possible given what appears to be enough deep layer shear for some
organization. Biggest limiting factor will be arrival of best
forcing past peak heating, which is why the SPC Slight Risk is
placed to our west.

A weak surface low will accompany the upper shortwave mentioned
above, and should pass up the Ohio River Valley Tuesday morning into
the afternoon. Will keep chances for showers and storms going later
Monday night into Tuesday ahead of this feature, albeit with
decreasing coverage as deep moisture is lost.

After Monday highs in the low to mid 70s, Tuesday will be a bit
cooler in the upper 60s to around 70.

Tuesday Night - Wednesday Night...

A little bit of uncertainty accompanies the mid week forecast as
shortwave ridging quickly builds and and may stall the weak frontal
boundary progression. The bulk of the data suggests that it may
linger close enough to our region to keep some small chances for a
shower or storm in the forecast on Wednesday. If this occurs, it
would only be slight chances and mainly diurnally driven. Overall,
the bigger story will be that most places stay dry with highs in the
upper 60s to low 70s on Wednesday. Tuesday and Wednesday night lows
should hang around the upper 40s to low 50s.

Thursday - Saturday...

Models generally agree that a series of closed lows will then parade
across our region into the weekend. The agreement is general however
as specific strength, placement, and timing are all in question.
Therefore, will keep the forecast general with chances for
precipitation each day and temperatures running just above normal
and mostly in the mid and upper 60s. The exception will be Thursday
where upper 60s and low 70s are possible.

Will note that recent Hovmoller Diagram analysis shows a parade of
signal crossings for the last week of March, which adds confidence
to the model solutions that this will be a fairly wet stretch of
weather. The analysis also indicates a quieter upper pattern (with
respect to anomaly crossings) as we enter the early to mid April
time frame.


.Aviation...(00z TAF Update)
Issued at 700 PM EDT Sat Mar 25 2017

Initial line of showers with a few embedded thunderstorms will cross
through SDF and LEX area between 00z and 03z. Behind it, expect
vicinity showers for a few hours before more showers and perhaps a t-
storm develop across TN and lift northward. Highest coverage of
showers should be between 06-13z. Not a lot of instability during
this time, so expecting mainly showers though can`t rule out
isolated thunder at the TAF sites. Expect a southwest to northeast
clearing line Sunday morning as southwest winds become gusty late in
the morning.

Ceilings will stay mostly VFR through the period with drops into
MVFR range possible overnight through 13-15z. Not a lot of low-level
saturation expected but intermittent drops between 2-3 kft are
possible. Vsbys should stay VFR outside of any heavier shower.




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