Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 260515
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
115 AM EDT Sun Mar 26 2017

...Updated Aviation Discussion...

...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
50s.

.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 (06Z TAF Update)...
Issued at 105 AM EDT Sun Mar 26 2017

Main challenge is the impact of the precip shield streaming
northward into central Kentucky. Vis is mainly VFR with precip
falling from a mid-level deck in most locations, and aside from a
lone fuel-alternate ceiling in Middle Tennessee, not much in the
upstream obs to suggest anything worse than MVFR vis and ceilings
remaining just barely in the VFR category around 4000 feet. NAM MOS
guidance seems to be way too pessimistic on ceilings, so have sided
with GFS LAMP and other hi-res data.

Will carry prevailing rain through the night, but instability is
lacking, so thunder seems too low a probability for any of the TAF
sites. Expect flight categories to remain high-end MVFR, perhaps
even VFR. Can`t rule out a brief dip into fuel-alternate at BWG but
confidence is too low.

Upper trof axis pushes to our east around daybreak, but low-level
moisture and cold pool aloft will keep a stratus ceiling in place.
Believe it will drop into MVFR for much of the morning, but should
stay above fuel-alternate thresholds. Lingering precip chances will
be enough to support VCSH, but still not at all bullish on thunder.
By late morning/midday expect mixing to deepen enough to lift
ceilings to VFR and kick winds up out of the SW with 20-25 kt gusts
at times. Toward sunset, expect winds to diminish. Clouds should
lift into a mid-level ceiling before dissipating late in the
evening.

&&

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

$$

Update.........ZT
Short Term.....BJS
Long Term......BJS
Aviation.......RAS



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