Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 261928

Area Forecast Discussion
National Weather Service Louisville KY
328 PM EDT Wed Jul 26 2017

.Short Term...(This evening through Thursday night)
Issued at 310 PM EDT Wed Jul 26 2017

Afternoon satellite imagery showed partly to mostly sunny skies
across the region.  Temperatures ranged from the middle 80s across
the Bluegrass region to the lower 80s across the I-65 corridor and
into western KY.  Higher dewpoints have pushed back northeastward
across the region.  Dewpoints were well into the mid 70s out across
western KY with lower 70 dewpoints confined to areas along and west
of the US 27/127 corridor.  A few isolated thunderstorms were
rumbling across our western areas.  These should continue through
the afternoon hours, with the best chances remaining along and west
of the I-65 corridor.  Afternoon highs should be met in the next
hour or two, with readings falling into the 80s this evening.

For tonight, a surface low pressure and attendant surface frontal
boundary will continue to move eastward and approach the Ohio Valley
from the west/northwest.  Latest guidance suggests and uptick in
convection out across MO later this afternoon and tonight with the
convective activity moving eastward toward our area.  We`ll see an
increase in cloud cover with storm chances picking up after midnight
as convection moves in from the west. We`ll solidly be in the warm
sector overnight and lows will only fall into the 70-75 degree range
in most areas.

For Thursday, convection is likely to be ongoing at the start of the
period across southern Indiana and portions of north central
Kentucky.  This activity should be weakening a bit as it moves
through the region.  However, the front will remain to our west and
we`ll continue to see moisture pool out ahead of the front.
Numerical guidance suggests a high plume of moisture residing across
the region on Thursday, characterized by dewpoints in the low-mid
70s and PWAT values possibly approaching record levels for upper air
soundings at KBNA and KILN.  Convective evolution is rather
challenging due to combination of poor lapse rates indicated by
model proximity soundings, plentiful cloud cover, and rather meager
lapse rates.  There is some indication that some boundary layer
heating may commence across southern KY which would result in decent
instability and perhaps the shot at seeing some strong to severe
convection.  Previous day two outlook had us in a slight and has
since been downgraded and based on the latest guidance and lack of
confidence, we do not see an issue with that.  We could see some
isolated strong/severe storms across portions of the area on
Thursday.  However, given the rich plume of moisture and high PWAT
values, it appears that our hazardous weather will likely be
confined to torrential rainfall and localized flooding issues.

In terms of QPF, run to run model consistency with respect to the
axises of QPF have been rather poor.  Initial early morning data had
the higher QPF axis to the north of the region, but majority of the
12Z data has trended a bit more south.  Widespread basin amounts of
1-2 inches look reasonable from late tonight through Thursday night.
Some isolated amounts of 2-4 inches will be possible in localized
areas.  Latest guidance suggests the heaviest QPF will fall over
areas that have been dry of late (Western/SW KY) where FFG values
are rather high.  For this reason, we collaborated with surrounding
offices and will hold off on any headlines.  This is due to the
expected very localized nature of flash flooding (not widespread
occurrences) and that expected QPF swath will affect areas that have
been drier over the last week or two.  However, we will highlight
the potential for local hydrologic issues in an SPS, our weather
story graphics, and the Hazardous Weather Outlook.

Showers and thunderstorms will continue into Thursday night with the
bulk of the action affecting mainly southern KY and into northern
Tennessee as the area of surface low pressure races eastward and the
associated surface frontal boundary settles southward.  Highs
Thursday will likely exhibit a gradient with lower 80s across
southern IN and northern KY, with mid-upper 80s down along the KY/TN
border region.  Lows Thursday night will remain mild with readings
mainly in the lower 70s.


.Long Term...(Friday through Wednesday)
Issued at 326 PM EDT Wed Jul 26 2017

As we get into the extended period, Friday looks to be a day of
transition from the heat/humidity to one of a drier/less humid
weather for the Ohio Valley.  Some post frontal cloud cover and
shower activity will be possible on Friday with drier conditions
emerging by the afternoon.  Highs Friday will range from the upper
70s to around 80 across southern IN/northern KY to the lower 80s
across southern KY.  The front edge of the drier air will move into
the region Friday night with lows dropping into the upper 50s to the
lower 60s.

High pressure will then build into the region for the weekend
resulting in a rather beautiful weekend with plentiful sunshine and
cool nights.  Highs on Saturday will range from the upper 70s to the
very low 80s, with overnight lows in the mid-upper 50s.  Similar
readings are expected on Sunday with highs in the upper 70s to the
lower 80s, with lows in the lower 60s.

Dry weather looks to continue into early next week.  The models are
still struggling with the overall pattern and while temperatures and
humidity will likely moderate somewhat, some diurnally driven
convection will be possible by Tuesday and Wednesday and afternoons.
High temperatures look to warm back into the mid-upper 80s with
overnight lows in the 60s.


.Aviation...(18Z TAF Issuance)
Issued at 120 PM EDT Wed Jul 26 2017

Isolated afternoon showers and thunderstorms will be possible west
of I-65 and should miss the terminal sites, so expect VFR conditions
through much of tonight. Thursday could feature multiple rounds of
showers and thunderstorms as a strong cold front approaches the
region, but confidence in the timing of showers/storms is low. Best
chance for widespread precipitation looks to be Thursday afternoon
and evening at this time. Any of the heavier showers and
thunderstorms could drop cigs/vis to MVFR/IFR.




Short Term...MJ
Long Term....MJ
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