Area Forecast Discussion
Issued by NWS Nashville, TN

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FXUS64 KOHX 202022
AFDOHX

Area Forecast Discussion
National Weather Service Nashville TN
322 PM CDT Thu Jul 20 2017

.DISCUSSION...

Will break discussion into two parts...convection chances and then the
heat.

Atmosphere will be capped over the next 2 days as mid level temps
too warm to support any appreciable cape to cap ratios. Late day,
00z subsidence is indicated today but not so much tomorrow. Could
see a few afternoon short lived tstms but areal coverage will be too
low to support a 20 pop.

As is largely the case this time of year, the upper level high and
its orientation and strength will be the governing factor for our
upcoming weather. When combining proximity with strength, the
influence of the upper high will peak on Friday afternoon. By
Saturday, suppression will commence and this will allow a frontal
boundary to sag our way this weekend. This will evoke a return of
shower and tstm chances beginning on Saturday and continuing
through Monday as the slow to weaken boundary hangs up.

By Tuesday, models lean toward and increase in the domination of a
sfc high to our north with w-e upper ridging returning. Will
therefore lean toward a marked decrease in pops with just 20 percent
at times, Tues through Thursday.

Now for the heat, as mentioned previously, the upper ridge
influence will reach its maximum on Friday afternoon. 850 mb temps
could approach 21c- 22c by then so I will opt for upper 90s for
highs for many areas west of Plateau. 925mb-850mb moisture is not
overly dominant and therefore, dewpoints in the afternoon should
hold in the lower 70s. This will lead to max heat index values of
near 105 for many areas west of Plateau. Will expand heat advisory
a little further eastward with the advisory remaining in effect
through Friday afternoon.

Any break from the heat?...not until Sunday. On Saturday, rain
chances will begin to increase but still more sun than clouds early
on. Highs will reach the mid 90s with dewpoints perhaps inching up a
degree or so. Will opt to delay the advisory expansion into
Saturday. But an extension may be needed soon.

On Sunday, heights will be lower with greater cloud coverage and
pops. Max aft Heat index values will be between 95-100 at that
point.

The great news, Tuesday through Thursday will feature high temps of
upper 80s to near 90 with dewpoints in the upper 60s to near 70.
Thats much more in the way of seasonal and certainly easier to
take.

&&

.AVIATION...
18Z TAF DISCUSSION.

Mainly VFR conditions this TAF cycle. The only issue might be some
overnight fog at KCKV and KCSV. Low level moisture and light to
calm winds could exacerbate the lowered visibility. Only going to
carry MVFR for now, but this might need to be dropped a little
more with subsequent TAF issuances.

Winds will be light to calm overnight and light and westerly
Friday.


&&

.PRELIMINARY POINT TEMPS/POPS...
Nashville      75  97  76  95  76 /   0  10  10  30  20
Clarksville    73  95  75  94  74 /   0  10   0  20  20
Crossville     71  90  72  89  72 /   0  10  20  30  20
Columbia       73  95  74  93  75 /   0  10  10  30  20
Lawrenceburg   73  96  74  93  74 /   0  10  10  30  20
Waverly        73  95  74  93  74 /   0  10  10  30  20

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon to 7 PM CDT Friday FOR Bedford-Macon-
Marshall-Robertson-Rutherford-Smith-Sumner-Trousdale-Wilson.

Heat Advisory until 7 PM CDT Friday FOR Cheatham-Davidson-
Dickson-Giles-Hickman-Houston-Humphreys-Lawrence-Lewis-Maury-
Montgomery-Perry-Stewart-Wayne-Williamson.

&&

$$

DISCUSSION......21
AVIATION........Unger



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