IND issues Area Forecast Discussion (AFD) at Jul 11, 3:07 AM EDT377
FXUS63 KIND 110707
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
307 AM EDT Thu Jul 11 2024
.KEY MESSAGES...
- Fog potential through 900 AM...locally dense fog possible
- Shower and thunderstorm chances today through Wednesday; Humid
- Hot on Sunday through Tuesday, nearing Heat Advisory criteria
&&
.SHORT TERM (Today and tonight)...
Issued at 305 AM EDT Thu Jul 11 2024
Near-zero winds under mostly clear skies will combine with damp
ground following recent appreciable rains...to promote ground fog
formation through 12Z this morning. Areas of reduced visibility
are expected, with possibly patchy dense fog...especially south
of a line from Terre Haute to Columbus.
Fog will dissipate, mainly during 700-900 AM, although light and
times variable winds will continue under broad high pressure with a
very weak surface gradient. The remains of this week's central-US
upper trough - a weak H500 short wave drifting east along a
positively-tilted axis from Illinois into the Great Lakes...will
promote increasing chances for convective showers through the midday
and afternoon hours. However, only modest ingredients for any
stronger cells are expected...with any CAPE values over 1000 J/kg
struggling to reach the Wabash Valley, coupled with overall
lackluster mid-level lapse rates and mediocre wind shear. Just the
same expect probably a couple hours in the late afternoon/late day
of scattered showers, focused along/south of the I-74 corridor. Cell
motion would be mainly to the east-southeast...with the potential
for a few collapsing showers producing isolated 40-45 mph gusts. At
times considerable cloudiness should hold readings near to slightly
below normal...with highs expected to range from around 80F over
north-central counties to upper 80s along the US-50 corridor.
Any lingering convection will diminish early this evening as lower
levels cool and instability quickly wanes to near-zero values around
sundown. Past a couple isolated showers lingering into the late
evening, expect fair weather under scattered clouds from the
lingering weak upper trough. Typical mid-July moderate humidity and
light winds will allow a seasonable night with lows in the mid-60s
for most locations, and probably at least patchy fog favored where
any additional organized rainfall occurred.
&&
.LONG TERM (Friday through Wednesday)...
Issued at 305 AM EDT Thu Jul 11 2024
Friday...
The upper pattern on Friday is expected to show strong high pressure
in place over the western CONUS, with NW flow aloft spilling into
Central Indiana from the upper midwest. An upper low is expected to
be over Ontario, pulling northeast through the course of the day.
This will place Indiana within an area of subsidence on Friday.
Within the lower levels broad high pressure begins to set up,
stretching from the deep south across the Ohio Valley to the
southern Great Lakes. Forecast soundings on Friday show attainable
convective temperatures in the lower 80s with near 2000 J/kg of CAPE
available. Some of the CAMS suggest isolated storm coverage on
Friday afternoon, so despite the subsidence, but favorable air mass
in place, some chance pops will be needed. Given the warm and humid
air mass, highs in the upper 80s will be expected.
Saturday Through Tuesday...
Little overall change is expected in the upper pattern during this
time. The strong, persistent area of high pressure will remain over
the western CONUS through the period. This will result in the upper
flow spilling over that ridge, into the northern plains before
spilling into the Great Lakes and Ohio Valley. A few weak embedded
waves within the flow are shown to pass, but none of the features
appear well organized. By Tuesday, the NW upper flow is strengthened
as a deep upper low settles over northern Ontario and Quebec. All
the while this is going on aloft, the previously mentioned area of
high pressure within the lower levels will continue to dominate our
weather as it slowly pushes to the east coast by Sunday. This will
allow for the start of warm air advection on Sunday within the lower
levels on southerly and southwest winds. Thus the already warm air
in place on Friday and Saturday will soar even higher by Sunday and
early next week. This could result in heat index values in the low
100s on Sunday through Tuesday. These values will be nearing heat
advisory criteria. Highs around 90 on Saturday, should reach the
lower 90s by Sunday through Tuesday. Forecast soundings on Saturday
again show attainable convective temperatures with CAPE available.
Thus, chances for afternoon convection will need to be included.
With the warmer air arriving on Sunday within the already very warm
and humid air mass, 700MB temperatures react by surging over 10C. A
weak cap appears in place on the soundings from Sunday-Tuesday. Thus
isolated convection seems possible at this point, but confidence is
less.
Wednesday...
Better chances for rain will be in place on Wednesday. Models
suggest the upper low and associated trough over Ontario will
strengthen and drop a wave and associated surface cold front south
across Indiana. With this upper support and very warm and humid air
mass in place, this appears to be a good set up for showers and
thunderstorms. For now, will include pops and cooler high
temperatures on that day.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 136 AM EDT Thu Jul 11 2024
Impacts:
- Tonight: MVFR or lower VIS in fog expected at all terminals
- Thursday: Scattered PM convection, especially along/south I-70
Discussion:
Isolated showers earlier tonight near KLAF/KHUF has since dissipated
and expect upstream weak convection to not reach any central Indiana
terminals tonight. Otherwise, diminishing winds and mainly clear
skies will combine with recent heavy rainfall to promote fog
formation...with visibility expected to deteriorate to at least MVFR
pre-dawn. TEMPO groups used outside of KIND to express lower
confidence in exact timing and/or duration of any IFR/LIFR VIS.
Fog is expected to mix out around 13Z Thursday morning. The next,
rather weak system should bring isolated to scattered convection
Thursday afternoon. Lower certainty in coverage and timing here as
well so kept mention to only VCSH for time-being...although TRWs are
possible, especially at KHUF/KBMG.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
SHORT TERM...AGM
LONG TERM...Puma
AVIATION...AGM
Source:
IND issues Area Forecast Discussion (AFD) at Jul 11, 3:07 AM EDT---------------
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