Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 181739
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1239 PM CDT THU AUG 18 2016

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 355 AM CDT Thu Aug 18 2016

At 3 AM CDT...a few lingering storms that developed in the evening
are moving east leaving mostly clear skies and light winds. Patchy
fog has developed in central Iowa with temperatures mostly in the
upper 60s to lower 70s. Upstream analysis shows limited forcing
for convection with possibly isolated in late PM hours once again
late today as convective temperature is reached.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 355 AM CDT Thu Aug 18 2016

Short Term Forecast Confidence Assessment...Good or above average. Main
issue is isolated storms that may develop in our moist airmass. Most
likely scenario is some popcorn type storms late PM into mid to late
evening hours after convective temperature is reached due to no significant
forcing mechanism. Temperatures for highs and lows should be within
3 degrees of forecast.

Today...very warm to hot under partly to mostly sunny skies with light
south to southeast winds. Low level thermal fields are slightly warmer
supporting highs of 85 to 90 degrees across the region with dewpoints
upper 60s to around 70F. This would allow for heat indices into the
middle to upper 90s for several hours.

Drier air aloft with MUCAPE AOA 2500 J/KG would allow for some risk
of hail AOA 1 inch and strong winds over 60 MPH that will need to be
monitored if conditions change. Probability considered low to very low
but due to environment...an issue to pass to day shift.

Tonight...partly to mostly clear with once again possibly isolated storms
in the early to mid evening hours. Lows 65 to 70 degrees with risk again
of patchy fog in the overnight hours but not quite as prevalent as tonight
due to slightly higher winds of 3 to 6 MPH.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 355 AM CDT Thu Aug 18 2016

Friday...Southerly sfc flow will organize ahead of a respectable
trough developing over the Northern Plains continuing the very warm
and humid weather. An elevated mixed layer, characterized by high
850mb temps in the mid to upper 20s Celsius over the Central Plains,
forecast to settle into E Iowa/NW Illinois but modify with time.
Similar to Thursday, we are looking at mid to upper 80s for highs
(850mb temps near 20 C). Otherwise, low chance for isolated air mass
showers and storms during the aftn/evening with most areas staying
dry.

Friday Night into Saturday...

The trough is forecast to deepen into Friday night, taking on a
negative tilt. Substantial 500mb height falls of ~6 mb/12hr are
forecast. Moderate 850mb WV transport and ongoing convection moving
into an unstable environment is supportive of a good chance for
storms. Have 60-80% POPs in the counties along and west of the
Mississippi through early Saturday morning, highest over the west.

Model variability: Models vary on the track and strength of the
low which affects the timing of the cold front and best chances
for storms. The NAM is the outlier forming a compact, fall-like,
sfc and 850mb low that takes a NW track through NE Iowa into
Central Wisconsin. This scenario would favor better chances for
severe storms, given the stronger dynamics and shear, and could
even result in storm redevelopment along the cold front late
morning/early aftn on Saturday. The GFS/ECMWF/GEM are not as
robust with the cyclogenesis - suggesting that an elongated low is
the more likely scenario.

Storm threats: Deep layer shear is low Friday night, increases into
Saturday morning slightly, and even more by Saturday aftn.
Instability is in the low to moderate range and will depend on many
factors. Appears main severe threat is sct strong wind gusts...it is
too early to make much more of an assessment for now. High PWATs of
1.75-2.00 inches are conducive for heavy rainfall rates with any
storms that occur Friday night through Saturday.

To summarize, potential exists for severe thunderstorms across the
outlook area Friday evening into Saturday morning, possibly a
secondary round during the late morning into the aftn for parts of
the CWA, that is if the NAM solution is correct. SPC has a slight
risk across the western third of the forecast area Friday evening
into early Saturday morning with a marginal risk to the east. Stay
tuned to updates as this weather situation unfolds over the next few
days.

Sunday and Monday...Cooler and drier post-frontal air mass to advect
into the Midwest. Lower humidity will be noticeable and feel like a
brief taste of early fall. 850mb temps bottoming out in the 8-10 C
range should yield highs in the 70s/lows in the 50s. Favored cold
spots may reach the upper 40s Sunday night.

Tuesday through Thursday...Significant 500mb height rises move in
behind departing deep trough axis. Sfc temps will warm to near 80 F.
Renewed 850mb WV transport and instability are the reason for the
shower and storm chances Wednesday into Thursday. Uttech

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1238 PM CDT Thu Aug 18 2016

Mainly VFR conds through this taf cycle. Lcl MVFR conds possible
in patchy fog 09-14z/19. South to southwest winds less than 10 knots
through this period.

&&

.DVN Watches/Warnings/Advisories...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...Nichols
SHORT TERM...Nichols
LONG TERM...Uttech
AVIATION...Haase



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