Area Forecast Discussion
Issued by NWS Des Moines, IA

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107
FXUS63 KDMX 280355
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1055 PM CDT Sat Aug 27 2016

.SHORT TERM.../Tonight/
Issued at 316 PM CDT Sat Aug 27 2016

Several concerns overnight.  Weak frontal boundary and low pressure
expected to drift across the area in the next 24 hours. Lower clouds
have been slow to respond to any heating due to the proximity of the
surface boundary...weak convergence and lift and continued slow
erosion of the lower clouds on the edges of the earlier widespread
low stratus and fog. Likely to see some limited sun after 21z this
afternoon as some improvement occurs. Models continue at odds
tonight with regard to any redevelopment of showers and
thunderstorms along the lingering boundary. Certainly enough surface
moisture to promote some additional showers and patchy to dense fog
by 09-12z Sunday but upper level forcing will be lacking overnight
once the current shortwave departs the region. Due to the weak
synoptic features...there is not much confidence as to where the
weak surface boundary will by 12z Sunday but models are suggesting
that it will be slightly displaced south into Missouri. This would
keep better...if any...chances for showers/isolated thunderstorms
over the far southeast. ESRL HRRR/ARW/NMM WRF and most of the
synoptic models void of much precipitation overnight across the
forecast area. Feeling is that the current 12z GFS is way overdone
in the southeast and will lean away from any consideration for
current forecast. Despite any shift in boundary placement overnight
patchy fog is again likely with pockets of dense fog toward morning.
Most likely will be covered with an special weather statement as
needed unless it expands and thickens earlier than midnight. Lower
stratus will likely reform again toward morning even if we break the
deck late this afternoon. Minimums tonight will be a bit warmer than
last night in the central and south and should range from the lower
60s north to the mid to upper 60s in the south.  Winds again will be
light/variable or from the southeast during the overnight.

.LONG TERM.../Sunday through Saturday/
Issued at 316 PM CDT Sat Aug 27 2016

Overview...No concerns over large, substantial systems moving
through. Rather, concerns remain over confidence in and coverage of
POPs through Tuesday. Temperatures remain on track in the low to mid
80s through Tuesday before cold front drops highs back into upper
70s.

Tonight through Tuesday...Plenty of uncertainty remains within this
time frame regarding coverage of showers/storms. A weak boundary,
currently situated over southern Iowa, will continue to hover in the
region, providing opportunities for at least some focusing and storm
development. MUCAPE values around and in excess of 2000 J/kg will
provide plenty of energy should enough lift be realized. Void of
larger scale support, coverage will depend greatly on what can
develop and how outflows then interact with the weak boundary and
each other. With regards to any severe potential winds appear most
likely if any occur, as storms should remain elevated in nature
within an environment void of supportive shear, relatively warm low
levels, and weak lapse rates. Otherwise, shortwaves riding along the
zonal flow look to remain primarily to the north of the state.

Wednesday through Saturday...Upper level flow will transition
northwesterly, while also ushering in surface high pressure and a
cool/cold front. Temperatures will cool back into the upper 70s for
highs and mid 50s to low 60s for lows. A bit of uncertainty remains
with how far west the surface high pressure will be able to
influence and keep things dry, however models continue to trend
drier, and remains reflected overall in forecast. Northwesterly
flow/ridging then quickly breaks down into the weekend, with
increasing possibility of showers/storms. However, models begin to
differ widely with EURO primarily returning to a zonal pattern and
GFS sweeping a trough along the US/Canada border and surface cold
front through the state.

&&

.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1052 PM CDT Sat Aug 27 2016

Fog development is expected across the area tonight with good
radiational cooling and ample low level moisture. Anticipate
widespread MVFR to IFR conditions during the early morning hours
until mid morning when the fog burns off. Will see VFR conditions
by midday tomorrow through the end of the forecast period. Surface
winds will be light and variable overnight becoming light from the
southeast on Sunday.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

SHORT TERM...REV
LONG TERM...Curtis
AVIATION...Cogil



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