Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 250444

Area Forecast Discussion
National Weather Service Des Moines IA
1144 PM CDT Sat Jun 24 2017

.SHORT TERM.../Tonight through Sunday/
Issued at 239 PM CDT Sat Jun 24 2017

Main concern this period will be winds...otherwise fairly quiet
conditions will prevail. Upper level trough swinging through the
region this evening with cool front early today over Central
Minnesota will take area of convection along with it to the east.
This boundary is expected to move southeast through the region
this evening resulting in yet another shot of cooler air aloft.
12z H850 analysis shows pocket of 0 to 5C temperatures from
Manitoba southeast into Minnesota with Minneapolis at 3C. Quite
cool compared to last week. After the convection exits the area
this evening expect skies to be mainly clear again for most of
the area with H850 temps cooling to about 3C over the north to
near 8C across the south. By 12z the surface boundary will make it
south into northern Missouri. Another approaching short wave
dropping southeast through the stronger parent H500 wave over the
Great Lakes may spread some stratus into northern Iowa toward
morning. Along with that some passing showers are possible over
the far northeast again into Sunday morning. Otherwise soundings
and moisture profiles suggest at least some cloud cover Sunday as
a mid level boundary begins to form on the back side of the
trough. With some clouds...especially over the northeast...high
temperatures Sunday will be cooler than today where afternoon
readings will likely struggle to reach 70 by late day. Winds will
again pick up Sunday after 15z as mixing commences. H850 winds of
20 to 25 kts and adiabatic lapse rates suggest afternoon wind
gusts of about the same magnitude for most of the region. All in
all...a comfortable day considering we are nearing the end of June.

.LONG TERM.../Sunday night through Saturday/
Issued at 239 PM CDT Sat Jun 24 2017

Long term period begins with a large upper level low still in place
over the Great Lakes region, which will deliver another day of below
normal temperatures. Another shortwave will rotate through the
cyclonic flow aloft. Weak isentropic lift in the 305-310k layer
may be enough to spark off some showers during the day, mainly in
western and southern Iowa. Weak MLCAPE of 200-400 J/kg may be
enough to support a few rumbles of thunder in the afternoon. An
area of surface high pressure dropping south out of MN will likely
limit the northern extent of the shower activity.

Pattern begins to shift on Tuesday as the surface high pressure
moves east. Ridging builds aloft in advance of the next upper level
low digging into the northern Rockies. Increasing southerly flow
will advect a warm, humid airmass back into much of the central and
northern Plains. A shortwave ejects into the northern Plains
Tuesday night and pushes a cold front into the CWA. The cold front
stalls out over Iowa on Wednesday as the shortwave advances east
and zonal flow becomes established aloft. Given the persistent
moist southerly low level flow into the area, periodic episodes of
showers and thunderstorms are likely within the vicinity of the
front. Severe weather will be possible, however the extent of
threat will be highly depend on the timing of convection and the
impact that will have on available instability. Another concern
will be the threat for heavy rainfall as model consensus continues
to paint 2-3+" of QPF over much of the area during the Wednesday-
Friday timeframe. Models diverge on their evolution of the upper
level pattern by the weekend, which lowers confidence in
precipitation chances toward the end of the forecast period.


.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1144 PM CDT Sat Jun 24 2017

Mostly clear skies and light winds expected overnight, with some
VFR ceilings possible across northern Iowa toward sunrise Sunday.
There is a small chance that MVFR ceilings could affect MCW for a
time, but probability is too low to include in the TAFs. During
the day Sunday northwest winds will pick up again, then diminish
again with sunset. Showers/thunderstorms may be possible at
MCW/FOD right at the end of the 06Z TAF period, but this will be
assessed for subsequent TAF issuances.





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