Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 260810

Area Forecast Discussion
National Weather Service Des Moines IA
310 AM CDT Tue Jul 26 2016

.SHORT TERM.../Today/
Issued at 308 AM CDT Tue Jul 26 2016

After patchy morning fog with a few pockets of dense fog
possible...there will be few concerns for todays forecast. High
pressure will move across the area today with light winds
throughout the day. Temperatures at H850 will warm by late
afternoon with the warmer readings west and northwest. By late
afternoon H850 readings will warm to 16C east and 20C northwest.
Other than a few clouds moving over the north and northwest...the
balance of the day will be sunny.

.LONG TERM.../Tonight through Monday/
Issued at 308 AM CDT Tue Jul 26 2016

Main concerns during the long term period include pcpn/tsra
chances and timing from Wednesday into Friday in conjunction with
a storm system to impact the CWA during that well as
from the weekend into the early part of next week.

Return flow on the back side of the departing surface high
pressure will already be in gear by the beginning of the long term
period. Models show 850-700mb theta-e advection persisting into
Wednesday as a warm front lifts across the CWA. An MCS that is
expected to develop tonight over the northern Plains will be
approaching the northwestern CWA...and decaying by Wednesday

The Wednesday into Friday storm system is being forecast with
lower than normal confidence due to divergence in model solutions.
ECMWF continues to advertise a relatively slow and abnormally
strong storm system for this time of year...while the GFS is the
opposite in its relatively fast and weaker system.

On Wednesday...thunderstorm chances will increase in the
afternoon with daytime heating and destabilization of the warm
sector. At the same time...a southward moving cold front will
help provide the focus for afternoon/evening thunderstorms. Per
SPC Day 2 outlook...marginal risk of severe weather exists across
the western half of the CWA. Best 0-6km bulk shear remains west of
the CWA. Even so...0-6km shear and instability will be sufficient
for severe weather in the CWA mainly western half. Looks to be a
relatively narrow temporal window for severe potential from late
Wednesday afternoon into early evening...with continued thunder
chances into the night as the front slides through the CWA. H5
shortwave will help develop a closed low along the frontal
boundary and lift it northeast from northern MO into the lower
Great Lakes by Thursday night. Precip chances continue into this
time across the CWA as ample moisture and ascent exist.
Temperatures will cool off slightly behind the departing storm
system due to combination of CAA and cloud cover. Highs only in
the middle 70s to lower 80s are expected on Friday.

System departs the CWA on Friday. Have timed POPs to show this
trend. Weekend brings renewed SHRA/TSRA chances as CWA is in a
broad trof with enough moisture for pcpn chances. Warm front again
attempts to lift northeast across the CWA late in the weekend.
Heat attempts to return to the CWA from early into the middle
parts of next week with highs in the middle 80s to lower 90s
expected by Tuesday. Have kept POPs across the northern CWA during
this time due to its proximity to the northern U.S. westerlies and
a shortwave advancing through the flow.


.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1204 AM CDT Tue Jul 26 2016

Confidence has increased somewhat in radiation fog development
with temp/dewpoint spreads now dropping to a few degrees at 05z
with nearly calm wind and clear skies. Thus have added a few hours
of MVFR fog outside of KDSM which will likely be warmer due to
heat island effects. Otherwise there is a high confidence in
mostly clear skies/VFR conditions through the daylight hours




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