Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 212031
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
331 PM CDT SAT MAY 21 2016

.SHORT TERM.../Tonight/
Issued at 327 PM CDT Sat May 21 2016

Few if any concerns tonight. Clouds over southwest in response to
warm frontal precip earlier today should advect southeast with time
and exit the region by 02-04z. Meanwhile Great Lakes High will drop
south and gradually warmer air will return. Over the east and valley
areas temperatures will drop to the upper 40s once again while urban
heat island may assist the metro in maintaining lower to mid 50s
overnight. Light winds overnight will assist in radiational cooling
with temperatures dropping quickly between 00 and 03z this evening.

.LONG TERM.../Sunday through Saturday/
Issued at 327 PM CDT Sat May 21 2016

Sunday...
High pressure will remain east of Iowa, placing the state in
WAA/return flow. After 850mb temps around +7C this morning, 850mb
temps will be up to the +12C range Sunday morning. Am expecting a
sunny day with temperatures a solid 5 or so degrees warmer than on
Saturday.

Monday through Thursday...
On the large-scale, longwave trough remains well-established over
the intermountain west. Meanwhile, a fairly amplified trough/cut-
off low will remain spinning over the east coast. Iowa will be
sandwiched between these two features, and with the broad high
pressure propagating towards the Great Lakes Region, southerly to
southwesterly flow will be in place over Iowa for much of this
week. By Monday, the thermal ridge will come crashing down over
the state, keeping max temps in the low to mid 80s.

More importantly, the gulf will open up and moisture will easily be
transported into Iowa by a broad 30kt LLJ. Models initialized
well enough with moisture from source region to feel comfortable
with a consensus blend, bringing dewpoints up into the mid to
upper 60s. Subsequently, peak heating MUCAPE values will have no
struggle in reaching the 1000 to 2000 j/kg range across the DMX
CWA next week..

Moisture and CAPE in place, but lift/focusing mechanisms/triggers
look somewhat nebulous at this point, so am tempering confidence
on significant svr wx outbreaks. For Monday, models try to
generate a pocket of isentropic lift across central Iowa around
peak heating. A band of PVA with good mid-level Q-vector
convergence will slide across the state to support convection.
PWATs are approaching 1.5 inches at this time, so if confidence in
storms increases, may need to significantly bump up QPF.

A series of shortwaves passing through the upper Midwest will keep
the DMX CWA active Tuesday through Thursday. Decent frontogenetical
forcing sets up across western Iowa Tuesday, making western Iowa the
focus for strong to severe storms. As hinted at earlier, models are
suggesting a nebulous boundary somewhere over Iowa Wednesday and
Thursday. With it being 5 plus days out, will not get too deep into
trying to pinpoint svr threat. Both PWATs and 850mb temps remain
around +1 std dev during this time period, so it should remain
stormy, humid, and warm into at least Friday.

&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1232 PM CDT Sat May 21 2016

Few concerns this period. Light winds and VFR conditions to
prevail. By 15z Sunday winds mix to 12-17kts at KMCW otherwise
most sites remain under 12kts. High pressure continues with few if
any clouds. /rev


&&

.DMX Watches/Warnings/Advisories...
None.
&&

$$

SHORT TERM...REV
LONG TERM...Kotenberg
AVIATION...REV



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