Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 251756

Area Forecast Discussion
National Weather Service Des Moines IA
1256 PM CDT Sun Jun 25 2017

.SHORT TERM.../Today through Tonight/
Issued at 326 AM CDT Sun Jun 25 2017

Aloft a large upper low will shift from Wisconsin into Michigan by
tonight. this will keep the Upper Midwest in a general northwest
flow aloft. A couple of shortwaves will impact Iowa. The first one
come across today but it is very weak and the forcing with this
will be mainly over MN and WI...possibly brushing northeast IA. In
addition, moisture is lacking and instability is weak. As a
result, I only expect a scattered to broken deck of clouds around
5Kft...mainly across the northeast and east this afternoon.
Soundings show pretty good mixing today and with winds in this
mixed layer around 20 kts it should be breezy today and diminish
by evening.

Tonight a second shortwave come across the state.  This second wave
isn`t much stronger than the first wave but the forcing with the
wave come right across our forecast area and soundings do show a
touch more moisture with this shortwave, though still not great.
MUCAPE`s around 350 to 500 J/Kg are not impressive by any stretch
but it may be enough to produce a rumble or two of thunder as the
wave passes...particularly in the 09Z to 12Z time frame and .
primarily across the western CWA.  Should be a fair amount of mid
level cloud cover with this wave so I will bump sky cover up across
the west especially for the overnight hours.

.LONG TERM.../Monday through Saturday/
Issued at 326 AM CDT Sun Jun 25 2017

PV anomaly and attendant cold front will be moving into central
Iowa by 12z Monday morning. A few showers and possibly an isolated
thunderstorm will be moving through central and southern Iowa
early. The boundary should refire during the afternoon over far
southern Iowa and into northern Missouri. Subsidence in the wake
of the PV anomaly and the arrival of surface high pressure will
dry the atmosphere out and bring light winds to the state. This
will allow temperatures to drop into the mid to upper 40s over
over portions of the area by Tuesday morning.

Tuesday will be dry though strong theta-e advection will be
developing over western Iowa by mid to late afternoon as return
flow arrives on the backside of the departing high. The return
flow will coincide with a transition to a more active zonal flow
that will have several short wave fragments moving through the
flow this week. Strong deep layer moisture transport develops
Tuesday night into Wednesday. This will push PWAT values over 1.5
inches and could reach localized 2 inches by Wednesday morning.
The increasing moisture and instability will bring thunderstorm
chances back to the area with a potential MCS arriving from the
west. Storms likely will redevelop during the afternoon along a
boundary entering the state though will be dependent on if the
atmosphere can recover after the morning storms.

The boundary will linger through the area into Thursday
though the boundary is trending farther south. Warm advection
ahead of the next approaching boundary should be enough to keep
the boundary in the vicinity through early Friday before a short
wave lobe rotating around the large Canadian upper low rotates
south into the Northern Plains and pushes the system to the east.
PWAT values will remain consistently at or above 1.5 inches
through Thursday followed by a brief reprieve then returning back
to the 1.5 to 2 inch range next weekend. In addition to a few
severe storms, the atmosphere will be conducive to the potential
for heavy rainfall. Temperatures will rebound this week,
especially Wednesday and Thursday. Much more humid conditions will
arrive as well with dew points reaching the upper 60s to low 70s.


.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1256 PM CDT Sun Jun 25 2017

Main concerns will be winds this afternoon and approaching short
wave/front overnight into Monday. Upstream wave expected to increase
shower activity aft 02z northwest and translate southeast through
12z. Cigs should remain VFR despite the potential for light rain.
By late in the period...toward 18z and beyond instability will
increase into the afternoon though by then most of the forcing
will be in southern Iowa. /rev




LONG TERM...Donavon
AVIATION...REV is the U.S. government's official web portal to all federal, state and local government web resources and services.