Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 191124

Area Forecast Discussion
National Weather Service Des Moines IA
624 AM CDT Mon Jun 19 2017

.SHORT TERM.../Today through Tonight/
Issued at 320 AM CDT Mon Jun 19 2017

Confidence: Medium to High

Overall...forecast on track with a few wrinkles dropping confidence
a touch...mainly for timing and placement of any afternoon showers
and thunderstorms. Trough/cool front moving into southeast Iowa now
with secondary surface trough/front with an associated upper level
H850 wave/trough moving into Central Minnesota at 06z. Looking at
water vapor this morning shows numerous rather small scale clusters
of vorticity in the northwest flow...all digging toward Iowa. Each
little ripple may initiate some showers or isolated thunderstorms
late this morning and afternoon with timing and placement somewhat
uncertain.  The better chances for any precipitation today will be
over the northeast half of the forecast area and have trimmed max
PoP to about 35 percent mainly due to some uncertainty of overall
areal coverage. Once this wave drops southeast of the area this
evening...generally dry until 12z Tuesday when the models suggest
another weak upper/sfc boundary will just brush the far north at
that time. Today highs will be similar to Sunday with mid 70s over
the north to the lower 80s in the south. Forecast soundings and
model CAPE suggest roughly 400-800 j/kg MUCAPE this afternoon. Again
today soundings are fairly dry in the lower levels so there will
once again be a chance for either small hail and some wind gusts
approaching about 45 to 50 mph if some slightly more robust showers
or isolated thunderstorms develop over the northeast. LCL heights
today are 5000 to 5500 feet with plenty of real estate beneath cloud
base to and accelerate rain cooled air downward in
a few cases. The better mid level moisture should exit toward 00z
with less activity after sunset. Have kept PoP near 0 at that time.
Mixing today will force winds to 20 to 30 mph at times so this
afternoon there will be a rather persistent breeze at times
northeast with 20 to 25 mph winds elsewhere. Lows tonight will dip
into the 50s to near 60 once again to help usher in the first day of
summer...on June 21.

.LONG TERM.../Tuesday through Sunday/
Issued at 320 AM CDT Mon Jun 19 2017

Summary...Temps continue to rise back into mid/upper 80s to near 90
by Wed then cool back into the 70s by Sat and the weekend. After
fairly quiet Tue, active weather/storms quickly return Wed-Sat and
showers may linger into Sun.

Tuesday...Far northeast Iowa may see a few showers as another large
vort max passes through, but should remain just outside the CWA.
Otherwise, largely dry through the day as a weak boundary sags
through the state. However, introduced some low end POPs Tue
afternoon/evening on the idea of just enough focus to spark a storm
or two in a 1000+ J/kg CAPE environment.

Wednesday through Friday...Active period with a pair of
opportunities for strong storms, and the potential for severe. First
of which presents itself Wed afternoon/evening on the heels of the
return of good southerly flow. Good agreement remains in the build
up of strong CAPE values in excess of 3000 J/kg ahead of a weak cold
frontal boundary. While effective shear remains borderline to
lackluster, threat for severe hail and winds in a steep lapse rate
environment will certainly exist. That frontal boundary will slowly
sag south through Iowa and will act as a focus once again Thur for
storms. Convective environment not quite as impressive, but should
once again provide at least a limited threat for severe hail and
winds. On Fri sizable shortwave moving off the Rockies looks to only
clip southern Iowa, primarily leaving the area quiet and a bit
cooler than previous couple of days.

Saturday and onward...Active to start, but for different reasons
than earlier in the week. Zonal flow to be replaced Sat by trough
pivoting in and through the region. Some disagreement in timing and
ultimate magnitude with Euro much more aggressive on precip Sat
depicting a large MCS moving through, while GFS keeps much of the
energy north of the state and Canadian remaining more zonal but wet.
Implications of a Euro solution obviously greater than GFS/Canadian,
but need to see consistency in Euro on that solution before trending
heavily that way. High temps either way will drop back into the 70s
Sat and into early next week.


.AVIATION.../For the 12Z TAFS through 12Z Tuesday morning/
Issued at 624 AM CDT Mon Jun 19 2017

Main concerns today will be mixing daytime winds aft 15z to 00z and
isolated/scattered thunderstorms. Cyclonic flow continues from the
northwest with several embedded short waves tracking southeast by
12z Tuesday. Upstream front/upper wave should increase convective
activity aft 19z through 01z this evening. Best coverage northeast
nearer KMCW and KALO possibly southeast to KOTM. Lesser chance at
KFOD and KDSM. Low confidence on areal coverage and somewhat on
placement today. With dry low levels...may see a few higher wind
gusts near storms and very small hail. Otherwise VFR conditions
expected with lighter winds aft 00z with no significant wx. /rev




LONG TERM...Curtis
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