Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 260432
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1132 PM CDT Sat Mar 25 2017

.UPDATE...
Issued at 1131 PM CDT Sat Mar 25 2017

Weak low pressure tracking into southern Iowa has enhanced sfc
moisture convergence enough on the north/northwest side of the low
to create areas of dense fog. With slow movement through 15z
Sunday morning...expecting the fog to track near the low and
slightly north overnight. Have issued a Dense Fog Advisory for a
small portion of southeast/eastern Iowa. Other areas will see
patchy to areas of fog...but generally remain in the 1 to 2 mile
range overnight. Light rain/drizzle is also moving into the
southeast as well...per earlier forecast. /rev

&&

.SHORT TERM.../Tonight through Sunday/
Issued at 347 PM CDT Sat Mar 25 2017

The primary concern through the period will be precip trends. The
parent upper low and its attendant short waves/PV anomalies
continues to slowly advance through MO this afternoon and should
only reach the IL/WI border by 18z Sunday. Our current deformation
zone precip band should continue to slowly deteriorate into Sunday
morning but not go away completely with precip just becoming more
spotty as forcing becomes neutral to subsident as sufficiently deep
moisture is less and less prevalent. Soundings suggest our moisture
depth should stay in the 1-3km depth so patchy light rain or drizzle
should be more common than steadier rain with persistent stratus in
the broad cyclonic flow. The only exception to this may be SE this
evening were weak convection is possible near the core of the upper
low. Have mentioned some fog potential too as the latest ESRL HRRR,
HRRR and RAP runs are all quite bullish. Do not expect anything
dense however due to the steady blanket of stratus.

The precip will likely end by Sunday afternoon however as the
moisture layer shrinks due to mixing from below and drier air above.
Temperatures should fall no more than several degrees tonight with
little rebound Sunday either, especially north. SE sections may mix
sufficiently to get well into the 50s however.

.LONG TERM.../Sunday night through Saturday/
Issued at 347 PM CDT Sat Mar 25 2017

Monday...
20z Sat water vapor imagery clearly picking up on an upper low
spinning near the four corners region of the SW CONUS. Now
approaching 48 hours out, models have finally begun to come into
agreement with one another...more or less beginning to cluster
around the ECMWF (southern) track for the track of this low and
the sfc reflection. Sfc low now slated to track through southern
Missouri towards Kentucky. Subsequently, best forcing looks to be
in Missouri, with a narrow ribbon of frontogenetical forcing near
900mb to 800mb barely clipping the 2 southernmost tier of counties
in the DMX CWA. KOTM Bufkit soundings show pocket of dry air
around 800mb to 650mb that will make notable precip growth
difficult. Thus have kept QPF less than 0.05 inches, which even be
too high yet.

Tuesday and Wednesday...
Sfc high pressure looks to fill in behind the Monday system.
Models in good agreement with placing the high near the
Minnesota/Canada border by 12z Tue, and by Lake Superior by 00z
Wed. Aloft, zonal flow should remain in place, accompanied by a
jet streak across Minnesota to Michigan, which should keep us
under upper to mid-level cloud cover. Though strength of
insolation not superb this time of year, depending on thickness of
clouds, temps may need to be knocked down a few degrees.

Thursday and beyond...
Models continue wild variation with tracking of the next system.
Most long-range models and ensembles now pick up on upper level
low swinging through the TX/OK panhandle around 00z Thu. Tracing
this low back to its source region, the low is picked up on water
vapor imagery, and it should come onshore around 12z Monday. So,
tonight`s 00z runs may not vary much...but hopefully the 12z Sun
and 00z Mon runs should begin to have better resolution with the
track of this system. 12z Sat long-range solutions holding
firm/stubborn with their 12z Fri solutions. 12z Sat GEM has
joined the ECMWF with the northern solution. In short, the 12z GFS
places the sfc low over the southeastern CONUS at 12z Fri, the
12z Sat ECMWF places the sfc low over central Illinois, and the
12z Sat GEM actually places the low over southern Iowa. Regardless
of location, warm sector side of low should be able to tap into
gulf moisture...and support may be there for strong/severe storms.

&&

.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1131 PM CDT Sat Mar 25 2017

Main concern will be LIFR cigs and fog over the region through the
overnight...with dense fog expected at KOTM through 14z. Over the
remainder of the area 2-5sm br conditions can be expected with a
few hours of 1-2sm. Cigs will be slow to lift back to MVFR and may
not last long once they do come up aft 20-22z. With weak flow
aloft and approaching low from west...weak high sandwiched in
between systems there will be little chance of much improvement
prior to sunset and the remainder of the period. Light showers or
-DZ may also accompany the weak low as it tracks north through 15z
 Sunday.  /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CDT Sunday for IAZ061-062-074-075-
084>086-095>097.

&&

$$

UPDATE...REV
SHORT TERM...Small
LONG TERM...Kotenberg
AVIATION...REV


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