Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 212019
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
319 PM CDT Sat Apr 21 2018

.SHORT TERM.../Tonight through Sunday/
Issued at 318 PM CDT Sat Apr 21 2018

Confidence: Medium to High

GOES16 mid level water vapor imagery shows occluded low over the
Central Plains spinning southeast and entraining drier into the
system as it works to the east southeast. Few areas of virga or very
light sprinkles have moved over the region today...but nothing to
alter any outdoor plans. Tonight clouds will continue over most of
the region with some partial clearing possible across the north.
Main concern overnight is the potential for fog across the remaining
snow pack. Dew points have risen into the lower 30s over the north
and with lows approaching those values tonight fog may develop.
Confidence is somewhat limited due to cloud cover potential and
likely will be a shorter term forecast. For now have left out of the
forecast...but will pass concerns along to evening crew. Winds will
diminish a bit after sunset tonight but with sfc low still south of
the area, gradient winds from the east will still force 8 to 10 kt
winds at times overnight. Lows will again be milder south with
overnight readings in the lower 30s north to the lower 40s in the
south.  Sunday will see a decrease in clouds by afternoon as lift
decreases and drier air from the Great Lakes gets entrained into the
system to our south. With stronger late April sunshine highs should
be able to warm into the 60s over a good share of the south while
lower to mid 50s more common across the north.

.LONG TERM.../Sunday night through Saturday/
Issued at 318 PM CDT Sat Apr 21 2018

Confidence:  Medium to High

Overall trends remain for a relatively quiet period.  The lowest
confidence period appears to be Tues/Wed when an approaching wave
tracks just to the west of Iowa by Tuesday.  Model forecasts diverge
abruptly at this time with the GFS moving the system east across
Iowa. However...NAM/Euro/GEM all occlude the low and drive it south
and west of our area keeping us dry during the period. A mean ridge
aloft and current evolution of today`s system suggests that the
three drier/dry models are more correct than the GFS. Cannot totally
discount some light precipitation either late Tuesday or Tuesday
night...but have trimmed back most PoP to slight ranges at this
point and might need to trend lower in coming days. The one greater
certainty will be temperatures. There is no Arctic air in sight or
projected to move across Iowa during the period...and at worst
Thursday H850 temperatures might briefing dip below 0C for a 12 to
24 hour period. Other than that we should be varying between the
lower single digits above zero to the upper single digits above zero
at H850 through Saturday. This bodes well for continued milder
temperatures with highs generally ranging from the 50s to the 60s
depending on cloud cover and mixing.  Our best chances for light
precipitation may be on Thursday as a weak cool front tracks
southeast across the area and with limited moisture it will likely
only result in passing showers not a lot of rainfall is anticipated.

&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1227 PM CDT Sat Apr 21 2018

Main challenge this period will be fog potential across northern
Iowa and relaxing winds this evening. Models showing some clearing
possible north aft 02z with potential for fog development north.
Some uncertainty remains and will only lower vsby to MVFR at this
time at KFOD/KMCW. Cigs expected to remain VFR unless thicker fog
develops north. Winds should relax to under 10kts by 23z...but
remain near 8 kts or so much of the period. Mid level bkn cigs aoa
10kft most areas through 15z with thinner areas expected
thereafter. /rev


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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


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