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Area forecast discussion
National Weather Service Des Moines Iowa
641 PM CDT Wednesday Apr 16 2014
Short term /tonight/...
issued at 340 PM CDT Wednesday Apr 16 2014
Strong south winds will persist into the evening given a tight
pressure gradient ahead of the low approaching from the northwest.
Relative humidity has not quite gotten down to 25 percent...but is
close enough that the red flag warning will remain in place until 6
PM along with the Wind Advisory. As the surface low and attendant
cold front sweep across the area overnight we will see a sharp wind
shift with much cooler temperatures moving into the area. Earlier
this afternoon in South Dakota Yankton...just ahead of the
front...was 61 degrees while Mitchell was at 35 degrees only about 50
miles to the northwest. Meanwhile radar imagery continues to return
widespread light intensity echoes all across north and northwest
Iowa and Minnesota...but forecast soundings and ceilometers indicate
a lot of low level dry air/high cloud bases and most observation are not
registering any precipitation south of the Iowa/Minnesota border. Have maintained
modest chance probability of precipitation across our far north this evening but any amounts
will be light and of no impact.
Long term /Thursday through Wednesday/...
issued at 339 PM CDT Wednesday Apr 16 2014
No significant weather is anticipated through the period...but a
progressive and somewhat active pattern nonetheless. Nothing of note
at onset with Iowa behind effects of current system with approach of
surface high pressure. First precipitation window is introduced by late
Thursday night with increased thermodynamic forcing. Anything with this
would be quite light with weak lift and dry low levels. Soundings
suggest warm layer would be just adequate enough to flip p-type to
liquid so resultant precipitation would likely be either sprinkles or
freezing sprinkles. Removed probability of precipitation by Friday afternoon with typical
decreasing diurnal warm advection cycle which leads into Sat.
Weak system finally deepens forcing and moisture sufficiently for
more robust and widespread probability of precipitation. Instability also increases with
MUCAPES at least several hundred into the state. Severe potential
rather low however with shear/kinematics weak. Big question with
this system will likely be how long to hold onto probability of precipitation. GFS places
more emphasis on the northern stream pushing things out quicker while the
European model (ecmwf) with its Central Plains focus is slower. A consensus would
suggest best potential Sat night into sun but lingering chance probability of precipitation
into Sun night and potentially Monday per the European model (ecmwf).
Drying is then expected into early next week with upper level ridge
building into the MO valley. Temperatures will be mild and just
above normal with increasing warm/Theta-E advection returning probability of precipitation
Tuesday night into Wednesday.
issued at 641 PM CDT Wednesday Apr 16 2014
Some middle clouds across the area...with a cold front progressing
across the County Warning Area this evening. This will bring a chance for a
scattered sprinkle or flurry to kfod or kmcw...and will allow
winds to shift from south to northwest from west to east this
evening. Some MVFR ceilings with just a few patches of IFR/LIFR behind
the front. For now dropped all sites to MVFR behind the front
with the low stratus expected to linger through the night and move
out during the morning hours Thursday. Winds will diminish some
overnight...but will still be somewhat gusty out of the northwest