Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Des Moines Iowa
335 PM CDT Thursday Oct 23 2014

Short term /tonight/...
issued at 335 PM CDT Thursday Oct 23 2014

Clouds are moving out of the County Warning Area with clear skies expected into the
evening. Winds are expected to go light and shift back around to the
south ahead of a weak wave expected to move through the region late
tonight. No precipitation is expected with the passage of the wave...just
some cloud cover into the far west. Bigger issue tonight is fog
possibilities. With the lingering moisture around from the
rain/cloud cover and southerly winds also expected to bring in some
additional near surface moisture. Fog was quite prevalent in areas
out to the west in previous nights with similar conditions expected
across Iowa tonight...therefore have added in areas of fog across
the entire County Warning Area. Eastern County Warning Area which has held on to the clouds the
longest will have best chances to see dense fog...and have ended up
going with an advisory for that area to also match up with offices
to the east.

Long term /Friday through Thursday/...
issued at 335 PM CDT Thursday Oct 23 2014

Lingering fog stratus on Friday morning...as discussed in more
detail in the short term section...will be slow to dissipate
during the day especially in the east where it will be reinforced
by slug of low level moisture advection ahead of a weak trough
approaching from the northwest. Have slowed clearing of skies on
Friday to account for this...but there is some question as to
whether they will clear at all in the east/northeast until the
trough moves through on Friday night. Meanwhile areas that do
clear out should warm nicely on Friday afternoon...mainly in the
south and west...with highs in the middle 70s making for a pleasant
fall day.

Once the low pressure trough moves through on Friday night the
weekend will start out somewhat cooler...but this will be short
lived as the trough lifts back northward as a warm front on Sunday
bringing more mild weather into Monday. Meanwhile...at 500 mb...a
large ridge will move overhead Sunday but a longwave trough will
already be progressing across The Rockies...and this will affect
Iowa early next week. The details of this system have been
resolved inconsistently by the prognostic models over the last few
days...but today there is more of a consensus with the overall
evolution as surface cyclogenesis ramps up across western Kansas
on Sunday night...and the resulting low pressure center then
moves over Iowa late on Monday. Some model runs are spitting out
light quantitative precipitation forecast ahead/southeast of the trough but this seems unlikely
given the timing and dry air indicated by forecast soundings. It
is more probable that precipitation will be oriented either in a swath
behind the trough or in a large shield around the deepening low
rocketing to the northeast. In either event Monday night would
seem to be the most likely period for rainfall and probability of precipitation are 40 to
50 across much of the area. If these solutions remain stable then
likely probability of precipitation may be needed soon. In any event this system will blow
out to the east/northeast on Tuesday and be followed by one or
more successive 500 mb waves through the remainder of the work
week...preventing any significant warming and possibly providing
additional rainfall chances.

&&

Aviation...23/18z
issued at 1200 PM CDT Thursday Oct 23 2014

IFR/MVFR ceilings beginning to break up and clear out of the
area...with VFR conditions expected across the area by middle to late
afternoon. Southerly to southwesterly winds will shift to the west
to northwest briefly this afternoon...before shifting back to the
south tonight.

&&

Dmx watches/warnings/advisories...
dense fog advisory from 1 am to 10 am CDT Friday for Appanoose-
Black Hawk-Bremer-Butler-Cerro Gordo-Davis-Franklin-Grundy-
Hardin-Jasper-Lucas-Mahaska-Marion-Marshall-Monroe-Poweshiek-
Tama-Wapello-Wayne-Worth.

&&

$$

Short term...beerends
long term...Lee
aviation...beerends

National Weather Service Glossary of Abbreviations