Area Forecast Discussion
Issued by NWS Des Moines, IA

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436
FXUS63 KDMX 170934
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
334 AM CST Fri Feb 17 2017

.SHORT TERM.../Today through Tonight/
Issued at 334 AM CST Fri Feb 17 2017

Today will be quite warm, with record or near record highs expected
across most of the area. The thermal ridge will be passing directly
overhead, with moderate southwesterly surface flow, ample sunshine,
and relatively low dewpoints. This will create an ideal scenario for
heating and given that Des Moines reached 65 degrees yesterday,
lower 70s from the metro southward looks very reasonable. Tonight a
very weak surface trough will move across Iowa from northwest to
southeast, but there will be little cold air advection. Even so, it
will allow winds to turn to northwest and lighten and temperatures
will fall into the 30s once again. No precipitation and virtually no
clouds are expected.

.LONG TERM.../Saturday through Thursday/
Issued at 334 AM CST Fri Feb 17 2017

Main focus through the long range will be on temperatures
throughout, precip chances late Sunday into Monday and again let in
the period.

Somewhat dampened upper ridge in place Saturday with it becoming
more amplified into Sunday as upper level trough digs into the
intermountain west. Weak sfc trough axis pushes through the state
late tonight with temps aloft dropping some into Saturday therefore
have slightly cooler temps than expected today. However westerly to
southwesterly flow in the low levels picks up Sunday with return
flow setting up and waa expected. This should shove Sunday`s temps
back up to values similar to today with mainly 60s across the entire
CWA. Temps will only fall a bit back to around 50 degrees Sunday
night as southerly flow remains in place and waa continues ahead of
a developing surface low across front range of the Rockies and the
very amplified upper level trough pushing east across the Rockies. A
long line of showers and isolated thunderstorms expected to move
into the state late Sunday night into Monday as the sfc low lifts
from the western Dakotas into southern Manitoba my late Monday. The
sfc trough axis to move through late Monday with little push of cold
air and mainly act as a wind shift/dryline. NAM showing around 200-
600+ J/kg of CAPE in the area from late Sunday night into Monday,
therefore expect at least isolated thunderstorms. PWAT values in
soundings well above the max for climatology so some heavier
rainfall possible with any thunderstorms moving through an area.
Depending on placement, this could lead to possible rises on local
streams and creeks especially given streamflows across the area are
all running high. Threat for ice jams starting to wane some given
the number of warm days above 40 degrees across northern IA,
especially given temps near 60 now into Monday and beyond.

Biggest chance for the long range, was to increase temps Tuesday
with westerly to southwesterly flow in the lower levels and the
thermal ridge now building back into the state with H85 temps
climbing to around +12C late Tuesday. An upper level trough to move
through the northern plains and US/Canada border with an associated
cold front dropping into the state Wednesday. However the push of
cold air stalls out and then gets pushed back northward into
Thursday as waa/southerly flow kicks back in ahead of the next
developing long wave digging through the Rockies. This system will
eject into the plains late Thursday into Friday and looks to bring
the next widespread push of precipitation to much of the region.
Tracks still uncertain with the GFS remaining further south than the
EC. EC has shown the most continuity suggesting a track across IA
with the sfc low which would keep much of the area in the warm
sector of the storm with mainly rainfall again to end the week. Will
have to monitor the potential for this storm to bring a chance for
heavy rainfall again to portions of the area and maybe a chance for
some isolated thunderstorms as well.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1136 PM CST Thu Feb 16 2017

There is medium to high confidence in VFR conditions through the
period. A weak warm front is in place from the Dakotas, NW to SE
through IA, and into northern IL at 05z. Along and north of the
front relative humidly has increased with light wind so there is
some radiation fog potential but confidence is not great enough to
introduce anything. Farther south in drier conditions there is
higher confidence in VFR staying in place. Winds should become
southerly and then SW into the evening with a weak diurnal peak.


&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...Beerends
AVIATION...Small



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