Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 121116

Area Forecast Discussion
National Weather Service Des Moines IA
616 AM CDT Mon Mar 12 2018

.SHORT TERM.../Today through Tonight/
Issued at 322 AM CDT Mon Mar 12 2018

Stratus cloud deck currently over much of Iowa except for the
northwest third of the state. The back edge of the status has
been moving southeast at around 20 kts and should be south of the
area by 15z. Mostly sunny skies will ensue as very dry air
arrives into Iowa. PWAT values at noon today to 0.15 inch or
less. The upper flow will become more northerly by this afternoon
due to ridging over the intermountain west and an upper low
dropping south through Ontario and into the Great Lakes region.
This will allow a weak cold front to pass through the state. The
cold front may bring a few clouds to northeast Iowa in addition
to breezy northerly winds to the entire area. In addition
scattered cirrus may begin to arrive over the west by this
afternoon. High temperatures today will be in the mid 30s north
to the mid to upper 40s south. No significant weather tonight
with only a few passing clouds and seasonably cool temperatures
again with lows in the teens and 20s.

.LONG TERM.../Tuesday through Sunday/
Issued at 322 AM CDT Mon Mar 12 2018

From Tuesday through Thursday Iowa will reside beneath
northwesterly flow aloft. Initially on Tuesday this will be a
cooler and tighter cyclonic flow, then it will gradually loosen up
as a deep thermal ridge slowly approaches from the west. At the
surface a cool high pressure area will move across the region
Tuesday and Tuesday night, then on Wednesday we will see a return
of modest southwesterly flow. This will result in a warming trend
and abundant sunshine around midweek. On Wednesday night a very
week surface trough will sag southward across Iowa resulting in
northeasterly flow by Thursday, but the thermal ridge will be
building overhead by that time and will no low-level cold air
advection, this should allow for slightly warmer temperatures
Thursday than Wednesday despite the surface wind direction. All in
all Wednesday and Thursday will be very pleasant early spring days
across the forecast area.

From Thursday night onward the long term forecast period becomes
generally more active and more uncertain heading toward the
weekend and into next week. On Thursday evening a large 500 mb
gyre will be wobbling around just offshore of the Pacific
northwest coast, extending its cyclonic influence far east over
the Rockies with shortwave impulses being ejected out toward the
high plains. This will slowly shunt the preceding deep-layer
trough eastward and southward. However, there are large
discrepancies amongst the various prognostic models, and from run
to run, in how this will evolve. The GEM and EC are now taking
a more aggressive approach with a compact and robust vorticity
maximum shooting eastward out of the gyre and across our region
around Friday/Friday night, while the GFS maintains a more open
and evenly distributed depiction of the gyre, scooping out much of
its energy northeastward across the northern Rockies and far from
our area. At the surface this would translate into a GEM/EC
depiction of a gradually weakening low pressure system drifting
eastward over or near Iowa at the end of the week, bringing clouds
and light rain with cooler temperatures, while the GFS would favor
a more open pattern with continued mild temperatures and sporadic
shower chances. All three of these models have flopped back and
forth between solutions over the last couple of days, and it is
difficult to have much confidence in the sensible weather forecast
at the end of the week. However, it can be seen that no weather of
any real impact is seen, with any precipitation likely being in
the form of light rain. The biggest impact will be on forecast
temperatures, which by Friday could range anywhere from the 40s to
the 60s across central Iowa.

Looking toward and just beyond the end of the long term forecast
period, from the latter half of the weekend into early next week,
things appear somewhat active yet again. This is because the
remaining energy from the western U.S. trough will finally eject
eastward and across the Midwest during this time frame, crossing
Iowa sometime around next Monday. This will result in additional
precipitation chances, primarily just beyond the current 7-day
period, and potentially even thunderstorms depending on the
northward extent of the system.


.AVIATION.../For the 12Z TAFS through 12Z Tuesday morning/
Issued at 613 AM CDT Mon Mar 12 2018

Stratus continues to depart to the southeast and will be past both
KDSM and KALO around the beginning of the period and at KOTM by
14z. Some potential for stratus vicinity of KMCW/KALO late this
afternoon and into the evening otherwise VFR conditions once the
morning stratus departs. Breezy north/northwest winds will
continue and will become gusty at times today.





SHORT TERM...Donavon
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