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Area forecast discussion 
National Weather Service Des Moines Iowa
921 am CDT Wednesday Apr 1 2015

issued at 321 am CDT Wednesday Apr 1 2015

Low pressure over western ND will move to James Bay by Thursday
night. A cold front extending southwest from the low will move
into Iowa tonight and pass southeast of the state by middle day
Thursday. A wave will move along the front passing south of Iowa
Friday with high pressure building in behind the wave.


Short term /today/...
issued at 321 am CDT Wednesday Apr 1 2015

Active day today with lots of headlines. A potent shortwave will
drive across the northern plains and upper Midwest late today
through tonight. At the surface...strong low pressure and
associated cold front will approach Iowa this afternoon. A
tightening pressure gradient will move into the state this afternoon
and result in strong southerly winds ahead of the front and upper
level system. This will drive temperatures into the 70s and 80s
across Iowa this afternoon as southerly winds increase to 25 to35
miles per hour with higher gusts. A Wind Advisory has been issued to account
for the strong southerly winds which is in effect until 02/00z.

Hi-res models do not bring the front into Iowa until between 21z and
00z and not into our forecast area until closer to 00z. Not
expecting convective development until this time but once storms go
they will quickly evolve into supercells this evening. From a
convective perspective...not looking for much today until right at
the end of the period. 0-6knm shear is virtually non-existent
through 00z. Soundings show southerly winds of 30-50kts right off
the surface so low level shear while unidirectional will be strong.
Instability is tied closely to the frontal boundary so cape through
the afternoon is none for most of the afternoon then really ramps up
across the far west near 00z. At this time best estimate for storms
in central Iowa for the afternoon appear to be west of an Algona to
Denison line between 22z and 00z. A few severe storms may approach
Estherville closer to 23z with hail the main threat initially.

Long term /tonight through Tuesday/...
issued at 321 am CDT Wednesday Apr 1 2015

The main weather focus will be on the cold front as it moves
across Iowa. Widespread thunderstorm activity is likely with the
front as deeper moisture is transported into the state. There is
the potential for severe weather...though it appears the severe
weather will not be widespread. MUCAPE increases into the 3000 to
4000 j/kg area over southeastern Nebraska...and strings out farther
northeast into Iowa. Still sufficient to support strong to severe
convection. Initially development may be discrete...but expect
the system to become linear as it moves farther into Iowa.
Presentation on the nmm short range model looks close to the
thinking here. With the strong winds in the low levels...feel the
main threats will be for wind and also threat for hail. Will carry
severe wording in the zones until around 06z.

Secondary consideration is the precipitable water values. At 1.3 to 1.4
inches...the values are at least 3 sigma above climatology. Given the
expected fast movement of the cells...feel the flooding potential
is limited.

Front slows down as it moves south of Iowa with low pressure moving
along the front on Friday. That will affect the south and
southeast with some light rain.

High pressure builds into the area Friday night into Saturday. The
next weather system will begin to affect the state later Saturday
night as Theta-E advection over the retreating frontal boundary
results in isolated to scattered thunderstorms. With the front
remaining in the area the chance for thunderstorms will be with US
into the early part of next week.


issued at 655 am CDT Wednesday Apr 1 2015

VFR conditions are expected through 00z however a south wind will
increase to 25 to 35kts with higher gusts. A strong cold front will
pass through the state tonight switching the wind to the northwest.
A line of showers and thunderstorms will progress across central
Iowa from northwest to southeast after 00z and should extend along a line from
Kalo to kdsm around 02/06z. MVFR conditions will accompany the
front due to ceilings from storms and visibilities from rain showers and some fog.


Fire weather...
issued at 321 am CDT Wednesday Apr 1 2015

Strong south winds increasing to 25 to 35 miles per hour this
afternoon with gusts around 40 miles per hour and still dry/cured fuels will
create extreme fire danger across central Iowa this afternoon.
Relative humidities will be lower across eastern Iowa and the
greater threat will exist there but during the early afternoon relative humidity
values west will get down to between 30 and 35 percent before 50
dewpoints start advecting into the state ahead of the system to
affect US later today and tonight. The combination of dry fuels and
very strong wind will produce extreme fire conditions across central
Iowa. Although forecast values of relative humidity west are 30- is quite possible that the strong winds will dry things out
more than anticipated and so it was prudent to extend the red flag
warning across all of central Iowa this afternoon.


Dmx watches/warnings/advisories...
red flag warning until 7 PM CDT this evening for Adair-Adams-
Appanoose-Audubon-Black Hawk-Boone-Bremer-Butler-Calhoun-Carroll-
Cass-Cerro Gordo-Clarke-Crawford-Dallas-Davis-Decatur-Emmet-

Wind Advisory until 6 PM CDT this evening for Audubon-Boone-
Bremer-Butler-Calhoun-Carroll-Cass-Cerro Gordo-Crawford-Emmet-
Palo Alto-Pocahontas-SAC-Webster-Winnebago-Worth-Wright.



Synopsis...MS Apr 15
short term...fab
long term...MS Apr 15
fire weather...fab

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