Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 281131
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
631 AM CDT Wed Jul 28 2021

.DISCUSSION.../Today through Tuesday/
Issued at 354 AM CDT Wed Jul 28 2021

Area of surface high pressure has moved little over the past 24 and
has only inched a bit further southeast over central Illinois. Low
pressure over the western Dakotas and into Wyoming is moving east as
well along with an attendant cold front. This boundary will make
progress southeast today as a short wave overtops the massive upper
high that is just west of the state. Storms have already fired on
the nose of the low level jet over northeast South Dakota and into
west central Minnesota. This activity will move southeast along the
instability axis and could reach north central Iowa before moving
further east along with the departing forcing.

Beyond that, the heat is the big weather story for central Iowa
today. An impressively large plume of 70+ dew points now extends
from eastern North Dakota to the Gulf Coast. Dew points finally
exceeded expectations and guidance on Monday with some ridiculously
high values at more accurate ASOS sites including touching 80 at
Estherville while the typically poor sited and less representative
AWOS sites had higher values. Today will feature a slightly warmer
thermal layer that will mix deeper this afternoon and note that
northwest Iowa is still progged to have deep mixing to near 700 mb.
Deeper mixing should help mix dew points down some but with the
environmental dew points already in the 70s and with the crop
evapotranspiration clearly near max capacity despite dry soils,
leaning toward some sultry dew points today along and east of
Interstate 35 with a bit lower values west. Due to these higher dew
points, have lowered high temperatures again with more low to mid
90s expected and again taking into account another round of smoke
moving overhead. These temperatures combined with mid 70s dew points
though will still place heat index values in the 105 to 110 range.
Have kept the Heat Advisory as is. Still not out of the question
some areas have heat indicies creep into the warning criteria of
110+.

A moderate risk for severe weather exists to the northeast over
parts of Wisconsin later today and into tonight. Not expecting much
in the way of storms across central Iowa as the boundary arrives
into the northern half of the state overnight as the boundary
remains capped with very warm air aloft. Temperatures overnight will
remain quite warm, especially south of the boundary where pooling
dew points will remain. Lows in the mid to upper 70s are likely. A
Heat Advisory remains in place for far southern Iowa Thursday where
another round of heat indicies near 105 will occur. The boundary
will not settle to far south of the state before stalling into
Friday. Elevated convection is still expected to develop over parts
of Nebraska and southwest Iowa late Friday through early Saturday.
How far northeast this convection reaches is still in question tough
greater confidence in northeast Iowa remaining dry. There is a
potential for heavy rain where this instability axis does set up
with 2 inch plus pwat and a good feed of moisture overtopping the
surface boundary along with storm motion nearly parallel to the
boundary leading to training storms.

A large area of high pressure settles in from Canada and into the
Upper Midwest this weekend and will be a big influence on the
weather through mid next week. The general trend will be cooler
weather with highs in the 80s and mostly dry conditions.

&&

.AVIATION.../For the 12Z TAFS through 12Z Thursday morning/
Issued at 628 AM CDT Wed Jul 28 2021

Mainly VFR conditions through the period. The main exceptions is
some fog early followed by a few chances for storms vicinity of
KMCW. Light wind early may become breezy at times this afternoon.
A boundary will enter northern Iowa overnight and bring a switch
to northwest wind.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 10 AM this morning to 9 PM CDT this evening
for IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>074.

Heat Advisory from 10 AM this morning to 7 PM CDT Thursday for
IAZ075-081>086-092>097.

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon


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