Scientific Forecaster Discussion
fxus63 kdmx 142008
Area forecast discussion
National Weather Service Des Moines Iowa
308 PM CDT Mon Oct 14 2019
Discussion.../tonight through Monday/
issued at 137 PM CDT Mon Oct 14 2019
Typical fall pattern sets up through the remainder of the week
highlighted by mainly dry conditions and some bouts of gusty
winds. Low pressure system crossing the upper Midwest sets up a
chance for isolated storms into eastern Iowa tonight, followed by
widespread gusty winds and cooler temperatures tomorrow. Quiet and
cool weather lingers through the middle of the week before a
warming trend commences into the weekend. Active weather is
looking more likely Sunday into Monday as the next storm system
crosses the region, bringing the potential for more precipitation
and blustery conditions to the state.
First forecast challenge is the potential for storms late tonight.
Low level jet ramps up as a vigorous shortwave trough enters the
northern plains. Increasing kinematic forcing for ascent aloft
interacting with a corridor of Theta-E advection may be enough to
trigger isolated showers and storms over eastern Iowa tonight.
Confidence is quite low due to limited moisture and rather weak
convergence for initiation, but hi-res models have shown a
persistent signal for some development. Shortwave eventually
shoves a strong cold front through the state Tuesday morning.
Gusty northwest winds quickly follow within a zone of pressure
rises and cold air advection. Gusty winds persist through the day
as the boundary layer mixes up to 850-800mb, tapping into stronger
winds just off the surface. BUFKIT sounding data shows winds on
average near 35 kts at the top of the mixed layer, so a few gusts
around 40 mph are possible until winds begin to relax by the
evening hours. Expansive area of stratocumulus eventually drops
southward into the state by late morning and afternoon. It is
possible we could wring out a few showers out of the cloud cover
over northern Iowa, but the shallow depth of moisture and
increasing deep layer subsidence may inhibit any activity in our
area. Any realized precip should be light and liquid form with
surface temps above 40f and dry air through the dgz.
Quiet and cool weather expected Wednesday as an expansive area of
high pressure settles over the central conus. Transition to
southwesterly flow aloft sets up late week as a large trough digs
out west. Southerly flow and warmer temperatures return in
response pushing highs back to near or above average in the 60s.
Chances for precip Friday night into Saturday as a weak lead wave
moves through, but the atmosphere looks relatively starved for
appreciable moisture at that time. Higher chances for
precipitation hold off until Sunday as a potentially potent upper
low ejects out of the mean longwave trough. Low confidence in
possible precip timing/amounts for the area as models still
exhibit a high degree of variability at this time range, but it is
looking more likely that we could be see another period of
blustery and wet conditions early next week.
Aviation.../for the 18z tafs through 18z Tuesday afternoon/
issued at 1214 PM CDT Mon Oct 14 2019
Main aviation concerns through the next 24 hours will be low level
wind shear tonight, followed by strong wind gusts tomorrow
morning. VFR conditions prevail through the rest of today.
Isolated -tsra possible late tonight in vicinity of kmcw and Kalo,
but confidence in any impacts to a terminal is not high enough to
warrant a mention in the taf at this time. Southwesterly low level wind shear
develops after 02z this evening with winds of 35-40 knots just
2kft above the surface. Wind shear subsides tomorrow morning, but
strong surface winds develop behind a passing cold front.
Northwesterly gusts approaching 30 knots are possible, potentially
higher at times. A stratus deck dropping south out of Minnesota may get
into northern Iowa by 18z, so went ahead and included mention of
MVFR cigs at kmcw late in the forecast.