Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Des Moines Iowa
332 PM CDT Thursday Sep 3 2015

Short term /tonight/...
issued at 332 PM CDT Thursday Sep 3 2015

Main forecast concern was focused on temperatures and fog
potential over northern Iowa. Overnight lows look to finally reach
the crossover temperature by b/T 07-09z over the north and likely see fog
develop during that time frame. NAM/sref suggest fog developing from
mcw to EST and possibly as far south as Highway 20. The caveat is a
weak shortwave over Nebraska/South Dakota may bring in some higher
clouds towards Friday only mentioned patchy fog at this time.
The latest hrrr (03.18z) and even the GFS have a hint of convection
developing over the northwest towards Friday morning in response to
the low level jet developing and associated with aforementioned weak
shortwave. Thinking the NAM/European model (ecmwf) has a better handle on timing and
location and left forecast dry.

Long term /Friday through Thursday/...
issued at 332 PM CDT Thursday Sep 3 2015

Pattern remains similar through the beginning of the middle/long range
with upper ridging in place aloft with a trough digging into the
western US. A few weak impulses will move just to the west of the
County Warning Area which could lead to some increased cloudiness...but overall
chance of precipitation is small so have a dry forecast into
Saturday. Upper level ridge to flatten some over the weekend as the
western US trough lifts northeastward into southern Canadian prairie
provinces by late Sunday. Southerly flow will increase ahead of this
system Saturday night into Sunday...with moisture advection and
moisture transport becoming oriented into western Iowa. May see some
storms bubble up across the western/northwestern County Warning Area...but overall
widespread precipitation chances not expected until the passage of
the cold front associated with the Canadian system Sunday night.
This front will eliminate the current hot and muggy
850 mb temperatures drop into the teens behind the front. Long range in models
in some disagreement into next week with how fast to push the front
south...with the ec hanging the front up across southern Iowa with
chances for storms continuing into Monday/Monday night. GFS tries to
push it into Missouri...which would keep Iowa drier Monday. Full
longwave western US trough to shove east Tuesday with the front
lifting back northward as a warm front late Monday night/early
Tuesday before a stronger cold front pushes through late Tuesday
into Tuesday night. 850 mb temperatures to drop another category into the low
teens behind this front with high pressure expected to build in for
the rest of the week. This should lead to mainly dry conditions for
much of Wednesday into the end of the week. Models do hint at a weak
trough clipping northern Iowa Thursday which could bring some
sprinkles to mainly northeastern Iowa. Have a small area of slight
chance pop for this feature. Otherwise relegated probability of precipitation mainly to the
time periods with the frontal passages with temperatures expected to fall
more toward or slightly below the seasonal averages.


issued at 1229 PM CDT Thursday Sep 3 2015

With the upper level ridge firmly planted above...anything of
consequence will stay to the west and northwest of the taf sites.
Model soundings hint at some localized fog tomorrow morning...but
with hrrr depicting otherwise and little change overnight
otherwise...have kept fog mentions out for this iteration.


Dmx watches/warnings/advisories...none.



Short term...podrazik
long term...beerends

National Weather Service Glossary of Abbreviations