Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS63 KDMX 220917

Area Forecast Discussion
National Weather Service Des Moines IA
317 AM CST Fri Nov 22 2019

.SHORT TERM.../Today through Saturday/
Issued at 315 AM CST Fri Nov 22 2019

Confidence: Medium to High

Cold air advection and shear driven cumuliform clouds with some 
flurries continue to migrate south southeast out of MN early this 
morning.  Meanwhile, mid to high level clouds are ejecting northeast 
out of Kansas and Missouri in advance of the southern stream system 
that is expected to just glance southern Iowa with a bit of light 
snow later today into the evening hours. With the majority of the 
isentropic lift well south of the region this evening, little if any 
accumulation is anticipated...maybe a tenth or two. The cloud cover 
associated with the cold air advection from the north will likely 
stick around for a portion of this morning and gradually mix out by 
noon today with more sunshine for the balance of the day. Highs 
today will be quite chilly again with mid to upper 30s north to the 
around 40 in the south.  Tonight clouds hold on over the far south 
as the southern stream system eventually pulls east of the area by 
15 to 18z Saturday.  Areas that receive ample sunshine Saturday will 
warm nicely. Over northern Iowa return west southwest flow will push 
H850 temperatures to about 2 to 3.5C by late afternoon. Highs 
Saturday will recover a bit with afternoon readings in the lower to 
mid 40s after overnight lows in the 20s.  

.LONG TERM.../Saturday Night through Thursday/
Issued at 315 AM CST Fri Nov 22 2019

/Saturday Night through Monday Night/...

Confidence: Medium to High

This period will be the transition between a quieter weekend pattern 
and a more active pattern next week. There is finally some consensus 
between the GFS/Euro and GEM with the continuing pattern change into 
next week.  All three medium range models, now including the GFS, 
recognize that the northern stream short wave that was being progged 
to move across the US Canadian border into Monday evening will 
indeed bring colder air farther south into the region by Monday 
night. It appears that the baroclinic zone will aloft will set up 
near Highway 20. As a strong jet and associated short wave crosses 
the Rockies Monday afternoon, a response at H850 will quickly 
enhance low level moisture return into a deepening surface feature 
over the Central Plains. Though the GFS and Euro are both now 
recognizing a Panhandle low will develop, the GFS is already 
beginning to speed things along with less amplification.  Both 
models begin to lift moisture into southern Iowa Monday night in the 
form of mid to high level clouds. Temperatures will likely steady 
off a bit in the south with mid to upper 20s in the north and lower 
30s in the south. 

/Tuesday through Thursday/...

Confidence: Low to Medium

Confidence begins to lessen with model solutions diverging through 
the period.  The GFS is faster to track the midweek system south of 
the area while the Euro, which is slower to develop the Colorado 
low, begins to bring the upper level system over the region by 
Tuesday night into Wednesday. The amplification process is already 
ongoing and continues as the low deepens into lower Michigan by 12z 
Wednesday.  The current track of the Euro model is a favorable track 
for moderate to heavy snow if the low drives northeast from near 
Kirksville, MO to just northeast of Chicago. Though the bulk of the 
Euro's precipitation could be snow over our area, an initial mix 
would be favored over the southeast half of the forecast area 
Tuesday afternoon. Available moisture should ramp up farther east 
and northeast as the storm intensifies. The Euro also suggests that 
winds would become a problem as well with north northwest winds of 
15 to 25 mph. The GFS is farther removed from the area, but still 
grazes the east and southeast with some light accumulating snowfall. 
Given typical winter model trends with time, there may be some 
additional northwestward migration of the track in the models as we 
near the event.  Given that it's too early to message much in 
detail, but certainly this would hamper travel over a good share of 
the area later Tuesday, Tuesday night and a portion of Wednesday if 
the stronger system depicted by the Euro comes to fruition. The 
various solutions complicate temperatures, but Tuesday should be 
cooler with clouds and eventual precipitation - highs in the 30s to 
perhaps lower 40s are more likely, with falling temperatures in the 
afternoon. Though the Euro shows a slightly colder solution into 
Wednesday following the system, neither the Euro/GFS are appreciably 
cold and this might also suggest that at most, a modest storm is 
most likely from Tuesday into Wednesday. Highs will probably be 
similar to Tuesday in the 30s to around 40 by afternoon. Looking 
well ahead to the holiday, both medium range models still show a 
large western trough with pieces of energy spinning off the main 
H500 low and propagating toward the Central US. The GFS is again 
faster with a northeast progression compared to the Euro, but both 
models are attempting to spread some light precipitation into Iowa 
by Thanksgiving with thermal profiles suggesting at least that rain 
would be the precipitation type. With a large trough entrenched in 
the southwest through the end of the period and beyond, plenty of 
clouds and at least light precipitation can be anticipated. A nearby 
boundary will also promote the potential for fog, even if the snow 
that the Euro suggests Tuesday into Wednesday don't occur. Temperatures
on Thanksgiving should be seasonal, with highs in the 30s to lower 
40s north to the lower to mid 40s south. 


.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1129 PM CST Thu Nov 21 2019

Low stratus deck with resulting MVFR cigs has been slowly eroding,
however many sites continue to see SCT to BKN MVFR cloud decks.
Gusty northwest winds have diminished some, and will continue to
do so through sunrise. VFR conditions are expect throughout the
day on Friday.




National Weather Service Glossary of Abbreviations