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FXUS63 KDMX 120840

Area Forecast Discussion
National Weather Service Des Moines IA
240 AM CST Tue Nov 12 2019

.DISCUSSION.../Today through Monday/
Issued at 240 AM CST Tue Nov 12 2019


High confidence in temperatures below normal through the end of this 
week and likely into next weekend, but temperatures will be 
generally trending upward each day. There is a chance of snow, 
perhaps starting as a brief bit of mix precipitation Wednesday with 
additional precipitation chances later this weekend.


High pressure just west of Iowa early this morning has promoted a 
clear sky as viewed by GOES-East Nighttime Microphysics RGB. With 
light winds and fresh snowpack over much of Iowa, temperatures are 
nearing record levels. The good news is that the GEFS, NAEFS, and 
NBM temperature guidance all show this morning as the coldest over 
the next 7 days. The high pressure will move over and to the east of 
the region today with winds becoming from the south toward this 
evening. Heights will be rising and with breezy conditions 
prevailing through the night, low temperatures should be in the 
evening with steady or slightly rising temperatures after midnight
tonight over much of central Iowa. 

The next shortwave trough will be approaching from the northern 
Rockies Tuesday night and reaching Iowa on Wednesday. Forecast 
soundings and cross sections show plenty of mid-level dry air 
initially that will need to be overcome before precipitation begins 
by mid-morning over northern Iowa and toward midday farther south 
over central Iowa. There is also a warm nose around +4C centered 
around 850mb as well that will cool as precipitation falls and 
evaporates. This warm nose of air may result in a few hour period
if that of mixed precipitation at precipitation onset followed by
a transition to snow as the profile cools sufficiently. Weak to 
low end moderate omega values through the saturated column will 
provide for a period of light precipitation, mainly snow. Liquid 
totals will generally be around a tenth with this event. With 
snow ratios ranging from 10-12:1 at the start to near 15:1 at the 
end, this will result in snow amounts around an inch over 
northern Iowa with little if not no snow over southern Iowa,
especially south of Highway 34. The snow will end Wednesday 
evening as the shortwave moves to the east. There will be slightly
cooler air, but no cold blast as occurred this past Sunday. Still,
temperatures will be well below normal on Thursday.

Another zone of high pressure will pass over the region Thursday 
into Friday with heights once again rising across the area. Another 
vigorous trough will pass through later Saturday into Sunday with a 
surface cold front. Moisture is not plentiful with this system, but 
there should be some precipitation as it passes. The airmass that 
follows behind this system will not be that much cooler with origins 
from the Pacific.


.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1029 PM CST Mon Nov 11 2019

Skies have cleared and are expected to remain clear through the
overnight hours with some high clouds towards late Tuesday and
Tuesday night. Northwesterly winds starting to diminish some as
the ridge axis moves toward central IA. They will continue to
diminish through early Tuesday and then shift around to the west
to southwest to south through the forecast period. Winds will then
increase again toward the end of the forecast period due to the
surface pressure gradient tightening ahead of the next weather
disturbance for Wednesday. 



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