Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Des Moines Iowa
658 PM CST Thursday Nov 26 2015
Short term /tonight/...
issued at 349 PM CST Thursday Nov 26 2015
Precipitation trends will be concern for tonight with system slowly
pushing southeast and precipitation ending. High res models have
handled system well throughout the day today...and have trended
towards high res for precipitation timing overnight...with
precipitation expected to end quicker. Current radar trends indicate
dry conditions across northwestern Iowa...and may still have held
onto precipitation chances too long overnight.
Main concern is precipitation type across County Warning Area throughout the
overnight period. Daytime trends have been for rain across the south
with a transition zone of freezing rain before changing to snow
across the northwest. This trend will continue as system pushes
south and surface temperatures drop to freezing or below...though
temperatures aloft remain warm enough with no ice introduction to
allow for period of freezing rain. Expect cooler temperatures to
push in after 00z and freezing rain to transition to snow more quickly.
However...will see lingering freezing rain across western/southwestern County Warning Area
with warmer temperatures aloft...and have kept higher ice
accumulations there. Will leave headlines as is as they are well
placed to highlight areas of concern and timing closely matches
current forecast. Will need to monitor south central Iowa and freezing rain
change over. At this time do not have high confidence in ice accumulations
in this area with current warm temperatures...but if temperatures
drop quicker after sunset...may need to expand Freezing Rain
Advisory into this area. In addition may see a few locations in
southwestern County Warning Area reach ice accumulations of a quarter of an inch if
change over to snow occurs more slowly.
Long term /Friday through Thursday/...
issued at 349 PM CST Thursday Nov 26 2015
Biggest concerns around lingering precipitation Friday am and then next
system to impact the region mainly Monday into Tuesday. Precipitation area
to push into far southern Iowa by Friday morning...and may have a
mix of rain/snow/fzra across the far south. System to quickly push
south though...so expect precipitation to taper off by middle/late morning.
Low level stratus expected to remain across much of the County Warning Area through
the day...with clearing skies expected into Friday night/Saturday as
high pressure builds into the County Warning Area. Models further south and west
with the precipitation chances for this weekend...with dry flow off the
area of high pressure expected. Therefore have gone mostly dry for
the County Warning Area through Sunday. Temperatures also to moderate some from the
chilly day Friday back to above freezing for highs Sunday across the
County Warning Area.
A large upper trough to spin across the intermountain west this
weekend which will slowly migrate eastward into the Central Plains
by early next week. Southwesterly flow and energy ejecting out of
the parent trough will push through the state Monday. Southerly flow
off the Gulf and increasing moisture will push into the state...with
precipitation chances expected by late Sunday night...and becoming more
widespread Monday into Tuesday. Temperatures warm enough initially
aloft and at the surface that may see a rain/snow mix across the
southern half of the County Warning Area...with precipitation leaning more toward snow
across the north. Colder air to them move in Monday night into
Tuesday...with precipitation changing over to all snow. There is
some potential for a period of freezing rain as well...but
confidence is low so have left out of the forecast for now. Some
refinement on precipitation type is expected as the period gets closer.
System to then push out of the County Warning Area by middle week...with dry conditions
resuming for the end of the week. Overall not too cold of air to
follow by the end of next week...with maximum temperatures mainly in the 30s
issued at 536 PM CST Thursday Nov 26 2015
Precipitation...in the form of rain changing over to fzrasn...and
IFR ceilings will gradually move off to the southeast in the next
several hours...likely clearing otm a little after 06z. This may
leave a light glaze in some areas. Thereafter...MVFR ceilings will
slowly improve to VFR on Friday. North winds will remain gusty
overnight...then decrease by Friday afternoon/evening.
Winter Weather Advisory until 6 am CST Friday for Black Hawk-
Freezing Rain Advisory until midnight CST tonight for Adair-
Freezing Rain Advisory until 6 am CST Friday for Adams-Clarke-